Deutsche EEG-Gesellschaft, 36th annual meeting

Electroencephalography and clinical Neurophysiology , 87 (1993) 1P-34P

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© 1993 Elsevier Scientific Publishers Ireland, Ltd. 0013-4694/93/$06.00

EEG 92572

Society proceedings

Deutsche EEG-Gesellschaft, 36th annual meeting C e l l e , 1 0 - 1 3 O c t o b e r 1991

Secretary: Prof. Dr. S. Kubicki Abt. fiir Klinische Neurophysiologie, Klinikum Rudolf Virchow, Standort Charlottenburg, Spandauer Damm 130, D-IO00 Berlin 19 (Germany) (Received for publication: 21 April 1992)

1. Is there an encephalic signal phase-coupled to the next ECG R wave? - - L. yon Klitzing (Dept. Clin. Res., Medical University of Liibeck, Liibeck)

In static magnetic fields we found spontaneous encephalomagnetic signals detected by coils fixed at the surface of the head. When averaging these signals by ECG R wave trigger and selecting into groups of subsequent increasing distances from trigger point to the next R wave there are different time functions of the summarized data. By Fourier Transformation we tested the frequency and time domains. For some frequency bands between 5 and 11 Hz there are distinct shifts of phase angles related to the trigger point when comparing the subsequent data blocs. Without magnetic fields we found corresponding data, sampled by surface electrodes. Our conclusion is that obviously encephalic signals know about the event of next R wave. 2. Cortical representation of erector spinae muscles. A study with focal magnetic stimulation. - A. Ferbert, J.C. Rothwell, D. Caramia, A. Priori and L. Bertolasi (London, U.K.)

We investigated the cortical representation of erector spinae muscles in 9 healthy subjects. We stimulated with a figure of 8 magnetic coil. The coil was placed over Cz and moved in 2 cm steps to either side. In most subjects this mapping was performed 2 cm before and 2 cm behind Cz in addition. We recorded from erector spinae muscles bilaterally 3.5 cm lateral of the processus spinosus of the third lumbar vertebra. Back muscles were slightly activated. In 5 subjects clear reproducible responses could be obtained with a latency between 13 and 25 msec. From this latency a transmission via fast conducting fibers and a mono- or oligosynaptic connection can be assumed. In the remaining 4 subjects responses were ill defined and could hardly be distinguished from the background activity. In these cases an inhibition of the background EMG could be observed. Different patterns of hemispheric representation were found from contralateral projection to a representation of both back muscles predominantly in one hemisphere (2 subjects). 3. Transcranial stimulation of the human frontal eye field by magnetic pulses. - R.M. Miiri and C.W. Hess (Department of Neurology, University of Bern, Inselspital, Berne, Switzerland)

Single transcranial magnetic stimuli were applied over the cortical area of the right frontal eye field (FEF) using an especially designed figure-of-eight shaped twin coil which delivers a focal stimulus. The intensity of the stimulus was adjusted to the individual

motor threshold of the left hand muscles. Eye movements were recorded by the infrared reflection technique. Three different experiments were performed in 11 healthy subjects. (1) Stimulation during different primary gaze position did not evoke any discernible eye movement. (2) Stimulation just prior to visually elicited horizontal saccades did not cause a significant alteration of the latency, velocity, or amplitude of the saccades. (3) Stimulation during an antisaccade task induced a significant prolongation of the latency between the target signal and the saccade, when the stimulus was applied between 50 and 90 msec after the target flashed up. The saccade delay was only obtained when the magnetic FEF stimuli were applied within a vulnerable period, which varied from subject to subject. The latency prolongation was found in all subjects for the antisaccades to the right. In contrast, the antisaccades to the left were prolonged in the female subjects only, whereas in the male subjects they did not alter with stimulation. 4. The origin of the postexcitatory inhibition after transcranial magnetic cortex stimulation. - H. Roick, H.J. von Giesen and R. Benecke (Department of Neurology, Heinrich-Heine University, Diisseldorf)

Transcranial magnetic cortex stimulation (TMS) is widely established in examining the pyramidal tract in man. A muscle action potential (MAP) elicited by TMS at tonic preinnervation is followed by a pause of the electromyographic background activity which could not voluntarily been broken through. We call this silent period 'postexcitatory inhibition' (pI). The mean duration of the pI shows only little difference at homonymous muscles, pI lasts 163+25 msec for the first dorsal interosseus muscle and 70 + 22 msec for the tibialis anterior muscle. There is no dependence on the degree of preinnervation. The duration of the pI increases with stimulation strength. There is no coherence with amplitude or latency of the MAP. Optimal coil position for the pI is nearly the same as for MAP. We think pI is cortically generated because (1) it lasts longer than the silent period after peripheral nerve or spinal cord stimulation, and (2) in patients with cerebral lesions the duration of pI can be found to be increased although the silent period after peripheral nerve stimulation remained unchanged. 5. Pathophysioiogic aspects of postexcitatory inhibition. - H.J. von Giesen, H. Roick and R. Benecke (Department of Neurology, Heinrich-Heine University, Diisseldorf)

Investigations in patients with hemispheric lesions of different localization and etiology favor a cortical genesis of postexcitatory

