Platform Sessions

Platform Sessions

S5

Platform Sessions

PARKINSON AND RELATED DISORDERS PS1-01

Intracortical excitability in early parkinsonian patients – a one year follow-up paired TMS study

Martin Bares, Petr Kanovsky, Ivan Rektor. Department of Neurology, St. Anne’s Hospital, Brno, Czech Republic Recent literature has addressed intracortical inhibition (ICI) and facilitation (ICF) and the impact of dopaminergic therapy in Parkinson’s disease (PD). Using a paired TMS, twelve newly diagnosed PD patients without any previous dopaminergic treatment were studied. Short (3, 5, and 7 msec), middle (10, 15, and 20 msec) and long (100, 150, 200, and 250 msec) interstimulus intervals (ISI) were applied prior to the first administration of L-DOPA, and three, six, and twelve months after the L-DOPA treatment. Ten age-matched healthy subjects were used as a control study group. There was significantly less ICI and reduction of ICF in the PD patients than in the control group. No change in the affected ICI and ICF was observed after three months of L-DOPA therapy. After six months, the L-DOPA therapy showed a restoration of disturbed ICI and ICF, which lasted after twelve months of L-DOPA therapy. No difference between the motor threshold of the PD patients and that of the control group was observed. Long ISI produced no effect on intracortical excitability (PD patients, control group). The UPDRS motor score was improved in the PD patients after three months of L-DOPA-therapy. The restoration of intracortical excitability in PD patients demonstrates modulation by dopaminergic stimulation of the neuronal inhibitory and facilitatory circuits of the motor cortex. The level of cortical excitability seems to be related to the nigro-striatal circuitry functioning indirectly. This research was supported by the Yamanouchi European Foundation; it is a part of Research Plan MSˇCR 112801.

PS1-02

ERD pattern changes and Parkinson’s disease through various movements

E. Labyt, F. Cassim, J.L. Bourriez, D. Devos, L. Defebvre, J.D. Guieu, A. Deste´e, P. Derambure. Neurology A, Salengro Hospital, Lille, France Parkinson’s Disease is clinically characterized by tremor, hypertonia and akinesia. This latter symptom has previously been related to abnormal activation of motor cortex. However, the role of motor cortex in the control of muscular tonus remains unclear. The purpose of this research was to analyze the quantification and the spatiotemporal display of event-related (de)synchronization (ERD/S) of mu and beta rhythms in 15 de novo hemiparkinsonian patients during a distal versus a visuo-guided targeting movement and during a passive muscular relaxation in order to assess changes of cortical activity. Our results show a delayed and disturbed ERD pattern over sensorimotor regions during the distal and targeting movements but in this latter, these changes also interested the associative parietal cortex. Related to the muscular relaxation, a global decrease ERD and an attenuation of postmovement ERS were observed. These findings suggest that akinesia could be explained by a dysfunction PII: S 1388-245 7(02)00165-7

of motor cortical areas resulting from a decrease of subcortical inputs and by an impaired sensory integration over associative cortex, leading to an incapacity to define the movement parameters required to elaborate the motor commands. Concerning the hypertonia, our results seem to indicate an impaired activation and a default of post-movement resting over sensorimotor regions. PS1-03

Scalp evoked potentials induced by therapeutic DBS of subthalamic nucleus

F. Ferna´ndez-Gonza´lez, F. Seijo, C. Valle´s, B. Lozano, L. Guisasola, C. Salvador, A. Galindo. Unidad Multidisciplinar para la CirugI´a de los Transtornos del Movimiento, Hospital Central de Asturias Therapeutic subthalamic-DBS is applied through standard chronically implantable tetraelectrodes. The mapping of evoked responses to scalp by STN-DBS shows the subthalamic volume as a very complex environment, in which small changes in stimulus dramatically affect the clinical results. Since 1998 we have applied bilateral STN-DBS surgery to 41 PD patients at the Hospital Central de Asturias. CAPIT evaluation of patients was performed and videotape recorded before and after surgery. UPDRS III was assessed in all possible conditions. To implant the tetraelectrode in dorsolateral STN, spontaneous and evoked multiunit neuronal activity is recorded every 1 mm step along the semi-microelectrode trajectory. In accordance with a patient informed Integrated Care Pathway, before the chronic stimulator is implanted, the final position of tetraelectrode is identified by MRI and neurophysiological techniques (tetraelectrode recorded somatosensory evoked potentials, and evoked responses to scalp and forearm extensor muscle by monopolar tetraelectrode stimulation). When the tetraelectrode is located near dorsolateral STN, therapeutic DBS evokes two specific frontopolar scalp short latency responses at 5 and 9 ms. When stimulus intensity is increased other evoked components were recorded. The correlation of clinical and neurophysiological data suggests that the DBS scalp evoked responses can be a functional reference of effectiveness in the PD surgery. PS1-04

Topographic arrangement of sensorimotor interactions is abnormal in dystonic patients

Stefano Tamburin, Giampietro Zanette, Paolo Manganotti, Antonio Fiaschi. Department of Neurological Sciences and Vision, University of Verona, Italy The aim of the study was to detect abnormalities of sensorimotor interactions and their topographic distribution in dystonic patients. We investigated the effect of digital electrical stimulation on the amplitude of motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) in two hand muscles on the affected and unaffected sides of 8 hand dystonia patients and 10 agematched controls. For each muscle, non-painful digital stimulation was applied to a contiguous finger (CF) and to a non-contiguous finger

S6

Platform Sessions

(NCF), and preceded TMS or TES at intervals from 10 to 100 msec. In normal subjects, a somatotopic inhibitory effect was detected, since the CF stimulation was significantly more powerful in determining MEP reduction at intervals of 20–50 msec. In dystonic patients, at the same intervals, the digital conditioning resulted in the absence or inversion of somatotopy. These abnormalities were present in the muscles of both the affected and unaffected hands. TES conditioning provoked MEP inhibition only at ISIs ,40 msec. These data demonstrate that MEP suppression in response to digital stimulation is preserved in dystonia, but the somatotopically distributed input-output organization of the sensorimotor interactions is completely lost or even reversed in dystonic patients’ hands. These abnormalities are present at both the spinal and cortical levels. Our data confirm that deficient inhibition plays a key role in the pathogenesis of dystonia; in particular, failure of spatial distribution of surrounding inhibition may account for the abnormal topography of sensorimotor interactions in dystonic patients.

effects of DBS and drug emerged. Preliminary evaluation showed that DBS shortened the late phase (loading), but not the early phases (grip preparation and preloading), while levodopa was effective on all phases of the grip task. An equal effect of DBS and drug on tapping, and on the total motor score was observed. We conclude that STN DBS does improve akinesia of the arm, but the improvement of the slowness of grasping is less pronounced than of the build-up of lifting force. This may be due to a less pronounced effect of STN DBS on the primary motor cortex compared to its impact on brainstem or premotor areas.

Preferential effect of subthalamic nucleus stimulation on proximal arm movements compared to finger movements

Introduction: To determine the anatomic location of the therapeutic stimulating electrode(s) in PD patients who benefited from subthalamic (DBS). Methods: Retrospective analysis of targeting and stimulation data from 62 successful subthalamic DBS procedures in 33 PD patients. Intraoperative single unit MER, stimulation, fluoroscopy and post-operative MRI were employed to confirm proper lead position. The position of the clinically most effective contacts were mapped to digitally scaled sagittal sections of the Schaltenbrand and Wahren atlas employing intraoperative recording. Results: All patients were at least 3 months post-op with documented improvements in their off state motor UPDRS scores (mean 43%). 32/63 (51%) leads mapped to 12 mm lateral of midline. Unipolar stimulation was employed with 49 and bipolar stimulation with 15 of the leads. 24/110 (44 total contacts employed) (22%) therapeutic contacts were located within the STN while 86 (78%) were located dorsal to the nucleus in the region of Forel’s H field (HFF) and ZI. Conclusion: In this series of PD patients with documented positive responses to STN DBS, 78% of therapeutic contacts are located within the HFF and the ZI, not the STN, suggesting that the clinical effects of subthalamic DBS may depend on mechanisms other than, or in addition to, depolarization blockade of STN transmission.

PS1-05

Roland Wenzelburger a, Florian Kopper a, Bao-Rong Zhang a, Delia Lorenz a, Jan Herzog a, Wolfgang Hamel b, Dieter Weinert b, Mukaddes Go¨ lge c, Michael Illert c, Gu¨ nther Deuschl a, Paul Krack a. aDepartment of Neurology; b Department of Neurosurgery; cDepartment of Physiology of the University Hospital Kiel. Parkinsonian patients (PD) suffer from an impairment of fine motor coordination of the hand due to akinesia. Deep-brain stimulation of the subthalamic nucleus (STN DBS) reduces motor disability, and we quantitatively investigated its impact on a grip-lift movement. 18 PD patients were investigated three months after surgery in 4 conditions of levodopa and stimulation. We assessed the patients’ ability of lifting an object using the precision grip and to perform finger tapping. We also evaluated the clinical status with the Unified Parkinson’s Disease Rating Scale (UPDRS) in a larger group of patients. The slowing of the task was reversed by both stimulation and drug. If the separate isometrical phases were evaluated in detail, however, differential

PS1-06

What is the true therapeutic target of subthalamic deep brain stimulation for Parkinson’s disease?

Jay Shils, Michele Tagliati, Ron Alterman. Beth Israel Medical Center, NY, NY

Platform Sessions

S7

VISUAL SYSTEM Visual System Graham Harding. NRI, Aston University, Birmingham, England It is possible to measure discreet responses of the visual system at three different levels: the retina; subcortical responses; and cortical responses. Each contributes information with regard to functioning of the visual system in health and disease. The ERG has been utilised for many years and provides an aerial measure of retinal responses usually to a bright light flash. More recent developments have utilised pattern reversal ERGs to obtain a picture of macular function. Now Multifocal ERGs are available in commercial and home made systems. They allow measurement of the response of the retina to discreet areas of stimulation within the visual field and provide retinal information similar to that obtained by static perimetry using subjective responses. Visual evoked subcortical potentials have also been recorded and although of very low amplitude, provide information on the function of lateral geniculate bodies. Although average visual evoked potentials have been used for four decades, and using flash responses, pattern-reversal responses and pattern-appearance responses, contributed to studies of the visual system in health and disease, the newer techniques of multifocal VEPs now provide more information of the response of the visual cortex to stimulation of discreet areas of the visual field. The use of either multifocal techniques or specific stimuli related to particular studies of the visual system have now contributed much more specific information. The combination of these techniques with magneto-encephalography allows the various specialised functions of the visual system to be identified and located with accuracy on specific areas of the visual cortex. This combination has the advantage of producing information on a millisecond basis with a similar degree of spatial accuracy to that provided by fMRI. PS2-01

Visual electrophysiological screening of children with nystagmus

J. Brecelj a,b, B. Stirn-Kranjc b. aInstitute of Clinical Neurophysiology; bUniversity Eye Clinic, Ljubljana, Slovenia Purpose: Ophthalmological examination may reveal the cause of nystagmus in some anomalies, e.g. congenital cataracts, glaucoma, aniridia, sclerocornea, Peter’s anomaly, and therefore do not pose a diagnostic problem. However, in infants with normal appearing fundus, some other diseases associated with nystagmus may not be as easily diagnosed. Electrophysiology could, theoretically, be helpful, but it is not known, how sensitive and specific electrophysiological changes are for detecting causes of underlying nystagmus and impaired vision from birth. Our aim was, therefore, to investigate whether ERG and VEP changes in children with such an affection could reveal the origin of the dysfunction, either retinal or along the visual pathway. Methods: ERG and VEP activity to bright white, red, and dim flashes, as well as to 30 Hz and pattern-reversal stimulation were recorded in 30 children with nystagmus. ERG were detected by skin electrodes. Results: Simultaneous ERG and VEP recordings in alert children could differentiate several patterns of changes which seem to be related to idiopathic nystagmus, Leber’s amaurosis, achromatopsia, and albinism. Conclusions: On the grounds of electrophysiological changes we could indicate the nature of the visual problem for diagnostic (and eventual therapeutic) purposes.

PS2-02

Electrical source activity of the human brain during visuomotor tasks

C. Oreja-Guevara, Felix Darvas, Anne Dieckhoefer, Helmut Buchner, Klaus-Peter Hoffmann. Neurobiology, University of Bochum, Germany

Imaging studies in humans suggest that visuomotor control of forelimb and eye movements involves reciprocal connections between striate, extrastriate, parietal, motor and frontal areas related to movement performance and visuospatial coding of movement direction. The aim of our study was to investigate the functional role of the extrastriate visual area V5 on the control of visually guided hand movements in the human, the interaction between extrastriate visual areas, parietal and motor cortex and its time course by EEG recordings with subsequent source reconstruction. Eleven subjects performed visually guided right hand movements, either tracking a horizontally moving target or performing a center out task to a stationary target by moving a cursor using a joystick. Continuous EEG with 96 electrodes was recorded. EEG signals were digitally filtered (1–60 Hz) and the location and time course of source activity were analyzed with the EASI reconstruction program. Our results show strong bilateral source activations in area V5 during visually guided hand tracking and reaching movements versus replay condition and as such demonstrated a neural network involving left sensorimotor cortex, bilateral SMA and posterior parietal cortex. The time course of activity for V5 could be grouped in two component, an early, which ranges from 125 ms to 295 ms and a late component from 771 to 884 ms, for M1 and PPC the first component was earlier. In conclusion visual monitoring during tracking and reaching requires the involvement of area V5 in a large-scale sensorimotor network.

PS2-03

The effect of task-difficulty history on current-trial visual attentional effort: an ERP study

Doron Urbach, Hedva Spitzer. Biomedical Engineering Department, Faculty of Engineering, Tel-Aviv University, Israel Visual attentional effort is not a fixed phenomenon, it can be modulated by task demands and task difficulty. Task difficulty can be determined in matching- to-sample paradigm due to the orientation differences in the nonmatching trails in an easy versus difficult block of trials. Event related potentials components N1-P2 to the sample (first) stimulus can be used as probe to measure current trials attentional effort, since this probe appear in both easy and difficult block of trials and subject cannot be aware to the level of task-difficulty of current trial till the test (second) stimulus appears. N1-P2 amplitude showed significant increase for more difficult trials. To measure the duration of this effect, the preceding block of trials, a training block with auditory feedback for correct response, was set to a different task difficulty than current block of trials (test block). No significant amplitude change in N1-P2 was found in sample stimulus of the test block due to the change in task difficulty of training block. We conclude that the effect of previous trials task-difficulty on the current trial attentional effort is short and limited to only few preceding trials.

PS2-04

Neuronal correlates of depth-perception – visually evoked potentials of a rotating Necker cube

F. Schoth, T.D. Waberski, H. Buchner. Klinik fuer Neuroradiologie der RWTH-Aachen, Germany; Neurologische Klinik der RWTH-Aachen, Germany; Klinik fuer Neurologie Recklinghausen, Germany Introduction: The change of depth-perception (FLIP) of the rotating Necker cube prefers certain flip-positions when edges overlap. Thus it is possible to study FLIPs without necessarily instructing the subjects to indicate a FLIP by pressing of a button. In this experiment we studied electrophysiologic correlates of FLIPs and the additional effects if the subject is nevertheless instructed to indicate FLIPs. Methods: 12 right-handed subjects observed a standardized rotating necker cube while recording 96 channel EEG under two conditions. They were instructed (A) to perceive the FLIPs or (B) additionally to indicate

S8

Platform Sessions

every FLIP by pressing a button with the right index. A fMRI-constrained minimum norm current-density-reconstruction calculated the electric activity of selected brain regions for every single epoch. Additional to averaging, a single epoch wavelet transform delivered the non phaselocked average in order to detect event related (de-)synchronisations. Results: No significant event related de- or synchronisations were found in condition (A). 170 ms after a flip-position a visual evoked potential was detected in 8 of 12 subjects, which at first activated the left visual cortex and, with a delay of 10 ms, also activated the right visual cortex. Multimodal parietal regions are activated at 280 ms. Response-locked analysis of the epochs in condition (B) showed mainly a movement related potential and desynchronisation in the left precentral region. Conclusion: The findings contradict the hypothesis of a role of synchronization in feature binding. According to our data the change of depth perception goes along with a phaselocked visual evoked potential.

PS2-05

Neural correlates of phosphene perception: a combined fMRI and TMS study

B. Boroojerdi a, I.G. Meister a, J. Weidemann a, H. Foltys a, R. Sparing a, T. Krings b, A. Thron b, R. To¨ pper a. aDepartment of Neurology; bDepartment of Neuroradiology, University Hospital Aachen, Germany Transcranial magnetic stimulation (TMS) applied to the occipital cortex can elicit elementary light perceptions (phosphenes). Phosphenes are potentially generated in extrastriate visual cortical areas. However, about half of the subjects tested with TMS do not report this phenomenon. The mechanisms underlying the lack of phosphene perception in this subpopulation of subjects are still unknown. We hypothesize that subjects who perceive phosphenes have a higher excitability of extrastriate cortical regions. In this study the visual cortex excitability expressed as the hemodynamic response to presentation of an alternating checkerboard pattern (frequency 8 Hz) was studied using functional magnetic resonance imaging (fMRI). Two groups of subjects were investigated, one reporting phosphenes (N ¼ 10), and the other lacking phosphene perception to TMS over the occipital cortex (N ¼ 10) to investigate the relationship between phosphene perception and visual cortex excitability. Using the random effects model, the group results of the fMRI data

revealed a larger extrastriate network activated by the checkerboard pattern in subjects who perceived phosphenes than in subjects who did not report them. We conclude that phosphene perception may be related to the extrastriate visual cortex excitability. PS2-06

Testing The Tweeniese: complex visual stimuli in paediatric VEPs

Fiona Fylan, Judith Dunne, Mitch Thomson, Stefano Seri. University of York, University of Aston, University of Derby, Birmingham Children’s Hospital Compliance can be problematic in paediatric visual electrophysiology: in order to obtain unambiguous pattern- VEP results the child is required to concentrate on the visual stimulus, and this concentration is rarely achieved if the child is upset or tired. In order to increase compliance, we have explored the use of a novel visual stimulus set: four coloured images of popular children’s television characters, The Tweeniese. Visual evoked responses were recorded from 100 normal children age 3– 16. Six stimuli were used: a checkerboard, an achromatic natural image, and four Tweeniee natural images. All stimuli had the same mean luminance and contrast, and were filtered with a Gaussian window to avoid edge effects. Stimuli appeared from a homogeneous grey background of the same mean luminance for a period of 350 ms, with an inter-stimulus interval of 350 ms. Responses to 50 stimulus presentations were recorded from O1, O2 and Oz using an FCz reference, and averaged off-line. Stimuli were presented to left and right eyes separately, and the stimulus order was randomised. Achromatic images consisted of a positive-negative-positive triphasic waveform with peaks at around 80 ms (C1), 140 ms (C2), and 180 ms (C3). A further component at about 210 ms occurred in some participants. Responses were dominated by C3. Chromatic images had peaks at the same latencies but opposite (negative-positive-negative) polarity and responses were dominated by C2. No significant differences were found between the amplitudes of major components of the check-, natural-image- and Tweeniee-evoked responses. We conclude that carefully calibrated novel visual stimuli can be used to increase compliance in paediatric clinical neurophysiology settings.

Platform Sessions

S9

NEUROPATHIES 1 PS3-01

Differences in classification of polyneuropathies

H. Tankisi a,b, B. Johnsen a,b, A. Fuglsang-Frederiksen a,b, M. de Carvalho b, P.R.W. Fawcett b, A. Labarre-Vila b, R. Liguori b, W. Nix b, I. Schofield b. a Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark; bThe ESTEEM Group There are several areas of controversy in classification of polyneuropathies (PNPs) regarding demyelination, axonal loss or mixed. The aim of this study was to examine possible differences in classification of PNPs among European physicians by use of the ESTEEM database. Methods: Seven physicians have prospectively collected cases to the database since 1992. We evaluated 156 cases of PNP from the database. Each case had a diagnosis given by the examining physician (Examination Diagnosis, 19–29 cases per physician). Each physician interpreted all cases (Interpretation Diagnosis, 150–156 cases per physician), which were subsequently discussed at consensus meetings and given a diagnose with a probability (Consensus Diagnosis, 156 cases). Results: Interpretation Diagnoses showed large differences among physicians regarding the classification of PNPs as mixed and axonal, but not regarding classification as demyelinating. The Consensus Group was more cautious than individual physicians in classifying PNPs. The probability of Consensus Diagnosis increased with increasing number of abnormal motor and sensory nerve segments tested, but not with number of performed tests. Conclusion: There are large differences in the classification of PNPs among European physicians. Recognition of differences and collaboration may promote standardization of good clinical practice and improve the quality of EMG practice.

PS3-02

Neurophysiological comparison between polyneuropathy associated with IgM vs. IgG monoclonal gammopathy

Nicola Reiser, Eva Svanborg, Magnus Vrethem. Department of Clinical Neurophysiology, University Hospital, 581 85 Linko¨ ping, Sweden Neuropathy associated with IgM monoclonal gammopathy of undetermined significance (MGUS) has been characterised as sensorimotor and demyelinating. The characteristics of neuropathy associated with IgG MGUS have not been described. We therefore wished to make a comparison. Method: 19 patients with IgM-associated neuropathy were compared with 12 age-matched (mean age 67 years) patients with IgG-associated neuropathy. Electroneurography was performed in bilateral median, peroneal and sural nerves. EMG was performed in m. tibialis anterior. Results: Motor conduction velocities were significantly lower in the IgM group than in the IgG group concerning both median nerves (38 vs. 47 m/s, P ¼ 0:08) and peroneal nerves (13 vs. 35 m/s, P ¼ 0:03). Distal motor latencies were more frequently selectively prolonged in the IgM group (6 cases vs. 3). Sensory conduction velocities were not significantly different in the median nerves, but were so in the sural nerves (9 vs. 33 m/s, P ¼ 0:02). Sensory amplitudes were not significantly different in either median or sural nerves. EMG studies did not reveal any clear differences between the two groups. Conclusion: Polyneuropathy associated with IgM-MGUS appears to be more demyelinating than polyneuropathy associated with IgG-MGUS, with slower motor and sensory conduction velocities. IgG-MGUS thus shows a milder deficit in electrophysiological studies. PS3-03

The electrophysiologic findings of the peripheral neuropathy associated with POEMS

G.A. Suarez, A. Dispenzieri, M.A. Gertz, R.A. Kyle. Mayo Clinic, Department of Neurology, 200 first St SW, Rochester, MN 55905, USA

Peripheral neuropathy (PN) is one of the main features of the POEMS syndrome. (P) Polyneuropathy, (O) organomegaly, (E) endocrinopathy, (M) M-proteins, (S) skin changes. Previous reports have only included small series of cases to allow adequate characterization. The purpose of this study was to characterize the spectrum of electrophysiologic (EMG) features in a large cohort of patients with POEMS seen at a single institution. We identified from the Mayo Clinic Rochester database 99 patients with this disorder. Eighty six patients had EMG studies performed using standard equipment and techniques. The principal EMG diagnosis was a mixed axonal and demyelinating PN with distinctive and relatively homogeneous features. Lower extremities were affected first in all cases. Nerve conduction abnormalities were distally accentuated with variable prolongation of distal and F-wave latencies and slowed motor nerve conduction velocities. Temporal dispersion and conduction block were rare. Needle examination revealed changes of distal denervation with length dependent features. In patients with serial EMG studies, proximal needle changes were more apparent with features of a polyradiculoneuropathy. The electrophysiologic features of the PN associated with POEMS syndrome are distinctive with a mixed axonal and demyelinating PN with distally accentuated demyelination. These features are different from idiopathic CIDP. PS3-04

Neurological complications syndrome. Report of 10 cases

of

primary

Sjo¨ gren

I.G. Gurtubay, C. Pe´ rez, O. Olaziregi, J. Urriza, G. Morales, O. Medrano, J. Iriarte. Clinical Neurophysiology, Internal Medicine, Hospital de Navarra and Virgen del Camino, Pamplona, Spain Introduction: Primary Sjo¨ gren syndrome (SjS) is a chronic inflammatory systemic autoimmune disease characterized by xerophthalmia, xerostomia, and dryness of other mucous membranes and the skin. Extraglandular manifestations in SjS are also common. Around 10–20% of cases associate central and peripheral nervous system complications. Distal sensorimotor neuropathy with mild to moderate deficits appears to be the most common type of neuropathy in SjS. Two rather uncommon but distinctive neuropathic syndromes have been described in association with SjS: trigeminal sensory neuropathy and severe sensory neuropathy with prominent sensory ataxia. Patients/methods: 10 patients with primary SjS and neurologic involvement are described. All of them fulfilled the criteria for classification as SjS, without clinical or serological abnormalities of other systemic disease. Results: 6 patient had polyneuropathy, 2 presented multiple cranial neuropathy. The remaining patients developed an acute encephalomyelitis and myasthenia gravis respectively. Conclusion: These cases illustrate the polymorphism of the neurological manifestations in SjS. Long term following of these patients is important because glandular manifestations may precede or follow neurological involvement. PS3-05

Nerve conduction studies in patients with diabetic neuropathy after hyperbaric oxygen treatment

Cecilia Viera, Coralina Ga´ lvez, Berta Carrasco y Rafael Castellanos. Hospital ClI´nico Quiru´rgico Hermanos Ameijeiras, La Habana, Cuba Introduction: Hyperbaric oxygen reverts hypoxia in the diabetic neuropathy. Patients and methods: We studied peripheral neuroconduction in nine diabetic patients, with distal symmetrical polyneuropathy, during normoglycemia. Four of them were insulin dependent. The electrophysiological studies were done before treatment with hyperbaric oxygen, a week

S10

Platform Sessions

and three months later. Results: The abnormal electrophysiological parameters detected were terminal latencies (enlarged), conduction velocities (slowed) and distal amplitudes of compound action potentials reduced). There were not significant changes in distal latencies, distal amplitudes and conduction velocities in peroneal nerve; the conduction velocities of the median motor nerve were slower; there was an increase of distal latency and retardation of the conduction velocities in the sensitive fibers of median

nerve; whereas the amplitude of sensitive action potentials decreased slowly after hyperbaric oxygen treatment. Conclusion: These changes suggest that large diameter peripheral fibers didn’t receive benefit with hyperbaric oxygen treatment. Dysesthesias, paresthesias, distal pains and cramps in the legs and arms, suggesting functional changes in small unmyelinated fibers, disappeared in all patients, but we can’t test fine fibers with conventional techniques.

Platform Sessions

S11

CLINICAL NEUROPHYSIOLOGY OF BRAINSTEM AND SPINAL REFLEXES PS4-01

Head retraction reflex (HRR) in the stiff man syndrome and its variants

C. Berger, C. Schranz, H.-M. Meinck. Department of Neurology, University of Heidelberg We investigated the HRR, a vestigial withdrawal reflex of the face in patients with stiff-man syndrome (SMS, n ¼ 28) and its variants stiff limb syndrome (SLS, n ¼ 2) and progressive encephalomyelitis with rigidity and myoclonus (PERM, n ¼ 20). In patients with a positive HRR on clinical testing, the electromyographic (emg) pattern was analyzed with surface recordings from the sternocleidomastoid, trapezius, and the paraspinal muscles at T5 and L3 levels. On clinical testing, 17/28 SMS patients, 10/20 PERM patients, and 0/2 SLS patients had a positive HRR ranging from a brief contraction of the neck extensors to violent retropulsion of the upper body. In all muscles, emg reflex patterns consisted of an early, synchronous and brief burst with shortest latency in the trapezius (12.5–20 ms) and a late, asynchronous and longer response with latencies between 44 and 70 ms. We conclude that the HRR is a cutaneo-muscular reflex that is probably related to the orbicularis oculi blink reflex, but involving trigemino-cervical and trigemino-spinal pathways. It is a valuable clinical tool in the diagnosis of SMS and its variants. PS4-02

Blink reflex recovery cycle. Proposal for a standard method of analysis

´ . Esteban, A. Traba, J. Prieto, A.B. Blanco, B. Godes, A. Polo. Depart. of A Clinical Neurophysiology, Hosp. General Universitario Gregorio Maran˜ o´ n, Madrid, Spain Results in the normal recovery cycle (RC) of the R2 component of the blink reflex (BR) present an enormous variability in the literature. One main reason is the difficult quantification of responses and the lack of an accepted method of measurement. Nine normal people and 8 patients with clear facilitated RC were studied. R2 test response was compared with the R2 conditioning response at interstimulus intervals (ISIs) of 100, 300, 500, and 1500 ms. Percentage of recovery of the total area, areas comprised in analysis windows (AW) of 40 and 50 ms from the start, and maximal amplitude were calculated in rectified and averaged responses. The highest sensitivity and specificity were obtained in each ISI with 40 and 50 ms AW. At 300 ms ISI, normal recovery values were of 24.9% (40 AW), and 24.1% (50 AW), which showed the highest significant differences related to the pathological ones. A standard criterion for evaluation of the R2 recovery is crucial to established consistent numerical data (recovery indexes) which permit the accurateness and simplification of these studies; present results support the use of 40–50 ms AW at 300 ms ISI as a good option. PS4-03

The startle reaction as a probe for the preparation of subcortical motor pathways before movement execution

Josep Valls-Sole´ , Christopher Summerfield, Joan Monells, Hatice Kumru, Maria Teresa Sanegre, Roberto Contreras. Unitat d’Electromiografia, Servei de Neurologia, Hospital Clinic, Barcelona, Spain The enhancement of excitability of subcortical motor pathways during preparation for execution of a ballistic movement was tested in 10 healthy volunteers by applying an auditory startling stimulus (ASS) prior to the presentation of the visual imperative signal (VS). Subjects were instructed to press a switch with their right or left hand to the presentation of the VS at the corresponding side of a computer screen. We examined 3 different paradigms. In simple reaction time (SRT), the VS appeared always in the

same side. In alternating reaction time (ART), VS was regularly alternated between sides. In choice reaction time (CRT), VS varied sides randomly. In 20% of the trials, an unexpected ASS was introduced at a fixed interval preceding the VS. In all subjects, presentation of the ASS caused the execution of the complete task. The duration of the pre-VS period of ASS responding was larger for SRT (672 1 /2122 ms) than for CRT (248 1 / 288 ms). In ART, the ASS induced responses only in the side that was being prepared. In CRT, the ASS induced responses more often in the dominant than in the non-dominant hand. Our results suggest that subcortical motor preparation takes place in all types of reaction time paradigms, and can be revealed by the analysis of the effects of external stimuli. PS4-04

F wave and H reflex studies in spasticity

Varli Kubilay, Temuc¸ in C¸ agri, Karatas Hu¨ lya. Department of Neurology, Hacettepe University Hospitals, Ankara, Turkey Spasticity is increased muscle tone caused by impaired suprasegmental inhibitory and facilitory balance that result in increase excitability of anterior horn motor neuron pool. Electrophysiologically, F wave and H reflex studies may reflect the increased excitability of motor neuron pool. We studied amplitude and area differences and correlation of CMAP, F wave and H reflex between normal volunteers and patients with spasticity. Despite some differences of mentioned parameters between controls and the spasticity group, the only statistical difference found in soleus CMAP amplitude. However, ratios of F/M and H/M in both amplitude and area increased in the spastic group compared to normal group. In normal group F/M amplitude and area ratios found 4.6% and in patient group 3.9 and 7.1 respectively. On the other hand the amplitude and area ratios of H/M were 27.9 and 26% in normal group and 63 and 33% in patient group. Those findings suggests that, despite there may not be individual amplitude or area increment in spastic patients, both amplitude and area ratios of F/M or H/M reflects the motor neuron excitability and it can be used an electrophysiologic parameter of spasticity in daily practice. PS4-05

Effects of target velocity on the timing of eye-hand coordination

Maria Teresa Sanegre, Roberto Contreras, Juan Manuel Castellote, Josep Valls-Sole´ . Unitat d’Electromiografia, Servei de Neurologia, Hospital Clinic, Barcelona. Spain Successful interception of a moving target relies partly on correct eyehand coordination. We investigated how target velocity influences the time relationship between eye and hand movements. We use two different forewarning characteristics: “verbal” in which only a verbal warning was issued 2 seconds before movement onset, and “visual”, in which an additional object moved towards the target. Reaction time of eye saccades and hand movements decreased in a direct correlation with increasing ball velocity up to the velocity of 1400 pixels/s in the condition ‘verbal’ (correlation coefficient r ¼ 0:55), but not in the ‘visual’ condition. With faster velocities, hand movement onset decreased significantly more than eye saccade latency and, in some instances, hand movements but not eye movements were made in the wrong direction. Movement precipitation and errors were more frequent in the condition ‘visual’ than in the condition ‘verbal’. Our findings suggest that hand and eye movements use different pathways. In certain task conditions, hand movements might be triggered before onset of target movement, possibly due to excessive preparation. This precipitated movement occurs significantly more often when an additional visual signal moved towards the target. Eye saccade latency shortened progressively in parallel to the increase in target velocity, with no signs of movement precipitation.