2P inhibition (pi). pi was determined after transcranial magnetic stimulation of the motor cortex both to the first dorsal interosseus (FDI) and tibialis anterior (TA) muscle and is symmetrical (quotient FDI ri/le 102-+ 12%, TA ri/le 101-+ 14%). 10 patients (motor cortex lesion) showed (n = 5) no answer or a shorter pi (FDI contralateral/ ipsilateral (FDI K / I ) 58.2-+ 19.7%). 21 patients (subclinical cortical lesion) (FDI K / I 154_+34.3%, TA K / I 239.8_+ 174.9%) showed prolongation of pi as did 8 parietal lesions (FDI K / I 148.7-+ 47.8%, TA K/1 193.8-+63.3%), 6 thalamic lesions (FDI K / I 168.5_+41.1%, TA K / I 198.4-+80.7%), 8 premotor lesions (FDI K / I 157.5_+81.3%, TA K / I 179 -+ 67.5%) and 6 temporal lesions (FDI K / I 127.8 -+22.5%, T A K / I 134.2-+21.8%). This favors a cortical genesis of pi, a sensitive parameter of heterogenous hemispheric lesions. 6. Transcranial magnetic stimulation excites the trigeminal nerve distally to the root exit zone. An intraoperative electrophysiological study in man. - U.D. Schmid, A.R. M~ller and J. Schmid (Dept. of Neurological Surgery, University of Pittsburgh, School of Medicine, Presbyterian University Hospital, Pittsburgh, PA 15213, U.S.A.) The site where transcranial magnetic stimulation (magStim) depolarizes the trigeminal nerve was investigated in 5 patients undergoing surgery. Masseter muscle responses were recorded to (1) magStim over the parietal area before, and (2) electrical stimulation (elStim) of the trigeminal (NV) and facial (NVII) nerves near the brain-stem (REZ) after craniotomy. Comparison of responses revealed: (1) The magnetically evoked muscle response was biphasic. (2) Already with low magStim intensity, a late component appeared that could also be evoked by elStim of NVII, but not of NV. This component was attributed to volume conducted muscle activity picked up from NVII coactivation by magStim. (3) At higher magStim intensities, an earlier component emerged that could also be evoked with selective elStim of NV, but not of NVII. This component was judged to correspond to NV activation by magStim. The differences between the latencies of responses to magStim and elStim of NV (AelStim- magStim) was 0.7_+0.5 (+0.04 to + 1.5) msec. When calculating with a supposed NCV of 50 m/sec, magStim activated the NV 3.5_+2.7 (0.2-7.6) cm distally to the REZ. Thus, the excitation site varied between subjects and lay between the porus trigeminalis and the exit of the mandibular nerve from the foramen ovale. 7. Transcranial magnetic stimulation depolarizes the labyrinthine segment of the facial nerve: intraoperative electrophysiological study in man. - U.D. Schmid, A.R. M¢ller and J. Schmid (Dept. of Neurological Surgery, University of Pittsburgh, School of Medicine, Presbyterian University Hospital, Pittsburgh, PA 15213, U.S.A.) The site where transcranial magnetic stimulation (magStim) depolarizes the facial nerve was investigated in 5 patients during surgery in the cerebellopontine angle. The nerve was stimulated (1) magnetically prior to craniotomy, (2) electrically near the brain-stem (elREZ), (3) at the entrance into the facial canal (elPorus), and (4) in the stylomastoid fossa (elStylo). The ranges of latency differences (A) of nasalis responses were 0.6-1.3 msec (AelREZ-magStim); 0.2-0.7 msec (AelPorusmagStim); 0.9-1.6 msec (AelStylo-magStim). Independent of modifications of stimulus parameters, magStim depolarized the facial nerve at a location 10-15 mm distally to the porus. The strength of a magnetic field is high close to a nerve foramen, and excitation to magStim is most likely to occur where the induced electrical field changes rapidly over distance. These characteristics are found at the end of the labyrinthine segment of the facial canal,

SOCIETY PROCEEDINGS where the nerve leaves the low resistance cerebrospinal fluid and enters the high resistance petrous bone. Thus recording muscle responses to transcranial magStim of the facial nerve does not reflect conduction in nerve segments that are located proximal to the facial canal, i.e., approximately 40% of the nerve length between the REZ and the stylomastoid fossa. 8. Motor potentials evoked by single and paired cervical stimulation. - M. Weis, D. Claus and A. Spitzer (Erlangen) Thirty-three healthy subjects were investigated by transcutaneous electrical stimulation at C7 (D180, Digitimer). In 4 subjects double stimulation at C7 was carried out using two D180 stimulators to generate pairs of stimuli with intervals of 2, 5 and 10 msec (intensity 100%). CMAPs were recorded from the tibialis anterior (TA) relaxed or exerting contraction. After cervical stimulation with single stimuli the latency is not affected by muscle contraction while amplitudes increase. When paired stimuli are used contraction of TA shortens the latencies (P < 0.001) and enlarges the amplitudes of CMAPs compared with those recorded at rest. In a relaxed condition most motoneurones respond to the second cervical stimulus, with contraction they respond to the first. With paired cervical stimulation CMAPs are more frequently evoked in relaxed TA than with single stimuli, especially with intervals of 2 and 5 msec. Therefore paired cervical stimulation is believed to be able to produce temporal summation at spinal motoneurones. Paired stimuli are most powerful at an interval of 2 msec similar to the DI wave interval after cortical stimulation. 9. Cortical motor representation areas in healthy subjects and hemiparetic patients. - K.M. Stephan, J. Netz and V. H6mberg (Diisseldorf) New coil designs for magneto-electrical stimulation allow a more focal stimulation of motor cortex and thereby a study of cortical representation areas of muscles in more detail. In this study we used a figure of 8-shaped coil and a flexible cap EEG to study the localisation and size of the areas from which muscle responses could be elicited. Muscle responses were measured with surface EMG recordings. In healthy subjects several proximal and distal muscles of the upper and lower extremities and of the trunk were investigated. In hemiparetic patients 4 muscles of the upper extremities were examined on the affected and non-affected sides. In healthy subjects these motor representation areas are reproducible on different days. Their size is influenced by stimulation intensity, the orientation of the coil and the degree of preinnervation of the muscle. Their proximodistal localisation is similar to the known motor homunculus, and there is no strict symmetry between the right and left hemispheres. In hemiparetic patients cortical motor representation areas of the affected and non-affected sides often show differences in localisation and size. Their size varies partly according to the level of preinnervation of the muscle. However, it is likely that these differences represent changes in plasticity as well. 10. Facilitation of transcranial magnetic cortical stimulation by voluntary preinnervation in hemiparetic patients after ischaemic stroke. - A. Minke, J. Netz and V. Hiimberg (Diisseldorf) Facilitatory effects at voluntary preinnervation of target muscles are a common observation in transcranial magnetic stimulation. They result in lower threshold, shorter latencies and higher amplitudes of the muscular response. One aim of this study was to analyse possible disturbances of these facilitatory effects in patients with ischaemic lesions of the upper motor neurone. Ten patients with hemiparesis of different