S12 PS4-06

Platform Sessions Peroneus longus muscle H reflex in L5 radicular compression

A. Recchia. Department of Neurophysiology, Hospital do Servidor Publico Estadual, Sao Paulo, Brasil Objectives: To determine the latencies of the H reflex of the peroneus longus muscle (HRPLM) and its recruitment curve in control subjects and compared to patients with L5 radicular compression. Methods: The control group consisted of 100 healthy adults, their ages varying from 18 to 72 years (mean 44.3 years) without history or signs of neurological disease. The patients group consisted of 115 patients with L5 radicular compression, their ages varying from 21 to 76 years (mean 51.2

years). The HRPLM was performed by surface electrodes in both, controls and patients. To elicit the HRPLM, the common peroneal nerve was stimulated at the knee with bipolar surface electrodes and it wasn’t necessary to employ techniques of facilitation. Results: In the control group latencies ranged from 24.1 to 31.4 msec and the mean latency was 27.1 1 /21.6 msec (mean 1 /2 SD). In the patients group, latencies ranged from 25.4 to 32.5 msec and the mean latency was 28.1 1 /21.9 msec (mean 1 /2 SD). In the patients group, the H reflex was absent on the affected side in 61 patients and present in 54 patients. In 39 patients latencies on the affected side were normal but the reflex amplitudes were up to 65% lower than those on the unaffected side. Conclusions: The HRPLM is an useful and sensitive tool for evaluating L5 radiculopathies and should become part of the routine EMG examination for whom this diagnosis is a consideration.

Platform Sessions

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MEDICAL TECHNOLOGIES ASSESSMENT 1 PS5-01

Time course of muscle MRI changes during denervation and reinnervation in an animal model: comparison with neurophysiology and histology

C. Wessig, M. Bendszus, K. Reiners, M. Koltzenburg. Wu¨ rzburg, Germany; London, UK After denervation, muscle shows MRI signal abnormalities. To study the time course and pathomechanism, we performed an animal study of MRI changes in comparison to electrophysiology and histology during nerve degeneration and regeneration. The sciatic nerve of adult rats was compressed by a tight suture which was opened after one week. Serial EMG and motor nerve conduction studies were conducted in parallel to MRI scanning and muscle histology. Hyperintensity on T2 weighted MRI of the soleus muscle started two days after lesion and reached a maximum after four weeks. Signal changes normalized after eleven weeks. Spontaneous activity in the muscles was found from day two after lesion, regressing after two weeks in lower leg and six weeks in foot muscles. First voluntary activity on EMG occurred four weeks after lesion in the lower leg, CMAP in the foot muscles reappeared seven weeks after lesion. Muscle atrophy in the lower leg was maximal after 6 weeks, normalizing after 13 weeks. On histology, beside the atrophy of muscle fibres, a marked increase of muscle perfusion was seen with a maximum four to six weeks after the lesion which regressed after that time point. In conclusion, MRI of the muscle shows signal changes in denervated muscle which normalize during regeneration in parallel to neurophysiological and histological alterations. PS5-02

Concurrent myoelectric signal detection by needle and surface EMG: correlations and disparities

J.-Y. Hogrel a, J.-P. Lefaucheur b, J. Ducheˆ ne c. aInstitut de Myologie, GH Pitie´ -Salpeˆ trie`re, 75651 Paris Cedex 13, France; bHoˆ pital Henri Mondor, Physiologie et Explorations Fonctionnelles, 94010 Cre´ teil Cedex, France; c Universite´ de Technologie de Troyes, 12, rue Marie Curie, 10010 Troyes Cedex, France Recent works have demonstrated the possibility of detecting single motor unit action potentials by means of high spatial resolution surface EMG. Few comparison data are available concerning the correlations between needle EMG and surface EMG. The aim of this preliminary work consisted in exploring the correlations and disparities between these two detection techniques when concurrently implemented. Needle and surface measurements were simultaneously performed on small muscles of he hand during short contractions at various force levels. Temporal and spectral parameters were estimated for both signals and examined by means of a correlation analysis. When the electrodes investigated nearby muscle volumes, high correlations between the parameters computed from needle and surface EMG signals were assessed. As expected, these correlations were lost as soon as the needle was located deeply within the muscle. As a conclusion, when proper detection conditions are reach, i.e. when skin and fat thickness are small, high spatial resolution surface EMG can provide the same information that needle EMG. However this technique is devoted to the detection of the most superficial motor units within superficial muscles. PS5-03

Early diagnosis of diaphragmatic involvement in ALS patients using diaphragmatic needle EMG

H. Lahrmann, G. Albrecht, P. Hitzenberger, M. Wild, U. Zifko, W. Grisold. Department of Neurology and L. Boltzmann Institute of Neurooncology, Kaiser Franz Josef Hospital, Private Ordination, Vienna, Clinic of Rehabilitation, Bad Pirawarth, Austria

Introduction: Early diagnosis of respiratory muscle involvement in ALS patients can help to plan mechanical ventilation and palliative care interventions before respiratory failure occurs. We investigated the correlation between pathological diaphragmatic needle EMG (EMGdia) and dyspnea, bulbar involvement, lung and respiratory muscle function and duration of disease. Methods: In 22 successive ALS patients (13 female, 9 male, age 47–81 yrs) we assessed Karnofsky and dyspnea score, EMGdia, phrenic nerve conduction, lung function (vital capacity, VC) and inspiratory muscle strength (maximal inspiratory mouth pressure, Pmo). Results: In 10 patients we recorded a pathological EMGdia (group I), in 12 it was normal (group II). There was no difference between groups regarding Karnofsky score (overall mean 69 ^ 19%) and duration of disease (13 ^ 9 months). Bulbar signs and dyspnea were observed in group I significantly more often. VC did not allow to differentiate between groups whereas Pmo was significantly lower in group I (group I: 35 ^ 19 cmH2O; group II: 62 ^ 21 cmH2O). Phrenic nerve conduction studies were not significantly different between groups. Conclusion: Our results indicate that EMGdia and Pmo are more valuable parameters for the early diagnosis of inspiratory muscle involvement in ALS than lung function alone. PS5-04

One method of fast-Fourier-analysis for evaluation of interference pattern in electromyography

J. Siivola, I. Mahjneh, J. Heino. Kainuu Central Hospital and Institute of Technology, Kajaani, Finland In this study we have used the new fast-Fourier method (FFT) in evaluation of interference patter (IP) in clinical electromyography (EMG). The power spectrum of IP has been calculated up to 400 Hz. This total spectrum has been divided to three different bands (slow, mid and fast). The powers for each of these bands have been calculated with our FFT-program. This calculation per one point in EMG takes time from one to two seconds. It means that practically our method is on-line evaluation. We propose the following hypothesis: in myopathy the fast band will be accentuated when compared to the controls, and in neuropathy; correspondingly the slow band. Our preliminary material consists of 12 controls and of 1 neuropathic and 3 myopathic disorders. The biceps brachii and/or rectus femoris muscles were examined in every subject. The patient material followed our hypothesis. The recordings of controls and patients will be continued. PS5-05

Simulation studies on irregular motor unit potentials

Ewa Zalewska a, Irena Hausmanowa-Petrusewicz b, Erik Sta˚ lberg c. aInstitute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences, Trojdena 4 Str, 02-109 Warsaw, Poland; bNeuromuscular Unit, Medical Research Centre, Polish Academy of Sciences, Banacha 1a Str, 02097 Warsaw, Poland; cDepartment of Clinical Neurophysiology, University Hospital, SE-751 85 Uppsala, Sweden The aim of simulation EMG study was to examine the structural conditions necessary to generate “irregular MUPs”. The structural features: fiber density, diameters and recording distance from end-plate zone were considered. Irregular potentials were generated more easily with low fiber density and with smaller fiber diameters. The irregularity of potential increases with recording distance from the end-plate zone beyond 20 mm. One fiber with a diameter difference of more than 10% from mean value, located close to electrode, affects MUP irregularity. We have derived an equation that allows to define when an irregular potential may be generated e.g. to approximate number of fibers contributing to the irregularity of MUP. Fibers located at distances exceeding a given

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Platform Sessions

distance rmin, typically about 400–500 mm, do not influence the MUP irregularity, but contribute to background activity only. If the number of fibers within this radius is small (typically 2–6) the MUP becomes irregular. The established relationships explain the occurrence of irregular potential in given structural conditions. The results may be useful in interpretation of MUP characteristics in various pathological processes.

PS5-06

Quantification of insertional activity by turn/amplitude analysis

J. Finsterer, B. Mamoli, A. Fuglsang-Frederiksen. LBI for Research in Neuromuscular Disorders, Vienna; Department of Neurophysiology, University Hospital, Aarhus, Denmark Quantification of needle- induced insertional activity (IA) by means of

the turn/amplitude analysis (TAA) has not been attempted so far. IA was recorded from the right brachial biceps and right anterior tibial muscle of 29 healthy subjects, 17 woman, 12 men, aged 24–79 years and 52 patients with neuromuscular disorders, 24 women, 28 men, aged 17–81 years. IA was analysed with regard to IA-duration (IAD), turns/second (T/S), amplitude/ turn (A/T) T/S:IAD and A/T:IAD. IAD was not significantly different between healthy and diseased subjects in either of the two investigated muscles. On the contrary, T/S, A/T, T/S:IAD and A/T:IAD were significantly increased in the biceps brachii muscle of patients with neuropathies and myopathies. Also T/S and T/S:IAD In the anterior tibial muscle were significantly increased in patients with neuromuscular disorders. It is concluded that TAA is effective to quantify IA, particularly by means of the parameters T/S and T/S:IAD, being increased in patients with neuromuscular disorders.

Platform Sessions

S15

SLEEP, NEW CLINICAL/CN DEVELOPMENT AND TREATMENT Sleep; new clinical=CN development T. Sagale´ s. S. Clinical Neurophysiology, Hospital Universitari Vall d’Hebron, Barcelona, Spain Sleep is the period in which patients are not aware but can be easily arise to wakefulness with external sensory stimuli. The conventional way to evaluate sleep is with polysomnographic recording of different parameters but several other ways of recording have been tried in order to classify sleep and to evaluate the limits between awareness and sleep. Sleep physiology and pathology is under continuos study and revision and new alterations are identified every year. Sleep repercussion is important for the quality of wakefulness of the next day, and daily activity is important for the quality of sleep. It is difficult to consider sleep without its daily repercussion. Every time is more important not to consider sleep as an isolated phenomena if not as part of the circadian activity and the evolution and maturation of the human been. This continuity in the physiology of the sleep is very important in the diagnosis and prognosis of sleep disorders. The combination of these techniques with changes in macro and microstructure of the different parameters will allow us to identify and make accurate evaluations of the different pathologies as insomnia, hypersomnia or circadian disorders.

PS6-01

Pathophysiology of periodic limb movement disorder (PLMD): activity patterns of the leg movements

A.W. de Weerd, R.M. Rijsman, A. Brinkley. Sleep Centre and Department of Clinical Neurophysiology MCH, Westeinde Hospital, The Hague, The Netherlands In PLMD specific leg movements have been described: lifting toe and foot (M.extensor dig.brevis: EDB and M tibialis anterior: TA), bending of the knee and hip (M.biceps femoris: BF and M.iliopsoas and M.tensor fasciae latae: TFL). There is doubt whether this is true. The study aimed at description and analysis of sequences of movements in PLMD. All leg movements in the before mentioned muscles together with those in the M.quadriceps: Q and M.soleus: S were recorded using surface EMG in 12 patients with severe idiopathic PLMD. Sleep was recorded simultaneously. 469 Movements were analyzed. The classical sequence: EDBTA-BF-TFL or its variants was found in only 11% of the movements. Most frequent were contractions starting in TA-EDB followed by all variations of other muscles (32%) and contractions starting in EDB-TA followed by all other variations of muscles (18%). Other combinations appeared in much smaller numbers, often only once. Three patients consistently started with the same muscle. One patient contracted all 6 muscles; 6 patients never contracted more than 3 muscles. The number of muscles contracted correlated positively with the appearance of arousal from sleep. All forms of movements occurred in deep as well as in superficial sleep. Conclusion: Many variations of leg movements were documented. The classic PLMD leg movement was seen in only 11%. Patterns of movements were recognisable. These patterns were related to arousals, but not to sleep stage. The patterns found suggest activation of motorneurons “jumping” through the spinal cord instead of an anatomic logical sequence of firing. PS6-02

Restless leg syndrome in patients with multiple sclerosis

P. Lo´ pez-Esteban a, C. de Andre´ s de Frutos b, R. Peraita-Adrados a. aSleep Unit; bNeurology Service, Hospital General Universitario Gregorio Maran˜ on, Madrid, Spain Objective: To determine the influence of RLS on the sleep of patients with Multiple Sclerosis.

Patients and methods: We studied 32 patients with MS: 12 men, 22 women; mean age 42.03 ^ 10.6 years; mean time of outcome of the illness 7.65 ^ 6.43 years. We gave all patients a Questionnaire on the presence of RLS. All patients underwent a standard nocturnal PSG recording. Results: 75% of patients referred RSL. Of those patients who said they slept well, 69.56% referred RSL and of those patients who slept badly, 88.8% had RLS. Taking the results of PSG, the patients with RSL, had a longer sleep latency (P ¼ 0:001), and clinically. We did not find statistically significant differences in relation to the number of sleep cycles, sleep efficiency and fragmentation indexes, WASO, PLM index and time of outcome, between patients with RLS and those who did not. Conclusion: The incidence of RLS in MS is 75%, and there is no relation with the presence of PLM. PS6-03

Obstructive sleep apnea in long term diabetic patients

M.J. Murillo a, J.M. Limin˜ ana a, F. RodrI´guez de Castro b, G. Pe´ rez b, P. Cabrera b, G. Julia´ b. aUniversity of Las Palmas; bPneumology Department, Dr. NegrI´n Hospital, Las Palmas, Spain Objective: To study whether differences exist in the sleep of long term diabetic and non-diabetic patients with obstructive sleep apnea syndrome (OSAS). Method: Of the 900 patients sent consecutively for a polysomnogram (PSG) with clinically suspected OSAS, we selected patients with OSAS (Apnea-Hypopnea Index (AHI) .10) and Diabetes Mellitus (DM) of more than ten years duration. We chose a control group of patients with OSAS, without diabetes, matched for age, sex, body mass index (BMI) and blood pressure. In both groups, we measured sleep latency (SL), sleep efficiency (SE), stages 1, 2, 3 and 4 of NREM sleep, REM sleep, AHI, frequency of desaturation events (FDE) and minimum oxygen saturation (MSaO2). The statistical comparison was carried out by means of the Wilcoxon test for matched groups. Results: The average age of the diabetic patients was 61.48 ^ 10.25 years and the mean BMI 33.57 ^ 5.87, and in the control group the mean age was 59.95 ^ 8.64 years and the mean BMI 33.42 ^ 6.29. The diabetic patients showed a mean AHI of 46.22 ^ 27.26, a mean FDE of 22.07 ^ 25.53, and a mean SaO2 of 76.62 ^ 13.68. The non-diabetic patients had a mean AHI of 30.55 ^ 18.11 (P , 0:020), a mean FDE of 7.90 ^ 15.19 (P , 0:039) and a mean MSaO2 of 85.10 ^ 7.48 (P , 0:049). There were no differences between both groups with regard to SL, SE, stages of NREM and REM sleep. Conclusions: OSAS in long term diabetic patients is more severe than in non-diabetic patients. PS6-04

Respiratory related evoked potentials as the trigger of cortical arousal in obstructive sleep apneas: preliminary results

M. Merino-Andreu a,d, I. Arnulf d, C. Raynaud a, M. Zelter a,b,d, J.-Ph. Derenne a,c, T. Similowski a,c, C. Straus a,b. aUPRES EA 2397; bExplorations Fonctionnelles Respiratoires; cPneumologie; dFe´ de´ ration des Pathologies du Sommeil, Hoˆ pital Pitie´ -Salpeˆ trie`re, AP-HP, 75651 Paris cedex 13, France Introduction: The obstructive sleep apnea syndrome (OSAS) is characterized by recurrent upper airway collapse. Each apneic episode include inspiratory efforts against the occluded airway and is terminated by a cortical arousal that restores upper airway patency, allowing ventilation to resume. Objective: Occluded inspiratory efforts being typically associated with evoked cortical potentials in awake normal subjects, we assessed the role of putative potentials evoked by the apnea-associated inspiratory efforts in the termination of obstructive sleep apneas.

S16

Platform Sessions

Methods: Inspiratory efforts (E) were identified from oesophageal pressure swings and apneas by the absence of nasal flow. We averaged EEG (C3-Cz, C4-Cz) epochs (from 200 ms before to 1000 ms after E onset) corresponding to the antepenultimate (E2), penultimate (E1) and ultimate (E0, arousal) efforts of 140–150 apneic episodes. Results: No potential was visible in relationship to E2. E1 evoked a positive component with a peak latency of 108 to 175 ms. E0 evoked potentials similar to those recorded in normal awake subjects. Discussion: If confirmed, these very preliminary results would suggest that the cortical arousal allowing ventilation to resume at the end of an obstructive sleep apnea depend directly on the processing of respiratory related afferences by the primary sensory cortex. Funded by ADOREP.

PS6-05

Ambulant polysomnographic daytime nap-features show differentiation between narcolepsy and hypersomnia eci patients

R.J. Schimsheimer, I.H. Linskens. Centre for Sleep and Wake Disorders, The Hague, The Netherlands

Objectives: Evaluation of the diagnostic value of daytime nap-features in Ambulant Polysomnography (APSG) for hypersomnolence complaints objectivated by MSL test. Patients: The records of 47 patients (17 narcolepsy, 30 hypersomnia eci), who underwent an APSG before MSL test, were screened. Results: The MSL test was positive in 20 patients; negative in 27 patients. The narcoleptics took on the average 1.4 daytime naps in their APSG versus 0.8 in the eci’s. The Total Sleep Time in all naps was average 22.5 minutes for the narcoleptics versus 26.2 minutes for the hypersomniacs eci. The narcoleptics spent 51.1% of the TST in stage II versus 76.3% in the eci’s. The percentage SWS/TST was in the narcolepsy group 23.9%, versus 19.1% in the eci group. The narcoleptics spent 25% of the TST in REM versus 9.2% in the eci’s. The mean REM latency was 14.1 minutes in the narcoleptics; 59.5 in the eci’s. Conclusion: Ambulant Polysomnographic daytime nap-features show differentiation in sleep architecture between narcolepsy and hypersomnia eci patients. The narcolepsy patients took more naps, shorter of duration but deeper in sleep stage and with more REM sleep than the hypersomnia eci patients.

Platform Sessions

S17

TELEMEDICINE AND SLEEP PS7-01

Neurophysiological correlates of dream recall and dream content in blind and sighted

Helder Bertolo, Tiago Mestre, Teresa Paiva. EEG/Sleep Laboratory, Egas Moniz Studies Center, Faculty of Medicine of Lisboa, Portugal Correlations between dream recall/ dream content and EEG spectral content and REMs both in sighted subjects and congenital blind. 10 congenital blind were compared with a control sighted group, through two consecutive home polysomnographic recordings, with periodic awakenings; dream recalls were tape recorded and REM awakenings were selected. FFT power spectra from C4-A1 and O2-A1; REMs detected by visual inspection on both EOG channels and classified as isolated or in bursts. Dream recall, defined by the existence of a report, implied content analysis using the Hall & Van de Castle criteria for visual activity. Both groups presented equivalent visual activity indexes (VAI); significant negative correlation between VAI and alpha power in the central and occipital derivations; average of REM awakenings per subject and identical the recall ability. Higher delta power in O2 was associated with no dream recall, whereas higher sigma was associated with the presence of dream recall both in C4 and O2. Blind had lower alpha activity and beta in the central derivation; higher values of delta, theta and sigma activity; lower REM density, bursts and isolated eye movements. REM dream visual content and recall are associated with changes in EEG frequencies and REMs. Blind and sighted had only minor differences in observed features. PS7-02

Rhythmic slow oscillations in human medial pulvinar during paradoxical sleep

He´ le`ne Bastuji, Marc Gue´ not, Jean Isnard, Philippe Ryvlin, Franc¸ ois Mauguiere, Michel Magnin. 1. EA 1880-IFR 19, Hoˆ pital Neurologique Lyon, France During Paradoxical Sleep (PS) as in wakefulness, the spontaneous thalamic activity is known, from animal studies (see Steriade et al. 1997), to be composed of preponderant fast frequency oscillations. Using intra-cerebral recordings for pre-surgical evaluation in epileptic patients, we disclosed rhythmic slow oscillations (RSO) so far not described in the human medial pulvinar nucleus during PS. RSO were present continuously during all PS episodes. They were clearly observable by visual inspection and yielded a specific peak between 1.3 and 3.3 Hz on spectral analysis. This peak was clearly distinct from the usual one observed between 0.5 and 1 Hz. This phenomenon was present when thalamic electrodes were located more anteriorly within the medial pulvinar, i.e. in 5 out of nine recorded patients. The PS specificity of these RSO is strongly suggested by their absence during both wakefulness and slow wave sleep. The functional significance of such slow oscillations in the medial pulvinar during paradoxical sleep remains to be determined as well as their possible relationships with some equivalent activities in the cortex and hippocampus recently described (Bo´ dizs et al. 2001). Steriade M, Jones EG and McCormick DA. Thalamus, 1997, Elsevier. Bo´ dizs et al. Hippocampus, 2001; 11: 747–753.

PS7-03

Excessive daytime sleepiness (EDS) and sleep-disordered breathing in patients with progressive supranuclear palsy (PSP)

M. Merino-Andreu, I. Arnulf, F. Bloch, M. Vidailhet, J.P. Derenne, Y. Agid. Fe´ de´ ration des Pathologies du Sommeil et CIC, Hoˆ pital Pitie´ -Salpeˆ trie`re, Paris, France

Introduction: REM sleep dysfunction has been reported in parkinsonian patients, caused by lesions in brainstem structures. In PSP, parkinsonism and ophthalmoplegy are associated with a decrease in REM sleep duration. Objective: To examine EDS and REM sleep abnormalities in patients with PSP. Methods: Eighteen patients (aged 55–81 years) with PSP lasting for 1–10 years, underwent polysomnography and multiple sleep latency tests (MSLT). Mean mini-mental score was 22 ^ 6. Twelve patients were treated with levodopa (480 ^ 170 mg/d), 6 with benzodiazepines and 6 with serotonergic antidepressant drugs. Results: The percentage of REM sleep was reduced in all patients (9.7 ^ 1.6%) and REM sleep without atonia was present in 7 patients (range: 0–98%). Mean daytime sleep latency was abnormally low (,2 minutes) in 5 patients with no narcolepsy-like pattern and normal values (.8 minutes) were found in 12 patients. Sleep fragmentation was severe (49 ^ 24 arousals per hour; range: 20–127), caused by obstructive sleep apnea syndrome in 14 (78%) patients, 6 of whom were receiving benzodiazepines, and periodic leg movement syndrome in 13 (72.2%) patients. Conclusion: One-third of PSP patients suffered from non-narcoleptic daytime sleepiness caused by sleep-disordered breathing and/or periodic leg movements. The prognostic importance of this finding remains to be evaluated. PS7-04

Alpha power and maintenance of wakefulness test

Jussi Virkkala, Mikko Ha¨ rma¨ , Susan Pihl, Kiti Mu¨ ller. Brain and Work Research Units, Finnish Institute of Occupational Health, Helsinki, Finland Our aim is to develop methods to predict unintentional sleep onset caused by sleepiness. Most sleepiness tests studies are done using the Multiple Sleep Latency Test (MSLT). However the ability to maintain wakefulness is more relevant in many occupations e.g. professional drivers and industrial operators. Sleepiness was evaluated by calculating eyes open Alpha Power. Ability to maintain wakefulness was tested with Maintenance of Wakefulness Test (MWT). A total of 1076 MWT were recorded and analysed from train drivers and remote controllers. The shortest S1 latency was 1.5 min, mean 32.3 min and in 685 recordings no sleep epochs were detected during the 40 minute MWT test. Power spectrum from O1-A2 channel was calculated from the first minute of MWT recordings. Due to instructions to stay awake it was assumed that eyes were open during the analysed one minute period. A slight but significant correlation was observed between the S1 latency of MWT and the relative alpha power of the first minute of MWT. PS7-05

Localization of human sleep spindles from whole night sleep

S.-L. Himanen, M. Tenhunen, P. Laarne, J. Virkkala, J. Hasan. Tampere University Hospital, Tampere and Finnish Institute of Occupational Health, Helsinki, Finland Purpose: The majority of slow and frontal sleep spindles are located in the beginning of night (Himanen et al. JSR 1/2002). Therefore the sources of the frontal and central spindles were compared in the beginning and end of night. Method: All-night 64-channel EEG was recorded from one healthy female. Frontal and central spindles from the first and last NREM-sleep episodes were selected by visual judgment and spectral mapping. Each spindle was modeled by single moving dipole with interval mode by Source program (Neurosoft Inc.). The best fitted time point was taken as a source estimate. Results: All dipoles were located in the thalamic area. The majority of

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Platform Sessions

dipoles (7/11) of the frontal spindles in the first episode pointed frontally and 2 parietally whereas in the last episode 7/10 pointed occipitally and 3 frontally. All 5 central spindles in the first episode pointed parietally (mainly posterior to frontal ones). In the last episode all 3 central spindles pointed caudally.

Conclusion: This pilot study showed the sources of the spindles to differ by type and by sleep episode. This strengthens our former observation, that the topography and temporal position (in all sleep stages) of spindles have to be taken into account when sleep spindles are studied.

Platform Sessions

S19

NEUROPEDIATRICS PS8-01

Visual evoked potential and ophthalmological pathology in children with Angelman’s syndrome

Maria Kraemer a, Anders Sjo¨ stro¨ m a, Ma˚ rten Kyllerman b. aPædiatric Eye Unit; bPædiatric Neurology Unit, The Queen Silvias Hospital for Sick Children, SE-416 85 Go¨ teborg, Sweden

tions, particularly ubiquitin 3A, when both clinical and EEG findings are positive despite normal methylation tests.

PS8-03

Seizure detection in the neonatal EEG with synchronization likelihood

J. Altenburg, R.J. Vermeulen, R.L.M. Strijers, W.P.F. Fetters, C.J. Stam. VU Medical Center, Amsterdam, The Netherlands

Purpose: Angelman’s syndrome (AS) is a genetic condition with mental retardation, motoric and sensoric impairments. Diagnose is made with genomic investigations (genotype) and/or by typical phenotypic features. Children with Angelman’s syndrome may have visual and ocular dysfunctions. We investigated the visual function with electrophysiological (VEP) and ophthalmological tests to evaluate the level and degree of dysfunctions and whether the genotype-AS differ from the phenotype-AS. Method: Children with verified AS (N ¼ 18) were examined with electrophysiology (VEP; supramaximal light flash stimuli, rec. sites O1, Oz and O2) and ophthalmic examinations (visual acuity, cover test, retinoscopy, ophthalmoscopy). Results: VEP was abnormal in 80% of the AS children; prolonged latencies, abnormal wave form and side asymmetries. Refractive errors and squint were found in approximately 50%. The genotype AS were generally more visually affected. Conclusion: Earlier studies reported that strabism and albinism (side asymmetries to monocular stimuli in the VEP) were common in patients with Angelman’s syndrome. We also found a high incidence of squint, albinism (VEP-verified) and several signs indicating subnormal and in many cases poor visual function (low estimated visual acuity, abnormal VEP-findings). The patients with genotype AS were more represented in the group with the poorest visual function. Thus, it seems that the electrophysiological and ophthalmological findings can add valuable information to the investigation of patients with suspected or verified Angelman’s syndrome. Additionally, it is important for the child, the family and the physician that the visual function is examined and that information and treatment is given when needed.

Objective: To investigate whether epileptic seizure activity can be distinguished from non-epileptic background activity in the neonatal EEG, using synchronization likelihood as a measure of synchronization between EEG channels. Methods: Forty-two 21s EEG epochs and 2 complete EEG’s from 21 different neonatal patients in a 12-channel bipolar recording were studied (AD conversion 16 bit; Sample frequency 200 Hz; filter setting 0.5–30 Hz) For each patient EEG we selected one epoch with epileptic discharge and one without. Synchronization was calculated in all epochs. In two complete EEGs synchronization was calculated and correlated with a visual scoring of the EEG. Results: Synchronization likelihood was higher in all the epochs with epileptic seizures as compared to the epochs without epileptic activity (P , 0:01). When synchronization likelihood exceeded 0.11 the sensitivity for the presence of epileptic activity was 0.86 (95% confidence limits ½CL95 ¼ 0:71–1) and the specificity was 0.76 (CL95 ¼ 0:58–0:94). Analysis of EEG score and synchronization likelihood of two complete EEGs revealed a high correlation between the occurrence of epileptic seizures and elevated synchronization likelihood (r ¼ 0:707, P , 0:001). Conclusions: The results of this study demonstrate that synchronization likelihood is a potential tool in the automatic monitoring of high-risk infants for epileptic activity on neonatal wards.

Angelman’s syndrome in twins with characteristic EEGs and the ubiquitin 3A mutation, but with normal chromosome 15 methylation

R.J. Vermeulen, L.T.L. Sie, E.J. Jonkman, R.L.M. Strijers, H.N. Lafeber, B.M. Uitdehaag, M.S. van der Knaap. VU Medical Center, Amsterdam, The Netherlands

PS8-02

J. Ray, T. Bukhari, K. Maw, H. Firth, E. Reid, S. Boniface. Addenbrookes Hospital, UK Background: Angelman’s syndrome is an inherited disorder that includes severe mental retardation and epilepsy. The majority of cases are secondary to a deletion or mutation affecting chromosome 15, associated with abnormal methylation of the CpG region of the SNRPN promoter. Here we present monozygotic twins in whom Angelman’s was diagnosed on the basis of clinical and EEG investigations. Genetic studies, however, revealed a statistically rare gene defect that occurs in less than 5% of cases. Clinical details: Monozygotic twins (male) presented at 3.5 yrs with seizures and developmental delay affecting both motor function and speech. Physical features included plagiocephaly and a spastic gait. Absences, myoclonic episodes and tonic-clonic attacks were observed. Investigations: Methylation studies were normal. Both EEGs, however, demonstrated characteristic triangular shaped posterior slow wave activity, accentuated with eye closure, with bursts of slow irregular spike and wave posteriorly maximal. Subsequent analysis revealed a point mutation affecting the Ubiquitin 3A gene on chromosome 15. Normal function of ubiquitin ligase has recently been shown to be involved in animal models of longterm potentiation. Conclusion: This case illustrates the probable need to study gene muta-

PS8-04

Predictive value of EEG in neonates with periventricular leukomalacia

We evaluated whether the EEG (i.e. positive rolandic sharp waves [PRSW] and background pattern) can be used to predict neurodevelopment in neonates with periventricular leukomalacia (PVL) in comparison with MRI. A sequential cohort of neonates (n ¼ 46) with periventricular hyperdensities on cranial ultrasound was recruited for this study. EEGs were analyzed for PRSW and background pattern (interburst interval, delta brushes, and encoches frontales). Neurodevelopment was evaluated at the corrected age of 12 and 18 months. The number of PRSW correlated with neurodevelopment (P , 0:01) and with the extent of the white matter damage on MRI (P , 0:01), whereas it did not show any correlation with background pattern. In the whole group the probability of a bad outcome (i.e. severely impaired development or death) was 24% and the probability of any impairment was 33%. If the number of PRSW was ,0.1 per minute, the probability of a bad outcome was reduced to 9% (95% confidence interval [CI95] 3–25%) and the probability of any impairment was reduced to 13% (CI95 5–30%). In all infants with PRSW .0.1 per minute, the probability of a bad outcome was 41% and of any impairment was 55%. If the EEG of an infant with PVL contains ?0.1 PRSW per minute the probability of a normal or mildly delayed development is high (0.91). MRI does enhance the accuracy of this outcome prediction. If the frequency of

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Platform Sessions

the PRSW exceeds a frequency of 0.1 per minute, MRI can enhance the precision of the prediction of outcome significantly.

PS8-05

Coma in infants: a clinical and EEG study

E. Esquivel-Walls, A. Rousset, P. Daoud. Paediatric Intensive Care Unit, Andre´ Gregoire Hospital, Montreuil/Bois, France The difficulties of the clinical approach in young children with impairment of consciousness are well known. Here, the clinical course, outcome and EEG features in 17 infants with a coma diagnosis are studied. All children were admitted to the Paediatric Intensive Care Unit at Montreuil Hospital from 1998 to 2002. Ages ranged from 1 to 22 months. The coma assessment was based on clinical examination and evaluated using the Glasgow coma scale modified for children.

The causes were; infection (6 infants), followed by sudden infant death syndrome (5), gastro-enteritis (3), foreign body obstruction (2) and near drowning (1). Eight children had seizures before admission but only five of them presented status epilepticus. Abnormal movements had been reported in eight infants, three of whom were monitored with EEG-video. The first EEG records showed various patterns; isoelectric (4), suppression-burst (3, including 1 with myoclonic status), high-amplitude slow wave (3), critical discharges (4), sleep activity (2) and asymmetrical activity (1). None of the children presenting isoelectric, suppression-burst or highamplitude slow wave features survived. Only five infants did survive, one with normal, three with moderate and one with severe outcomes. EEG is thus a useful tool not only for diagnosis and monitoring of status epilepticus, but also for the prognosis of outcomes in infant coma.

Platform Sessions

S21

AGING AND DEMENTIA: NEUROPHYSIOLOGY, NEUROPSYCHOLOGY AND NEUROIMAGING PS9-01

In vivo neurophysiological evaluation of cholinergic cortical activity in Alzheimer’s disease

V. Di Lazzaro, A. Oliviero, P.A. Tonali, C. Marra, A. Daniele, P. Profice, E. Saturno, F. Pilato, C. Masullo, J.C. Rothwell. Institute of Neurology, Universita` Cattolica, L.go A. Gemelli 8, 00168 Rome, Italy A recently devised test of motor cortex excitability (short latency afferent inhibition) has been shown to be sensitive in healthy subjects to blockade of muscarinic acetylcholine receptors. We have used this test to assess cholinergic transmission in the motor cortex of patients with Alzheimer’s disease. We evaluated short latency afferent inhibition in 15 patients with Alzheimer’s disease and compared the data with that from 12 age-matched healthy individuals. Afferent inhibition was reduced in the patients (responses reduced to 85.7 1 15.8% of test size) compared to controls (responses reduced to 45.3 1 16.2% of test size, P , 0:001, unpaired ttest). The administration of a single oral dose of rivastigmine improved afferent inhibition in a subgroup of 6 patients. The findings suggest that this method can be used as a non-invasive test of cholinergic pathways in Alzheimer’s disease. Future studies are needed to evaluate whether short latency afferent inhibition can aid diagnosis of AD and monitor treatment efficacy. PS9-02

Involvement of motor control in Alzheimer’s disease: EEG and behavioural evidence

L. Leocani a, G. Magnani b, I. Tikhonova a, M. Cursi a, A. Inuggi a, G. Comi a,b. a Clinical Neurophysiology; bNeurology, University Vita-Salute, Scientific Institute Hospital San Raffaele, Milan, Italy Background: Involvement of motor function is considered to occur at relatively late stages of Alzheimer’s disease. Movement-related potential (MRP) and event-related desynchronization(ERD) of the sensorimotor EEG rhythms indicate cortical activation during movement preparation and execution, while post-movement beta synchronization (ERS) is considered a correlate of cortical inactivation. We investigated motor function in AD patients asymptomatic to motor deficits using motor tapping and EEG analysis. Methods: Twenty patients affected by probable AD, without clinical motor (age 68 1 9 yrs) and 17 normal subjects (age 59 1 6 yrs) were studied. Finger motor tapping was measured 3 times for each side. MRP and mu and beta ERD/ERS to self-paced right thumb movement were measured with 58 channel EEG in 12 AD patients and 10 normal subjects. Results: Motor tapping was significantly slower in AD patients (right: 3.1 1 1 Hz; left: 2.9 1 0.8 Hz) than in normal subjects (right: 4.5 1 1 Hz; left: 3.8 1 0.8 Hz, P , 0:006). Movement-related potential had significantly reduced amplitude in AD patients compared to normal subjects (P , 0:05). Mu and beta contralateral sensorimotor ERD/ERS did not significantly differ in the two groups; beta ERD/ERS were significantly more widespread in AD patients being larger over frontal and parietal electrodes (P , 0:05). Conclusions: These results suggest that subclinical motor involvement may be present in Alzheimer’s disease; these abnormalities are related to changes in the activation of cortical motor circuitries in relation to selfpaced movement.

PS9-03

Cortical excitability in patients with dementia (transcortical magnetic stimulation study)

Varli Kubilay, Mavilioglu Aylin, Temuc¸ in C¸ agri. Department of Neurology, Hacettepe University Hospitals, Ankara, Turkey Cortical excitability can be altered by various diseases that affect the motor control. Some different parameters can be used to investigate the cortical excitability in transcortical magnetic stimulation studies. Those parameters are motor excitability threshold, MEP amplitude, silent period, intracortical inhibition and intracortical facilitation. In this study we studied cortical excitability treshold, silent period (also by median nerve stimulation) and MEP amplitudes in 9 patients with dementia, 7 patients with Parkinson’s Disease (PD) and 22 normal healthy control. The patients evaluated by means of history of disease, neurologic examination, standardized mini mental state test, cranial MRI. Transcortical magnetic excitability threshold found to be low and silent period found to be prolonged in patients with Alzheimer Disease (AD) compared to controls. Long loop reflexes were prolonged in the patients with PD and AD. MEP amplitude ratio (cortical/root stimulation) was decreased in dementia patients and this is more prominent in the patients with lokoariosis and Huntington Disease (HD). Those findings are suggestive for altered cortical inhibitory–excitatory balance and decreased inhibitory activity and this is more prominent in HD. Those changes might be due to decreased GABAergic activity. PS9-04

Effect of aging on selective attention to touch: evidence of a reduced inhibitory control in old subjects

Francesca Ranghi a, Massimiliano Valeriani b,c, Salvatore Giaquinto a. aCasa di Cura San Raffaele Pisana, Tosinvest Sanita`, Roma, Italy; bDepartment of Neurology, Universita` Cattolica del Sacro Cuore, Roma, Italy; cDepartment of Neurology, Ospedale Pediatrico Bambino Gesu`, IRCCS, Roma, Italy Our study aimed at investigating whether the brain mechanisms operating during the attention to touch in elderly subjects are different from those of young subjects. We studied two populations of 17 elderly (mean age: 71.7 years) and 12 young (mean age: 26.9 years) subjects. Somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded in a neutral condition (NC), in which subjects had no task, and in a selective attention condition (SAC), in which the subjects were asked to count tactile stimuli given on the same hand of the stimulated median nerve. The SEP amplitude increase during the SAC was lower in old than in young subjects. Moreover, while in young subjects the N140 potential was identifiable only in the SAC, it was evoked in both the NC and the SAC in the elderly population. Old subjects are probably unable to diverge their attention from the median nerve electric stimuli during the NC, therefore they have lower attention resources to invest during the SAC compared to young subjects. These findings agree with recent hypotheses suggesting a decreasing inhibitory control of the attention mechanisms during aging.

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Platform Sessions

NEUROMONITORING IN ICU AND IN BRAIN DEATH J.M. Gue´ rit. Clinical Neurophysiology Unit, St-Luc Hospital, Louvain-enWoluwe, Belgium The electrophysiological techniques (EEG, evoked potentials: EP) aim at confirming brain death (BD), whose diagnosis is primarily clinical. These bedside techniques do not require patient transportation, contrary to arteriography. As it corresponds to the destruction of the whole encephalon, BD gives rise to the total disappearance of intracranial electrogenesis: electrocerebral silence in the EEG, loss of all cortical and subcortical components of visual, somatosensory, and brainstem auditory EPs. By contrast, all activities generated by the retina, spinal cord, and peripheral nerve are preserved. An optimal confirmatory test must provide unambiguous results and rule out potentially reversible situations that mimic BD. The EEG differentiates BD from nonreactive states due to polyradiculopathies but is hardly interpretable in major sedation. It is also often contaminated by the ICU electrical noise. These drawbacks are not shared by the EPs provided that any peripheral sensory or spinal pathology liable to interfere with brain electrogenesis be ruled out. The choice of a technique should depend on both legal contingencies and local expertise. We usually use 3-modality EPs as the only test to confirm clinically suspected BD whose cause was clearly demonstrated.

related potentials (ERPs) have been shown to provide useful prognostic value when recorded during the acute phase of coma. They can be used to assess prognosis for return to consciousness and for later functional recovery. A multivariate approach would lead to models performing well enough to be useful in clinical practice. Methods: In a prospective cohort study 290 comatose patients (mostly brain injury, vascular insult or anoxia) have been recorded and studied for 3 years 1998–2000. Clinical, paraclinical and electrophysiological data have been collected. Univariate and multivariate analysis have been performed. Regression models to predict return to consciousness at 3 months, vegetative state or disability at 12 months were produced using combination of 20 variables including BAEPs, MLAEPs, LAEPs and mismatch negativity (MMN). Results: The sensitivity and specificity of Pa, N100 and MMN components were assessed. A simple model including only 4 variables predicted vegetative state with a probability greater than 90%. The presence of LAEPs and ERPs components was correlated with return to consciousness. The presence of cognitive components at an early stage in comatose patients precludes vegetative state at 12 months.

PS10-03 PS10-01

Changes in EEG synchronization level during seizures in ICU patients

E.M. Vriens a, C.J. Stam a, M.C. Visser b, W.P. Vandertop c, A.R.J. Girbes d, J.J. Spijkstra d. aDepartment of Clinical Neurophysiology; bDepartment of Neurology; cDepartment of Neurosurgery; dDepartment of Intensive Care, VU University Hospital Center, Amsterdam, The Netherlands Introduction: Automatic detection and prediction of seizures depends upon the ability to characterize dynamical changes at seizure onset 1. We studied changes in EEG synchronization in relation to seizures in an ICU population. Methods: Seven ICU patients (mean age 50 yrs) with clear electroencephalographic seizures (visual assessment) during routine EEG (21 chan.) or continuous EEG (6 chan.) were selected. Underlying disease was neurotrauma (3x), infection (2x) status epilepticus e.c.i. (1x) and postanoxic encephalopathy (1x). Synchronization likelihood, a measure of coupling between EEG channels, was calculated for the complete EEG 2. Results: In 4 patients synchronization clearly increased during the seizures. In the remaining 3 patients, however, we observed the same hypersynchrony during the seizures, but due to increased hyper-synchronous background activity, seizure onset in itself could not be recognized. In these patients background activity consisted of periodic discharges. The end of each seizure was marked by a sudden drop in synchronization (postictal exhaustion). Conclusion: Although seizures in ICU patients were always hypersynchronous, detection of onset was complicated in case of very synchronous background activity. However, seizure offset was marked by a sudden desynchronization in all cases. References 1. Le Van Quyen M et al. J. Clin. Neurophys. 2001:18;191–208. 2. Stam CJ and Van Dijk BW. Synchronization likelihood. Physica D 2002:163;236–251.

PS10-02

Predicting outcome after coma. A multivariate analysis including sensory EPs and ERPs in 290 cases

Catherine Fischer, Jacqques Luaute´ , Franc¸ ois Artru, Dominique Morlet. Neurological Hospital and Inserm U280, Lyon, France Background and purpose: Sensory evoked potentials (Eps) and event-

Prognostic role of neurophysiology assessment of cortical activity in post-traumatic comatose patients: EEG, SEP and ERP

P. Lanteri, A. Polo, R. Damante, L. Cristofori, R. Gambin, C. Vivenza. Department of Neurosurgery, Verona University, Hospital, Italy Introduction: In literature SEPs have been shown to be the most powerful of the evoked potentials modalities in the prediction of outcome. After closed head injury with predominantly diffuse axonal injury (DAI) bilateral loss of the cortical SEPs is usually regarded as a strong predictor of very poor clinical outcome. Materials and Methods: We monitoring all patients with DAI admitting in our Neurologic Intensive Care Unit with serial EEG, SEPs, BAERs and P300 ERP. Results: All patients without cortical SEPs died or remained in permanent vegetative state except two deeply comatose patients with a favorable clinical recovery, with persisting bilateral loss of the cortical SEPs found in repeated recordings and in all scalp derivations. These two patients differs from others for EEG activity modified by dolorous and/or acoustic stimulation and P300 response to passive auditory and/or electrical oddball paradigm. Conclusion: A bilateral loss of cortical SEPs should not be considered alone for outcome prediction. A multimodality approach with EEG and ERP responses obtained with different kind of stimulation and different paradigms permit a more accurate assessment of cortical activity and outcome prediction useful for decision on further therapeutic strategy in cerebral injury.

PS10-04

Primary cortex somatosensory and auditory evoked responses in the prognosis of comas

F. Logi a,b, C. Fischer a, F. Sartucci b, L. Murri b, F. Mauguie`re a. aFunctional Neurology, Hoˆ pital Neurologique, Lyon, France; bDepartment of Neuroscience, Institute of Neurology, University of Pisa, Italy The aim of this study was to analyse the role of primary cortex somatosensory (SEPs) and auditory (MLAEPs) evoked responses in comatose patients (GCS , 8), to predict recovery of consciousness. We examined 131 patients comatose after cardio-respiratory failure (CRF: 49), stroke syndrome (45), traumatic brain injury (TBI: 22), complications of neurosurgery (12) and encephalitis (3). SEPs from bilateral

Platform Sessions median nerves, BAEPs and MLAEPs were recorded at the patients bedside in the ICU. By 3 months 54 patients had died without recovering consciousness, 15 were still comatose, 62 had recovered consciousness. In CRF group none of the patients with SEPs N20-P27 amplitude , to 1.2 mV recovered, while in the TBI patients who recovered such values ranged from 0.13 to 4.5 mV. For SEPs the positive predicting value was 100% in CRF and 14% in TBI; for MLAEPs respectively 85% and 50%. Analysing the concordance between SEPs and MLAEPs it emerged that they provide complementary information, especially in TBI patients. We underline that the most important prognostic element in coma is the cause itself; recording primary cortex SEPs and MLAEPs may foresee poor evolution after CRF or TBI, but it is never sufficient to predict awakening, better evaluated by late Eps. PS10-05

Neonatal EEG. Indications and prognostic value

J. Iriarte, O. Olaziregi, I.G. Gurtubay, G. Morales. Hospital Virgen del Camino, Pamplona, Navarra, Spain

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Objectives: The aim of this study was to know the indications of EEG in a paediatric intensive care Unit (PICU), the reasons to perform the EEG, and its value for outcome. Method: We reviewed the EEGs requested by the PICU in the last 3 years. The EEG and the original medical records were reviewed. The EEG abnormalities, its severity, the EEG evolution, and the clinical factors of the patients were evaluated. Results: 92 EEGs in 70 patients (31 females, 39 males), with age 37.6 weeks (27–45). The EEG was performed because abnormal behaviour, hypotonia, perinatal suffering or neonatal convulsions. Most of the EEG were normal (58 patients). Evolutive EEG were performed in 13 patients. Epileptiform activity was seen in 8 patients. An abnormal EEG was related to severe brain damage confirmed by other techniques. A normal EEG was correlated to a better clinical outcome, but the positive predictive value was only moderate. Conclusions: This series confirms that EEG is a good tool to evaluate patients in the PICU. In spite of the clinical suspicion most of the EEGs were normal. This was correlated with good outcome.

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Platform Sessions

QUANTITATIVE ASSESSMENT OF PAIN PS11-01

Laser-evoked responses to distinguish neuropathic from ‘nonorganic’ (sine materia) forms of pain

Luis Garcia-Larrea, Carmen Montes, Nathalie Andre´ -Obadia, Franc¸ ois Mauguie`re, Michel Magnin. INSERM, and EA1880 UCB Lyon, France Nonorganic (“sine materia”) forms of pain may mimic neuropathic pain, either by the presence of lateralised symptoms or by the description of the pain itself. We recorded CO2-laser evoked potentials in 15 patients with different ‘pseudo-neuropathic’ presentations who were eventually classed as “nonorganic”, and compared them with those obtained in normal controls and in chronic neuropathic pain. In patients with neuropathic pain, LEPs were always attenuated after stimulation over the painful territory, even in case of hyperalgesia to laser. In contrast, LEPs were never attenuated in patients with nonorganic forms of pain, and could even be enhanced in response to stimulation of the painful territory. Hyperenhanced LEPs were not encountered in patients with truly neuropathic hyperalgesia, and appear to be particular to cases where pain develops in the context of an intact nervous system, including nonorganic pain. This pattern of response enhancement has been described in fibromyalgia, and is reminiscent of the LEP (and sensation) up-regulation that occurs when attention is willingly directed toward the laser stimulus. We therefore suggest that an attentional mechanism may be the primary contributor to LEP enhancement in nonorganic pain. In selected contexts normal or enhanced LEPs may support a psychogenic participation to the syndrome.

PS11-02

Contact heat evoked potentials to painful and non-painful stimuli: effect of attention towards stimulus properties

Domenica Le Pera a,b, Massimiliano Valeriani b,c, David Niddam a, Andrew C.N. Chen a, Lars Arendt-Nielsen a. aLaboratory for Experimental Pain Research, Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark; bDepartment of Neurology, Universita` Cattolica del S. Cuore, Rome, Italy; cDepartment of Neurology, Ospedale Pediatrico Bambino Gesu`, IRCCS, Rome, Italy The aim of our study was to evaluate the effect of different attentional tasks on the amplitudes and latencies of painful contact heat evoked potentials (CHEPs). CHEPs were recorded in 12 healthy subjects in three experimental conditions, in which attention was oriented towards different properties of the stimulus: number, intensity and distress. The painful heat stimulation produced a negative potential focused at Cz vertex with a latency around 540 ms (Cz/N540), a positive potential picked up by the Cz electrode at a latency around 730 ms (Cz/P730). CHEP topography was explained by a dipolar model which included sources in brain regions involved in pain processing: two sources located bilaterally in the perisylvian region, one dipole in the mesial frontal region and two sources located bilaterally in the deep temporal lobe. Varying the attentional target towards the different properties of the stimulus was ineffective in producing any change in CHEP responses. Our results suggest that CHEPs represent a reliable and safety functional measure of the nociceptive pathways, scarcely influenced by attention manipulation and, hence, suitable for clinical purposes.

PS11-03

Nociceptive CO2 laser evoked potentials during migraine attack

Marina de Tommaso, Giuseppe Libro, Marco Guido, Luciana Losito. Neurologic and Psychiatric Sciences Department, Section of Nervous System Diseases, University of Bari, Italy

In previous studies cutaneous allodynia was showed by measurements of mechanical and thermal pain thresholds of periorbital and forearm skin areas during migraine attacks and it was attributed to phenomena of central sensitisation occurring during the critical phase (Burstein, 2001). The aim of the study was to examine the cutaneous pain threshold by CO2 laser stimuli during migraine attacks, defining also the feature of the cortical potentials evoked by nociceptive laser input. Ten migraine without aura patients, were studied during the attack and 72 hours after the end of headache. The stimulus was laser pulse generated by a CO2 laser and the dorsum of both hands and the right and left supraorbital zones were stimulated. Absolute latency of scalp potentials were measured at the highest peak of each response component; the N-P components peak-to-peak amplitude was detected. The cutaneous pain threshold was significantly reduced on both the symptomatic and not symptomatic sides at the supraorbital level during the attack in comparison with the headache-free phase. In addition a significant N-P complex amplitude increase was detected on the symptomatic side in comparison with the pain-free side. This study confirm cutaneous allodynia during migraine attack, subtended by central sensitisation phenomena, probably involving the cortical level of pain elaboration. PS11-04

Gating of laser evoked potentials by transcutaneous electrical nerve stimulation (TENS)

Misericordia Veciana, Alvaro Cervera, Roberto Contreras, Josep VallsSole´ . Unitat d’Electromiografia, Servei de Neurologia, Hospital Clinic, Barcelona, Spain Transcutaneous electrical nerve stimulation (TENS) is used for the treatment of chronic pain. This effect is probably based on central nervous system gating mechanisms. Laser evoked potentials (LEPs) are the consequence of nociceptor activation. Therefore, we examined the effects of electrical stimuli on the size of LEPs. Two experiments were carried out in 6 healthy volunteers in whom single laser stimuli were used to induce control LEPs. In the first experiment, we modulated the LEPs by single electrical stimuli (SES) applied 0 to 200 ms before. In the second experiment, laser stimuli were applied during repetitive high frequency (100 Hz) electrical stimulation (HES). In all instances, we requested a subjective evaluation of the laser stimulus perception with a visual analogic scale (VAS). SES induced a significant decrease of LEP amplitude at intervals of 0 ms, with a tendency to recover beyond 50 ms, but the VAS score was not different between control and test conditions. During HES, mean LEP amplitude was reduced to 44.7%, and mean VAS was reduced to 49%, of control values. We conclude that gating mechanisms operate between electrical and laser stimuli, but the decrease in the perception of pain stimuli is only reduced with repetitive TENS. PS11-05

Effect of attention to the stimulus on ultra-late CO2 laser evoked potentials

Liala De Armas a,b, Massimiliano Valeriani a,c, Domenico Restuccia a, Domenica Le Pera a,b, Toni Maiese a, Pietro Tonali a. aDepartment of Neurology, Universita` Cattolica del Sacro Cuore, Roma; bCasa di Cura San Raffaele Pisana, Roma; cDivision of Neurology, Ospedale Pediatrico Bambino Gesu`, Roma This study aimed at investigating whether modifications of the attention level affect the ultra-late (UL) CO2 laser evoked potentials (LEPs). LEPs were recorded in 10 healthy subjects after stimulation of the right and left perioral region. The intensity of the CO2 laser pulses was adjusted to deliver an energy of around 5 mJ/mm2. All our subjects referred a burning sensation, due to activation of the unmyelinated C fibres. LEPs were obtained in

Platform Sessions 3 different conditions: i) attention condition (AC), in which subjects were asked to count the number of laser stimuli; ii) neutral condition (NC), in which subjects did not have any task; iii) distraction condition (DC), in which subjects received an arithmetic task. LEP recordings during AC revealed two main vertex components: a negative UL-N2a potential at a mean latency of 234.38 ms, followed by a positive UL-P2 response at a mean latency of 408.2 ms. In both NC and DC the UL-N2a and UL-P2 potentials were markedly reduced in amplitude and were even unidentifiable in some subjects. Our findings show that UL-LEPs are strongly reduced by any attention deviation from the stimulus, thus a strict control of subject’s attention level is mandatory when UL-LEPs are recorded. PS11-06

Long lasting visceral pain relief after midline dorsal columns myelotomy

B. Cioni, M. Meglio, F. Doglietto, B. Tirpakova. Neurochirurgia, Universita` Cattolica, Roma, Italy Animal studies from the group of Willis demonstrated that visceral pain afferents depolarize segmental spinal neurons close to the central canal and then they travel in the medial part of the dorsal columns to the ipsilateral gracilis nucleus and reach the controlateral thalamus. Surgical observations suggest that a visceral pain pathway in the dorsal columns may exist also in man. We report the case of a 50 years old man who in 1972 suffered from a Th11–12 spinal cord injury (Asia group A). The patient was complaining of a visceral burning and tearing pain in the left abdominal region, and he was assuming narcotics to partially control his pain. His pain was worse during a test of spinal cord stimulation, and was relieved by an intrathecal bolus of Morphine 0.5 mg, but 1 week later he developed a true tolerance to intrathecal Morphine. In February 2000 we decided to perform a posterior columns myelotomy at Th8 level. The operation was followed by a complete pain relief. At 26 months, the patient is still pain free, without any medication.

S25

This case confirms that a visceral pain pathway exists in man in the dorsal columns. Midline dorsal columns myelotomy interrupts this pathway and is followed by long lasting pain relief. PS11-07

Dermatomal laser-evoked potentials in postherpetic neuralgia

A. Truini a, M. Haanpa¨ a¨ b, F. Galeotti a, G.D. Iannetti a, A. Romaniello a, R. Zucchi c, G. Cruccu a. aDepartment of Neurological Sciences, University of Rome “La Sapienza”, Italy; bUniversity Hospital, Helsinki, Finland; cIstituto Dermopatico Immacolata, Rome, Italy We aimed at evaluating the reliability of dermatomal laser evoked potentials (LEPs) as a diagnostic tool and gaining information on the pathophysiology of postherpetic neuralgia (PHN). Using a CO2-laser stimulator we recorded LEPs after stimulation of the supraorbital, cervical and thoracic territories in 12 control subjects and 40 patients with postherpetic neuralgia. In all patients we also correlated LEP data with pain intensity and pain characteristics (paroxysmal, constant, allodynic). CO2laser pulses readily evoked high-amplitude brain potentials related to small-myelinated (A-delta) fibre activation from all the different sites of stimulation. The laser perceptive threshold and LEP latency were positively correlated with the distance of the dermatome from brain (P , 0:001). In the affected dermatomes of patients, the perceptive threshold was higher and the LEP amplitude lower in comparison with the contralateral side (P , 0:001). Twenty patients had absent LEPs after stimulation of the affected dermatome and 6 had abnormal LEPs bilaterally. We found no significant correlation between LEP and pain data. Dermatomal LEPs are a promising diagnostic tool in assessing sensory function also in cervical and thoracic territories. Small-myelinated fibres are severely impaired in PHN. The lack of a significant correlation between LEP abnormalities and pain suggests that pain in PHN is prominently secondary to unmyelinated afferent dysfunction.

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Platform Sessions

TRANSCRANIAL MAGNETIC STIMULATION USES FOR DIAGNOSIS AND TREATMENT 1 PS12-01

Ipsilateral MEPs: a new electrophysiological marker in ALS

Klaus Krampfl, Bahram Mohammadi, Reinhard Dengler, Johannes Bufler. Department of Neurology of the Medical School Hannover, 30623 Hannover, Germany The intention of our study was to detect discrete signs of upper motor neuron (UMN) involvement in ALS by a new approach. 25 patients with possible, probable ore definite ALS, six patients with clinically suspected ALS without detectable signs of UMN involvement, 19 disease controls and five healthy volunteers were included. In five ALS patients (16%) mirror movements of the resting hand were observed when contralateral sequential finger-thumb opposition was performed. In 17 (55%) of the ALS patients surface EMG allowed the registration of muscle activity in the contralateral first dorsal interosseous muscle upon sequential finger-thumb opposition in the contralateral hand. MEPs in response to single shock TMS were bilaterally recorded from the abductor pollicis brevis muscle. M and F waves were elicited by supramaximal stimulation of the median nerve and central motor conduction times (CMCTs) were calculated using the F wave latencies. Ipsilateral MEPs could be obtained in 21 (84%) out of 25 ALS patients and in four out of six patients with clinically suspected ALS. CMCTs were prolonged in 16 ALS patients (64%). The occurrence of mirrored EMG activity and ipsilateral MEPs may be an early electrophysiological sign of the involvement of UMN in ALS, even with higher sensitivity compared to CMCTs.

Tonali, J.C. Rothwell, V. Di Lazzaro. Istituto di Neurologia, Universita Cattolica, L. go A. Gemelli 8, 00168 Rome, Italy; IRCCS E.MEDEA “Associazione la Nostra Famiglia”, Ostuni, Italy Descending corticospinal volleys were recorded from a bipolar electrode inserted into the cervical epidural space of four conscious human subjects after monophasic transcranial magnetic stimulation over the motor cortex with a figure-of-eight coil. We examined the effect of reversing the direction of the induced current in the brain from the usual posterior-anterior (PA) direction to an anterior-posterior (AP) direction. The volleys were compared with D waves evoked by anodal electrical stimulation (two subjects) or medio-lateral magnetic stimulation (two subjects). As reported previously, PA stimulation preferentially recruited I1 waves, with later I waves appearing at higher stimulus intensities. AP stimulation tended to recruit later I waves (I3 waves) in one of the subjects, but, in the other three, I1 or D waves were seen. Unexpectedly, the descending volleys evoked by AP stimulation often had slightly different peak latencies and/or longer duration than those seen after PA stimulation. In addition the relationship between the size of the descending volleys and the subsequent EMG response was often different for AP and PA stimulation. These findings suggest that AP stimulation does not simply activate a subset of the sites activated by PA stimulation. Some sites or neurones that are relatively inaccessible to PA stimulation may be the low-threshold targets of AP stimulation. PS12-04

Motor excitability increase in myopathy

Task-dependent modulation of excitatory and inhibitory functions within the human primary motor cortex

J. Liepert, B. Schoser, C. Weiller. Department of Neurology, University of Hamburg, Germany

Simona Farina, Michele Tinazzi, Tiziana Rosso, Stefano Facchini, Stefano Tamburin, Antonio Fiaschi. Department of Neurological Sciences and Vision, University of Verona

Objective: To explore if neuronal motor excitability is modified in myopathic patients. Methods: Ten patients with well-defined myopathies were studied with single and paired pulse transcranial magnetic stimulations and electrical nerve stimulations. Recordings were taken from right first dorsal interosseous muscle and, in 6 patients, from right deltoid muscle. Results: Compared to a sex and age matched healthy control group myopathic patients showed a reduction of intracortical inhibition, enhancements of alpha motoneuron excitability and increased amplitudes of motor evoked potentials during target muscle contraction. In contrast, motor thresholds, intracortical facilitation, silent period duration, M-potential amplitudes and central and peripheral conduction times were identical in both groups. Conclusion: In myopathy, nervous system excitability may be altered, presenting as a motor disinhibition on cortical and subcortical levels. These changes are independent of the type of myopathy and could reflect a compensatory mechanism.

PS12-02

In 10 normal subjects we evaluated motor evoked potentials (MEPs) and silent period (SP) from the right FDI to left motor cortex TMS during performance of complex and simple tasks. Subjects were asked to perform: 1) tonically pressure of thumb and index finger to the contact surfaces of a strain gauge (precision gripping); 2) isometric power grip of a brass cylinder involving all digits (power gripping); 3) simple isometric abduction of the index finger (abduction task). The level of FDI EMG activity (20% of the maximal voluntary contractions) across tasks was kept constant by providing subjects with acoustic-visual feedback of their muscle activity. MEPs were significantly larger in amplitude during complex (pincer and power) than simple (abduction) task. MEPs during pincer was also significantly greater than during power task. Conversely, the SP was significantly shorter during complex (pincer and power) than simple (abduction) task. SP during power was significantly shorter than during pincer task. These results suggests that changes of motor cortex excitation and inhibition on FDI muscle are task dependent. The greater motor cortex excitation during the performance of tasks requiring the activation of several muscles (complex tasks) than in a simple abduction task may be due to a corticomotoneuron facilitation induced by the activation of synergist muscles. On the other hand, the greater motor cortex inhibition during simple than complex task may be due to an activation of cortical inhibitory circuitry induced by muscles uninvolved in the task. PS12-03

Descending volleys evoked by transcranial magnetic stimulation of the brain in conscious humans: effects of reversing the direction of induced current

P. Profice, A. Oliviero, E. Saturno, F. Pilato, A. Insola, P. Mazzone, P.A.

PS12-05

Paired transcranial magnetic stimulation in hemifacial spasm

¨ ge, Elif Kılıc¸ , Hulki Forta. Departments of Mu¨ nevver C¸ elik, A. Emre O Neurology, S¸ is¸li Etfal Education and Research Hospital and Istanbul Faculty of Medicine, Istanbul, Turkey The aim of this study was to investigate cortical excitability in HFS patients to find out if it reveals any changes indicating nuclear hyperexcitability. Paired transcranial magnetic stimulation was performed in 19 patients and 13 healthy controls at rest. The procedure was repeated during voluntary contraction in 6 control subjects. Paired stimuli, adjusted to 130% of the threshold stimulus intensity, were delivered to the recording site (bilateral orbicularis oculi muscles) contralaterally. In all patients and control subjects, conditioning and test MEPs could be recorded at interstimulus

Platform Sessions intervals (ISI) equal or longer than 20 ms. The ratio of the test MEP peakto-peak amplitude to that of the conditioning MEP (RT) was calculated. In control subjects at rest, ISIs of 20, 25, 30 ms revealed facilitation of the test MEP. Inhibition developed at ISIs 75 and 100. Statistically significant differences were observed between RTs of control group examined at rest and the RTs of control group examined during voluntary contraction and those of the symptomatic sides of the HFS patients at ISI 25.