G E R M A N E E G SOC1ETY severities following ischaemic stroke were examined regarding wether or not the focal preinnervation of the target muscle (thenar, extensor digitorum, biceps and triceps brachii) of the paretic side resulted in facilitatory effects. The results were compared to those of healthy controls with respect to quality and selectivity of facilitation. It could be shown that marked facilitations are possible even in severely paretic patients. The selectivity of voluntary facilitation was however reduced compared to controls and was reduced in direct proportion to the severity of paresis. 11. Pathophysiological aspects of weakness after stroke. Investigations with transcranial magnetic stimulation. - M. Schubert, K.R. Mills a, S.J. Boniface a, A. Konstanzer, A. Stallkamp and R. Dengler (Bon, and a Oxford, U.K.) Transcranial magnetic stimulation allows to investigate corticospinal functions. In patients with upper motor neurone lesions abnormalities of latencies and amplitudes of evoked c o m p o u n d muscle action potentials can be found. In order to better understand the pathophysiology in these conditions single motor unit (MU) responses in 8 patients with stroke were analysed. The first period of increased firing probability in peri-stimulus time histograms was studied in M U s in the first dorsal interosseous muscle. O n e hundred to five h u n d r e d transcranial magnetic stimuli were applied over the vertex. In healthy subjects each of the 26 M U s showed an excitatory response at 17-3(l msec after the stimulus. In patients normal responses, absence of responses and abnormal increase of latency and duration of responses were detected. In the latter case the firing peak was bi- or trimodal in shape with inter-modal intervals of 4 - 1 8 msec. We conclude that the results are compatible with a conduction block or a dispersion of conduction velocities in corticospinal axons and activation of other descending pathways. 12. Focal stimulation of the unaffected hemisphere during recovery from ischemic stroke. - M. Kneip, A. Ferbert, H. Buchner and U. Milde (Dept. of Neurology, RWTH, Aachen) If one stimulates the motor cortex focally with an 8-shaped coil, one gets responses from contralateral small hand muscles, but not from ipsilateral small hand muscles. It is, however, unknown whether ipsilateral projections are activated during recovery from stroke. We stimulated with an 8-shaped magnetic coil the unaffected motor cortex 6 - 7 cm lateral of Cz in 10 patients with stroke in the chronic state and hemiparesis. Recordings were made from the first dorsal interosseus muscle (FDI) bilaterally. In only 1 patient a small response in the FDI of the paretic side could be elicited after stimulation of the unaffected hemisphere, while stimulation of the affected hemisphere resulted in responses in the paretic muscles. We conclude from these results that during recovery of hemiparesis after stroke ipsilateral projections do not play a dominant role in small hand muscles. As the degree of paresis was comparably mild in our group of patients it remains to be settled whether the same holds true for patients with severe hemiparesis. 13. Prolonged central conduction times in hereditary spastic spinal paralysis. - H. Goossens-Merkt, Th. Emskiitter, K.R. Held a, H.C. Hansen, A. Arlt and K. Kunze (Neurologische Universitfitsklinik, and a Institute fdr Humangenetik, Hamburg Eppendorf) Hallmarks of hereditary spastic spinal paralysis are the signs of central motor dysfunction like exaggerated tendon reflexes, increase of tone in the leg muscles and extensor plantar responses. Additional evidence of central motor pathway involvement by neurophysiological findings was not available before the introduction of magnetic stimulation techniques. We investigated this condition in a family that presented with 3 affected m e m b e r s (2 brothers and one of their daughters). While

3P somatosensory evoked potentials after median nerve stimulation were completely normal, tibial nerve stimulation yielded unconclusive findings with early loss of peripheral responses. Transcortical magnetic stimulation showed borderline central conduction times (cct) for the upper extremity distal muscles (M. opponens pollicis) ranging from 7.9 to 9.2 msec while delayed responses (range 18.9-25.7 msec) were always found for distal leg muscles (anterior tibial muscle). We conclude that magnetic stimulation studies are useful in monitoring the function of long spinal motor tracts in this condition. 14. Central motor conduction time in Wilson's disease. - A. Jasper[, D. Claus, C. Lang and B. Neund6rfer (Neurologische Universifiitsklinik, Erlangen-Niirnberg) The most prominent neurologic manifestations of Wilson's disease are those of extrapyramidal and cerebellar disorders. Pyramidal signs are occasionally noted. To study a possible subclinical involvement of the pyramidal motor system in the disease, central motor conduction time (CMCT) was measured in 11 patients with Wilson's disease (age 20-50 years, mean age 35 years). Recordings from abductor digiti minimi showed normal latencies to cortical stimulation in 21 of the 22 sides examined. Only in one patient we found a slightly prolonged central motor conduction time on one side. To the tibialis anterior abnormal cortical responses were obtained bilaterally in one patient; in 14 of 16 sides examined normal latencies after central and peripheral stimulation could be elicited. The neurophysiological data are compared to the results of clinical and neuroradiological examinations. The two patients with delayed C M C T showed the most severe clinical damage of the motor system. In conclusion, in Wilson's disease cortical magnetic stimulation mostly reveals normal results. Also in severe long-standing disease C M C T only presents minor changes. Accordingly, the pyramidal motor system shows late involvement in Wilson's disease. 15. The influence of repetitive transcranial magnetic stimuli on visual language perception. - D. Claus, S.M. Weis, T. Treig, K.F. Eichhorn and O. Sembach (Erlangen) We investigated whether repetitive magnetic stimulation can be used to determine the language dominant hemisphere. Twenty-five healthy subjects were investigated (22-53 years). H a n d e d n e s s was assessed with the Edinburgh H a n d e d n e s s Inventory (left handed 9, right handed 16). A series of 4-word sentences was then presented in a computer screen in order to ascertain the presentation time (200-350 msec). Thereafter, 4 blocks of 4-word sentences were presented at random (each block consisted of 10 sentences). The subject was asked to read the sentence presented on the computer screen. Simultaneously a train of magnetic stimuli was applied at the parietotemporal scalp using a figure of eight coil (right and left at random, stimulus train 30-50 Hz, 300-500 msec). Magnetic stimulation was tolerated without severe side effects. The rate of error was not associated with magnetic stimulation but with difficulty of sentences. There was no difference found between right and left in discomfort caused by the stimulus. A distinct influence was seen of the magnetic stimulus on language perception. The results depend however on the cooperation of the subject and they are not very striking in some cases. (This work was supported by the W. Sander Foundation.) 16. Temporary suppression of motor activity following transcortical magnetic stimulation. - B. Kukowski (Giittingen) The temporary suppression of motor activity ('silent period'), which follows the early excitatory response, was analysed in 20 healthy volunteers and in 10 patients with previous stroke in the territory of the middle cerebral artery.

4P Magnetic stimulation (Novametrix Magstim 200) was performed at the vertex during sustained contraction of the first dorsal interosseus muscle. Stimulus intensities of 50% above the threshold able to produce an inhibitory effect were used. In the control subjects, the latency of the silent period showed a m e a n value of 48.5 m s e c / 4 8 . 2 msec (right/left side). Duration varied considerably between subjects, with m e a n values of 81.5 m s e c / 8 0 . 9 msec. Yet, interside differences were small. Stimulation of the non-affected hemisphere in the patients produced comparable results for latency (mean 46.7 msec) and duration (mean 93.6 msec). Yet, on stimulation of the affected hemisphere silent period duration was markedly prolonged (mean 145.8 msec), the side-to-side-difference (mean 52.2 msec) exceeding the normal limits significantly. Our H reflex studies suggest an unchanged m o t o n e u r o n e excitability during the silent period. Thus, spinal inhibition does not seem to contribute substantially to the p h e n o m e n o n . Instead, cortical mechanisms have to be considered. 17. Influence of non-invasive magnetic stimulation of the brain on visual perception. - H. Masur, K. Papke, C. Oberwittler and G.G. Brune (Department of Neurology, University of Miinster, Miinster) The influence of non-invasive stimulation of the brain on visual perception was examined in 14 healthy volunteers. Three letters were presented with a tachistoscope for 1 msec (white letters on a black ground). Letters were 5 m m high. T h e distance between the stimuli and the eyes was 50 cm. The visual perception was dependent on the brightness of the surrounding and the contrast on the screen. Magnetic stimulation was performed with an intensity of 1.5 tesla placing the coil over the occipital cortex. The time interval between presentation of the visual stimulus and application of the magnetic stimulus could be freely determined. Visual perception was significantly reduced when a time interval of 60-100 msec was chosen. The method showed a good intraindividual reproducibility. In 3 patients with neuritis of the optic nerve (prolonged VEP) the time interval of reduced perception was delayed and prolonged. This method provides the possibility to examine different perceptual functions. 18. Effects of transcranial magnetic stimulation on short-term memory of epileptic patients. - A. Hufnagel, C. Helmstaedter, E. Diizel, J. Wygrala, T. Sudhop and C.E. Elger (Dept. of Epileptology, University of Bonn, Bonn) T h e effects of transcranial magnetic stimulation on the immediate verbal and visuo-spatial memory span were assessed by computerized psychometric testing during presurgical evaluation of 20 medically intractable epileptic patients. T h e patients had to memorize n u m b e r s (digit-span) or cubes (corsi-block) presented to them on a computer screen. They actively had to reproduce the items in the sequence of the demonstration immediately after the presentation. Synchronous to the appearance of each item a magnetic stimulus was delivered to the vertex or the temporal areas (T4-T6; T3-T5). T h e stimulation intensity was set 20% above the cortical threshold to induce motor evoked potentials at the abductor pollicis brevis. Delays of 0 msec and 200 msec between the presentation of the item and the stimulus were tested. The following results were obtained. During stimulation 8 of the 20 patients had a temporary decrease of memory performance which was higher than 2 S.D. of the base-line evaluation. This diminution of m e m o r y performance was independent of the location of the epileptic focus. However, 7 of the 8 patients had deficits of both memory functions during standardized memory testing. Conclusively, transcranial magnetic stimulation may induce temporary disturbance of short-term memory function in patients with low memory performance.

SOCIETY PROCEEDINGS 19. No effects of transcranial magnetic stimulation on short-term memory of healthy subjects. - E. Diizel, A. Hufnagel, C. Helmstaedter, J. Wygrala, T. Sudhop and C.E. EIger (Dept. of Epileptology, University of Bonn, Bonn) The effects of transcranial magnetic stimulation on the immediate verbal and visuo-spatial memory span were assessed by computerized psychometric testing in 12 healthy volunteers. The subjects had to memorize numbers (digit-span) or cubes (corsi-block) presented to them on a computer screen. They actively bad to reproduce the items in the sequence of the demonstration immediately after the presentation. Synchronous to the appearance of each item a magnetic stimulus was delivered to the vertex or the temporal areas (T4-T6; T3-T5). The stimulation intensity was set 20% above the cortical threshold to induce motor evoked potentials at the abductor pollicis brevis. We tested different delays between the presentation of the item and the stimulus. The following results were obtained. The average m a x i m u m n u m b e r of items memorized during 5 series of base-line evaluations was 7.75 +0.98 digits and 7.38_+ 1.2 cubes. During a total of 24 series of stimulation with different combinations of stimulation sites and latencies the memory performances were either slightly lower or slightly elevated. No statistically significant differences were obtained. Conclusively, no evidence for an affection of the short-term memory of healthy individuals by transcranial magnetic stimulation was found. 20. VEPs during disturbances of consciousness and coma. - H. Eckardt (Erfurt) VEPs offer additional non-invasive possibilities for the clinical and prognostic assessment of coma patients. D u e to difficult registration conditions, stimulation should be made by L E D glasses to eliminate all visual environmental stimuli. T h e relatively sensitive reaction of VEPs to drug influences (e.g., barbiturates) and the higher variability of lightning-evoked potentials as compared with pattern reversal-evoked VEPs also pose problems. A literature survey shows that most different potential modifications have been found in comatose patients: (1) changes in early VEP components; (2) changes in late potential components and afteroscillations; (3) reduction of the total amplitude; (4) VEP rarefaction with phase inversion of the main complex. The aetiology of a narrowed consciousness and the coma stage influence the type of VEP changes. A persistent lack of visually evoked potentials in comatose patients is to be judged as a prognostically unfavourable sign. We are reporting on patients who suffer from reversible and irreversible comas and underwent examinations of the course of visually evoked potentials. 21. The use of the visually evoked P3 as a diagnostic tool in the locked-in syndrome. - H. Emmert and K.A. Fliigel (Neurology and Clin. Neurophysiology, KH Bogenhausen, Munich) Brain-stem lesions can lead to a state of deefferentation known as locked-in syndrome. Unable to speak or move, these patients may wrongly be considered to be comatose and treated inadequately. The diagnosis of this syndrome therefore is of great importance. Laboratory techniques offer little support. Only the EEG, which is fairly normal, is helpful. T h e event-related potential P3 seems to be suited to demonstrate a patient's ability to respond to external stimuli. We chose the visually evoked P3 as the integrity of the acoustic and the somatosensory tract may not in all cases be given. The visual stimulation was performed with light-emitting diode (LED) goggles. The 'oddball paradigm' was used with stimulation of one eye being the frequent and stimulation of the other eye being the rare stimulus. A 'missingstimulus paradigm' in conjunction with L E D goggles had shown to be

GERMAN EEG SOCIETY

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less suited when tested in control subjects. In addition to the 'oddball' normal L E D stimulation of each eye was performed in all patients. In control subjects the LED-evoked P3 was only found in about 70%. In locked-in patients, however, the P3 was seen in 6 out of 7 cases. O n e patient was tested too late; the infarction had increased to the whole brain-stem. 22. Central motor conduction Firsching and J. Vicevic

time in comatose patients.