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The main finding in our study was lessening of the facilitation found in control subjects during voluntary contraction and on the symptomatic sides of HFS patients. Hemifacial spasm and voluntary contraction revealed the same effect on cortical excitability, that of reducing facilitation at ISIs 20, 25 and 30 ms.

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Platform Sessions

MAGNETO-ENCEPHALOGRAPHY

Exploring human brain function with magnetoencephalography Alfons Schnitzler. Department of Neurology, Heinrich–Heine University Duesseldorf, Germany MEG allows non-invasive measurement of brain activity with millisecond temporal and high spatial resolution. Modern systems with large arrays of sensors covering the whole scalp and the availability of advanced analysis tools provide the basis for investigating temporo-spatial dynamics of brain activations and neural interactions between different brain areas. To illustrate current applications and new developments I will present results of several studies investigating sensorimotor, nociceptive and cognitive processing. For example, using the recently developed analysis tool DICS (Dynamic Imaging of Coherent Sources) we have shown that during voluntary finger movements the involved agonist/antagonist muscles are driven by a synchronized 8-Hz oscillatory network comprising ipsilateral cerebellum, contralateral thalamus, premotor and motor cortex. This neural mechanism results in well-known 8-Hz movement discontinuities evident in the velocity profile and represents the basis of an intermittent control of voluntary movements. Examples of studies investigating sensory and cognitive processes will be presented as well to demonstrate the particular usefulness and potential of MEG to explore human brain functions at high temporal resolution. PS13-01

Dynamic neural patterns revealed by MEG/EEG during visual perception

D. Cosmelli, O. David, J.P. Lachaux, L. Garnero, B. Renault, F.J. Varela. Laboratoire de Neurosciences Cognitives et Imagerie Ce´ re´ brale LENA (CNRS UPR640), Hoˆ pital de la Salpe´ trie`re, 47 Bd de l’Hoˆ pital, 75651, Paris Cedex 13, France We present a MEG/EEG framework to reveal dynamic patterns of synchronous neural activity in human beings. By using a frequency tagged optical-flow stimulus we are able to guide the localization of neural activity correlated to its conscious perception. To take into account the richness of single trials we have developed a robust surrogate-based approach to the MEG/EEG distributed inverse problem. The method can be summarized as follows: i) estimation of source location for each single trial at the tagging frequency; ii) detection of stable, i.e. recurrent, sources between (or within) trials, and iii) dynamical analysis of the time series to reveal interaction between sources. We use phase-locking analysis among estimated sources in order to define a specific synchronous network. MEG data has been recorded on a CTF 151 sensor system from subjects viewing the frequency tagged stimulus. Without resorting to averaging procedures, we are able to reveal recurrent although variable synchronous neural patterns correlated to the conscious perception of the stimulus. We do not consider such variability as noise but rather as an important part of the neural response that could reflect the uniqueness of each cognitive act. PS13-02

Tomographic mapping of functional connectivities from MEG recordings

J. Gross a, J. Kujala b, M. Ha¨ ma¨ la¨ inen b, L. Timmermann a, R. Salmelin b, A. Schnitzler a. aNeurologische Klinik, Heinrich-Heine-Universita¨ t, D-40225 Du¨ sseldorf; bBrain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, FIN 02015 HUT, Espoo, Finland Synchronization of oscillatory activity has been suggested as a fundamental mechanism for neural communication. The transient nature of these interactions requires time-sensitive tools such as magneto- or electroence-

phalography (MEG/EEG). We present a new method, Dynamic Imaging of Coherent Sources (DICS) for the tomographic mapping of power and coherence from MEG recordings in the entire brain. Coherence describes the dependence of two signals and is commonly taken as a measure of functional coupling. Reference points for the computation of neural coupling may be based on brain areas of maximum power or other physiologically meaningful information, or they may be estimated starting from sensor coherences. DICS employs a spatial filter together with a realistic head model to estimate cerebro-muscular or cerebro-cerebral coherence. After identification of coherent areas phase synchrony can be quantified between the areas. The performance of DICS is evaluated with simulated data and illustrated with recordings of spontaneous activity in a healthy subject and a parkinsonian patient. Cerebro-cerebral interactions and their time courses can now be evaluated to address the intriguing questions of coupling within distributed cortical networks during rest or task performance in physiological and pathological conditions.

PS13-03

Preoperative magnetic source imaging and intraoperative cortical mapping: comparative results

M. Gonza´ lez-Hidalgo a, C.J. Saldan˜ a Gala´ n b, F. Maeztu c, C. Amo a, A. Ferna´ ndez c, T. Ortiz c, P. Mata Gonza´ lez b. aDepartment of Clinical Neurophysiology; bDepartment of Neurosurgery, Hospital ClI´nico San Carlos; c Magnetoencephalography Centre, Complutense University, Madrid, Spain Introduction: The management of lesions involving eloquent cortex engender significant functional risk. Presurgical localization of this functional areas can aid in planning the therapeutic options and surgical approaches. Magnetoencephalography is a non-invasive imaging technique that provides preoperative functional location of somatosensory and language cortical areas related to anatomical landmarks. Objective: To validate presurgical functional information obtained from magnetic source imaging in patients operated on awake with realization of intraoperative cortical stimulation mapping. Patients and Methods: Six patients with intra axial cerebral lesions located close to eloquent brain cortex were studied preoperatively underwent magnetic source imaging technique. MEG data were collected using a 148-channels Magnes 2500WH biomagnetometer. The patients then underwent awake craniotomy and direct cortical electrical stimulation, mapping areas related to motor, somatosensory and language functions. The accuracy of presurgical studies were assessed by gross visual comparison and by integration of MEG data into a neuronavigational system. Results and conclusions: MEG data show reasonably good concordance with somatosensory and language intraoperative mapping, letting us to achieve anatomo-functional presurgical planning that can be validated by intraoperative cortical stimulation.

PS13-04

Pathological corticomuscular coupling underlying miniasterixis in hepatic encephalopathy

Lars Timmermann, Joachim Gross, Gerald Kircheis, Markus Butz, Dieter Ha¨ ussinger, Alfons Schnitzler. Department of Neurology, Heinrich–Heine University Duesseldorf, Germany The neurophysiological basis of “Mini-Asterixis” in hepatic encephalopathy (HE) is unknown. We therefore investigated in 6 patients with miniasterixis and HE (grade 2–3) due to chronic liver cirrhosis and in 6 healthy controls the coupling between the surface EMG of hand muscles and motor cortical activity recorded non-invasively with magnetoencephalography (MEG). A second control group consisted of 6 patients with liver cirrhosis but no mini-asterixis or manifest HE. During rest, no subject showed significant MEG-EMG coherence. On elevation of the forearm patients with HE grade 2–3 developed clearly visible mini-asterixis of varying frequencies

Platform Sessions (6–12 Hz) that was reflected in EMG oscillations. In these patients, excessive corticomuscular coherence occurred at the individual tremor frequency between EMG and primary motor cortex (M1) activity. In contrast, M1EMG coherence in both control groups was significantly smaller and of higher frequency (.15 Hz). The pathological corticomuscular coherence in HE-patients with miniasterixis demonstrates the involvement of primary motor cortex in miniasterixis. Mini-asterixis reflects most likely a pathologically decelerated and augmented synchronized rhythmical motor cortical output possibly due to functional alterations in the basal-ganglia-thalamo-cortical loops. Pathological synchronization of neuronal activity may turn out to be a promising pathophysiological concept for other clinical deficits of HE.

PS13-05

MEG/MRI correlation analysis differentiate AD and LBD patients

Astrid Thomas, Diego Iacono, Anna Lisa Luciano, Giordano D’Andreamatteo. Neurophysiopathology, University “G.D’Annunzio”, Pescara, Italy Alzheimer’s Disease (AD) and Lewy Bodies Dementia (LBD) present different clinical, neuropsychological and neurophysiological characteristics. Fluctuating cognition (FC), an important clinical symptom in LDB (80–90%). We investigate the EEG/MEG activity correlations in AD and

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LBD patients and specificity of MEG data for AD and LBD. Methods: We studied 10 AD patients (67.4 ^ 5.3 y.o.), 6 LBD (68.2 ^ 4.9 y.o) patients and 11 controls (66.9 ^ 2.3 y.o) using EEG/MEG techniques during spontaneous activity and mental tasks. 5 LBD patients had visual hallucinations and 1 patient suffered by psychosis. All patients underwent neuroradiological and neuropsychological evaluation. MEG was performed by a 165-multichannels whole head-helmet during spontaneous activity (15 min) with open and closed eyes and photic stimulation at different frequencies (5–15 and 30 Hz). The MEG activity was performed during a mental task (auditory odd-ball paradigm). All patients underwent quantitative-EEG recording and event related potential recordings (P300). All AD and LBD patients and controls successfully performed EEG/MEG and P300 sessions: two LBD patients had a 90% of successful responses at odd-ball auditory paradigm. Results: EEG/MEG/MRI recordings in AD patients showed an alpha activity reduction in temporal and frontal areas with low frequency increasing for the response to mental tasks. In LBD patients no specific brain regions were interested. The recording showed a diffuse abnormal signal in spontaneous and mental performances. LBD patients MEG analysis showed fluctuating activity every 4 sec. Different underlying pathophysiological mechanism in AD/LBD can be differentiated by MEG/MRI correlation analysis also useful during treatment evaluation.

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Platform Sessions

CLINICAL NEUROPHYSIOLOGY OF SPHINCTER DISORDERS David B. Vodusˇek. Division of Neurology, University Medical Centre, 1525 Ljubljana, Slovenia Lower urinary tract, anorectal and sexual function rely on neural control, the integrity of which is tested by clinical examination and several diagnostic methods, among them clinical neurophysiological tests. These comprise tests of conduction through motor and sensory pathways (both peripheral and central), EMG methods, and quantitative sensory testing. The EMG signal can be used as an indicator of pelvic floor muscle activity patterns (kinesiological EMG), or can be analysed to reveal signs of denervation (by concentric needle EMG-CN EMG) or signs of motor unit changes after reinnervation (CN EMG, Single Fibre EMG). Tests of conduction include responses recorded on stimulation of pudendal nerve, sacral roots, and motor cortex. Sacral reflexes and the sympathetic skin response can be recorded on either electrical or mechanical stimulation. The recording of smooth muscle EMG (from corpora cavernosa and detrusor) is still controversial. Clinical neurophysiological testing is contributory to research in sacral dysfunction. In selected patients with sacral dysfunction, particularly those with suspected or known involvement of the peripheral sacral reflex arc, CN EMG and recording of the sacral reflex response should assist in documentation and further characterisation of the neuromuscular lesion. PS14-01

Bladder neck responses below a complete spinal cord lesion elicited by pudendal nerve stimulation

A. Reitz a, D.M. Schmid b, A. Curt a, P.A. Knapp a, B. Schurch a. aParaCare, Institute for Rehabilitation and Research, Balgrist University Hospital, Zurich, Switzerland; bDepartment of Urology, University Hospital Zurich, Switzerland Purpose: Pudendal nerve stimulation (PNS) is known to have a potential neuromodulative effect on bladder function. The underlying neuronal mechanism and the involved pathways in human remain unknown. In this prospective study we focused on PNS in patients with complete spinal cord injury (SCI) in order to identify neuromodulative processes. Material and Methods: 20 complete spinal male presenting with upper motor neuron lesion underwent electrical PNS. 56 stimulations using biphasic rectangular impulses (0.2 ms, 10 Hz) with intensities up to 100 mA were applied to the dorsal penil nerve. In six patients 18 stimulations were repeated after intravenous application of 7 mg of phentolamine. Bladder, bladder neck, and external urethral sphincter pressure were continuously recorded. Data were statistically evaluated by analysis of variance for repeated measurements. Results: Mean initial bladder neck pressure increased during stimulation from 27 to 64 cm H2O (P , 0:001). Mean initial external urethral sphincter pressure increased during stimulation from 57 to 136 H2O (P , 0:001). Phentolamine decrease initial bladder neck pressure and reduced the pressure rise during stimulation significantly (P , 0:05). Conclusion: Pudendal nerve stimulation provide a neuromodulative effect in the isolated spinal cord. Somatic afferent fibres of the pudendal nerve project on thoracolumbar sympathetic neurons controlling the bladder neck. PS14-02

Pudendal nerve latency and anal sphincter fiber density in suspected pelvic floor lesions

R. Conteras, G. Lacima, M. Espun˜ a, J. Valls-Sole´ . Unitat d’Electromiografia, Servei de Neurologia, Hospital Clinic, Barcelona, Spain Pudendal nerve latency (PNL) is commonly evaluated in the electrophysiological assessment of suspected pelvic floor lesions. However, a delay in PNL may only partly contribute to sphincter weakness in incontinent

patients. In this study, we determined PNL and anal sphincter motor units fiber density (MFD) in 100 patients (95 women and 5 men, between 28 and 75 years of age) who complained of faecal incontinence of a variable degree of severity, due to obstetric or surgical lesions. PNL was measured as the onset latency of the earliest identifiable action potential using the StMark’s electrode. MFD was measured as the mean of 4 to 10 motor unit action potentials identified with concentric needle EMG recordings in both sides. PNL values ranged from 1.8 to 7.1 ms (mean of 2.9 1 /21.0 ms), and mean MFD ranged from 1.8 to 9.0 peaks per recording site (mean of 4.0 1 / 21.6). Abnormal delays of PNL (latency longer than 2.9 ms) were identified in 12 patients in the right side only, in 26 patients in both sides, and in 3 patients in the left side only. Abnormal bilateral MFD (5 or more peaks per recording site) was observed in 27 patients, 12 with normal PNL, 8 with bilateral PNL abnormalities, 5 with only right side PNL abnormalities and 2 with only left side PNL abnormalities. Our data suggest that PNL delay is not well correlated with MFD. A bilateral increase in MFD occurs in 7% of patients with unilateral PNL abnormalities and in 12% of patients with normal PNL. The study of MFD brings specific information on anal sphincter function, that may complement the information brought by determination of PNL. PS14-03

Transcranial magnetic stimulation and urethral sphincter. Methodological problems and normative data

S. Brostrøm, G. Lose, P. Jennum. Department of Clinical Neurophysiology, Glostrup Hospital, Denmark Introduction: Transcranial magnetic stimulation of cortical motor centers is broadly focused, and each stimulation evoke concomitant responses in adjacent muscle groups. The specificity of the method therefore rests on the precision in registering the motor evoked potentials from the target muscle. The urethral sphincter is a small muscle with a unique motor innervation. Stronger signals from larger, surrounding muscles (i.e. pelvic floor and gluteals) might contaminate results if surface electrodes are used. Methods: We compared two different surface electrodes (intra-vaginal and intra-urethral) with the concentric needle as a gold standard, and by concomitant testing of the levator ani as a potential contaminator. We studied 30 healthy women with a mean age of 52.1 years. Results: There was no significant difference between the latencies recorded with the various electrodes from either muscle, but the limits of agreement were wide. However, the concentric needle electrodes proved more reliable with a higher rate of reproducible responses. Conclusions: We did not encounter major difficulties in using the concentric needle electrode for recordings in the external urethral sphincter, and this electrode was also more reliable than either surface electrode. We therefore advocate the use of concentric needle electrodes in further studies. PS14-04

Bulbocavernosus reflex and pudendal SEP in sexual female dysfunction

Manuel Mora´ is Delgado, Cecilia Viera. Servicio Neurofisiologia ClI´nica, HCQ, Hermanos Ameijeiras, C. Habana, Cuba The objective of this study was to evaluate the pudendal neuropathy in women with different sexual dysfunction: anorgasmia, dyspareunia, vaginism and without libido. To obtain support to the hypothesis of pudendal nerve damage, 111 women were studied: 16 anorgasmia, 7 dyspareunia, 6 vaginism, 8 without libido and 74 mixed. Clinical and electrophysiological studies (Bulbocavernosus reflex and Somatosensory evoked potential of pudendal nerve) were carried out. Statistical analysis was performed with the chi2 test. SEP results was under normal value. The bulbocavernosus reflex classification (40 ms) showed a delayed responses in 70/111 of patient (63%). A significant (P ¼ 0:001) positive relation was found

Platform Sessions between bulbocavernosus reflex classification and type of sexual dysfunction. This result showed a pudendal neuropathy in most of women with sexual dysfunction and utility of bulbocavernosus reflex to confirm it. PS14-05

Neurophysiological evaluation related to stimulus frequency in S3 electrical modulation for voiding disorder

Silvia Malaguti, M. Spinelli, M. Lazzeri, G. Giardiello. Department of Clinical Neurophysiology S. Maugeri Foundation, IRCCS Scientific Institute of Montescano, Spinal Unit Magenta Hospital Milan, Medtronic, Italy Sacral Neuromodulation (SNM) is an exciting and effective therapy in patients implanted for voiding difficulties. Despite of the large number of literature about results, poor are related to stimulus parameter of SNM and neurophysiological monitoring. Aim of the study is to find out a relationship between SNM stimulus frequency and Pudendal Somatosensory Evoked Potentials (SEPs). Three females (with complete urinary retention) and 2 males (with a detrusor hypocontractility due to incomplete peripheral lesion), mean age 41 yrs (range 21–71), were submitted to S3 monolateral left sacral percutaneous staged implant (SPI). All patients underwent Pudendal and Tibial nerve SEPs at baseline and during chronic SNM at 21 and 40 Hz. Results in following charts: Our preliminary results suggest that SNM acts on somatosensory afferent fibers, shortening the latency of cortical responses, improving clinical symptoms.

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Further and more extensive studies (related to variation in pulse width, pulse shape, polarity, intensity) are necessary to better understand mechanism of action of SNM and lead to a less empiric way to setting stimulation parameters. PS14-06

Pudendal vs. posterior tibial N. SEP: sensitivity in MS with or without sexual/sphincter problems

Sh. Nafissi, G.R. Naderi. Tehran University of Medical Sciences Introduction: The aim of study was to compare the sensitivity of pudendal SEP (PSEP) and posterior tibial SEP (TSEP) in patients affected by clinically definite multiple sclerosis with or without sphincter/sexual problems. Methods: For this purpose twenty-five 20–50 years old male MS patients were selected. All of them had clinically definite MS by poser’s criteria. Dorsal n. of penis and posterior tibial nerves were stimulated individually and cortical SEP was recorded with standard Cz 0 -Fz montage. Results: Overall, PSEP was abnormal in 19(76%) and PSEP was abnormal in 21(84%). From the four patients with normal TSEP one had abnormal PSEP and from six patients with normal PSEP three had abnormal TSEP. The cumulative SEP sensitivity was 88%. Nineteen patients (76%) had sphincter problem. Of these, 15 (78%) and 17(89%) had abnormal PSEP and TSEP respectively. Thirteen patients (52%) had impotence and in all of them (100%) both PSEP and TSEP were abnormal. Conclusion: TSEP is superior to PSEP in male patients with clinically definite MS even in those with sphincter problem or impotence.

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Platform Sessions

CONSCIOUSNESS, ATTENTION AND PERCEPTION 1 Catherine Fischer. Neurological Hospital, Lyon, France Unconscious states are probably the period in which patients are least (or not) aware of external sensory stimuli. Until recently a question was pending: which cognitive process, if any, would be active in unconsciousness? This presentation will review the use of auditory event-related potentials (ERPs) as indicators of sensory input during unconscious states. Two unconscious states will be discussed: drug-induced anaesthesia and coma. In the waking state attention and consciousness have a marked effect on the N100-P200 potential and on the P300 and mismatch negativity (MMN) components. Unconscious states have a much more marked effect on these components. During onset of anaesthesia the P100 and P200 components increase in amplitude while the N100 decreases. Re-emergence to a conscious state appears to slowly reverse this trend, the MMN remaining abnormal as late as 24 hours after the end of anaesthesia. The MMN provides a measure of pre-attentive sensory memory operations and probably the perceptual process involved in auditory discrimination. The MMN can be recorded in some deeply comatose patients although it is smaller than in healthy subjects. There is evidence that MMN recorded in comatose patients is nevertheless a true MMN. When present in comatose patients the MMN is an indicator of the patient being in the process of returning to consciousness. PS15-01

The time course of auditory cortex activation in first and second language processing

Alon Sinai, Hillel Pratt. Evoked Potentials Laboratory, Technion-Israel Institute of Technology, Haifa 32000, Israel The study purpose was to specifically compare auditory cortex activation during first and second language processing. Brain potentials were recorded from 17 normal hearing, right handed, native Hebrew (first language) speakers that also speak English (second language). Subjects performed a lexical decision task with speech stimuli from both languages. Brain sources of activity were estimated by calculating current densities from the scalp distribution of the ERPs, using lowresolution electromagnetic tomography analysis (LORETA). LORETA voxels were compared between pre stimulus baseline and post stimulus activation by non-parametric t-test adjusted for multiple comparisons. The Auditory cortex responses to words in either language were maximal around 100 msec. The right and left auditory cortices were symmetrically active around the activation peak, and alternated at later times. At times later then 300 msec the left side was more active. Up to around 30% of the maximal activity was evident as late as 650 msec post stimulus onset. The auditory cortex exchanges information with other brain region continuously. Early language-specific processing takes place at primary and secondary auditory cortex. PS15-02

Complex sound perception: binding harmonics with combination-sensitive neurons

A.V. Medvedev, F. Chiao, J.S. Kanwal. Department of Neuroscience, Georgetown University Medical Center, Washington, DC 20007 Perception of complex communication sounds is a major function of the auditory system. Spectral representation of sounds performed by the basilar membrane “place-coding” mechanisms is then maintained to the higher levels of the auditory system. To create a coherent percept of complex sounds consisting of multiple frequencies, the auditory system should instantaneously group or bind the individual harmonic components (spectral grouping). Based on experimental data and our realistic neural network model, we propose that associative learning of combinations of harmonic frequencies and nonlinear facilitation of responses to those combinations,

also referred to as “combination-sensitivity”, may provide a mechanism for spectral grouping. The neural network was created with commercially ˆ ). It had seven layers for processing available software (NeuroimitatorO auditory inputs between the periphery and the midbrain and included a parallel tonotopic input that converges and diverges within the network. We simulated combination-sensitivity using Hebbian and associative synaptic plasticity. After associative learning of harmonic combinations, neurons in higher-order layers of the network exhibited an emergent property of multifrequency tuning that is consistent with experimental findings. Spectral grouping was demonstrated as the capacity of the network to “recognize” the fundamental frequency of a harmonic complex even when the fundamental frequency itself was missing.

PS15-03

Participation of frontal opercular system and its righthemispheric homolog in musical processing

R. Kristeva-Feige a, V. Chakarov a, J. Schulte-Mo¨ nting b, J. Spreer c, C.H. Lu¨ cking a, M. Wiesendanger d. aDepartment of Neurology; bDepartment of Medical Biometry; cDepartment of Neurosurgery, University of Freiburg i.Br, Germany; dDepartment of Neurology, University of Berne, Switzerland Recent neuroimaging studies suggest that, besides activation of a number of cortical areas, including the sensorimotor, premotor and supplementary motor areas, playing a musical sequence activates also the left and right frontal opercular areas possibly including Broca area and its right-hemispheric homolog (Koelsch et al., 2000; Maess, Koelsch et al., 2001; Nirkko et al., 2000). The temporal activation sequence of the above cortical areas with respect to music execution and imagining is unknown, however. We investigated this question by means of high-resolution EEG (58 scalp positions). Two amateur violin players and 5 professionals or advanced students were studied in 3 conditions: 1) playing repeatedly a short musical sequence on a sham violin (no sound production), 2) the same on a violin, and 3) imagining of the same musical sequence. Cortical DC-potentials were averaged, time-locked separately to the start and end of the musical sequence. We found that, in all three conditions, EEG negativity began to build up slowly about 3 s prior to execution (or to imagining) in Broca’s area and its right homolog; the negativity was maintained, or rose further continuously during the whole musical sequence. The lateral sensorimotor/premotor and the medial (SMA/pre-SMA/ cingulate) motor areas became active, respectively, 1.6 s and 2.0 s, prior to the start and prior to the end of the melody sequence. In four cases, the medial focus of negativity persisted also during the whole musical sequence. We conclude that the Broca area and its right homolog are involved in the earliest preparation of playing and imagining a musical sequence, because their activity started earlier than that of the lateral sensorimotor and lateral/medial premotor areas. Koelsch S, Maess B, Friederici AD (2000) Musical syntax is processed in the area of Broca: an MEG study. Neuroimage 11: S 56. Maess B, Koelsch S, Gunter TC, Friederici AD (2001) Musical syntax is processed in Broca’s area: a MEG study. Nat. Neurosci. 4: 540–545. Nirkko AC, Baader AP, Loevblad K-O, Milani P, Wiesendanger M (2000) Cortical representation of music production in violin players: Behavioral assessment and functional imaging of finger sequencing, bimanual coordination and music specific brain activation (Abstract). Neuroimage 11: S106.

PS15-04

The frontal ERPs to fearful facial expression in depressed patients

E.S. Rozenberg, E.S. Mikhailova, V.V. Artioukh, E.S. Krylova. Mental Health Research Center, Moscow, Russia In 20 nontreated depressed male patients and 20 matched healthy

Platform Sessions controls the time of motor reactions and frontal ERPs were studied under recognition of fearful, angry and happy facial expressions. The findings showed impaired recognition of all facial expressions in patients compared to healthy subjects. Remarkably, compared to healthy subjects the depressed patients revealed increased frontal ERPs late negativity N400 that was contrasted with decreased N400 to happy and angry facial expressions. Further, this finding was accompanied by significant prevalence of “false alarms”. Also we have obtained some data concerned negative correlation between N400 amplitude and level of anxiety in depressed patients (according to Hamilton Rating Scale) and fear emotional attitude in control subjects. Taking in account the important role of amygdala in fear conditioning and fear perception we can suppose somewhat peculiar functional state of amygdala in depression. The revealed neurophysiologic abnormalities agree with magnetic resonance imaging data showed increased amygdala volume in depressed humans (Tebartz van Elst et al., 2000). (The study was supported by Grants of RFBR # 00-04-48232 and RFH #00-0600092a). References: 1. Tebartz van Elst L, Woermann F, Lemieux L, Trimble MR. (2000) Increased amygdala volumes in female and depressed humans. A quantitative magnetic resonance imaging study. Neurosci Lett. 281:103–106. PS15-05

Flexor reflex inhibition during a motor learning task

H.J.A. Van Hedel a,b, V. Dietz a. aParaCare, Paraplegic Centre University

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Hospital Balgrist, Zurich, Switzerland; bCatholic University Nijmegen, dept. Biophysics, Nijmegen, The Netherlands Introduction: The flexor reflex causes a motor action directed away from the nociceptive source. Does it change when a motor task becomes learned? Methods: Ten subjects were asked to step repetitively as low as possible over a moving obstacle. The approaching obstacle was signalled by a tone. Subjects had no visual control and received acoustic feedback about the distance between the foot and the obstacle (height). EMG activity of four leg muscles, knee and ankle joint trajectories and height were recorded. Performance increased when subjects used less EMG activity, performed stable joint trajectories, decreased their swing phases over the obstacle and reduced height. Flexor reflexes, elicited during mid stance phase, were recorded in the m. tibialis anterior. During 5 runs, reflexes were elicited. Run 1, 2 and 5: normal treadmill walking. Run 3 and 4: obstacle runs. Results: Performance was significantly higher in run 3. Reflex responses were not different between run 1 and 2, were lower in run 3 compared to run 2 and not different between run 3, 4 and 5. Conclusions: Subjects inhibit the flexor reflex when learning to step over an obstacle, thereby reducing the ‘disturbance’ and increasing the chance of a better performance.

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Platform Sessions

NEUROPHYSIOLOGICAL CORRELATES OF MEMORY DISORDERS PS16-01

Memory encoding, stimulus awareness and event related potentials. Lessons from a forced awakening test

Luis Garcia Larrea a,b,c, Fabien Perrin b, He´ le`ne Bastuji b. aINSERM; bEA 1880, University Claude Bernard; cCERMEP, Lyon, France The ERP P3 has been considered as a possible concomitant of the access of sensory information to consciousness. However, its presence is not a guarantee of stimulus access to consciousness, since this component may persist in patients apparently unaware of the stimulation. We used the forced awakening test (FA) to explore the relationship between ERPs, stimulus awareness and subsequent recall. Twenty one controls and 40 hypersomniac patients performed a typical auditory “oddball” paradigm, with a silent counting task, during full wakefulness and on “forced awakening” by stimulus after 3 minutes of sleep. After FA subjects were questioned about quantitative and qualitative aspects of stimulus recall. In subjects whose quality of recall was excellent, P3 waves during FA were indistinguishable from those obtained before the nap. When P3 was found attenuated, delayed and desynchronised, recall was quantitatively degraded. P3 was concomitant to (or replaced by) sleep negativities in subjects in whom stimulus recall was severely degraded or absent. These results suggest that the presence of a P3 is crucial to ensure stimulus encoding in a retrievable format, the quality of encoding being related to P3 characteristics. P3 might reflect the passage between ‘instant awareness’ of a stimulus and a more permanent mode of encoding permitting subsequent retrieval, while sleep negativities may act as ‘erasers’ preventing accurate memory encoding and retrieval of the stimulus.

PS16-02

Neural correlates of long-term picture priming: a fMRI study

J. Weidemann a, I.G. Meister a, B. Boroojerdi a, R. Sparing a, A. Thron b, R. To¨ pper a. aDepartment of Neurology; bDepartment of Neuroradiology, University Hospital RWTH Aachen, Germany Priming is a form of implicit memory formation with a high temporal stability: behavioural studies showed that priming effects last over months. Imaging studies have suggested that the latero-occipital and the temporooccipital cortex are the neuroanatomical correlate of perceptual priming. This network is probably independent from the network underlying explicit memory. So far, these imaging studies investigated relatively short retention intervals. The functional anatomy for long-term priming remains unclear. We investigated the priming-effect in 12 healthy subjects and compared retention intervals of 1 day and 6 weeks using event-related fMRI BOLD imaging. Results were calculated with SPM99 according to the random effects model. For both retention intervals a priming effect in the latero-occipital network (BA 18/19) and in the temporo-occipital conjunction area (BA 37) was found bilaterally. The priming effect consisted in a reduced activation for naming of known vs. unknown pictures. This reduction of activation was less pronounced after 6 weeks than after 1 day. We conclude that picture priming is mediated by a bilateral occipital network, extending to the posterior inferior temporal cortex. In concordance with data of behavioural studies, the priming effect is traceable even after weeks but decreases with increasing retention interval.

PS16-03

Non-verbal memory in patients with lateralized epileptic foci: inaccurate neuropsychological construct or methodological ambiguousness?

N. Krstic´ , J. Martinovic´ , M. Gojkovic´ , Zˇ . Martinovic´ . Institute for Mental Health, School of Special Education, Belgrade University Referring to inconsistent findings on relationship between lateralization of epileptic focus and verbal/non-verbal profile of memory functions, the performance on neuropsychological tests of 56 children and adults with lateralized focal seizures (confirmed by focal/lateralized discharges in EEG studies during wakefulness & sleep) was performed. The analysis was focused on tests purported to measure selectively verbal (word list learning, story reproduction) or non-verbal (ROCF, memory for designs) memory, while age, general intellectual abilities, education, handedness, epilepsy type, duration of illness and medication were attended to as control variables. The data revealed significantly lower evidence of mnestic disturbances in patients with right hemisphere foci in general, and confirmed the presence of stronger correlation between left hemisphere EEG lateralization and verbal memory performance. However, the ‘strength’ of particular tests in detection of possible mnestic deficit considerably differed, especially regarding intra-subject dissociation in achievement on two nonverbal tests. The findings were consistent across all age groups, with the exception of the youngest children (7–10 yrs. old) in the study. The results suggest the need for cautiousness in interpreting attainment on figural reproduction tests, particularly ROCF, as a measure of ‘laterality’ of memory disturbance in epileptic patients. PS16-04

Counting omissions. Attention dependent gamma band activity

I.G. Gurtubay a,b, M. Alegre a, A. Malanda c, A. Labarga d, J. Artieda a. aNeurophysiology, ClI´nica Universitaria de Navarra; bNeurophysiology, Hospital de Navarra, Electronic Engineering; cNeurophysiology, ETSIIT, UPNA, Pamplona, Spain; dNeurophysiology, ESII, San Sebastia´ n Objectives: A time-frequency analysis method was applied to examine the characteristics of gamma band oscillatory responses occurring when subjects count omissions using different strategies during and auditory omitted potential paradigm. Methods: 25% of the auditory tones in a rhythmic sequence were randomly omitted. 7 healthy volunteers were asked to count omissions and, in separated and repeated series, to count all the stimuli, omitted or not. Results: An induced response 205 ms after target stimuli onset was found, with a spectral peak around 43 Hz, bilateral temporal posterior topography and mean energy increase of 156% (125–195) with respect to prestimulus, with P , 1028 comparing to rest. The energy of this late oscillatory activity had a positive correlation (r ¼ 0:79, P , 0:001) with the correct count of the omissions. When counting all stimuli mean energy increase was of 89% (P , 1025 ). Conclusions: Counting omissions induces gamma band oscillations. When attention is diverted energy decreases. We suggest a relationship of these oscillations with memory storage or interval timing production processes.

Platform Sessions

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EPILEPSY 1 PS17-01

Seizure anticipation in partial epilepsy

Michel Le Van Quyen a, Vincent Navarro a, Mario Chavez a, Michel Baulac b, Jacques Martinerie a. aLaboratoire de Neurosciences Cognitives et Imagerie Ce´ re´ brale; bUnite´ d’Epileptologie, Hoˆ pital Pitie´ Salpeˆ trie`re, 47 Bd. de l’Hoˆ pital, 75651 Paris, France Objective: Previous studies have shown that nonlinear analysis of intracranial can identify a “pre-ictal phase” several minutes before partial seizures. These studies investigated time intervals of a few hours before the seizure. Here we evaluated a measure of synchronization between several combinations of electrode pairs for anticipation purpose and we evaluate its sensibility and specificity over long-term continuous intracranial recordings. Methods: We analyzed continuous epochs of intracranial EEG, ranging from 6 to 15 days for 5 patients. The data were obtained from EEG-video recording sessions of patients suffering from intractable neo-cortical epilepsy. The instantaneous phase was extracted for consecutive windows by the Hilbert transform and the strength of phase synchrony between pairs of channels was statistically characterized by the Shannon entropy of the phase differences. Each frequency range was analyzed to cover the whole part of the spectrum. Results: A decrease in synchrony was observed to be specific of the period before seizure onset. Some synchrony changes were induced in the interictal dynamics by transition between normal brain states but were always under the detection threshold. These systematic changes were mostly observable in the alpha (8–12 Hz) and beta band (12–20 Hz). The time course of the preictal changes allowed to anticipate 80% of the seizures with a mean anticipation time of 25 minutes. Conclusions: The present results suggest that the loss of synchronization is unique to the period prior to seizure and is sensitive enough to anticipate the ictal onset. PS17-02

Usefulness of SPECT on definition of epileptogenic foci in extratemporal epilepsy

J.E. Ramalheira a,b, M. Pinto a, R. Ribeiro da Silva d, J. Lopes a,b, H. Rodrigues a, A. Martins da Silva a,b,c. aServic¸ o Neurofisiologia, Hospital Santo Anto´ nio, Porto; bIBMC; cICBAS, Universidade Porto; dServic¸ o Psiquiatria, Hospital V.N. de Gaia, Porto, Portugal Relevance of SPECT/EEG on epileptogenic focus characterisation of Extra-Temporal Lobe Epilepsy (ETE) was assessed in patients with medically refractory Epilepsy. Out of 73 epileptic patients studied 43 had TLE (58.9%) and 30 ETE (41.1%). In these we performed 33 SPECT studies during a EEG-Video session: nine ictal, 22 inter-ictal, 2 post-ictal; 24 using 99m Tc-ECD and 9 using 99m Tc-HMPAO. Two patients underwent ictal and interictal studies, one both post-ictal and interictal studies. Localisation given by SPECT was compared to MRI, CT and clinical data, to define epileptogenic area and SPECT accuracy. A positive correlation was found in 90% patients (9 ictal, 2 post-ictal and 19 interictal); in three interictal studies there was no agreement. Ictal SPECT sensitivity reach 100%. We emphasise the relevance of combining SPECT and EEG to improve focus characterisation in ETE patients. Fusion techniques could be extra aid.

sies. Source analysis in OLE has been seldom attempted, and no clear picture of its value in clinical practice established. Objectives: Source analysis of paroxysmal activity is performed in 4 cases of symptomatic OLE, trying to establish the value of these methods in the correlation between clinical symptomatology and scalp EEG. Methods: In all patients long-term EEG recording with 27–32 scalp electrodes was done. Electrode positions were determined and a BEM volumetric model built from high resolution head MRIs, including the fiducial points. Results: All patients had lesions extending to or contained in the occipital lobes (displasias, angiomatosis and periventricular heterotopias). Spike activity was restricted to the occipital lobes in 2 patients, while the others showed temporal or fronto-temporal spike activity. Good correlation between the sources locations and the lesions was apparent, and an occipital source was found in all cases, with a good agreement between the sources and the symptomatogenic area. Conclusions: Source analysis is an effective method to improve localization of the epileptic focus in OLE and leading to good agreement between epileptic and symptomatogenic areas. PS17-04

P. Boon a, K. Vonck a, M. D’Have´ a, B. Vanrumste a,d, G. Van Hoey a,d, Ph. Van Walleghem a, J. Caemaert b, E. Achten c, J. De Reuck a. aReference Center for Refractory Epilepsy, Department of Neurology; bDepartment of Neurosurgery; cDepartment of Radiology (MR), Ghent University Hospital; dDepartment of Electronics and Information Systems, Ghent University, Ghent, Belgium Purpose: Source localization of epileptic foci using ictal spatiotemporal dipole modelling (ISDM) yields reliable anatomical information in presurgical candidates. It requires substantial resources from EEG and neuroimaging laboratories. The profile and number of patients who may benefit from it are presently unknown. The purpose of this study is to demonstrate the clinical usefulness of source localization in a prospectively analyzed series. Methods: One hundred patients (51 M, 49 F) with mean age of 31 years (range: 2–63 years) and mean duration of refractory epilepsy of 20 years (range: 1–49 years) were consecutively enrolled in a presurgical protocol. Ictal EEG was available in 93 patients. ISDM was performed when suitable ictal EEG files were available. The clinical applicability of ISDM was examined in three patients groups; 37 patients in whom ictal EEG recording and MRI were congruent (group I); 30 patients in whom results were not completely congruent but not incongruent (group II) and 26 patients in whom the results were incongruent (group III). Results: ISDM could be performed in 31/100 patients: 11 in group I; 8 in group II and 12 in group III. ISDM influenced decision-making in none of the patients in group I; in 4/8 in group II and in 10/12 in group III. Typically, the results of ISDM directed to avoid intracranial EEG recordings in what appeared to be unsuitable candidates for resection by clearly confirming the discongruency between ictal EEG and MRI findings. Conclusions: In this series of 100 presurgical candidates, ictal source localisation could be performed in 31% of patients. In 14% of patients, it proved to be a key element in the surgical decision process. PS17-05

PS17-03

EEG source analysis in occipital lobe epilepsy

Alberto Leal. Hospital Fernado Fonseca, Department of Neurology, Ammadora, Portugal Introduction: Well documented cases of occipital lobe epilepsy (OLE) constitute a small percentage in most series of focal symptomatic epilep-

Prospective evaluation of ictal source localization in presurgical patients with refractory epilepsy

long term amygdalo-hippocampal stimulation for refractory temporal lobe epilepsy

Kristl Vonck a,c, Paul Boon a,c, Jacques Caemaert b, Pieter Claeys c, Jacques De Reuck a. aDepartment of Neurology, Reference Center for Refractory Epilepsy; bDepartment of Neurosurgery, Reference Center for Refractory Epilepsy; cExperimental EEG Laboratory Ghent University Hospital, Belgium

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Platform Sessions

Purpose: Short-term deep brain stimulation (DBS) in medial temporal lobe structures has recently been shown to be efficacious in patients with medically refractory temporal lobe epilepsy. To date there is little information on chronic DBS in these structures. The purpose of the present study was 1. to evaluate the efficacy and safety of long-term DBS in medial temporal lobe structures and 2. to evaluate the feasability of using chronic DBS electrodes for the localisation of the ictal onset zone prior to DBS. Methods: In three patients with refractory complex partial seizures (CPS) and negative MRI findings four DBS electrodes were bilaterally implanted in the amygdalohippocampal region to identify and subsequently stimulate the ictal onset zone. Mean monthly CPS frequency

was compared before and after chronic DBS. Side effects were carefully monitored. Results: DBS electrodes yielded high-quality EEG recordings that showed unilateral focal or regional seizure onset in medial temporal lobe structures. In all patients unilateral amygdalohippocampal stimulation was performed. After a mean follow-up of 5 months (range: 3–6 months) all patients had a .50% reduction in seizure frequency. None of the patients reported side effects. Conclusions: This study shows the feasibility of consecutive EEG recording and DBS in medial temporal lobe structures using DBS electrodes implanted during a single surgical procedure. Chronic DBS is an efficacious and safe treatment for refractory temporal lobe epilepsy.

Platform Sessions

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AUTONOMIC SYSTEM PS18-01

Sympathetic skin responses in spinal human elicited by pudendal nerve stimulation

Andre Reitz a, Daniel M. Schmid b, Armin Curt a, Peter A. Knapp a, Brigitte Schurch a. aParaCare, Institute for Rehabilitation and Research, Balgrist University Hospital, Zurich, Switzerland; bDepartment of Urology, University Hospital Zurich, Switzerland Aims: Spinal cord injury (SCI) due to serious disturbances of the sympathetic nervous system. The control of sympathetic neurons in the isolated human spinal cord remain unclear. Materials and methods: We studied sympathetic skin responses (SSRs) in 14 patients with complete SCI on cervical, thoracic and lumbar level. SSRs were provoked by auditory bursts and electrical stimulation of median, pudendal and tibial nerve and recorded from the palmar and plantar skin. Results: Appearance or absence of the SSRs following stimulation above the lesion depend on the level of lesion and on the location of stimulation. Lesions below T3 show palmar and lesions below T12 palmar and plantar SSR. Pudendal nerve stimulation evoked plantar SSRs in patients with complete cervical and thoracic SCI. No SSRs were obtained in patients with complete lumbar lesions. Tibial nerve stimulation did not elicit SSRs below a SCI lesion. Conclusions: The isolated human spinal cord can generate sympathetic cholinergic impulses. SSRs following pudendal nerve stimulation in complete SCI above T12 are mediated by somatic pudendal afferents and a sympathetic pathway originating at the thoracolumbar segments. The underlying sacro-lumbar reflex circuit is organized exclusively on spinal level and requires intact lumbar segments. Tibial nerve stimulation cannot activate this reflex circuit. PS18-02

Treatment of cardiac dysautonomia in Rett syndrome: prevention of sudden death?

M. Acampa, F. Guideri, Y. Hayek, M. Zappella. Department of Internal Medicine; Department of Child Neurology, University of Siena, Italy Introduction: Incidence of sudden death in Rett syndrome is greater than that of the general population. Cardiac dysautonomia is a prime suspect cause. Carnitine may have beneficial effects on cardiac and nerve function. We describe the effects of a six months treatment with acetyl-L-carnitine (ALCAR) on heart rate variability (HRV) in 10 Rett girls (1–13 years) with cardiac dysautonomia (HRV , 2000 msec2). Methods: HRV (expressed as total power) was evaluated before and after treatment with ALCAR (50 mg/kg/die). Three main spectral components (FFT) were distinguished in a spectrum calculated from short-term (5 0 ) ECG recordings: a very low frequency (VLF), a low frequency (LF) and a high frequency (HF) component. A t test was performed for analysis of HRV. Results: In girls treated with ALCAR a significant increase of total power (1004 ^ 430 vs 3094 ^ 2108 msec2, P ¼ 0:01), VLF (369 ^ 235 vs 1003 ^ 697 msec2, P ¼ 0:01) and LF (369 ^ 181 vs 963 ^ 564 msec2, P ¼ 0:009) was observed. Conclusions: We hypothesize that ALCAR may exert neurotrophic properties on cardiac autonomic nervous system, reducing the risk of sudden death. PS18-03

Water immersion skin wrinkling is due to vasoconstriction

E. Wilder-Smith, A. Chow. Singapore Background: Water immersion skin wrinkling of the hand depends on

intact sympathetic innervation but the underlying physiology has never been elucidated. Since blood flow regulation is one of the main functions of hand sympathetic nerves, we chose to measure blood flow before and with immersion wrinkling. Design/Methods: Blood flow in ulnar, digital artery and skin vessels was measured using Doppler. Resting blood flow was recorded prior to and at the end of immersion in 40 [degree] C 0.5 mol/l NaCl solution for 30 minutes. Results: 23 healthy volunteers, 6 males and 17 females, with a mean age of 35 years (range: 24–52), participated. Blood flow significantly decreased post immersion in all vascular territories (P ¼ 0:016 ulnar artery, P ¼ 0:001 digital artery, P ¼ 0:01 skin vessels) with a maximum in the digital artery. Conclusion: Water immersion skin wrinkling is accompanied by significant vasoconstriction of hand blood vessels of all sizes. The greatest decrease occurs at the digital artery level. Since sympathetic nerves control vasoconstriction, we postulate that the major component of this phenomenon is caused by vasoconstriction. PS18-04

Sympathetic skin response in dialysis and renal transplanted patients

H. Ayromlou, H. Aragani, M. Raisii. Departments of Neurology and Dialysis, Imam Hospital, Tabriz, Iran Introduction: Neurological disorders, especially autonomic neuropathy, are among the most bothersome complications in renal failure. Methods: We evaluated sympathetic skin response (SSR) of lower and upper limbs in three groups: 17 chronic hemodialysis (HD) patients, 18 patients with renal transplantation (RT) and 20 healthy controls (CT). Latencies and amplitudes of SSR of median and tibialis nerves were registered by TOENNIES Neuroscreen w Plus machine. Also correlation between SSR with hemoglobin, calcium, phosphorus, cholesterol, triglyceride and protein catabolic rate was studied. Mann Whitney U test and Pearson coefficient were used for analysis. The mean age of HD and RT groups was 46.8 1 /218 and 37.2 1 /211 years, respectively. Results: In the HD group, the average of latency time of SSR in both limbs was 2.03 1 /20.37 seconds. It was significantly longer than 1.85 1 / 20.32 s and 1.64 1 /20.22 s in RT (P ¼ 0:008) and CT (P ¼ 0:007), respectively. Differences of amplitudes of SSR between the three groups were even more significant it was 1160.6 1 /2375.8 in HD, 1940 1 / 21102 in RT and 2487 1 /21253.1 microvolt in CT groups (P , 0:001). It was a positive correlation between Hb concentration with better SSR. Although age and months of dialysis had clear negative impacts on SSR. Conclusion: In HD sympathetic nerve of skin is involved. The sluggish and weak response would be improved after RT. PS18-05

Sympathetic skin response of arm in assessing spared spinal afferents in paraplegia

M. Klopcic Spevak. Rehabilitation Institute, Ljubljana, Slovenija Somatosensory cortical evoked potentials (SsCEPs) on tibial nerve stimulation and recording hand SSR (above the lesion) after electrical stimulation of mixed (tibial and femoral) and segmental sensory nerves L3, L4, L5, S1, S2–3 in incomplete and complete SCI patients were assessed. 15 patients with complete SCI (ASIA A) and 17 with sensory incomplete (ASIA B and C), below level Th4, were investigated. Hand SSR, as diagnostic tool, was checked by stimulation of supraorbital nerve. Diagnostic criterion was present or absent hand SSR. SsCEPs are standardized method. Results: SsCEPs and SSR after low intensity stimulation (0.2 ms, 150 V) both offer evidence of preserved somatosensory afferent function. In incomplete group of 17 patients, in 6 it was confirmed by

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Platform Sessions

SsCEPs and in 7 by SSR. Applying stronger, painful stimuli, SSR confirmed spinal sensory afferent function by evoked hand SSR in additional 5 patients of the same group (in 13 out of 17). In incomplete SCI group, SsCEPs or hand SSR after short electrical stimuli were evoked in

none, after strong stimuli 1 ms 300 V, in 8 patients out of 15 hand SSR was obtained. Benefit of SSR method is ability to test spinal afferents of many dermatomal nerves for shorter time and make “mapping” of preserved spinal sensory afferents in SCI.

Platform Sessions

S39

MUSCLE DISEASES AND NEUROMUSCULAR TRANSMISSION PS19-01

Correlation between muscle fiber conduction velocity and fiber diameter in vivo

Paul J. Blijham, Baziel G.M. van Engelen, Machiel J. Zwarts. Department of Clinical Neurophysiology, Institute of Neurology, University Medical Center Nijmegen, The Netherlands Using an invasive technique with intramuscular stimulation and recording of action potentials, we prospectively measured muscle fiber conduction velocity (MFCV) in 69 patients with suspected myopathic disease, who afterwards underwent a needle muscle biopsy on clinical grounds. We calculated correlation coefficient (R) for upper and lower limits of MFCV and diameter range, and for variability, as expressed in the ratio of the upper to the lower limit, for all patients, using linear regression analysis. Of the 69 patients included, 44 were diagnosed with a myopathy, 5 with neurogenic disease, and 20 patients with no neuromuscular disorder (NMD). We found significant correlations (P , 0:0001) for slowest to smallest fiber (R ¼ 0:56), fastest to largest fiber (R ¼ 0:50) and MFCV variability to diameter variability (R ¼ 0:63). We conclude that the relationship between propagation velocity and fiber diameter is confirmed in vivo in patients with suspected NMD. Our results indicate that variability of MFCV can be used as a tool to detect increased fiber diameter variability, as can be seen in early myopathic disease. Resume: we found a significant correlation between muscle fiber conduction velocity and fiber diameter in patients with neuromuscular diseases. PS19-02

Single fiber electromyography by axonal stimulation in orbicularis oculi muscle in ocular myasthenia gravis diagnosis: sensitivity and specificity

M. Gonza´ lez-Hidalgo, C. Franco Carcedo. Departament of Clinical Neurophysiology, Hospital ClI´nico San Carlos, Madrid, Spain Introduction: The diagnosis yield in patients with pure ocular myasthenia gravis (OMG) is considerably lower than in those with generalized forms, even when facial muscle were examined. Often a clear clinical picture is not present and OMG diagnosis is very difficult because gold standard tests are not available. Objective: To determinate the usefulness of single fiber electromyography by axonal stimulation (SFEMG-AS) in orbicularis oculi muscle in OMG. Patients and methods: We studied 142 patients with suspected diagnosis of OMG (female: 96, male: 46; age range: 10–87). The diagnosis of OMG was based on historical, clinical, pharmacological, neurophysiological and immunological findings, following international diagnosis criteria. Then, they were classified according to Ossserman: type I and IIa and correlated to the electrophysiological findings. SFEMG-AS sensitiveness was analysed detecting neuromuscular transmission abnormalities. Results: The clinical form observed were: type I (20 patients), type IIa (38 patients), without pathology (20 patients) and other diagnosis non myasthenic pathology (64 patients). In OMG I sensitivity was 65% and specificity was 97.5%. In OMG IIa sensitivity was 94.3% and specificity was 98.7% (CI:95%). Conclusions: SFEMG-AS is a very sensitive electrophysiological tool, detecting abnormalities in neuromuscular transmission in OMG patients with an excellent clinical correlation.

PS19-03

Single fiber EMG by means of axonal stimulation and voluntary activation: a comparative study

Pedro de Mingo, M. Luisa RuI´z-Cabello, Jesu´ s Mesones. Hospital Virgen de la Arrixaca, El Palmar, Murcia, Spain We have compared the jitter values obtained by voluntary activation and axonal stimulation in the muscles frontal and orbicular of the eyes, into a group of 41 subjects without pathology and another group of 23 diagnosed patients of Myasthenia Gravis. In the normal group statistically significant correlations were obtained between the age and the value of the mean jitter (mcd and msd), as well as of the value of the mcd with the existence of some abnormal pear. In the group of myasthenic patients a correlation of very high statistical significance was found between the jitter values obtained with both procedures. Three discriminants analysis were carried out. For voluntary activation, the negative predictive value was of 97.1% and the positive predictive value of 89.5%. For axonal stimulation, these values were respectively of 100% and 96.7%. When variables of both procedures were take into account the obtained predictive negative value was of 100% and the positive predictive one of 90.5%. Results show the existence of significant statistical correlation in the abnormalities detected in the SFEMG of myasthenic patient by both procedures. As well as a higher sensibility and specificity of the axonal stimulation technique for the diagnosis of this illness. PS19-04

SFEMG study of neuromuscular transmission in migraine

A. Kostera-Pruszczyk, I. Domitrz, H. Kwiecinski. Department of Neurology, Medical University of Warsaw, Poland It is known that mutations of CACNA1A, which encodes a neuronal P/Q Ca(2 1 ) channel, are present in patients with familial hemiplegic migraine and possibly other types of migraine. These channels are also found in motor nerve terminals, where they control acetylcholine release, influencing neuromuscular transmission. To asses if routine SFEMG can disclose neuromuscular transmission deficit in a group of patients with migraine, a group of 26 patients with different types of migraine was studied. The electromyographer was unaware of clinical presentation of migraine. The patients were divided into three groups: 8 patients with migraine without aura (M) (disease controls), 12 with hemiplegic form, paresthesias, or speech disturbances (HM) and 6 with visual aura (VA). SFEMG of voluntarily activated extensor digitorum communis muscle was performed. The SFEMG results were normal in group M (mean MCD 27.4 msec, 26–29, all pairs ,55 msec). In the remaining groups slight neuromuscular transmission disturbances were present in 6 of 12 patients with HM (mean MCD 32.1 msec, 25–36.9) and in 1/6 patients with VA (mean MCD 31.1 msec, 28–36.2) (P , 0:05 Duncan test). Our study revealed mild neuromuscular transmission disturbances in half of the patients with hemiplegic migraine, only one with migraine with visual aura, but none of the patients with migraine without aura. Slight abnormalities of neuromuscular transmission detectable by SFEMG might reflect genetic dysfunction of P/Q Ca(2 1 ) channels in a group of migraineurs with aura.

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Platform Sessions

EPILEPSY 2 Carlo Alberto Tassinari. Department of Neurology, Bellaria Hospital, Bologna, Italy Encephalopathy with electrical status epilepticus during sleep or ESES is an age-dependent and self-limited syndrome whose distinctive features include a characteristic age of onset (with a peak around 4–5 years), heterogeneous seizures types (mostly partial motor or unilateral seizures during sleep and absences or falls while awake), a typical EEG pattern (with continuous and diffuse paroxysms occupying at least 85% of slow wave sleep) and a variable neuropsychological regression consisting of IQ decrease, reduction of language (as in acquired aphasia or Landau-Kleffner syndrome), disturbance of behaviour (psychotic states) and motor impairment (in the form of ataxia, dyspraxia, dystonia or unilateral deficit). Despite the long-term favourable outcome of epilepsy and status epilepticus during sleep (SES), the prognosis is guarded because of the persistence of severe neuropsychological and/or motor deficits in approximately half of the patients. No specific treatment has been advocated for this syndrome, but valproate sodium, benzodiazepines and ACTH have been shown to control the seizures and the SES pattern in many cases, although often only temporarily. Subpial transection is proposed in some instances as in non-regressive acquired aphasia. Recent data support the concept that ESES syndrome may include a large subset of developmental or acquired regressive conditions of infancy. PS20-01

Outcome in infants with epilepsy: effect of seizure type, EEG findings and frequency of seizures

L. Vanderlinden, L. Lagae. Department Paediatric Neurology, University Hospitals, Leuven, Belgium We investigated the developmental and epileptic outcome in 60 children who had their first epileptic seizures before the age of 1 year. Infants with febrile seizures and infants with West syndrome were excluded. All children were diagnosed and treated according to a standardized epilepsy protocol. The infants were divided into 2 groups: a symptomatic group (n ¼ 24) and an idiopathic group (n ¼ 36). By definition, development was normal at the start of the epilepsy in the idiopathic group. The follow up period ranged from a minimum of 7 months to 60 months (median 24 months). It was found that in both groups, the epileptic seizures could be controlled in about 60% (14/24 symptomatic group and 22/36 idiopathic group). The type of the seizures nor the EEG abnormalities at the start of the epilepsy were predictive for control of the epilepsy. However, in the idiopathic group, there was a strong tendency for generalized seizures to be better controlled. In the symptomatic group, only 4 children showed a completely normal psychomotor development at the end of the follow up, reflecting the underlying brain abnormality. In the idiopathic group, 19/36 showed a normal development. The major predictive factor for normal development in this group was the controllability of the epilepsy. In the 14/36 children with uncontrolled epilepsy, only 3 showed a normal development. This study underlines the negative effect of uncontrolled seizures at a young age on the psychomotor development.

PS20-02

Focus localization using dipole modeling and spike related functional MRI in benign rolandic epilepsy

Rainer Boor, Goran Vucurevic, Georg Kutschke, Thomas Bauermann, Stephan Boor. University Children’s Hospital, Department of Child Neurology, Langenbeckstr. 1, D-55101 Mainz, Germany The value of non-invasive methods such as dipole modeling of EEG spikes, and the EEG-assisted functional magnetic resonance imaging (fMRI) has not been sufficiently investigated in children with focal epilep-

sies. As a model of extratemporal epilepsies, we studied 9 patients aged 4 to 13 (median 10) years with benign rolandic epilepsy. Interictal EEGs were recorded with 23 channels and included 4 lower temporal electrodes. The spikes were averaged and the dipoles were modeled with the BESA 2000 program, and then imported into the anatomical 3D-MRI (T1-weighted 3DMPRAGE). Additionally, interictal spikes were recorded during the fMRI acquisition (BOLD, 1.5 Tesla, EPI T2-sequence, TR 6000 ms, TE 66 ms, matrix 128x128, slice thickness 6 mm, 16 transversal slices) on a MRcompatible battery-powered digital EEG system with 16 channels. The fMRI sequences were correlated off-line with the EEG spikes and analyzed with the SPM 99 software. The EEG source analysis demonstrated the spike onset in the central region in all patients, and the EEG-assisted fMRI results were consistent with the modeled dipoles in five patients. We could not demonstrate any fMRI activation despite active spiking in 2 patients, and 2 patients did not produce enough spikes for fMRI analysis. In conclusion, the non-invasive techniques of EEG dipole modeling and of spike related fMRI may facilitate interictal focus localization in patients with focal epilepsies.

PS20-03

Epileptiform spikes desynchronize and diminish fast (gamma) activity of the brain. An “anti-binding” mechanism?

A.V. Medvedev. Department of Medicine, Flinders University, Bedford Park, SA, 5041, Australia Fast (20–100 Hz) rhythms of brain electrical activity have been suggested to be important for temporal binding of neural activities underlying mental representations in perception and cognition. Also, intense fast rhythms often precede epileptiform discharges in patients and some experimental models e.g., generalized spike activity (2–3 Hz) after systemic kainic acid in the rat. Power, multiple coherence and phase were analyzed at frequencies 1–100 Hz in the hippocampal and neocortical EEG. Gamma rhythms were extremely intense and highly coherent at the onset of kainateinduced epileptiform discharges. During and immediately after each discharge, gamma power and coherence were significantly decreased. These data show the ability of epileptic spikes to desynchronize and suppress gamma activity. A novel hypothesis is advanced that epileptic activity results from the extreme activation of “anti-binding” controlling mechanism. When fast activity is abnormally intensified, “over-binding” with global synchrony of gamma rhythms can occur in neural networks leading to inadequate synaptic modifications and false associations. To prevent this, epileptic discharge develops as a protective mechanism suppressing fast activity. Similar mechanism may be related to spikes normally occurring in sleep. This proposal has implications for our understanding of temporal binding and how its excessive activation may lead to pathological states. PS20-04

Low EEG photosensitivity in patients with alcohol related seizures

T. Sand, G. Bra˚ then, R.P. Michler, G. Helde, E. Brodtkorb, G. Bovim. Department of Clinical Neurosciences, Medical Faculty, Norwegian University of Science and Technology Trondheim, Norway We investigated if the EEG response to flickering photic stimulation in the 18–24 Hz frequency range, (the so-called “H-response”) could be used as a biological marker for alcohol related seizures. Method: The AUDIT questionnaire was applied to score the amount of alcohol use. An alcohol-related seizure (ARSwE) was defined as: 1) AUDIT score 3 8, and 2) No history of epilepsy. Twenty-two ARSwE patients, 21 epilepsy patients with seizures (ES), 30 AUDIT negative

Platform Sessions patients with seizures (OS) and 37 well-controlled epilepsy outpatients were included. QEEG from 79 sciatica patents served as an additional control group. EEG was recorded in relaxed wakefulness with eyes closed. Spectral analysis of ongoing resting EEG was performed. The spectral responses to 18 Hz and 24 Hz photic stimulation were calculated from occipital O1 and O2 electrodes. Results: Photoparoxysmal responses were not observed in ARSwE patients. Reduced response to 24 Hz photic stimulation (low 24 Hz/18 Hz ratio) was found in the ARSwE group compared to the sciatica control group. Conclusion: Photosensitivity in ARSwE patients is seemingly low. Flicker following response to 24 Hz stimuli was reduced in ARSwE patients. The latter effect was rather small, however, and it could not be used in categorisation of individual patients. PS20-05

Early SII (secondary somatosensory area) SEPs. Data from intracerebral recordings in humans

C. Barba a, M. Frot b, F. Mauguie`re b. aDepartment of Neurology, Universita` Cattolica del Sacro Cuore, Rome, Italy; bFunctional Neurology and Epileptology Department, Hopital Neurologique, Lyon, France Objective: To record SEPs to median nerve stimulation by chronically implanted electrodes in the parieto-rolandic opercular area of nine epileptic patients, in order to evaluate whether somatosensory evoked responses could be generated in the SII area earlier than 40 ms after stimulus. Methods: Nine patients (4 males, 5 females) with drug-resistant partial epileptic seizures were investigated using stereotactically chronically implanted electrodes in the parietal cortex, posterior to VAC plane (SII area) and in the frontal opercular region rostral to VCA. Results: The main finding of this study is the recording of an early somatosensory evoked potential, (N30op), by chronically implanted electrodes in the SII area of eight epileptic patients. In three patients where SEPs were performed after ipsilateral MN stimulation, a N30op was recorded 5.8 ^ 2 ms later than contralateral one. Furthermore, short and

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long-latency SII SEPs seemed to originate from different neurons clusters with different sensitivity to high frequency stimulation. Conclusions: This is the first report of early SEPs recorded by chronically electrodes implanted in SII area. The N30op potential, even if less consistent than later potentials, confirmed the important role of the SII area in the early processing of somatosensory inputs.

PS20-06

Unusual epileptiform EEG variants – a case-control study of their clinical associations

Z. Martinovic, V. Radivojevic. Institute for Mental Health, Belgrade, Yugoslavia Purpose: To analyse physiological and clinical associations of unusual epileptiform variants (UEV). Methods: During a three-years period, standard EEG recordings of patients (aged 12–66 years), were analysed for the following UEV: the 14 and 6 Hz positive bursts (14 and 6 Hz PS), small sharp spikes (SSS), wicket spikes (WS), 6-Hz spike-and-wave paroxysms (6 Hz S-W) and rhythmic temporal epileptiform activity (RTEA). Control group consisted of EEGs of age- and sex matched healthy subjects with UEV, and patients without UEV. All EEGs were read by two independent electroencephalographers whose concordance rate in assessing UEV was 92–95%. Results: We reviewed 4102 EEGs, found 128 (3.12%) with BEV, and compared the findings with control groups. All UEV types were mostly age- and physiological state dependent, and significantly more common in patients. Excepting WS, UEV were commoner in patients with epilepsy associated with various neuropsychiatric disorders. Clinically relevant UEV were found in 9 patients (mostly with RTEA and 6 Hz S-W). Conclusions: The findings of BEV should be interpreted in the context of the overall clinical picture. Further studies are needed to determine if BEV could serve as markers of epilepsy comorbid with various neuropsychiatric disorders.