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R.

Transcranial magnetic evoked potentials were registered in 50 patients in coma of various origin. After demonstration of the F wave the central motor conduction time (CMCT) was computed. After consideration of the patients' heights C M C T was compared with the severity of coma. A correlation of the CMC'T with coma grade was established. The clinical significance of C M C T is considered similar to the somatosensory central conduction time. 23. Reversible blockade of efferent systems and pathologic spontaneous activity on EMG during midazolam/fentanyl induced prolonged coma. - J. Rakicky, J. Ebert, C. Heckerodt-Liithe and U.A. Besinger (Westerstede) In patients with surgical or pulmonary complications a combined midazolam ( D o r m i c u m ® ) / f e n t a n y l anesthesia is sometimes necessary for a prolonged external ventilation. We report on 2 patients with a m i d a z o l a m / f e n t a n y l induced prolonged coma with motor paralysis and respiratory insufficiency. Clinically both patients were unconscious without any reaction to painful stimuli; there were no spontaneous m o v e m e n t s and no respiratory activity. Brain-stem reflexes were absent, the muscles flaccid, the tendon reflexes not to obtain. The Babinski sign was plantar. Tibial and median nerve SSEP and B A E P showed normal responses, only in 1 patient there was no B A E P response except of wave l on the left side. T h e blink reflex showed only ipsilateral R1 responses in 1 patient. There were no M E P responses from cortical, but normal responses after spinal stimulation. The E M G showed marked pathological spontaneous activity in the muscles of the upper and lower limbs. After injection of 1 mg of the benzodiazepine antagonist fiumacenil (Anexate ~) intravenously the coma was immediately brought to an end, the brain-stem reflexes recovered and the cortical M E P were normalized at the same time. The tetraplegia disappeared within a few days together with the pathologic changes in the EMG. Anesthesia with m i d a z o l a m / f e n t a n y l can obviously cause a prolonged coma with motor paralysis and need of respiratory care. 24. Barbiturate induced EEG changes in the diagnosis of primary brain-stem lesions. - S.A. Rath and H.J. Klein (Department of Neurosurgery, University of UIm/Giinzburg, Giinzburg) In 6 patients with primary brain-stem lesions (spontaneous hemorrhages or contusions after head injury), repeated E E G leads with spectral analyses were taken during the course of coma. The likewise in 5 cases performed SSEP leads showed a bilateral pathological finding with marked decrease of amplitude or complete disappearance of the cortical response. In most of the cases predominating alpha frequencies were found, in patients with head injuries a marked part of delta and theta activities shortly after trauma. After barbiturate bolus (thiopentone), a marked stimulation of all frequencies, especially of the slower ones as delta and theta was observed during the first days. In the patients with favorable outcome, this effect was restricted later to the higher frequencies as is known also from healthy subjects, e.g., during induction of anesthesia. In one case with bilateral disappeared cortical response in SSEP and preser-

vation of induction of the faster frequencies after thiopentone, a complete recovery of all cerebral deficits and the reappearance of a normal cortical signal could be seen after more than 1 month of coma. As the thalamus is important in the generation of barbiturate induced fast activities, this pharmacological test seems to reflect the integrity of thalamic structures. 25. Severe anoxic brain damage: outcome, clinical parameters and SEP. - B. Riffel, M. St6hr, B. Sommer-Edlinger and H. Kroiss (Augsburg) Of 126 patients with severe anoxic brain damage (coma longer than 6 h), 101 patients (80%) died. 46 patients died due to brain damage, 55 died due to extracerebral organ failure without regaining consciousness. 25 patients survived, five of them in the vegetative state, five with severe disability and three with moderate disability. Only 5 patients had a good recovery (4% of all patients). Seven patients regained consciousness, but died later on due to the underlaying disease (e.g., cardiac failure). The Glasgow coma score reliably predicts outcome in most of the patients. However, some patients regain consciousness despite a GCS of 3 points. Brain-stem function can also reliably predict outcome, if the function is severely impaired; a normal brain-stem function, however, cannot identify good-outcome patients. Myoclonus points toward a poor prognosis, but not in any case to a fatal outcome. The most reliable indicator of poor outcome is the bilateral absence of the cortical response after median nerve stimulation. Normal SEPs point toward the possibility of regaining consciousness for the comatose patient. 26. Prognostic significance of EEG and evoked potentials in severe anoxic brain damage. - B. Riffel, A. Beltinger, M. St6hr, H. Kroiss and B. Sommer-Edlinger (Augsburg) Certain E E G findings (isoelectric EEG, burst suppression EEG, generalized periodic epileptiform discharges or aperiodic polyspike waves accompanied by myoclonus, recorded more than 24 h after the anoxic event) as well as certain SEP findings (bilateral loss of primary cortical responses N 2 0 / P 2 5 following median nerve stimulation) or B A E P findings (loss of wave V or more waves generated within the brain-stem) reliably predict fatal outcome or - at best survival in persisting vegetative state. 34 patients have been seen, who died due to the cerebral damage caused by severe anoxia, and were assessed by E E G and SEP or BAEP on the same day; at least one of these electrophysiological methods indicated a fatal prognosis. E E G findings identified 76% of patients with fatal outcome, whereas SEP reliably predicted the outcome in 93% of patients who died from the cerebral anoxia. BAEP findings were of less prognostic value. BAEPs indicating a fatal outcome were to be found mainly in final clinical stages with severe impairment of brain-stem function, whereas E E G as well as SEP succeeded in identifying a considerable n u m b e r of fatal cases with comparably favorable clinical findings. 27. EEG response to the administration of benzodiazepines and barbiturates as prognostic criterion in comatose patients. - S.A. Rath and H.J. Klein (Department of Neurosurgery, University of Ulm/Giinzburg, Giinzburg) In 28 patients with severe intracranial lesions (head injuries, spontaneous hemorrhages) and a Glasgow coma score of less than 7, an E E G frequency analysis was performed mostly several times before and after administration of benzodiazepines (midazolam 7.5 mg) and their specific antagonist (flumazenil) and barbiturates