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Platform Sessions

CLINICAL NEUROPHYSIOLOGY OF THE ‘CRITICAL ILLNESS’ AND NEUROPATHIES Application of clinical neurophysiology in CI patients in ICU W. Trojaborg. Helleruplund Alle 3, Hellerup, Denmark Unexplained weakness in critical illness is often not classified by conventional EMG and NC studies as they often fail to distinguish between neuropathy and myopathy. Both conditions are characterized by low CMAPs and show “denervation activity”. Voluntary MU evaluation is often problematic as data are limited due to poor voluntary effort. To improve diagnostic yield and overcome the pitfalls, measurements of muscle fiber excitability by direct muscle stimulation, QEMG, and MUNE were added to the electrophysiological test battery. In a cohort of consecutive CI patients the applied techniques supported an underlying myopathy as the cause of the paresis or paralysis in all patients, findings that were supported by muscle biopsy. PS21-01

The effects of activity-dependent hyperpolarization on impulse conduction in carpal tunnel syndrome

C. Cappelen-Smith, C.S.-Y. Lin, D. Burke. Department of Neurology, Prince of Wales Hospital and The Prince of Wales Medical Research Institute, Sydney, Australia Previous studies indicate that the hyperpolarization of motor axons produced by a maximal voluntary contraction may precipitate conduction block in chronic acquired demyelinating polyneuropathies. The present study investigated whether this axonal hyperpolarization can produce or accentuate conduction block in carpal tunnel syndrome (CTS), thereby implicating demyelination as a factor in the pathogenesis of CTS. Studies were performed in 12 patients with mild-moderate CTS and compared with 12 healthy controls. Using the technique of threshold tracking the compound muscle action potential (CMAP) of abductor pollicis brevis (APB) was recorded in response to supramaximal stimuli to the median nerve at the wrist, alternating with measurements of axonal excitability. After a voluntary contraction of APB for 60 s, there was a lesser degree of hyperpolarization in the patients ,18%, compared with controls at ,40%. The changes in strengthduration time constant and supernormality were appropriately smaller in the patients. The amplitude and area of the maximal CMAP was not significantly altered in either group. Activity-dependent conduction block was not precipitated in the CTS patients even though this degree of axonal hyperpolarization had produced conduction block in chronic inflammatory demyelinating polyneuropathy. These studies support the view that demyelination may not be a major factor in the pathophysiology of mild-moderate CTS.

PS21-02

Auditory neuropathy in the autosomal dominant axonal Charcot-Marie-Tooth disease linked to the CMT2E locus

Dusˇan Butinar a, Arnold Starr b, Domna-Maria Georgiou c, Kyproula Christodoulou c, Janez Zidar a. aInstitute of Clinical Neurophysiology, University Medical Centre, Ljubljana, Slovenia; bUniversity of California, Irvine, California, USA; cThe Cyprus Institute of Neurology & Genetics, Nicosia, Cyprus Hearing impairment found in both hereditary and acquired forms of peripheral neuropathies is due to associated auditory neuropathy (AN). Its characteristics are abnormal auditory brainstem responses (ABRs) and normal cochlear receptor measures. We have searched for the presence of AN in 14 members of two families with the axonal dominant CharcotMarie-Tooth (CMT) disease that showed linkage to the CMT2E locus on chromosome 8p21. DNA sequencing revealed a novel missense mutation in

the neurofilament-light gene in family #1 and no mutation in the coding region of this gene in family #2. Auditory function was assessed by ABRs, distortion product otoacoustic emissions (DPOAE), tonal and speech audiograms, and by middle ear reflexes. In addition to typical clinical and electrophysiological signs of the axonal CMT disease, members of family #2 exhibited also signs of pyramidal tract involvement. We found absent or abnormal ABRs beginning with the auditory nerve response, normal DPOAE, and abnormal speech audiograms in all five members of family #2, but family #1 members had completely normal tests. Thus, the genetic defects in these two families, despite being linked to the same gene locus, have different effects on both auditory nerve and central motor pathways and may be caused by mutations in different genes.

PS21-03

Pathophysiological states of nerve segments inferred from electrophysiological tests

H. Tankisi a,b, B. Johnsen a,b, A. Fuglsang-Frederiksen a,b, M. de Carvalho b, P.R.W. Fawcett b, A. Labarre-Vila b, R. Liguori b, W. Nix b, I. Schofield b. a Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark; bThe ESTEEM Group In this paper we suggest criteria for pathophysiological interpretation of electrophysiological tests based on seven neurophysiologists’ experiences and discussions at workshops in the ESTEEM project since 1992. The degree of conduction slowing taken to indicate demyelination is a decrease of 40% or 5.5 SD compared to the average of controls or 70% of LLN. The criteria for distal latencies and F-wave latencies are an increase of 100% (6.0 SD) and 40% (7.0 SD) compared to the average of controls, respectively, which roughly corresponds to 150% increase of ULN for both. For definite/probable conduction block, we take the limit of 50%/ 40–50% decrease in CMAP amplitude in upper extremities and 60%/50– 60% in lower extremities. SNAP amplitude reduction taken to indicate axonal loss is a decrease of 75% (2.5 SD) or more compared to average of controls in the presence of normal or slightly reduced conduction velocity (2 SD–2.5 SD). SNAP amplitude reduction in association with a decrease in conduction velocity (more than 2.5 SD) is considered as neuropathic, i.e. the abnormality shows no clear evidence of demyelination or axonal loss. The aim of this study is to initiate a discussion about the electrophysiological evaluation of pathophysiological state of nerves rather than trying to implement strict criteria.

PS21-04

Hereditary motor and sensory neuropathy I and II type: analysis of the amplitude and the area of compound muscle action potential

V. Khodulev, V. Ponomarev, S. Vlasova. Research Institute of Neurology, Neurosurgery and Physiotherapy, Hospital # 5, Research Institute of Medical and Social Evaluation and Rehabilitation, Minsk, Belarus There are no uniformly accepted criteria for the identification of conduction block. The hereditary motor and sensory neuropathy I and II type (HMSN) are the most common forms of hereditary neuropathy without conduction block. The aim of this work was the evaluation of the maximal reduction in compound muscle action potential (CMAP) amplitude and area on proximal versus distal stimulation in 18 patients with HMSN, aged 8–45 years. We investigated the motor fiber median, peroneal and tibial nerves on the distal segments of the extremities. We, in retrospect, determined the amplitude reduction degree of negative peak and “peak to peak”, the area of the negative phase and total CMAP on proximal versus distal stimulation in percentage. In the nerves of the lower extremities had been revealed that the area of

Platform Sessions the total CMAP was the less changeable index, the reduction in CMAP total area did not exceed 40% and the shape of CMAP may be changed on proximal versus distal stimulation. In the median nerve, CMAP area and amplitude reduction did not exceed 25%. This results may be useful in distinguishing hereditary from acquired demyelinating polyneuropathies and for more exact definition of motor conduction block.

PS21-05

Compensatory mechanisms in the course and progression of axonal polyneuropathy

Barbara Emeryk-Szajewska, Jerzy Kopec´ , Anna Karwan´ ska. Department of Neurology, Warsaw Medical University, Poland The objective of this study was to evaluate the compensatory mechan-

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isms in axonal polyneuropathy. Using the classical ENG and needle EMG criteria, 41 patients have been enrolled into the study. FID BB, RF, and TA muscles (119) were investigated and analysed with our own “Functional-QEMG system”. Contrary to classical quantitative methods we analysed dynamic changes of MUAPs size and their variability. The all acting MUs were analysed in terms of their structural reorganisation and functional consequences reflecting the compensatory mechanisms. The recordings were assessed in the stage of initial and full reinnervation and decompensation. In the initial and full reinnervation the muscular weakness was fully compensated. It was documented as increased MUAPs area with great variability, indicating ongoing reinnervation, reduced of MUs population, but still normal muscle electrical force. In the following stages of damage, the compensatory process was dissolved due to the completed reinnervation and secondary denervation as documented by reduced MUAPs sizes and their variability, reduced firing rate of IP at maximal contraction and decreased muscle force.

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Platform Sessions

NEUROMONITORING IN THE OPERATING ROOM 1 V. Deletis. Department of Intraoperative Neurophysiology, INN, Beth Israel Medical Center, New York, USA Recent developments in intraoperative monitoring methodologies and in technological advances are opening new possibilities in the prevention and/ or documentation of intraoperatively-induced neurological injury as well as introducing a closer re-evaluation of conventional approaches to (neuro)surgery. Of particular interest are efforts to integrate video recordings from the operating field (in real-time), neurophysiological traces, and anesthesiological data into a single event and equipment, which can help both intra- and post-operative assessment. This particular effort promises not only to give us a comprehensive approach to (neuro)surgical procedures, but also to introduce a new metaphor for (neuro)surgery: the comprehensive intraoperative monitoring (CIM). Conceptually, for instance, CIM would allow for critical intraoperative data to be presented in a single screen and to be recorded, in real time, into a DVD that can be reviewed at a later time for post-operative analysis, educational, and even legal purposes. CIM indeed promises to further integrate Intraoperative Neurophysiological Monitoring into the fields of (neuro)surgery and neuro-radiology, helping our understanding of the mechanisms underlying neurological injury during neurosurgical procedures.

PS22-01

The D wave collision technique: a new tool for the intraoperative assessment of the functional integrity of fast conducting neurons (FCNs) of the corticospinal tract (CT)

V. Deletis, A.B. De Camargo, J. Shils, K. Kothbauer. Beth Israel Medical Center, New York, NY, USA

By subtracting B from the amplitude difference in A, one can determine the amount of desynchronized but still functioning FCNs of the CT [(blocked 1 desynchronized) 2 blocked ¼ desynchronized]. Thus, this method gives us the ability to locate the CT within the spinal cord and to measure the relative amount of a) non-affected, b) desynchronized and c) blocked FCNs of the CT. PS22-02

D.B. MacDonald, I. Khoudeir, A. Al-Khani, E. Al-Shail, B. Stigsby. King Faisal Specialist Hospital & Research Center, Riyadh, Saudi Arabia We present four cases of facial motor evoked potential (MEP) monitoring using transcranial electric stimulation. A Nicolet Viking IV was used to deliver 0.5 ms duration stimuli through scalp electrodes 1 cm anterior to C1 and C2. Orbicularis oris, 1st dorsal interosseous and tibialis anterior responses to single and train stimuli (interstimulus interval 2–3 ms) were compared. High intensity single pulses produced short-latency facial but not limb MEP, suggesting extracranial facial nerve excitation by current spread. At lower 200–300 V intensities, facial and limb MEP were absent to single pulses but present and monitored with 3–5 pulses, suggesting facial nucleus excitation through temporal summation of several corticobulbar volleys analogous to corticospinal activation of spinal motor neurons. In one case, intraoperative pontine hemorrhage obliterated facial and limb MEP, with congruent deficits. The results imply a central and supranuclear origin of monitored facial MEP and document the feasibility of this method, provided that absence of single pulse responses at monitoring intensity is demonstrated. Potential indications include posterior fossa surgeries and systemic MEP control in cervical or craniocervical procedures. PS22-03

The D wave represents synchronous activity of the CT. When elicited by transcranial electrical stimulation (TES) and recorded caudally to a lesion, the D wave has an excellent correlation with motor outcome after spinal cord surgery. A complete disappearance of the D wave during surgery correlates with permanent motor disabilities, while its preservation is predictive of a good motor outcome. Therefore, a critical amount of FCNs of the CT, although not yet known for humans, is crucial for the maintenance of postoperative motor performance. The presence of a spinal cord tumor or irradiation (post-radiation myelopathy) can completely desynchronize the D wave and prevent its recording when using the present methodology. However, motor evoked potentials following TES continue to be recordable from the limb muscles confirming the preserved functional integrity of desynchronized FCNs. In 18 patients undergoing surgery for thoracic intramedullary spinal cord tumors, we elicited D waves by TES and recorded them cranially and caudally to the lesion. Simultaneous to TES we stimulated the exposed spinal cord (caudal to the lesion) with a miniature bipolar hand held probe (tips 1 mm apart, with stimuli of 2 mA intensity, 0.5 ms duration and 1 Hz repetition rate). The D wave elicited by TES collided with the “anti-D wave” elicited by spinal cord stimulation whenever the stimulating probe was in close proximity to the CT. This collision resulted in a diminished amplitude of the D wave recorded cranial to the lesion. This method allows for the calculation of: A) BEFORE COLLISION: the amplitude of the cranially recorded D wave representing the amount of the FCNs of the CT approaching the lesion. The amplitude of the caudally recorded D wave represents the non-affected transversing the lesion. The amplitude difference between the cranially and caudally recorded D waves represent the amount of blocked 1 desynchronized FCNs. B) AFTER COLLISION: The amplitude of the cranially recorded D wave represents the amount of blocked FCNs since stimulation of the spinal cord activates both non-affected and desynchronized FCNs transversing the lesion which antidromically collide with the descending D wave.

Intraoperative facial motor evoked potentials elicited by multiple pulse transcranial electric stimulation

The Impact of intraoperative neurophysiological monitoring on early neurological outcome after surgery for intramedullary spinal cord tumors

F. Sala, E. Basso, P. Lanteri, F. Faccioli, A. Bricolo. Department of Neurosurgery, Verona University Hospital, Italy In this historical control study we assess the impact of intraoperative neurophysiological monitoring (INM) on the early neurological outcome after surgery for intramedullary spinal cord tumor (ISCT). A group of 38 ISCT patients operated with INM-assisted surgery (INMas) since September 2000 was matched to a control group of 38 patients, selected from a series of 300 consecutive ISCTs operated on by the same surgeon (A.B.) before September 2000. Matching was blind as regards the McCormick Scale at discharge, and performed according to the following variables, in decreasing order of priority: pre-operative neurological status (McCormick Scale), histology, surgical removal, tumor location/extension, age. Besides SEPs, INM consisted of MEPs elicited using multipulse transcranial electrical stimulation and recorded from limb muscles and the epidural space (D-wave). ANOVA and bivariate analyses with association in two-way tables (Chi-square test of significance and a ¼ 0:05) were performed. The two groups were similar with regards to pre-operative neurological status (P ¼ 0:94), histology (P ¼ 0:87), surgical removal (P ¼ 0:67), tumor location (P ¼ 0:20) or extension (P ¼ 0:31), and age (P ¼ 0:65). Although the McCormick Scale at discharge also did not differ significantly (P ¼ 0:33), the INM-as group presented a higher rate of postoperative unchanged/improved motor outcome (77% vs 63%), and a lower incidence of worsen motor outcome (23% vs 37%) than the control group. Moreover, only 1 patient worsen to grade 4 of the McCormick Scale in the INM-as group as compared to 6 in the control group. Although not statistically significant yet, this study supports a better

Platform Sessions outcome and only mild to moderate neurological impairment in monitored patients. These results warrant further investigations to assess if larger series of patients and/or long-term follow-up may statistically support the advantage of INM. PS22-04

Motor evoked potential monitoring compared with SEP and micro Doppler in cerebral aneurysm surgery

G. Neuloh, J. Schramm. Department of Neurosurgery, University of Bonn, Germany Objective: Does motor evoked potential (MEP) monitoring with cerebral aneurysm surgery reduce the rate of false negative SEP and micro Doppler (MD) results with regard to new postoperative motor deficit, in particular with subcortical ischemic lesions? Methods: MEPs after transcranial electrical pulse train stimulation were monitored during 95 operations of 117 cerebral aneurysms in 90 patients, along with SEPs and MD. Monitoring results were correlated with intraoperative findings and clinical outcome. Results: Significant intraoperative events (e.g., deliberate or inadvertent vessel occlusion) occurred in 40 cases. Eleven patients sustained new postoperative weakness, which was permanently disabling in 2; early CT revealed subcortical (7) or cortical (1) infarction, or edema (2). MEP recording was successful in 91.6%, SEP in 94.7%. MEP changes reflected vessel occlusion in 13/22, and led to MD exploration and clip replacement in 2 and to readjustment of retractors in 6 cases. SEPs reflected vessel occlusion in 7/23, and triggered retractor changes in 2 cases. MEP deterioration predicted postoperative motor impairment in all but 1 (late edema) cases, while SEPs indicated new paresis in only 3/11 patients. MD revealed inadvertent vessel occlusion in 8/10 cases first, and led to readjustment of insufficient aneurysm clips in another 4 cases, but missed impending new paresis from subcortical stroke. Conclusions: MEPs monitored during aneurysm surgery are superior to SEP and MD in detecting impending motor impairment from subcortical stroke, whereas MD recording seems superior to evoked potentials in early detection of inadvertent vessel occlusion, if applied immediately after clipping. PS22-05

Temporal and spatial facilitation of motor evoked potentials during spinal cord monitoring

Gert Andersson. Lund, Sweden Monitoring of Motor Evoked Potentials (MEPs) during spine surgery is now a routine method. Responses are usually recorded from the tibialis

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anterior muscles. In most cases, reliable MEPs can be evoked with transcranial electrical stimulation of the motor cortex using a train of pulses (i.e. temporal facilitation). In some patients, no responses can be elicited even with maximal output of the stimulator. We have developed a method of spatial facilitation, where the foot sole is stimulated with a train of pulses ca 60 ms before the cortical stimulus (Clin. Neurophys. 110: 720–24, 1999). It has now been tested in combination with train stimulation of the cortex in more than 80 patients. Combining spatial and temporal facilitation gave reliable MEPs in all cases. In at least ten patients, no or only small and unreliable MEPs could be evoked with transcranial stimulation alone. Thus, spatial facilitation increases the number of patients that can be monitored with MEPs. It also allows a reduced number of shocks in the transcranial stimulus train, thereby reducing the contractions in more proximal muscles interfering with the surgical procedure. PS22-06

Cerebral function under cardiopulmonary bypass in children

M. Thordstein, S. Andreasson, A. Hedstro¨ m, K. Lindecrantz, N. Lo¨ fgren, B.G. Wallin. Department of Clinical Neurophysiology, University of Go¨ teborg, Sahlgrens University Hospital, Go¨ teborg, Sweden Postoperative cerebral dysfunction in children after open heart operation for cardiac malformation, is believed to be due largely to perioperative events. In a new monitoring system EEG and cardiovascular parameters were followed continuously in seven children during operations using hypothermic CPB. Under periods fulfilling criteria for preserved cerebral autoregulation, reversible falls of arterial blood pressure were identified. EEG power spectra were estimated before, during and after the fall. In six/seven patients, parallel, reversible blood pressure falls and EEG spectral alterations were found. In the two children where profound hypothermia was used (19 8C), continuous EEG activity of low amplitude was recorded. These findings indicate that at least in terms of cerebrocortical performance, homeostatic mechanisms are insufficient to protect function during blood pressure falls under conditions where clinically accepted criteria for preserved cerebral autoregulation are met. Further, under profound hypothermia, the cerebral cortex can be continuously active, at least in young infants. These results may reveal part of the background to the still worryingly high incidence of cerebral dysfunction after cardiac surgery in children.

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Platform Sessions

CNS PLASTICITY AND RESTORATIVE NEUROLOGY PS23-01

Stimulation-induced within-representation and acrossrepresentation plasticity in human motor cortex

Ulf Ziemann (presenting author) a,b, George F. Wittenberg a, Leonardo G. Cohen a. aHuman Cortical Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1428. bPresent address: Clinic of Neurology, JW Goethe-University of Frankfurt, D-60590 Frankfurt am Main, Germany Formation, maintenance, and modification of representations in motor cortex is an activity-driven process. We showed previously that repeated transcranial magnetic stimulation (rTMS) of the arm representation resulted in an increase of that representation (“within-representation plasticity”) when rTMS was delivered during transient ischemic nerve block (INB) of the contralateral hand. INB reduces motor cortical inhibition and thus lowers the threshold for stimulation-induced plasticity. Here we studied the effects of rTMS delivered to nearby body part representations on the arm representation. Six healthy subjects underwent INB-alone (control), or INB plus 30 min of focal 0.1 Hz rTMS of either the face, hand, arm, leg or overlap arm/hand representation. INB-alone, and rTMS of the leg representation resulted in only a short-lasting (,20 min) increase in motor output from the arm representation, as measured by motor evoked potentials in the biceps. RTMS of arm and arm/hand representations induced a prolonged (.60 min) within-representation increase. In contrast, rTMS of face or hand representations led to a long-lasting decrease of the arm representation. Therefore, rTMS of the experimentally disinhibited motor cortex induces within-representation increase, and across-representation decrease of motor cortical output. This bidirectional plasticity might be employed for purposeful modulation of human cortical function.

PS23-02

Corticomotor threshold in stroke: the unaffected hemisphere

V.K. Kimiskidis a, G. Dimopoulos a, S. Papagiannopoulos a, D. Kazis a, A. Kazis a, K.R. Mills b. aC Department of Neurology, Aristotle University of Thessaloniki, Greece; bDepartment of Clinical Neurophysiology, King’s College London, UK Objective: To investigate serially threshold (Th) in the unaffected hemisphere (UH) of stroke patients. Methods: 18 patients (mean age ¼ 60 1 = 2 4) and 41 normal subjects (mean age 51 1 /216) entered the study. Entry criteria included first-ever monohemispheric stroke occurring ,24 hours from session 1 (S1). Patients were re-examined 1 week (S2) and 1.6 and 12 months (S3-S5) later. Transcranial stimulation (recording: FDI) was performed with a figure of 8 coil. Th was measured at rest in 1% steps and defined as lower Th (LT, the highest intensity which evokes MEPs with a probability of zero) and upper Th (UT, the lowest intensity which evokes MEPs with a probability of one). Mean Th (MT) is the mean of UT and LT. Results: Data on S1-S3 sessions are presented. At S1 controls had an MT of 40.77 1 /28.75 and patients had an MT of 36.47 1 /25.49 (P , 0:05, ttest). In the patient group, MT decreased to 36.41 1 /5.14 at S2 and 34.94 1 /4.47 at S3 (P . 0:05, repeated measures ANOVA). In the control group, MT was remarkably stable as in a subgroup of 17 subjects reexamined at S2 and S3 mean differences of MT were 0.13 and 0.03, respectively. Conclusion: A small but significant decrease of Th occurs in the UH poststroke possibly relating to diaschisis and/or preferential use of the “healthy” upper limb.

PS23-03

Repeated premotor rTMS leads to cumulative plastic changes of motor cortex excitability in humans

A. Mu¨ nchau, T. Ba¨ umer, C. Weiller, J. Liepert, J.C. Rothwell. Hamburg University, Germany 1 Hz premotor rTMS leads to specific changes of intrinsic motor cortex excitability. We examined the effects of repeated premotor rTMS on two consecutive days. Methods: Twelve healthy right-handed volunteers received 20 min 1 Hz rTMS trains over the left premotor cortex at an intensity of 80% active motor threshold once daily for two consecutive days. Left motor cortex excitability was determined daily at baseline and 5, 30, 60 and 120 min after rTMS and again 24 h after the second rTMS session, i.e. at day three, using the Kujirai paradigm with conditioning pulses of 80% active motor threshold at interstimulus intervals (ISI) of 2, 3, 4, 5, 6, 7, 10, 15 ms. Results: In keeping with previous experiments we found a significant increase of paired pulse facilitation at ISI of 7 ms but not at other ISI after premotor rTMS on day 1. This effect lasted for less than 30 min. The facilitation at 7 ms ISI also occurred following rTMS on day 2 with the same magnitude as that on day 1 but it persisted for 120 min. At day three there was a trend for a persisting facilitation at 7 ms ISI. Conclusion: Repeated 1 Hz premotor rTMS induces cumulative plastic changes of motor cortex excitability. PS23-04

Cortical hand representation estimated by electrical and mechanical stimulated 96-channel SEP

W. Kawohl, C. Norra, T.D. Waberski, R. Gobbele´ , H. Buchner. Klinik fu¨ r Psychiatrie und Psychotherapie, Universita¨ tsklinikum der RWTH Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany We compared artificial and natural stimulation for the determination of the hand area by dipole source estimation. Electrical and pressure-stimulation was performed simultaneously on the thumb and fifth finger of nine healthy volunteers. Recording was done using a 96-channel electrode array. Dipole source analysis was performed for the sources representing each finger and both methods. The SEPs following electrical stimulation show a sharper peak and a higher amplitude compared to the pressure-stimulated potentials. Both methods provide a correct distinction between the cortical sources of thumb and fifth finger. Although different receptor types are involved, both methods deliver a valid estimation of the cortical hand representation. Pressure stimulation is less invasive, while electrical stimulation can be applied with higher stimulus rates. The choice of methods, for example in studies investigating cortical plasticity, may depend on practical considerations. PS23-05

Impaired motor potentials in acute traumatic brain injury: a one year follow-up

Holger Wiese a, Philipp Stude a, Katharina Nebel a, Dorothea Osenberg b, Werner Ischebeck b, Hans Christoph Diener a, Matthias Keidel c. aDepartment of Neurology, University of Essen; bKlinik Holthausen, Hattingen; c Department of Neurology, District Hospital Bayreuth, Germany Focal brain lesions following traumatic brain injury (TBI) disturb the structurally intact neuronal network connected to the lesion site. Dysfunctions of cortical motor networks after frontal TBI are hypothesized. The aim of our study was to demonstrate alterations and recovery of cortical motor networks after TBI (left frontal contusions) by analyzing motor potentials (MPs). MPs are movement related EEG-potentials consisting of the Bereitschaftspotential, the Negative Slope (NS), and a maximum

Platform Sessions negativity after movement onset. They depend on interrelations of the network’s single components. EEG of 22 patients 6 and 52 weeks after TBI and of 28 healthy subjects was recorded. The paradigm consisted of self-paced right-index-fingerabductions. Differences of corresponding left and right hemispherical channels were calculated. 6 weeks after TBI, NS was significantly less pronounced in left central as well as central and fronto-central midline leads. Decreased peak negativity was observed. One year after TBI, NS exceeded normal controls in left

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central and fronto-central leads. The same holds true for peak negativities in central and fronto-central midline leads. A more pronounced left-hemispherical preponderance was found in central and fronto-central leads. Dynamic changes of the movement related potentials following frontal TBI point to a functional reorganisation of the motor neuronal net. The increased left fronto-central negativity and the prominent left-hemispheric preponderance of the motor potential one year after TBI may reflect a plastic capacity of the brain reorganising the global neuronal network function.

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Platform Sessions

CONSCIOUSNESS, ATTENTION AND PERCEPTION 2 PS24-01

Cognitive potentials in the basal ganglia – cortical circuits. A SEEG study

I. Rektor, M. Baresˇ, M. Bra´ zdil, P. Kao`ovsku´ , H. Klajblova´ , H. Streitova´ , I. Rektorova´ , D. Sochurkova´ , D. Kubova´ , R. Kuba. 1st Department of Neurology, Masaryk University, Brno, Czech Republic The contribution of the basal ganglia (BG)–frontocortical circuits to cognitive functions was studied in fifteen epilepsy surgery candidates. We studied Bereitschaftspotential (BP), CNV and ERPs that were directly recorded from BG and from the primary motor, premotor, dorsolateral prefrontal, orbitofrontal, and anterior cingulate cortices. Studied ERPs: auditory and visual odd-ball; and the potentials evoked by stimuli in CNV protocol. Results: ERPs were displayed in all the investigated structures. There was no significant difference between the ERPs in motor and in non-motor tasks. BP was displayed in MC, SMA, anterior cingulate and in the BG. CNV was displayed in the motor, premotor, prefrontal and cingulate cortices and in the BG. All cognitive potentials occurred significantly more frequently in the BG than in the cortex. Conclusions: 1. Cognitive processing in all tested protocols occurred in BG; the occurrence in cortical areas was more selective. The BG may play an integrative role in cognitive information processing, in motor as well as in non-motor tasks. 2. We suggest: the BG form a non-specific system that progressively converges and processes data concerning various functions from various parts of the cortex; and positively or negatively modulate the frontal cortices. BG are the site at which information from various functional may be processed in a mutual context. This contextual modulation may be important for the functioning of the individual cortical areas that are the target of the loop. Supported by MSˇ E`R 112801.

PS24-02

Improving P300 latency determination by 128-channel measurements

N.M. Maurits, J.W. Elting, J. van der Naalt, T.W. van Weerden. Groningen University Hospital, Department of Neurology, P.O. Box 30001, 9700 RB Groningen, The Netherlands The P300 event related potential is a measure of cognitive function and its latency and amplitude are thought to quantify information processing. P300 latency is known to be increased in patients with dementia and severe head injury. Recently subcomponents of P300 have been defined; the more frontally distributed P3a (novel stimuli) and the centro-parietal P3b (stimulus processing). The large intra-individual inter-trial P300 latency variation in normal controls makes it hard to distinguish between normal and abnormal P300 results. One of the causes of variation is the overlap in P3a and P3b potentials resulting in inaccurate latency determination of P3b (P300). Conventional P300 registration only allows for separation of the two potentials in approximately 25% of the measurements. We use 128-channel EEG and a new dipole source analysis technique for data reduction, to overcome this problem. We are able to separate the P3a and P3b components and thereby reduce the spread in P3b (P300) latencies compared to single-channel analysis in normal controls. Preliminary results in mild head injury patients suggest that increased (conventional) P300 latency actually corresponds to diminished P3a activity. This indicates that our method may help to interpret P300 results in head injury patients and improve the prognostic value of abnormal P300.

PS24-03

Development of neurophysiological responses to novel stimuli in infants during the first year of life

K. Werner, R. Scott, T. Baldeweg, S.G. Boyd, B.G.R. Neville. Neurosciences Unit, Institute of Child Health, WC1N 2AP, London, UK Objectives: To determine whether novel environmental sounds elicit prominent event-related potentials (ERPs) in infancy and if there are developmental changes over temporal and frontal cortex. Methods: Twenty-five term infants (range 46–300 days) were recruited. EEG was recorded continuously from 19 electrodes (10–20 system), referred to CPz. An oddball paradigm was used with frequent sounds (P ¼ 80%, 1 kHz), deviants (P ¼ 10%, 1.5 kHz) and brief novel sounds (P ¼ 10%), delivered binaurally (interstimulus interval 700 ms) via speakers at a distance of 30 cm. Infants were either asleep or awake. 2–3 blocks were recorded, each with 88 deviant and novel sounds. Results: Robust and reproducible temporal and fronto-central ERPs to novel stimuli were detected in all infants. Negativities at the vertex but not over temporal lobes showed progressive reduction in latency (796–500 ms, P ¼ 0:001) with respect to age. Temporal amplitudes were dependent upon a quadratic function of age (P ¼ 0:004). From the model, a maximum amplitude of 15 microvolts was reached at 184 days. Conclusions: Novelty-ERPs can be recorded reliably from 1.5 month of age. Temporal amplitudes and vertex latencies show age dependencies and are consistent with maturation of networks responsible for processing novel information.

PS24-04

The impact of motor activity on intracerebrally recorded event-related potentials: P3 latency variability in modified auditory odd-ball paradigms involving a motor task

Petr Kanˇ ovsky´ , Hana Streitova´ , Hana Klajblova´ , Martin Baresˇ, Pavel Daniel, Ivan Rektor. 1st Department of Neurology, Masaryk University, Brno, Czech Republic P3 were intracerebrally recorded in three paradigms with different cognitive loads and motor tasks in 24 patients. The recordings were done in three paradigms: 1) classical auditory odd-ball paradigm (PGI); 2) a modified paradigm (PGII), in which the subject executed a simple movement in reaction to a target tone; 3) a modified paradigm (PGIII), in which the subject counted target stimuli and executed simple movement. P3 latency ranged from 257 to 320 ms in PGI; they significantly varied in PGII and PGIII. The P3 latency prolongation in PGII was present in the dorsolateral frontal and parietal cortex and in the mesial parietal cortex. The mean latency was further prolonged within the mesial temporal and parietal, and dorsolateral temporal and frontal cortex in PGIII. The results might reflect that the different cortical sites are related to different cognitive and motor processes.