6P (thiopentone 0.2-0.3 g). All the 8 patients who showed a stimulation of higher frequencies (beta) as known from healthy subjects survived. Five out of them were not or only slightly disabled after 6-12 months, only one remained in vegetative state. In 19 other cases, solely a reduction of the electric brain activity could be seen after midazolam bolus. Nine of them died, 9 others remained in coma vigile and one survived severely disabled on long term. In the case of this E E G feature, favorable outcome could never be observed. If no reversion of the midazolam conditioned E E G changes or even synergistic effects occurred after administration of the specific antagonist flumazenil, all patients died or remained in vegetative state. Seven out of the 9 patients who did not show any increase of fast activities after thiopentone bolus died, the two others remained vegetative. 28. Combined motor and somatosensory evoked potentials in coma predict fatal outcome, but not quality of survival: a prospective study. - U.D. Schmid, Z. Ying, K.M. R6sler and C.W. Hess (Departments of Neurosurgery and Neurology, University of Berne, Berne, Switzerland) Central sensory and motor conduction was studied in coma (n = 23) and brain-death (n = 3) using median nerve SEPs and motor evoked potentials (MEPs) recorded from the hypothenar muscle to transcranial magnetic (mgMEP) and electrical (elMEP) stimulation. Comparison of clinical with evoked potential (EP) findings revealed: (1) MEPs but not necessarily SEPs were preserved if the motor pattern was normal. (2) If the motor pattern was abnormal, MEPs could be abolished or present. (3) Facilitation with a painful skin stimulation was a prerequisite to obtain MEPs in 14 instances (9 patients). (4) EPs and coma severity (Glasgow Coma scale, GCS) did not correlate. (5) Only brain-dead patients had all EPs abolished simultaneously and bilaterally. Assessing the outcome of coma 10 months later revealed: (1) Of the 13 cases with fatal outcome, 54% had a GCS of 3, a n d / o r abolished brain-stem or pupillary reflexes, bilaterally abolished SEPs (23%), or elMEPs (38%), or mgMEPs (38%). One or more of the above criteria were found in 85% of cases with fatal outcome ( P < 0.005, Fisher's exact test). (2) Good outcome was predicted by a GCS of ~> 8 in post-traumatic coma, and EPs did not help to predict quality of survival. 29. Electrophysiological, CT and MRT findings in three patients with central pontine myelinolysis. - N. Skiba (Bayreuth) Three patients with typical CT and MRT findings of central pontine myelinolysis were examined in the course of the disease with somatosensory evoked potentials of median nerve (SEP), early acoustic evoked potentials (EAEP), transcranial magnetic stimulation (TMS) and the 'blink reflex' (BR). In spite of severe neurological deficits (tetraparesis up to incomplete 'locked-in syndrome') and vast central hypodense lesions in the pons the electrophysiological findings showed only few abnormalities. In 2 patients the SEPs were absolutely normal, in 1 case there was only a mild cortical amplitude depression bilaterally. With respect to the E A E P there were normal findings in 2 cases, in 1 patient a mild latency delay of wave V bilaterally was evident. The TMS as well as the BR showed only discrete pathological results in 2 cases, the remaining findings were normal. With the unexpected few abnormalities of electrophysiological methods correlated the astonishing favourable course of disease of all 3 patients in spite of persisting marked central pontine defects in imaging methods. Possibly, with the help of electrophysiological investigations there can be made an early prognostic statement just at the beginning of the disease.

SOCIETY P R O C E E D I N G S 30. Trancranial Doppler sonography as a method to assess the effectiveness of osmotherapy. - S.A. Rath, G. Antoniadis and H.-P. Richter (Department of Neurosurgery, University of UIm/ Giinzburg, Giinzburg) To evaluate the therapeutical benefit of osmotic agents in comatose patients with severe cerebral lesions accompanied by brain edema and increased intracranial pressure (ICP), commonly indirect parameters such as intracranial pressure monitoring are used. To assess the influence of osmotherapy on hemodynamics and on transcranial Doppler parameters, an analysis of Doppler spectra was performed before and after therapy in 10 patients. As already known from previous studies, heart rate increased by 14%. High frequencies increased in intensity attesting to a higher percentage of fast moving blood cells. In the same pace, however, turbulence increased as testified by negative frequencies. The mean blood flow velocity in the middle cerebral artery increased by at least 20% up to 140%, in average by 85%. In all cases, the pulsatility index (P.I.) according to Gosling decreased, but this effect was not significant in patients with severe disturbances of blood-brain barrier. In cases with simultaneous ICP monitoring, a clear intraindividual correlation between raised intracranial pressure and pulsatility index was found, whereas no interindividual relation could be seen. 31. Vascular indentations on the brain-stem: a comparison of morphological (MRI), clinical and electrophysiological (SEP, AEP, MEP) data. - H. Masur, G. Reuther, S. Miiller, C. Oberwittler and G.G. Brune (Department of Neurology, University of Miinster, Miinster) In case reports clinical symptoms of the brain-stem (cranial nerve signs or signs of the long ascending or descending tracts) are sometimes referred to contour indentations of the brain-stem by adjacent vessels (vertebral or basilar arteria). It was the purpose of this study to record and to assess the significance of contour indentations of the brain-stem by adjacent vessels. 1000 consecutive MR exams were analysed for infratentorial neurovascular relationship. The total incidence of neurovascular contour alterations was 8.3%, increasing with age. All patients without cerebrovascular disease or other neurological disorders were examined for functional impairment of cranial nerves and long ascending or descending tracts. Additionally, evoked potentials (SEP, AEP, MEP) were evaluated in all these patients. No correlation between morphological and clinical or electrophysiological data was found. Indentation of the brain-stem by adjacent vessels is not too rare especially in the elderly. But only very severe findings may occasionally be of clinical importance. 32. Neurophysioiogical data and therapeutic problems in 15 children with cortical malformations. - H. Bode and R. Bubl (Basel, Switzerland) Modern imaging techniques have identified disorders of neuronal migration as important causes of neurological anomalies and epilepsy in infancy. Fifteen infants with cortical malformations are presented: lissencephaly (4), pachygyria (6), gray matter heterotopia (2), agenesis of corpus callosum (4), diffuse polymicrogyria (2), and schizencephaly (1) were diagnosed alone or in combination. Underlying diseases were Miller-Dieker, Walker-Warburg, Aicardi, neurocutaneous syndromes, congenital cytomegalovirus infection, midline malformations, and isolated cerebral malformations. Eleven of 15 children suffered from epilepsy. Multiple E E G anomalies were observed during the years. In lissencephaly abnormally high voltage regular rhythms in the alpha and beta range, hypsarrhythmia, irregular epileptic activity,

GERMAN EEG SOCIETY and frequently epileptic status occurred. Medication had little influence both on the EEG and the epilepsy. In pachygyria regular theta and delta rhythms, hypsarrhythmia, and irregular epileptic activity in the area of the malformation were observed. EEG and epilepsy were improved moderately by medication. In gray matter heterotopia focal epileptic discharges were found. Agenesis of corpus callosum with diffuse polymicrogyria showed discontinuous hypsarrhythmia, while the EEG was normal or unspecific in isolated agenesis of corpus callosum. Evoked potentials (visual, auditory) were pathological in some cases but less informative than the EEG. 33. Some genetic aspects of symptomatic generalized tonic-clonic seizures: waking and sleep EEGs in siblings. - R. Degen, H.E. Degen and K. Ahlemeyer (Epilepsy Center Bethel, Bielefeld) Waking and sleep EEGs were recorded in 83 siblings of 54 patients suffering from symptomatic generalized tonic-clonic seizures. Epileptic activity (e.a.) was recorded in at least one sibling of 27 (50%) of the 54 patients. If the 83 siblings are taken as a basis, e.a. was found in 34 siblings (41%). Generalized spike wave discharges were seen in 32 cases, a lateral emphasis being present in two. Two siblings showed benign sharp wave foci in the right centro-temporal and right parietal area. One epileptic discharge (e.d.) was recorded every 299.3 sec. E.d. were exclusively seen in waking in 2 siblings (5.4%), in waking as well as sleep in 20.5% and only in sleep in 18.1%. Most e.a. was found in waking during hyperventilation (18.7%), during sleep in stage C (81.24%). The highest activation rates were seen in the age range between 3 and 5 (83.3%) and 10 and 15 years (51.6%), followed by that between 5 and 10 years (47.4%). E.a. was found in 15 of 50 male siblings (30%), but in 18 of 33 female siblings (54.5%). The results demonstrate that genetics also play a considerable role in symptomatic generalized tonic-clonic seizures. 34. Sleep analysis in Parkinson's disease. - J. Haan and B. Lackmann (Department of Neurology, Krankenhaus Maria-Hilf, Moenchengladbach ) Investigations were made on 20 parkinsonian patients (42-81 years of age), 9 male (42-72 years of age), 11 female (49-82 years of age). All patients were under medication (5 times L-DOPA monotherapy, 15 times L-DOPA in combination with merely bromocriptine, some with additional deprenyl a n d / o r amantadine). EEG recordings were performed with an 8-channel cassette recorder over a period of 12 h (8 p.m. to 8 a.m.). The sleep analysis was done automatically using the Oxford sleep stager. Our results - regarding to those of healthy probands - are the following: (1) loss of sleep stage profile; (2) loss of sleep stage 4 (deep sleep stage) in almost all patients; (3) in 50% less than 60 min duration of sleep stage 3; (4) lowering of REM sleep (in the mean 1-2 REM sleep periods). 35. Retarded development of EEG frequencies in children with a higher load of biological a n d / o r psychosocial risks. - R. Cammann and G. Cammann (Rostock) EEGs were recorded in 111 children at 6, 10, and 14 years of age. All children were classified at birth as either risk children or as controls. The term 'biological risk' was used to denote prenatal and perinatal risks, and the term 'psychosocial risk' denotes detrimental milieus. A strong increase in the 10, 11, 12, and 13 c / s e c waves could be observed up to the age of 10 years. The formation of two subsamples, one consisting of subjects with a high index of biological risk and the other without a high index of biological risk, revealed that the low-index subsample exhibited a higher increase of fast alpha activity from 6 to 10 years. This effect was almost the same after reclassifying the sample into two subsamples, one having a high

7P index and the other a low index of psychosocial risk. Interestingly, this tendency was not maintained for the ages of 10-14 years. Our results imply that the sensitivity of certain brain structures for continuous psychosocial risks including negative environmental influences and the subsequent effects of very early biological risks clearly increases from the age range of 6-10 years. 36. The relation of periodic movements in sleep to sleep stages. Th. Pollmficher (Munich) To explore characteristics of periodic movements in sleep (PMS) in relation to sleep stages we analyzed the sleep recordings including the EMG of both anterior tibialis muscles of 13 unmedicated patients, who suffered from PMS syndrome. Eleven of them, in addition, suffered from restless legs syndrome. Patients were off medication for at least 1 week before recording. Scoring of PMS was done according to standard criteria. Out of 2917 periodic movements 30.7% occurred during wakefulness, 15.5 during stage 1, 46.3% during stage 2, 3.3% during slow wave sleep (SWS) and 4.2% during REM sleep. Analysis of variance (P < 0.01) showed that duration did not differ between stage 2, SWS and REM sleep. It was significantly longer, however, during stage 1 and even longer when awake. Distance between movements also did not differ between stage 2, SWS and REM sleep, whereas it was significantly shorter during stage 1 and even shorter when awake. By chi-square tests (P < 0.01), it could be shown that the relative amount of movement arousals was highest for stage 1 and lowest during SWS. It did not differ between stage 2 and REM sleep. The results show that a substantial number of leg movements fulfilling accepted criteria for periodic movements during sleep occur when patients are awake. 37. REM sleep behavioral disorder. Case report of a 58-year-old patient. - D. Hasse, J. Wilde-Frenz, W. Christe and D. Schmidt (Department of Neurology, Free University of Berlin, Kiinikum Rudolf Virchow, Berlin) Sleep is characterized by cyclic recurrence of non-REM and REM sleep (REM = rapid eye movement). Deepening of non-REM sleep is associated with increasing synchronization of EEG, while REM sleep is characterized by desynchronization of EEG and an inhibition of tonic motor activity, interrupted by short phasic events such as rapid eye movements and muscle twitches. REM sleep behavioral disorders (RBD) are characterized by a disinhibition of REM sleep atonia resulting in complex motor behavior such as sleeptalking, yelling, laughing, gesturing, punching, kicking, and even leaping out of bed. RBD should be differentiated from non-REM sleep phenomena such as sleepwalking, night or sleep terrors as well as from nocturnal seizures, sleep apnea, and periodic movements in sleep. Simultaneous video-EEG registration and polysomnographic data of a 58-year-old man who had suffered from increasing sleep problems for 10 years, leading to severe consequences in his social life will be presented. Our data confirm the diagnosis of a REM sleep behavioral disorder. 38. Changes of EEG spectral parameters under the influence of oxcarbazepine. - W. Meier, R. Besser and G. Kr~imer (Dept. of Neurology, University Clinic, Mainz) Anticonvulsants have different influence on the EEG resting activity. The present study investigates the drug induced EEG changes under oxcarbazepine (OCB), an anticonvulsant related to carbamazepine (CBZ) but without the epoxide metabolite. Six healthy male subjects (mean age 26 years) were given 450 mg OCB over 1 week. The EEG was recorded (bandpass 0.3 sec to 30 Hz, 16 channels, 10/20 system, sampling rate 128 Hz) before medi-