PS24-05

Middle-latency SEP modifications due to selective attention to touch in patients with cerebral ischemic lesions

Domenica Le Pera a,b, Massimiliano Valeriani b,c, Francesca Ranghi a, Salvatore Giaquinto a. aCasa di Cura San Raffaele Pisana, Tosinvest Sanita`, Roma, Italy; bDepartment of Neurology, Universita` Cattolica del Sacro Cuore, Roma, Italy; cDepartment of Neurology, Ospedale Pediatrico Bambino Gesu`, IRCCS, Roma, Italy Our aim was to investigate whether: i) the middle-latency somatosensory evoked potentials (SEPs) recorded in patients with cerebral stroke are

Platform Sessions modified by selective attention to touch, ii) SEP changes are different from those observed in healthy subjects and iii) they depend on the lesion side. Twenty patients with brain stroke and 17 age-matched healthy subjects were studied. Scalp SEPs were recorded after right and left median nerve stimulation in a neutral condition (NC), in which subjects had no task, and in a selective attention condition (SAC), in which the subjects were asked to count tactile stimuli given on the same hand of the stimulated median nerve. Our patients showed an N120/N140 amplitude increase during SAC after stimulation of the median nerves contralateral and ipsilateral to the cerebral lesion. When the non-damaged hemisphere was stimulated also the P100 amplitude was increased during SAC. SEP amplitude modifications during SAC were not significantly different in patients and healthy subjects. SEP latencies were longer in patients than in healthy subjects in NC and this difference was even larger in SAC. No effect of the lesion side on SEP changes during SAC could be demonstrated. Our findings suggest that the brain functions underlying easy attention tasks are not impaired by cerebral ischemic lesions whatever hemisphere is damaged. PS24-06

Intensity dependence of the N1/P2 component during acute tryptophan depletion in healthy females

Ch. Norra a, S. Becker a, W. Kawohl a, A. Broecheler a, S. Vreemann a, K. Haacke b, H. Buchner b. aDepartment of Psychiatry and Psychotherapy; b Department of Neurology, Technical University, Aachen/Germany Introduction: Previous animal and human studies suggest an inverse influence of the serotonergic system on the intensity dependence of early

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event-related potentials for the primary acoustic cortex, namely the N1/P2 component; meanwhile the tryptophan depletion test (TDT) represents an established human challenge tool for a temporary reduction of tryptophan levels and central nervous serotonin. Methods: In a double-blind cross-over study 15 carefully selected healthy females volunteered twice to ingest a highly concentrated amino acid mixture with TRP (control) or without TRP (verum). Sinus tones of 1000 Hz of different intensity levels (60–90 dB) were presented binaurally. A 32-multichannel extended 10/20 EEG was recorded continuously.Following the averaging procedures we performed dipole source analysis [BESA] applying a model of a tangential and radial dipole per hemisphere. Results: All subjects showed increasing N1/P2 amplitudes of the relevant tangential dipole in series of higher stimulus intensity with significant differences of the individual change rates (P , 0:001–0:05). Augmentation of tangential N1/P2 activity was partly more pronounced in the (2)TRPcondition while there were some trends for an increase of the overall resulting intensity dependence as opposed to the control (1)TRP-condition. Plasma tryptophan levels decreased extensively to 18.69% (1/25.32) in the (2)TRP-condition in relation to the individual basic value. Conclusions: Our results of a homogenous female population provide further arguments for the hypothesis of an influence of serotonin on the N1/ P2 intensity dependence although the effect was not as prominent as expected despite a strong depletion situation. A low serotonergic neurotransmission seems to contribute to the intensity effect in AEP but interactions with other neurotransmitters of the CNS might also have to be considered.

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Platform Sessions

MEDICAL TECHNOLOGIES ASSESSMENT 2 PS25-01

A comparison of the accuracy of EEG head nets in inverse source modelling of the EEG using a realistic head phantom

Louise Enfield, David Holder. Department of Clinical Neurophysiology, Outpatients Department, Middlesex Hospital, Cleveland Street, London, UK Several different headnets are commercially available for recording EEG for inverse source modelling, but may not employ skin abrasion and so signal quality could be degraded. The purpose of this study was to compare the effectiveness of various designs in localising up to 6 artificial dipole sources (3 deep and 3 shallow) using a head-shaped phantom constructed using a human skull and saline, alginate and the skin of the giant zucchini to simulate brain, scalp and skin. Data were recorded with standard cup EEG electrodes, QuikCap, Electrical Geodesic Sponge and Physiometrix Hydrodot head nets (21 electrodes each) and a Micromed EEG system and dipoles modelled with Advanced Source Analysis (ANT, Netherlands). Preliminary analysis using a standard 3 shell boundary element model and one way analysis of variance, comparing the average of all errors, indicated no significant difference (P ¼ 0:18). The Electrical Geodesics Sponge headnet was easiest to apply, and this preliminary analysis indicates that there is no significant penalty for the lack of skin abrasion. Further analysis will include the use of a volume conductor model using a CT of the phantom actually employed and a similar analysis of reconstruction of impedance images with the same headnets. PS25-02

New wireless protocols for EEG telemetry?

A.C. Worley, M. Hair, J.H. Cross, S.G. Boyd. Great Ormond Street Hospital for Children NHS Trust, London, UK Aim: Can low-cost new wireless network standards improve the flexibility of long-term continuous monitoring of epilepsy patients? Background: Long-term video/EEG is being used increasingly for accurate diagnosis and characterisation of episodic events. Patients being monitored are connected to recording equipment via an electrical cable, which provides the transmission path for the EEG signal, and in some instances supplies the power to the patient-worn electronics. This recording cable can be particularly restrictive when monitoring children. Method: New wireless standards (802.11b and ‘Bluetooth’) for computer networks have the capability of overcoming the inherent limitations of previous implementations of wireless telemetry such as absence of error correction and narrow bandwidth. Results: In initial indoor trials utilising 802.11b, EEG signals could be reliably transmitted through 2 walls and up to a distance approaching 30 metres. Further evaluation of emission patterns related to hospital architecture together with the presence of other medical equipment, wireless local area networks and communication devices are required before this promising technology can be implemented for EEG video-telemetry. PS25-03

A computer-based system for the detection and analysis of the EOG for the control of the eye’s position

B. Estrany a, A. Garcia-Mas b, L. Valverde a. aDepartment of Mathematics and Informatics; bDepartment of Psychology, University of the Balearic Islands The “state of the art” interfaces between man and computer includes the extensive use of “multimedia” communication devices, which offers more control and “friendly using”. But there are some possibilities to explore:

one of which is the use of the electrophysiological signals from the computer-user. The aims of our project are: 1) design and build a system capable of the detection and on-line analysis of the human electrooculographic (EOG) signals; and 2) after the phase 1, control and display the user’s eye position on a standard computer screen. The design includes: 1) software for the digitalisation of the EOG signal; 2) a set of stimular paradigms to elicit and analyze several visual following movements (saccadic, smooth, regular); and 3) build a reliable and valid electrode’s fixation device on the head of the user. The results of each phase show: the eye’s control displays, and the parameters that allow the software to control the eye’s position on the computer screen. Conclusion: Is possible to use a very adaptable system to control the display of the eye’s movement on a computer screen, as a first step to use the eye’s movement as interface between man and computer.

PS25-04

Electrical impedance tomography of neonatal brain activity

A.T. Tidswell, J.S. Wyatt, R.H. Bayford, D.S. Holder. University College Hospital, London Electrical Impedance Tomography (EIT) is a new, fast, portable neuroimaging technique which produces images of the electrical impedance of the head using scalp electrodes. The purpose of this work was to determine whether accurate EIT images could be obtained during evoked responses in neonates, during visual stimulation with 8 Hz flash (n ¼ 4) or passive motor-flexion/extension of either wrist at 1.5 Hz (n ¼ 7). 3 images per second were obtained with the UCLH-1b EIT system using 21 EEG electrodes, during 10–15 repetitions of 10–25 s. There were consistent impedance decreases of 20.4 1 /20.1% and 21.1 1 /20.4% during motor and visual stimulation respectively. Changes occurred 2.1 1 /20.4 s and 0.5 1 /20.1 s after stimulus onset, and returned to baseline within 7.6 1 /20.9 s and 7 1 /22.0 s. Images were noisy, but demonstrated stimulus related impedance changes in the visual cortical area in 3/4 infants and the contralateral motor cortex area to the hand stimulated in 3/7 infants. This is the first time impedance changes have been imaged in infants during evoked responses. These have a similar time course to those measured with fMRI and are probably due to increased cerebral blood volume. With improvements to hardware and the reconstruction algorithm, EIT should become a standard method for monitoring of neonatal brain function during intensive care.

PS25-05

Dichotomous EEGs as a tool for numerical characterization of sleep/wake phases

A. Chornet a, J.A. Oteo b, J. Ros b. aCasa de Salud, Valencia, Spain; bUniversitat de Valencia, Spain Dichotomous EEGs (DEEG) are time series made up of the signs of the differences between the records of raw EEGs and their average. We point out that DEEGs may provide quantitative indexes for sleep/wake phases. The 1058 samples used are 30 seconds night polysomnographies epochs (C3-A1, C4-A2) from 18 subjects, free from artifacts, representative of sleep phases and wakefulness. Histograms of residence times (waiting time until next sign change) unveil underlying universal structure of every sleep/wake phase, suggesting the existence of characteristic time scales. We study texture, information content and left-right channel synchrony of DEEGs through lacunarity, entropy and Hamming distance respectively.

Platform Sessions Numerical values of these time scales are (in seconds): 0.47, 0.70, 1.11 (phases 1–3), 0.65 (REM), 0.12 (wake). These values translate the qualitative findings on residence times. Intrasubject universality for every phase is noteworthy. REM sleep classes between phases 1 and 2, disentangled from wakefulness. We contrast these findings against synthetic samples of different nature. One way ANOVA analysis buttresses our conclusions. We deem this study contributes to automatic identification of sleep/wake phases, and to better understanding of sleep dynamics. It paves the road to application to further physiological processes either normal or pathological.

PS25-06

EEG brain mapping by burch period analysis in diagnosis of ischaemic cerebrovascular diseases

L. Giuca a, D. Cioroianu a, N. Rusca b, Cornelia Zaharia a, Cristina Petrica a, A. Nestianu a, V. Nestianu a. aUniversity of Medicine and Pharmacy of Craiova; bGenesys General Systems Inc, Bucharest, Romania

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The authors developed a new, original, method of EEG mapping based, on the period analysis, imagined by Burch in ¢60 years (BPA) witch implies the digital determination of the period between two consecutive zero-crossing of the EEG waves. The resulting maps showed the cerebral localisation of the different frequency bands regardless the amplitude (as in FFT (Fast Fourier Transform) analysis). We studied a group of 97 patients using a digital equipment developed by General Genesys Systems Inc. and performing monopolar EEG recordings. The correspondence between clinical and CT-scan focus and lesional EEG focus using BPA was in stroke patients 86% comparative with FFT analysis in witch case the correspondence was only 28%. In addition, using BPA mapping, we succeeded to recognize between old and recent lesions and also to emphasize the clinical active focus from a set of multiple ischaemic lesions (determined by CTscan).

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Platform Sessions

NEUROMODULATION AND NEUROSTIMULATION IN MOVEMENT DISORDERS, PAIN AND EPILEPSY Functional neurosurgery and clinical neurophysiology Marc P. Sindou. Hoˆ pital Neurologique P. Wertheimer, 59 Bd Pinel, Lyon, France Recourse to Functional Neurosurgery is more and more justified since the goal of modern surgery is not only to save lives but also to improve quality of survival. According to the definition given by WERTHEIMER in his visionary book in 1956, Functional Neurosurgery is “that branch of neurosurgery which aims at correcting the functional disorders which cannot be normalized by direct cure of the causative lesion… Operations are based on neurophysiological informations…”. Also interesting enough to recall, the organ published by the World Society for Stereotactic and Functional Neurosurgery – before being named “Journal of Stereotactic and Functional Neurosurgery” – was entitled “Applied Neurophysiology”. Neurophysiology has demonstrated to be of considerable utility in almost all the domains of Neurosurgery, not only during the operation itself, but also in the patients’ selection process and for post-operative evaluation. Chronic pain, especially in its neuropathic forms, often needs the recourse to neurosurgical techniques. Spinal cord neurostimulation, which aims at reinforcing spinal inhibitory modulation, can only be effective if the lemniscal and dorsal column systems are functional; this can be confirmed and quantified with somatosensory evoked potentials (SEPs). When a percutaneous test of spinal stimulation is conducted previously to definitive implantation, assessment of nociceptive reflexes (RIII) allows observing a stimulation-related depression, which has been shown to be associated to a good and long-lasting clinical efficacy of the procedure. Concerning the analgesic stimulation of the pre-central cortex, intra-operative SEP recording allowing to identify the phase inversion of the N20/P20 potentials, makes easier the localisation of the central sulcus, which in turn enables a correct positioning of the stimulating electrodes. Neurophysiological studies using SEPs, laser-evoked potentials, nociceptive RIII reflexes and PET-scan, have contributed to our (still partial) understanding of the mechanisms underlying this novel and still mysterious analgesic procedure. In the context of analgesic operations based on the selective destruction of microsurgical targets (such as surgery in the Dorsal Root Entry Zone, where hyperactive neurons have been found in situations of deafferentation), intraoperative recordings of surface SEPs enhance both the precision and the safety of the operation. Simultaneous microelectrode recordings from the targets to be operated upon have contributed in turn to the understanding of the pathophysiology of these pain syndromes. In the context of disabling hyperspasticity, measurements of the myotatic H-reflex and the nociceptive RIII-reflex in the lower limbs, as well as urodynamic and sphincterian explorations, are important for quantification of spasticity. It is also important from a functional point of view to have an objective analysis of movement and gait by means of poly-EMG and VICON methods. These investigations are most useful for surgical teams who deal with harmful spasticity, whatever the techniques used: neurolytic blocks, botulinum toxin injections or neurosurgical operations. Among neurosurgical procedures, one has to mention Intrathecal Baclofen infusion with implantable and programmable pumps and also ablative procedures (selective peripheral neurotomies, dorsal rhizotomies, surgery in the Dorsal Root Entry Zone: the so-called microsurgical DREZotomies, …). For the later ones, intra-operative neurophysiologic monitoring is of considerable help for achieving selectivity and make surgery safer and more effective. No doubt that the neurophysiologists are largely implicated in Surgery of drug-resistant Epilepsy, especially in complex cases in whom intracranial depth electrodes have to be implanted because the sole imaging and videoEEG data are not sufficient to decide whether or not a surgical resection is indicated and to determine its limits. In addition to EEG recording function, intra-cerebral electrodes can be utilized to perform direct electrical stimu-

lation of the implanted anatomical structures, and also to record intracerebral evoked potentials. In the near future, unitary microelectrophysiological recordings combined with neurochemical studies by means of the microdialysis methods should take a large place in the field of epilepsy research. Intraoperatively, before resection of epileptic foci, contribution of clinical neurophysiology may be useful for mapping the cortex by direct electrical stimulation, not only in the anesthetized patient for motor identification, but also in the awake patient for determination of speech areas. For Surgery of Parkinson Disease and Dystonias, resistant to medications, microelectrode recordings are routinely used during surgery for electrode guidance into to the appropriate (thalamic, subthalamic or pallidal) targets, whatever the technical surgical modality may be: thermolesioning or chronic stimulation. The recorded microelectrophysiological activities, especially when associated to neurochemical studies, may provide interesting data for a better understanding of basal ganglia physiology. The neurosurgical treatment of Trigeminal neuralgias may benefit from clinical neurophysiology. During percutaneous trigeminal thermorhizotomy, the thermolesion can be guided by evoked motor facial responses to direct electrostimulation of the trigeminal root (blink-reflexes,, trigeminofacial reflexes) and also – although more difficult to record – trigeminal somesthetic evoked potentials. Microvascular decompression for treating Neuro-Vascular-Conflicts, of the Vth, IXth and Xth, and above all VIIth and VIIIth nerves, may – or rather must – for the later ones, benefit from monitoring the BEAPs all along the microsurgical time of the operation. Obviously, in all these domains, Neurophysiology cannot be dissociated from the surgical action. Even more Functional Neurosurgery is by essence applied neurophysiology. For this reason, we do think that the concept of Interventional Neurophysiology must be recognized and acknowledged. The close relationships of Clinical Neurophysiology with Functional Neurosurgery are practical reality.

PS26-01

Modulation of sensorimotor integration of sternocleidomastoid muscles in cervical dystonia

M. Wittstock, A. Wolters, D. Dressler, R. Benecke, E. Kunesch. Department of Neurology, University of Rostock, Germany In limb dystonia alteration of sensorimotor integration in the affected limb has been demonstrated. It remains unclear whether corresponding changes occur in neck muscles in cervical dystonia (CD). We investigated the modulation of motorcortical excitability of the contralateral sternocleidomastoid muscle (SCM) following conditioning peripheral electrical stimulation (PES) of accessory nerve in 6 patients with CD and 5 controls. Motor evoked potentials (MEP) elicited by focal transcranial magnetic stimulation (fTMS) at the point of optimal excitability with 1.3x resting motor threshold (RMT) were recorded from both SCM at rest and with 30% of maximum innervation. PES (3x perceptual threshold) was delivered before fTMS with conditioning-test intervals (CTI) from 50 to 300 ms. Whereas RMT were comparable for both sides all right-handed controls had higher MEP amplitudes at rest for the left SCM (1 40%) indicating a correlation between handedness and visuo-motor coupling of neck muscles. Controls showed a significant facilitation (s.f.) of MEP size for all CTI (conditioned vs. TMS alone: 1229 ^ 105%; s.f. also vs. nuchal sham PES: P , 0:05). In CD a significant inhibitory effect (MEP-size reduction 21% vs. unconditioned situation; 22% vs. nuchal sham PES, P , 0:05) was demonstrated for a CTI of 100 ms, whereas other CTI led to a slight facilitation (n.s.). These data support the hypothesis that polysynaptically mediated sensory modulation of motorcortical excitability is altered in affected neck muscles of CD. Afferent feedback loops may fail to reduce upregulation of central motor drive to dystonic muscles.

Platform Sessions PS26-02

Influence of subthalamic nucleus and internal globus pallidus stimulation on gait in Parkinson’s disease

L. Defebvre, P. Krystkowiak, J. Blatt, J. Bourriez, S. Blond, A. Deste´ e, J.D. Guieu. EA 2683, Hoˆ pital Salengro, CHRU, Lille, France We evaluated and compared by using a video motion analysis system, the influence of bilateral subthalamic nucleus (STN) or internal globus pallidus (GPI) stimulation on gait in Parkinson’s disease (PD). Gait kinematic parameters (cadence, velocity, stride and step times, single and double support times, stride and step lengths) were studied in 10 PD patients with STN stimulation and 7 patients with GPI stimulation, before and 3 months after surgery, in off drug then in on drug conditions. In the STN group, L-dopa and stimulation induced a clear benefit on gait velocity (100% and 90%) and on stride length (68% and 54%). In the GPI group a lower improvement was obtained (respectively 38% and 26%). The benefit on swing phase duration (ratio single/double support) was also more important in the STN group. The best effect of STN stimulation might be explained by a better restoration of functional basal ganglia disturbances observed in advanced PD patients, both on thalamo-cortical pathways and on descending basal ganglia connections to the brainstem. This study confirms that bilateral STN stimulation induces more beneficial effects than GPI stimulation on gait disturbances in PD.

PS26-03

Motor cortex stimulation for pain control and cognitive ERPs

C. Montes a,d,e, P. Mertens b, P. Convers c, R. Peyron c, M. Sindou b, B. Laurent c, F. Mauguie`re a, L. Garcia-Larrea a,d. aEquipe d’accueil EA1880 UCB Lyon; bService de Neurochirugie Fonctionnelle, Hoˆ pital Neurologique, Lyon, France; cService de Neurologie, Hoˆ pital Bellevue, St E´ tienne, France; dLaboratoire de Neurophysiologie humaine, CERMEP, Lyon, France; eDepartamento de FisiologI´a, Facultad de Medicina, Universidad de Ma´ laga, Spain Electrical stimulation of the motor cortex (MCS) is a promising neurosurgical technique for the control of refractory pain. Its mechanisms of action remain unknown but functional imaging suggests involvement of the thalamus, brainstem and anterior cingulate/orbitofrontal cortex. Since some of these areas are involved in higher cognitive functions, we analysed cognitive “oddball” auditory ERPs in 11 consecutive patients submitted to

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this procedure. ERPs were obtained both during the application of MCS, and within the 10 minutes following its discontinuation. In 5 patients, ERPs were also obtained just before MCS. Although no consistent effects were observed with the patients’ sample taken as a whole, there was a significant interaction of MCS with patients’ age, with significant delays of ERPs N2 and P3 during MCS in the group of patients older than 50 years exclusively. Changes were rapidly reversible after MCS discontinuation, and no effects whatsoever were observed on N1. These results suggest that MCS may interfere with relatively simple cognitive processes such as target detection, and that the risk of abnormal cognitive effects may increase with age. Although the procedure appears on the whole remarkably safe, complementary neuropsychological studies are advised, notably when age increases in the presence of cerebral lesions. PS26-04

Efficacy of electric stimulation in rehabilitation of the external popliteal neuropathy

R. Vladutu a, S. Bezna a, D. Poenaru b. aHospital No1, Craiova; bUniversity Hospital, Bucharest, Romania The analysis of the efficacy of electric nervous stimulation (ENS) in rehabilitation of “a frigore” external popliteal neuropathy (EPN). Material and Methods: 24 patients (8 women, 16 men, aged between 36– 58 years) were observed, randomly assigned into two groups. We made the assessment by testing of the affected nerve territory at the beginning (fibrillation potentials were observed) and each week, since the 5th week of treatment. We estimated superficial sensory disturbances with visual analogue scale VAS (0–10). Group 1 patients were daily treated by medicalkinetic program; group 2, performed medical-electro (ENS)-kinetic program. ENS was applied in association with muscle stretching. Results: Applying the electric treatment we succeeded to accelerate with 10 days, in a better manner the rehabilitation of the EPN paresis. Also both groups improved in pain and quality of life, the differences between mean scores were statistically significant better in the group 2. ENS is a considerable alternative therapy, with no adverse effects, applied in neuropathy. With stretching association, ENS represents a simple efficient therapeutic method in rehabilitation program of EPN. ENS assures of a shorter rehabilitation in a better proportion, with elimination of classical therapeutic methods. Electric nervous stimulation – a simple efficient therapeutic method – assures a shorter rehabilitation of peripheral neuropathy.

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Platform Sessions

TRANSCRANIAL MAGNETIC STIMULATION USES FOR DIAGNOSIS AND TREATMENT 2 PS27-01

The physiological basis of transcranial magnetic and electric stimulation of motor cortex leg area in conscious humans

A. Oliviero, V. Di Lazzaro, P. Profice, M. Meglio, B. Cioni, P. Tonali, J.C. Rothwell. Institute of Neurology, Catholic University, L.go A. Gemelli 8, 00168 Rome, Italy Descending corticospinal volleys evoked after transcranial magnetic or electrical stimulation of the leg area of the motor cortex were recorded from an electrode in the spinal epidural space of six conscious patients who had electrodes implanted for treatment of chronic pain. At threshold, the shortest-latency volley (L1 volley) was evoked by stimulation with an anode 2 cm lateral to the vertex. Anodal stimulation at the vertex also elicited a volley at this latency in two patients, but in the other patients the first volley evoked appeared 1–1.3 ms later (L2 volley), at the same latency as the initial volley evoked by magnetic stimulation. High-intensity stimulation of any type could evoke both the L1 and L2 waves as well as later ones (L3, L4, etc.) that had a periodicity of about 1.5 ms. Voluntary contraction increased the amplitude of the L2 and later volleys, but had no effect on the L1 volley. The L1 volley is likely to be a D wave produced by the direct activation of pyramidal axons in the subcortical white matter; the L2 and later volleys are likely to be I waves produced by the trans-synaptic activation of corticospinal neurones. The implication is that electrical stimulation with an anode at the vertex is more likely to evoke I waves preferentially than stimulation over the hand area. PS27-02

Visual cortex excitation by repetitive transcranial magnetic stimulation (rTMS) with different interstimulus intervals

L. Niehaus, M. Gerwig, O. Kastrup, B.U. Meyer. Department of Neurology, Charite´ , Berlin, Germany; Department of Neurology, Universita¨ tklinikum Essen Background: Subjective visual sensations (phosphenes) elicited by cortex stimulation have been used to develop visual prostheses, to study cortex activation by functional MRI, or to measure changes in cortical excitability e.g. in patients with migraine. To induce phosphenes rTMS was found to be more effective than single pulse TMS. Aim of the study was to investigate the influence of the interstimulus interval (ISI) on the thresholds for eliciting phosphenes by rTMS. Methods: In 20 healthy subjects TMS of the visual cortex was performed with a focal coil of a Dantec Magpro stimulator centred 0–3 cm lateral and 1–5 cm rostral the inion. Phosphene thresholds (PT) were measured for TMS with single and five pulses applied with ISI between 40 and 200 ms. To avoid effects of hysteresis, three series of increasing and decreasing stimulus intensities (in steps of 2% of maximum stimulator output) were applied in a randomized order. As control condition sham stimulation was performed. Results: PT for single pulse TMS was 60 ^ 8%. In all subjects rTMS elicited phosphenes with significantly lower stimulus intensities than single pulse TMS. PT for rTMS correlated significantly with the ISIs (Spearman correlation r ¼ 0:62, P , 0:001) and were lowest with short ISIs: The thresholds amounted to 42 ^ 8% (25 Hz), 46 ^ 10% (10 Hz), and 53 ^ 12% (5 Hz). Conclusions: Thresholds for eliciting phosphenes by rTMS were lowest with high stimulus frequencies even when only short series of stimuli (five stimuli) were applied. Therefore the use of high stimulus frequencies is advisable when subjective visual sensations shall be studied as a correlate of visual cortex excitation with low (and painless) stimulus intensities.

PS27-03

Long term bilateral motor cortex disinhibition after unilateral finger movement

T. Ba¨ umer a, C. Babiloni b, C. Weiller a, J. Liepert a. aDepartment of Neurology, University of Hamburg; bDipartimento di Fisiologia Umana e Farmacologia, Universita di Roma “La Sapienza”, Rome, Italy We performed a TMS study to examine the effect of a unilateral finger movement on post-movement motor cortex excitability in both hemispheres. Methods: Subjects (n ¼ 10) had to elevate the index finger as fast as possible after a visual cue. Three conditions were tested: left (1) and right (2) -sided finger elevation and (3) the free choice of the moving side. TMS was applied with a round coil over the vertex producing similar magnetic evoked potentials in both extensor indices muscles. Paired TMS were applied according to the Kujirai paradigm. The conditioning pulse was 75% of resting threshold. Interstimulus intervals were 2 ms for measuring intracortical inhibition (ICI) and 13 ms for testing intracortical facilitation (ICF). TMS were given 100 ms before and 550/900/1400/1900/2400 ms after the visual cue. Results: ICI was significantly reduced in both hemispheres for up to 2000 ms after a unilateral finger movement. This was significantly pronounced in the right motor cortex irrespective of the movement side or the free choice which side to move. Test pulse amplitudes, and ICF were unchanged. Conclusion: After a unilateral finger movement a long-lasting reduction of ICI occurred in both hemispheres, indicating interhemispheric interactions. This disinhibition was more pronounced in the non-dominant hemisphere. PS27-04

The pathophysiology of encephalopathy in severe hepatic failure: a TMS study

A. Oliviero, F. Pilato, E. Saturno, M. Di Leone, V. Versace, F. Ranieri, R. Gaspari, M.A. Pennisi, P.A. Tonali, V. Di Lazzaro. Institute of Neurology, Catholic University, Largo A Gemelli 8, 00168 Rome, Italy Severe liver failure (SLF) causes accumulation of both albumin-bound and water-soluble substances that exhibit toxic effects on the brain determining hepatic encephalopathy. We used transcranial magnetic stimulation (TMS) to explore cerebral cortex function in seven patients affected by SLF. We found hypoexcitability of the motor cortex in patients with SLF. Recently, a molecular adsorbent recirculating system (MARS) has been proposed as a new extracorporeal detoxifying treatment. We used TMS to evaluate the effects of MARS on cerebral cortex functions in these patients and also the effects of orthotopic liver transplantation (OLT) in two of them. Cortical hypoexcitability of the motor cortex as demonstrated by TMS could be reversed by MARS treatment or by OLT. These preliminary observations suggest that TMS may be a useful tool in assessing patients with SLF and in monitoring the effectiveness of therapies. PS27-05

Motor responses evoked by transcranial magnetic stimulation (TMS) in amyotrophic lateral sclerosis: the TMS index

Mamede de Carvalho a, Anto´ nia Turkman b, Michael Swash c. aDepartment of Neurology, Hospital de Santa Maria, IMM, Lisbon, Portugal; bDepartment of Statistics and Operational Research, Faculty of Sciences, Lisbon, Portugal; cDepartment of Neurology, The Royal London Hospital, London, UK The value of the conventional neurophysiological parameters obtained by TMS in the diagnosis of ALS has been questioned. We addressed this problem studying the upper (UMN) and lower motor neuron (LMN) inner-

Platform Sessions vation of 159 hands from 81 patients with amyotrophic lateral sclerosis (ALS). Eleven patients with various chronic LMN disorders causing weakness in the abductor digiti minimi (ADM) muscle served as LMN controls. Thirty healthy subjects served as normal controls. Cortical motor threshold (CMT), central conduction time (CMCT), and motor evoked response amplitude (MEP) after transcranial magnetic stimulation (TMS) were studied, and the MEP/M wave ratio, was calculated. The data was analyzed in the ALS subjects in groups defined by the ADM muscle strength, and the presence or absence of clinical signs of UMN involvement. CMCT was not increased in the ALS or LMN disease groups. CMT was higher in limbs with weak ADM muscles and UMN signs. MEP/M wave amplitude ratio was increased in weak muscles in the ALS population, notably in limbs with no UMN signs, and also in weak muscles in patients with other chronic neurogenic disorders. A TMS index derived from the CMT and CMCT showed increased variance in all ALS groups as compared with controls. This index was abnormal in 24% of limbs with normal strength and no signs of UMN. We conclude that conventional TMS studies are not useful in confirming signs of UMN lesion in ALS, but the TMS index can be a sensitive parameter in the early phases of the disease. PS27-06

Transcranial magnetic stimulation in subclinical hepatic encephalopathy and its correlation with magnetic resonance

N. Raguer a, J. Cordoba b, A. Rovira c, J. Alonso c, N. Navarro a, S. Perez a, L. Montserrat a. aClinical Neurophysiology Department; bLiver Unit; cMag-

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netic Resonance Unit, Hospital Universitari Vall d’Hebron, Barcelona, Spain Objective: Some patients with hepatic cirrhosis develop asymptomatic T1-hyperintensity along the corticospinal tract in magnetic resonance (MR), that is reversible after liver transplantation. The aim of this study is to evaluate functional involvement of corticospinal tract assessed by transcranial magnetic stimulation (TMS). Methods: 21 cirrhotic patients (17 males and 4 females) without signs of hepatic encephalopathy were studied previous (n ¼ 21) and 6 months after liver transplantation (n ¼ 14). TMS were performed and motor evoked potentials (MEP) recorded in upper and lower limbs. Central motor conduction time (CMCT), MEP amplitude and motor threshold were measured. MR with quantification of the T1-signal along the corticospinal tract and calculation of the magnetization transfer ratio were also performed. Results: A significant increase in motor threshold and CMCT, and decrease in MEP amplitude were seen in cirrhotic patients compared to controls. MR studies were compatible with the development of edema along the corticospinal tract. This abnormalities improved after liver transplantation. Conclusions: TMS show corticospinal tract involvement in cirrhotic patients without clinical encephalopathy, with some degree of improvement after 6 months of liver transplantation. There is a good correlation between TMS and MR, suggesting that cerebral edema may be related with the pathogenesis of hepatic encephalopathy.

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Platform Sessions

EEG RHYTHMS AND TRANSIENTS PS28-01

Beta changes during S1-decide and S2-decide CNV go/ no-go paradigms

M. Alegre, A. Labarga, I.G. Gurtubay, M. Valencia, J. Arcocha, A. Malanda, J. Artieda. Clinica Universitaria de Navarra and ETSIT-UPNA, Pamplona, Spain A beta decrease (beta-ERD) has been described during CNV paradigms. We studied beta changes during two different double-stimulus (CNV) go/nogo paradigms in seven subjects. Randomized pairs of 90 dB tones separated by 1.5 s were used. In the first paradigm, the first tone (S1) was a constant cue and the second tone (S2) indicated whether to move or not after it. In the second paradigm, S1 indicated whether to move or not after S2. 100 sweeps per subject and condition were collected, synchronized with S1. Changes in the 15–35 Hz range were computed with time-frequency transforms; the results were compared statistically with a prestimulus period. An interstimulus beta-ERD was only found in the go condition of the paradigm with decision to move in S1. In all conditions, a beta-ERS was observed with a frontal maximum, after S1 or S2 depending on when the decision (go and no-go) was taken. We conclude that rolandic beta-ERD is just related to motor preparation while frontal beta-ERS is linked to the decision process.

azu, A. Malanda, J. Artieda. Clinica Universitaria de Navarra and ETSI de Telecomunicaciones, UPNA, Pamplona, Spain A beta energy decrease (beta ERD) has been described before selfinduced movements and during CNV paradigms. We studied beta ERD during two different stimulus-induced movement paradigms, with rhythmic and arrhythmic stimuli, in a group of 6 subjects. 1000 Hz acoustic stimuli were delivered to both ears in two recording sessions, either at a fixed rate of six seconds, or with a random interval between 5 and 13 seconds. 150 artifact-free sweeps were collected per subject, synchronized with the stimuli. Changes in the 15–35 Hz range were determined by means of Gabor transforms; the results were compared statistically with those obtained in a rest period. A typical pre-stimulus beta ERD was only found in the paradigm with rhythmic stimuli. In the arrhythmic paradigm, a non-significant pre-stimulus ERD was found only for frequencies around 25 Hz. Beta changes during and after movement were similar in both conditions. These results show that pre-stimulus beta ERD only appears when the subject has an estimation of when to move. This suggests that pre-movement beta ERD is linked specifically to movement preparation and not to unspecific attentional processes.

PS28-04 PS28-02

Neurophysiological correlates of frontal lobe involvement in patients with multiple sclerosis

G. Comi a,b,c, V. Martinelli b, M. Filippi c, G. Santuccio b, M. Rovaris c, F. Possa b, G. Magnani b, L. Leocani a. aClinical Neurophysiology; bNeurology; c Neuroimaging Unit, University Vita-Salute, Scientific Institute Hospital San Raffaele, Milan, Italy Background: Involvement of frontal lobe executive functions is a relatively frequent finding in Multiple Sclerosis (MS Frontal lobes also play an important role in the control of voluntary movements, particularly in motor planning and execution. Event-Related Desynchronization (ERD) of the sensorimotor EEG rhythms indicates cortical activation during movement preparation and execution, while event-related synchronization (ERS) of the same rhythms, occurring after movement termination, is considered a correlate of cortical idling or inhibition. We evaluated the pattern of cortical activation during voluntary movements in MS patients with frontal lobe involvement by means of ERD/ ERS analysis of self-paced finger movements. Methods: Ten MS patients with and 11 without neuropsychological frontal lobe deficits, with similar disability and disease duration were studied. Data were compared to 11 age-matched normal subjects. Patients also underwent quantitative assessment of brain magnetic resonance imaging (MRI) lesion load. Results: ERD onset to movement preparation was delayed in frontal patients compared both to normal subjects (P ¼ 0:01) and to non frontal patients (P ¼ 0:003). Post-movement ERS was not significantly different in the two MS groups, and it was reduced in both of them when compared to normal subjects (P , 0:02). Frontal MS patients had higher MRI lesion burdens than control MS patients, overall and in the frontal lobes. Conclusion: Delayed ERD onset during movement preparation in frontal patients is consistent with the role of frontal lobes in motor programming, and with the MRI findings. Reduced post-movement ERS, which reflects inefficient cortical inhibitory mechanisms, is not specific of frontal lobe involvement, but rather to MS pathology. PS28-03

Beta changes during rhythmic and arrhythmic stimulusinduced movements

M. Alegre, I.G. Gurtubay, A. Labarga, M. Valencia, J. Iriarte, E. Urrestar-

Organization of EEG quasi-stable alpha rhythms for schizophrenia in adolescents

A.Y. Kaplan, S.V. Borisov, N.L. Gorbachevskaya. Moscow State University, 119992, Moscow, Russia Introduction: The aim of this topic is twofold: 1) to present the methodology for quasi-stationary analysis of EEG alpha-activity with evaluation of EEG structural synchrony and 2) to present experimental data about EEG manifestation of schizophrenia in adolescents. Experimental procedures: EEG data was obtained involving 13 adolescents (10–14 years) with schizophrenia and healthy control (11 adolescents, 11–12 years). EEG data were derived from 16 electrodes referenced to linked earlobes. Special nonparametrical procedures “SECTION” (A. Kaplan, 1999) were used for search of quasi-stationary segments in alpha-activity and “JUMPSYN” for the evaluation of structural synchrony as value of over the Monte-Carlo level of coincidence between alpha segments in different channels (A. Kaplan, 2000). Results of the research: It was shown in schizophrenics the amplitude and amplitude variability of quasi-stable alpha segments were significantly higher on 6–20% and 11–27% with compare to normal control practically in all derivations. The duration of EEG alpha segments in schizophrenics was less than in healthy adolescents with maximal effect in central and frontal locations. The level of structural synchrony in schizophrenics was less than in normals especially for central and left temporal cortex areas and higher in occipitals and right central locations. A conclusion: Characteristics of segmental organization and structural synchrony of EEG alpha-activity could be useful in diagnostic of schizophrenia in adolescents. PS28-05

Acute, maintained and superimposed topographic pharmaco-EEG mapping of repetitive paroxetine intake in healthies

M.J. Barbanoj a, P. Anderer b, A. Morte a, J. Riba a, J.L. Lorenzo a, S. Clos a, B. Saletu b, F. Jane´ a, A. Luque c, R. Dal-Re´ c. aInstitut de Recerca de l’HSCSP, Departament de Farmacologia i Terape`utica, UAB, Barcelona, Spain; b Department of Psychiatry, University of Vienna, Austria; cMedical Department, GlaxoSmithKline, Madrid, Spain

Platform Sessions Background: Although like any pharmacological treatment of depression a repetitive schedule of at least 10–15 days of paroxetine is necessary to start to show antidepressant activity, only acute effects on EEG are well documented. Objective: To evaluate neurophysiological acute, maintained and superimposed effects of paroxetine. Methods: Twenty-two healthies participated in a randomised double blind, crossover trial. They received during 15 days one morning administration of paroxetine 20 mg or placebo. On day 1 and day 15 at PRE, 11, 12, 14, 16 and 18 hours: 3-minute, vigilance-controlled EEG was assessed through 16 leads. FFT (1.3–30 Hz) to 5 s artefact-free epochs after common average reference calculation was computed. Descriptive data analysis by Hotelling T2- and t-maps was applied.

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Results: Acute: Increase in total power and in total centroid and its deviation; no relevant changes in slow activity; increase in relative alpha power (mainly alpha-2); increase in beta activity (more important beta-3 and beta-4). Maintained: Changes only observed in alpha activity, but different to those in acute (decrease in relative alpha-2). Superimposed: similar (total power, slow and fast activities) together with different (increase in alpha-1, decrease in alpha-2 relative powers) changes to those in acute. Conclusions: Like what happens at the biochemical level paroxetine EEG effects were qualitative different between acute and repetitive administration.

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Platform Sessions

INTERVENTIONAL CLINICAL NEUROPHYSIOLOGY Angel Esteban. Department of Clinical Neurophysiology, Hospital General Universitario Gregorio Maran˜ o´ n, Madrid, Spain Interventional clinical neurophysiology (ICN) is a recently coined term to describe the use of neurophysiologic techniques in the therapeutic procedures of some neurological disorders. Many of these techniques are actually being used since long time ago. Methods of ICN and their fields of application are multiple: One type of ICN precisely define the site over which an accurate treatment’s procedure has to be exerted, so preventing a blind or tentative actuation, increasing the therapeutic efficacy and decreasing the risk of side effects; i.e., EMG-guided botulinum toxin injections in focal motor disorders. Other ICN methods provide a therapeutical action based on the presumed pathophysiological mechanisms of the neurological derangement; i.e., the use of rTMS for central pain relief. A third category of the ICN methodologies is mainly referred to monitoring and participates, along with others, in a collaborative treatment’s action; i.e., the definition and prolonged functional control of different peripheral and central nervous segments in the intensive care unit and the operating theatre. This platform session will deal with the present state of the art of many of the currently ICN implications. PS29-01

Repetitive transcranial magnetic stimulation of the parietal cortex transiently ameliorates phantom limb pain-like syndrome

I.G. Meister, B. Boroojerdi, H. Foltys, R. Sparing, R. To¨ pper. Department of Neurology, University Hospital Aachen, Germany Phantom pain is thought to be due to a reorganization of the partially deafferented cortical sensory system. Repetitive transcranial magnetic stimulation (rTMS) has been shown to selectively influence the activity of cortical systems. In this study we investigated whether it is possible to change the intensity of chronic pain with rTMS. Two patients with a longstanding unilateral avulsion of the lower cervical roots were studied. As control the effect of rTMS on experimentally induced pain in 4 healthy subjects was studied. Pain intensity was assessed with the Visual Analogue Scale. In the patients, rTMS (15 Hz, 2 s) of the posterior parietal cortex led to a reproducible reduction of pain intensity which lasted up to 10 minutes. Stimulation of other cortical areas produced only minor alteration in the severity of pain. A 3 week series of rTMS with frequencies of either 1 Hz or 10 Hz, however, did not result in persistent analgetic effects. In normal subjects, rTMS had no influence on pain induced by cold water immersion of the right hand. The results support the concept that phantom pain is due to a dysfunctional activity in the parietal cortex. The transient analgesic effect may be due to temporary interference with the cerebral representation of the deafferented limb. The results, however, do not favor the use of rTMS as treatment for phantom limb pain. PS29-02

Repetitive transcranial magnetic stimulation in the management of chronic neurogenic pain

Jean-Pascal Lefaucheur, Xavier Drouot, Isabelle Menard, Jean-Paul Nguyen. Service de Physiologie, Hopital Henri Mondor, 51 avenue de Lattre de Tassigny, 94010 Creteil, France Chronic electrical stimulation of the precentral motor cortex by means of surgically-implanted epidural electrodes is a treatment of medicationresistant neurogenic pain. Our first goal was to study the ability of repetitive transcranial magnetic stimulation (rTMS) of the motor cortex to relieve neurogenic pain as epidural stimulation does. A 20-minute session of rTMS at 80% rest motor threshold was applied over the motor cortical

area corresponding to the painful zone, in patients suffering from neurogenic pain of various origins. A placebo-control was performed by using a ‘sham’ coil. The pain relief was assessed on visual analog scale before and after rTMS. We found a significant pain relief after ‘real’ rTMS applied at 10 Hz (20 trains of 10-sec duration with 50-sec intertrain intervals) but neither at 0.5 Hz nor after ‘sham’ rTMS. The best results were obtained when pain predominated at the face or the upper limb, in patients presenting with thalamic stroke, brachial plexus or trigeminal nerve lesion and without complete thermal sensory deafferentation. The pain decrease was significant up to 8 days after a single rTMS session. At present, our experience covers more than 100 patients. The mechanisms of action of rTMS on pain could pass through changes in cortical excitability or in sensory discrimination which was quantitatively tested.

PS29-03

Repetitive transcranial magnetic stimulation over the cerebellum as an effective therapy for spinocerebellar degeneration

Yusei Shiga a, Hiroshi Shimizu a, Koichi Miyazawa b, Kazutaka Jin c, Yasuto Itoyama a. aDepartment of Neurology, Tohoku University School of Medicine; bKohnan Hospital; cMiyagi National Hospital A placebo-controlled study was performed to evaluate the therapeutic efficacy of repetitive transcranial magnetic stimulation (rTMS) for spinocerebellar degeneration (SCD). Eighty-three patients gave written informed consent. Thirty pulses at a strength of 2.5 times the motor threshold were applied daily for 21 consecutive days using a Magstim 200. The inter-pulse interval was six seconds. A 14-cm circular coil was placed tangentially (active-group; n ¼ 48) or vertically (sham-group; n ¼ 36) over the posterior cranium. The age, disease-duration, disease-type, and disease-severity were matched. Standing capacities, walking capacities, the time and steps required during a 10-m walk, and the number of practicable steps on the tandem gait were evaluated. We judged an item as “improved” when the value of each item improved more than 2.5 SD of that of the sham-group. When the patient had one item improved, we judged the rTMS as “effective”. When more than two items improved, we judged the rTMS as “very effective”. Active-rTMS was “very effective” for 16.7% of the patients and “effective” for 29.2%. Sham-rTMS was “very effective” for none, and “effective” for 16.7%. Active-rTMS had a significant therapeutic effect compared to sham-rTMS (P , 0:005) without any adverse effects. rTMS is a promising therapy for SCD.

PS29-04

EMG-guided low dosage botulinum toxin treatment of the infantile spastic equinus foot

A. Traba a, A. Esteban a, J. Prieto a, C. Garzo b, P. Cervera c, J. Espinosa d. a Department of Clinical Neurophysiology; bDepartment of Neuropaediatrics; cDepartment of Orthopaedics; dDepartment of Rehabilitation, Hospital General Universitario Gregorio Maran˜ o´ n, Madrid, Spain The botulinum toxin (BT) has been successfully used in the treatment of the infantile spasticity. We present the results of the spastic equinus foot treatment in a series of 9 patients using low doses BT (7.5–10 units/Kg DysportR) injected with EMG guidance to assure the correct administration of the toxin. Apart from equinus gait, varus foot deviation was associated in 2 cases and hip adductors and flexors spasticity in other 3 cases. 5 patients were hemiplegic and 4 diplegic. Only one patient had fixed contracture of the ankle. The BT was injected in the calf muscles, in the motor point or in the areas with more intense EMG activity. In 7 patients a significant improvement was obtained in the gait pattern, with increase in the ankle mobility. We did not obtained improvement in the patient with fixed ankle contracture and it was of brief duration in the remaining case that had

Platform Sessions associated hip spasticity. No patient presented side effects. These findings indicate that the EMG guidance in the BT administration in the treatment of the infantile spasticity should be considered indispensable because reduce the total dose of BT employed.

PS29-05

Functional identification of targets for deep brain stimulation based on SEP criteria

F. Klostermann a, J. Vesper b, G. Curio a. aNeurophysics Group, Department of Neurology; bDepartment of Neurosurgery, UKBF, FU Berlin, Germany This study aimed at identifying thalamic and subthalamic brain sites on the basis of SEP criteria. The analysed structures are targets of deep brain stimulation (DBS) for the treatment of movement disorders. Median nerve SEP (1000 sweeps / average; 8.1 Hz) were recorded from

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the stimulation electrode in 12 parkinsonian (subthalamic nucleus, STN) and 10 tremor patients (ventral intermediate nucleus, VIM). The electrodes feature four contacts of 1.5 mm width, spaced at 0.5 millimeters. Three bipolar channels were derived, referencing the cranial contact against the caudal ones. Recordings were performed 1 and 2 cm above and in STN and VIM. After digital filtering (430 Hz), high and low frequency SEP components were analysed separately. The high frequency (1000 Hz) burst signal was always larger in VIM than in STN. The low frequency components peaking around 18 ms was negative in VIM and positive in STN. The SEP waveshape in recordings above target positions were similar to STN SEP, but of lower amplitude. Thus, VIM and STN can be functionally distinguished by SEP criteria. This approach provides a reliable tool for the final assessment of DBSelectrode positions at the last instance during surgery when revisions can be easily performed. Supported by DFG Kl-1276/1 and Ma 1782/1-4.

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Platform Sessions

SPINAL CORD AND ROOTS ASSESSMENT Spinal Cord and Roots assessment

PS30-02

History of polio and negative neurophysiology, is that possible?

V. Dietz, Univ. Hospital Balgrist, Switzerland Following central motor lesions two forms of adaptation can be observed which lead to improved mobility: 1. The development of spastic muscle tone, and 2. The activation of spinal locomotor centres induced by specific treadmill training. 1. Tension development during spastic gait is different from that during nornal gait and appears to be independent of exaggerated monosynaptic stretch reflexes. Exaggerated stretch reflexes are associated with an absence or reduction of functionally essential polysynaptic reflexes. When supraspinal control of spinal reflexes is impaired, the inhibition of monosynaptic reflexes is missing in addition to a reduced facilitation of polysynaptic reflexes. Therefore, overall leg muscle activity becomes reduced and less well modulated in patients with spasticity. Electrophysiological and histological studies have shown that a transformation of motor units takes place following central motor lesions with the consequence that regulation of muscle tone is achieved at a lower level of neuronal organization which in turn enables the patient to walk. 2. Based on observations of the locomotor capacity of the spinal cat, recent studies have indicated that spinal locomotor centres can be activated and trained in patients with complete or incomplete paraplegia when the body is partially unloaded. However, the level of electromyographic activity in the gastrocnemius (the main antigravity muscle during gait) is considerably lower in the patients compared to healthy subjects. During the course of a daily locomotor training program, the amplitude of gastrocnemius electromyographic activity increases significantly during the stance phase, while inappropriate tibialis anterior activation decreases. Patients with incomplete paraplegia benefit from such training programmes such that their walking ability on a stationary surface improves. The pathophysiology and functional significance of spastic muscle tone and the effects of treadmill training on the locomotor pattern underlying new attempts to improve the mobility of patients with paraplegia are reviewed. PS30-01

The influence of hip angle and load on medium-latency reflexes

C.M. Bastiaanse, A. Curt, B.C.M. Baken, V. Dietz, J. Duysens. Research ParaCare, Paraplegic Centre of the University Hospital Balgrist, 8008 Zurich, Switzerland Introduction: Hip angle and body loading are known to be important in the reflex control of gait. However, it is largely unknown whether they play a role in phase-dependent modulation of reflexes during gait. To examine this we compared gait with static conditions (standing, lying). Methods: Medium-latency reflex responses were elicited by electrical stimulation of the posterior tibial nerve in healthy subjects during lying, standing on a tilt-table and during different phases of the step cycle. EMG recordings were performed in tibialis anterior (TA) and gastrocnemius medialis (GM) muscles of both legs. Results: During static condition, there was no influence of hip angle or load on the reflexes. However, during walking the reflexes were modulated. TA responses were phase-dependent but not load dependent. GM responses were also load dependent. In both conditions, the reflex response was dependent of the stimulation intensity. Conclusion: It is concluded that the phase-dependent modulation of medium-latency reflexes are not explained by changes in hip angle or in limb loading since variations of these parameters under static conditions did not induce modulation.

Arne Sandberg, Erik Sta˚ lberg. Department of Clinical Neurophysiology, Uppsala University Hospital, Uppsala, Sweden Objective: Patients suffering from paralytic polio typically show neurophysiologic signs of permanent anterior horn cell loss. In a small number of patients the neurophysiology is negative. The aim is to study in some detail this group of patients. Methods: Neurophysiologic methods including concentric needle EMG, Macro EMG (including Single fiber EMG) and neurography were performed in different combinations in 688 patients. 35 patients with normal or minimally abnormal neurophysiology (other reason than polio) were included. Results: In 6 patients the diagnosis of polio was rejected and was instead found to be stroke, meningioma, cerebral palsy, Guillain-Barre´ syndrome and hysteria respectively. Two patients showed sequelae from polio meningitis. In 17 there was a strong suspicion of a history of paralytic polio, without any neurophysiologic signs of remaining anterior horn cell involvement. The explanation for this could be a transient functional loss (apraxic reaction) in the anterior horn cells. Conclusions: When negative neurophysiology is present in patients with a history of polio, one should usually reconsider the diagnosis. However there is the possibility of an acute polio in which the initial involvement of anterior horn cells does not lead to degeneration. Late transsynaptic or metabolic changes may cause the present symptoms of weakness, fatigue and pain. PS30-03

Preoperative and postoperative changes in somatosensory evoked potentials in rheumatoid arthritis patients with cervical spine disorder

T. Hayashida, T. Ogura, H. Hase, D. Tokunaga, T. Kubo. Department of Orthopaedic Surgery, Kyoto Prefectural University of Medicine, Kyoto, Japan The purpose of this study was to analyze waveform changes of shortlatency somatosensory evoked potentials (SSEPs) in association with clinical variables in rheumatoid arthritis (RA) patients with cervical spine disorder. We also examined the diagnostic utility of SSEPs for rheumatoid cervical myelopathy before and after surgery. We studied SSEPs in eleven rheumatoid patients with cervical myelopathy treated by surgical procedure. Ten patients had atlanto-axial subluxation. The SSEP recordings were performed before and after surgery (average period after surgery: 7.4 months). For clinical evaluation, we used rating score developed by Japanese Orthopaedic Association (JOA score). As regards preoperative SSEPs, spinal N13 amplitudes were normal in all patients who have the only C1-C2 spinal cord compression by radiological examination. The N9-P14 interpeak latencies were prolonged in seven (63.6%) patients. There was a statistical correlation between N9-P14 interpeak latency and JOA score (r ¼ 20:746, P , 0:01). With respect to SSEP changes after surgery, N9-P14 interpeak latencies were improved in all patients; besides, there was a correlation between postoperative N9-P14 interpeak latencies and the recovery rate of JOA score (P , 0:05). The result of this study confirmed that SSEPs are valuable in the assessment of cervical cord dysfunction in patients with RA who have cervical spine lesions.

PS30-04

Neurological complications secondary to abdominal aortic aneurysm surgery

A. Recchia. Department of Neurophysiology, Hospital do Servidor Publico Estadual, Sao Paulo, Brasil

Platform Sessions Objectives: The objective of this study was to establish a correlation between electrophysiological data and neurological findings in eight patients that presented neurological deficits after surgical treatment of abdominal aortic aneurysm. Methods: Eight patients with their ages varying from 55 to 72 years, with no previous history or signs of neurological disease were studied. Six patients underwent elective surgery and two patients underwent emergency surgery (ruptured abdominal aortic aneurysm). In the postoperative period, six patients presented unilateral weakness, numbness and burning pain in the lower extremity and two patients developed paraparesis (spinal level loss at T10 and L1 respectively). Results: Electrophysiological studies have been performed in all patients, six to nine weeks after the onset of the neurological deficits. Clinical and electromyographic findings indicated moderate to severe axonal damage revealing a lumbosacral plexopathy in six cases (affecting predominantly anterior/posterior divisions of lumbar and sacral plexus) and a radiculopathy (predominant L4/L5/S1 root involvement) associated with a spinal cord damage in two cases. The neurological complications were developed mainly as an impairment of the blood supply to the injured region (lumbar arteries) as a consequence of surgical manipulation (clamping in a bypass procedure) or due to a vascular lesion. Conclusions: The present study had the intent to put in focus these potentials neurological complications that, although uncommon, must be always considered.

PS30-05

S61 Partial return of motor function in paralysed legs following surgical bypass of the lesion site by nerve autografts three years after spinal cord injury

Y. Pe´ re´ on, A. Faure, S. Liu, B. Perrouin-Verbe, P. Guihe´ neuc, R. Robert, J.F. Mathe´ , M. Tadie´ . Laboratoire d’Explorations Fonctionnelles, Service de Neurotraumatologie, Service de Re´ e´ ducation Fonctionnelle, Hoˆ telDieu, University Hospital, Nantes, France; Service de Neurochirurgie, Hoˆ pital de Biceˆ tre, AP-HP, Le Kremlin-Biceˆ tre, France Spinal cord injuries often result in irreversible loss of motor and somatosensory functions below the lesion level. In animal models, re-establishment of tissue continuity can be achieved through nerve autografts implanted between the rostral spinal ventral horn and the caudal ventral roots. Rostral motor neuron axons could thus reach peripheral targets, leading to some return of motor function. These observations were applied in the treatment of a paraplegic man with stabilized clinical states three years after spinal cord traumatic damage at the T-9 level. Three segments from autologous sural nerves were implanted into the right and left antero-lateral quadrant of the cord at T7–8 levels, then connected to homolateral L2–4 lumbar ventral roots, respectively. Eight months after surgery, muscular contraction of the both adductors and the left quadriceps occurred voluntarily. Such activity was confirmed by EMG with the reappearance of MUPs in response to attempted muscle contraction. Motor potentials evoked by transcranial magnetic stimulation could also be recorded from these muscles. These data support the hypothesis that muscles have been re-connected to supra-spinal centres through motor neurons located in the rostral stump of the damaged cord. They suggest that delayed surgical reconstruction of motor pathways may contribute to partial functional recovery.

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Platform Sessions

NEUROMONITORING IN OPERATING ROOM 2 PS31-01

Motor improvement revealed by repetitive transcranial stimulation during occipital craniotomy for Sirinx 1 Chiary II

L. Leo´ n a, J. Conill a, E. Cardona b. aServicios de NeurofisiologI´a; bServicios de y NeurocirugI´a, Hospital Infantil Sant Joan de Deu, Barcelona, Spain Intraoperative Neurophysiological Monitoring allows to detect early neurological damage. The most serious consequence is the motor postoperative deficit, so then we must use neurophysiological techniques for motor pathway control. Methods: Repetitive Transcranial Electrical Stimulation (RTES) in trains from 4 to 7 stimuli, interval of 4 msec. and a 50 msec. duration. Motor potentials were recorded in both abductor digiti minimi. Somatosensory evoked potentials, elicited by ulnar nerve stimulation. Subject: A 15 year old female patient undergoes to occipital craniotomy for scoliosis, Sirinx C1-T12 and Chiary II, with progressive pre-surgical upper right limb paresis. Results: 1) gradual intraoperative improvement of asymmetric upper limbs RTES responses. 2) no changes in asymmetric SEP from both ulnar nerve during surgery. 3) progressive post-surgical recovery in right upper limb and sirinx reduction controlled by RM. Conclusions: Intraoperative Monitoring provides instantaneous information about functional spinal cord level, essential for detecting new neurological damages. RTES allows reliable control of motor pathways, their results are reproducible and consistent along the operation and correlate well with post-surgery clinical evolution.

PS31-02

Normative values and variability of intraoperative muscle MEP

Z. Rodi, D.B. Vodusek. Institute of Clinical Neurophysiology, Ljubljana Medical Center, Ljubljana, Slovenia There was 57 consecutive patients operated for spine fracture, with no neurological deficit, and 5 with neurological deficit postoperatively. Anesthesia was conducted with propofol and fentanyl. Stimulation was at points 2 cm frontally to C3 and C4 of 10–20 international EEG system, using train of 5 pulses. Detection was in abductor pollicis brevis (APB) and tibial anterior (TA) muscles bilaterally. Median MEP amplitude at the beginning of monitoring was 2100 microvolts (380–10000) in APB and 650 microvolts (60–3600) in TA. Median side to side ratio was 1.4 (1–2.4) in APB and 1.6 (1–6.2) in TA. Median amplitude at the end of monitoring was 2100 microvolts in APB (180–9700), and 640 microvolts (0–3500) in TA. Median ratio of end-to-beginning amplitude was 1 (0.3–1.5) in APB, and 1 (0–4.2) in TA. Median ratio of lowest-to-beginning amplitude was 0.9 (0.1–1) in APB, and 0.8 (0–1) in TA. A lower-to-beginning APB MEP fell bellow 0.3 in 2 patients (both thoracolumbar fracture), and a lower-tobeginning TA MEP fell bellow 0.1 in 2 patients (both thoracolumbar fracture). Reduction or loss of MEP was overcome by rising stimulus intensity by up to 20 mA.

PS31-03

Motor evoked potentials monitoring has changed spinal neurosurgeons attitude to intraoperative neurophysiological monitoring

B. Cioni a, M. Meglio a, V. Perotti b, S. Mannino a. aNeurochirurgia; bAnestesiologia, Universita` Cattolica, Roma, Italy The inaccuracy of SEPs monitoring to guide the neurosurgeon during spinal cord surgery, produced a certain skepticism about intraoperative

monitoring. The possibility to have direct informations about the motor function through MEPs, is changing this attitude. We report our experience with MEPs monitoring during 100 consecutive spinal cord operations: we will analyze the monitorability of MEPs under general anesthesia, and their clinical usefulness. Transcranial electrical stimulation was applied to the motor cortex using the single pulse technique with recording from the spinal epidural space (D-wave), and using the multiple stimuli technique with recording from limb muscles. After anesthesiological induction, MEPs could be recorded in 83% of the cases at upper extremities (muscle response) and in 93% of the cases at lower extremities (muscle responses and D-wave). In 11 cases (9%) MEPs deteriorated during the operation and then recovered following counteraction from the surgeon. In these cases no new motor deficit developed. At the end of surgery we had 1 false positive and no false negatives in our series. We conclude that MEPs monitorability is high (82–93%) under general anesthesia; the technique has high sensibility and specificity; it has shown its clinical usefulness in preventing surgical induced motor deficits. In our opinion, MEPs monitoring is an essential guide for the spinal neurosurgeon.

PS31-04

Intraoperative neurophysiological monitoring and mapping during surgery in and around motor cortex

P. Lanteri, F. Sala, G. Pinna, A. Bricolo. Department of Neurosurgery, Verona University, Hospital, Italy There is an increasing evidence that the aggressive surgical resection of supratentorial intrinsic brain tumor pays off in terms of survival and quality of life. To safely maximize glioma resections in functional area, intraoperative neurophysiological monitoring and mapping (INM) may be used to identify cortical anatomical landmarks as central sulcus, primary motor cortex and motor tracts, and continuous on line assessment of sensory and motor pathways. From September 2000 to January 2002, 48 patients (28 males, 20 females) underwent INM during resection of glial tumors located in sensory-motor cortex (36) or insula (12). The INM consists of monitoring with somatosensory and motor evoked potentials (SEPs, MEPs), mapping with SEPs phase reversal and direct cortical and subcortical stimulation of motor pathway. Histology was: 38 astrocytoma, 10 oligodedroglioma. During removal of tumor, in 9 cases the use of INM modified the surgery planning for modification of neurophysiological signal. No one presented grave disability or death. After the operation 28 patients showed no deficits, 2 improved, 15 had light new deficits or worsened neurological deficits, 2 showed supplementary motor area syndrome, 1 had a Steven-Johnson syndrome. Conclusion: In our preliminary experience, the INM of the functional integrity of the sensory and motor areas and pathways, is non-invasive and safe technique for more accurate and precise resection of tumor of eloquent cortical areas and subcortical pathways.

PS31-05

The usefulness of electromyographical monitoring with intraoperative brain mapping during lesionectomy

M. Gonza´ lez-Hidalgo a, C.J. Saldan˜ a Gala´ n b, C. Franco Carcedo a, P. Mata Gonza´ lez b. aDepartment of Clinical Neurophysiology; bDepartment of Neurosurgery, Hospital Clinico San Carlos, Madrid, Spain Introduction: Surgery for resection of supratentorial lesions near motor functional cortex carries an associated risk of damage to cortical or subcortical motor pathways. The technique of observing movements elicited by direct cortical electrical stimulation has been proved useful for intraoperative localization of motor pathways but it is difficult to observe the entire body at once. Thus, a small movement may be missed while attention is

Platform Sessions focused on another site. Patients and methods: We recorded multichannel electromyography activity during cortical/subcortical electric stimulation in a series of 40 patients undergoing craniotomies for lesionectomy near sensorimotor cortex. Because the aim of the electromyography recordings was to sample as many muscles as possible, the two electrodes connected to each different amplifier input were placed in different muscles in the same region of the body. Results: No motor responses were detected by either EMG monitoring or visual inspection in 20% patients. EMG activity was the only indication of motor response in 17%. Motor responses were detected simultaneously by either EMG monitoring and visual inspection in 76%. Seizures occurred in 17% patients. Conclusions: Electromyography monitoring enhances the ability to detect the location of primary motor cortex and subcortical pathways with electrical stimulation during neurosurgery. PS31-06

Pre- intra-postoperative tibial-SSEP monitoring in scoliosis surgery

O.N. Hausmann a,b, K. Min b, Th. Bo¨ ni b, V. Dietz a, A. Curt a. aParaCare, Swiss Paraplegic Center, Institute for Rehabilitation and Research; b Department of Orthopedic Surgery, University of Zurich/Switzerland

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The impact of spine deformity in patients with idiopathic scoliosis (IS) on tibial nerve somatosensory evoked potentials (t-SSEP) and the influence of spine correction upon postoperative SSEP recordings was assessed. In 61 consecutive IS patients undergoing 64 spinal instrumentations, 129 pre- and postoperative SSEP were analysed. The degree of spine deformity was assessed by the Cobb angle. Reference values of t-SSEP latencies were established with respect to body height in a control group. In a cohort study t-SSEP analysis of latency, amplitude, configuration and interside difference of the IS patients was compared to healthy controls. Preoperative body height corrected t-SSEP latencies were prolonged in 61% with a pathological interside difference in 23.4% of patients. The impairment of t-SSEP was not related to the extent of spine deformity. Postoperative t-SSEP showed significantly increased latencies. The prolongation of t-SSEP latencies was related to the surgical procedure (i.e. combined ventro-dorsal approach), but not to the extent of spine correction. t-SSEP are significantly affected in IS patients although these patients show no obvious clinical neurological deficits. The extent of t-SSEP impairment is not related to the severity of scoliosis. Even in uneventful surgery the postoperative t-SSEP evaluation may deteriorate depending on the surgical approach.