8P cation and after 1 week of medication. Reaction times after acoustical stimuli were measured as vigilance control. In each session, 40 epochs of 4 sec duration were analyzed by m e a n s of the Fourier transformation. T h e m e a n spectra of the 6 subjects revealed a stable E E G activity throughout the analysis time of 4 min before and u n d e r medication. A marked difference was found between the spectra under the two conditions, especially in the occipital leads (O1, O2), where the power in the alpha band (8-12.75 Hz) decreased by 5%, whereas the delta and theta power increased by a comparable amount. Furthermore, the center frequency in the range of 4-12.75 Hz was shifted from 10.5 Hz to 9.5 Hz. The results showed no relevant hemisphere differences. In general, the O C B induced E E G changes were comparable to those described for C B Z medication. 39. EEG in cerebral infarction ofA. cerebri posterior. - B. Griewing, A. Liitcke and L. Mertins (Neurologische Univ.-Klinik mit Poliklinik, M a r b u r g / L ) Using frequent E E G s we examined 45 patients with a clinically obvious cerebral infarction in the supply area of the A. cerebri posterior. The according CT demonstrated a posterior lesion with additional pathological findings in the thalamus region or not. The E E G showed not only pathological findings in the posterior region of the infarction, but also bilateral dysfunction in the temporal region with dominance on the side of the infarction. Aim of the study is to show the pathological changes in E E G and their correlation to CT findings. 40. Neuropathological findings in Creutzfeld-Jacob disease with lateralised EEG foci. - A. Heinz, N. Heye, M.L. Hansen, T. Biittner, W. Kuhn, L. Gerhard a and H. Przuntek (Neurologische Universitfitsldinik St. Josef-Hospital, Bochum, and a Universitfitsklinikum, Essen) We report a correlation of neuropathological and neurophysiological findings in 2 patients with lateralised E E G findings in initial stages of Creutzfeld-Jacob disease (CJD). Additionally we performed serial cranial M R T and CT scans in 1 patient. O n e 57-year-old m a n suffered from acute memory disorders, later followed by predominantly right-sided myocloni. The patient developed a progressive disturbance of consciousness and died. The initial E E G showed a left temporo-parietal theta-delta focus. Neuropathological examination revealed the typical findings of CJD with vacuolisation predominantly in the temporal lobe, the insula and the thalamus of the left hemisphere. An 80-year-old woman suffered from an acute hallucinatoryparanoid psychosis. After 2 weeks she developed a progressive disturbance of consciousness and right-sided myocloni. In the initial E E G we observed a slowing of background activity and a left temporal delta focus. Cranial M R T and CT scans showed a general cerebral atrophy, predominantly in the left temporal lobe, corresponding to the E E G findings. Additionally, the E E G showed focal, right temporo-occipital triphasic sharp waves. The topography of the neuropathological findings corresponds with the E E G findings. We suggest that lateralized E E G findings in the initial stages of CJD are related to focal cortical lesions. 41. Topographical brain mapping in Parkinson's disease (PD). - M. Krause, R. Massetani, R. Calabrese and L. Murri (Clinical Neurophysiology, Department of Neurology, University of Pisa, Pisa, Italy) Electrical brain activity of 34 patients with idiopathic Parkinson disease (PD) was m e a s u r e d by topographical EEG. We aimed to evaluate alterations in E E G features comparing our patients to an

SOCIETY PROCEEDINGS age and sex matched normal group (N = 38), and to correlate our findings with neuropsychological ratings. Compared to normals, demented PD patients (N = 15) showed a significant increase of power in the delta and theta frequency band, mainly located over the right posterior quadrant of the brain. Non-demented PD patients (N = 19) showed a significant increase of power only in the theta band when compared to normals. D e m e n t e d PD patients differed significantly from non-demented patients in delta and theta activity, but showed no significant differences in alpha and beta activity. Further, there were significant correlations between increase of mean power in the delta and theta band and decrease of the Folstein score. In addition there were significant correlations between the centroid locations of delta and theta power maps and the Folstein score. In both bands, the more the centroid was located to the right, the lower was the score. 42. Changes in visuomotor information processing in HIV positives and AIDS patients. - M.-L. Hansen, H. Henkes a, G. Scholz, K. Terstegge, St. Kubicki et al. (Abt. f. Klin. Neurophysiologie and a Radiologische Klinik, FU Berlin, Berlin) In order to investigate the development of motor disturbances in HIV infected we applied computer-aided videotracking. The videotracking system indirectly seizes subsystems of information processing: visual and motor information processing and visuomotor coordination. These are measured by a global variable: the deviation between the course of a given stimulus at the system's monitor and the course of a second stimulus that has to be manipulated by the subject in order to superimpose the second on the first stimulus. E E G was registered before and during the test to see if changes in electrocortical activity could be detected as to changes caused by the disease and by the task. Eight HIV-positive asymptomatic volunteers and 8 AIDS patients with cerebral manifestation of the disease participated in the pilot study. Two groups of 8 normals each served as controls. Analysis of the visuomotor performance revealed increasing impairment of fine adjustment to subtle changes of the stimulus course in HIV positive and AIDS patients. Power spectrum analysis of the E E G data indicated that the diminished performance accompanied by an increased spectral power across the entire frequency range measured before and during the test, could be an expression of an enhanced synchronization in cortical neuronal networks resulting from HIV infection. 43. Quantitative EEG analysis in hyperactive children. - M. Menzel and G.-E. Trott (Wiirzburg) Genetic, immunologic, neurochemical and toxicologic aspects are discussed in the etiology of this frequent child psychiatric disease. Evoked potentials and E E G examinations are abnormal in up to 40%. New brain imaging techniques (rCBF, SPECT, PET) showed a frontal cerebral dysfunction. We examined whether there were similar Q - E E G changes. We examined 12 hyperactive children (ICD 314; mean age 9.7 years, S.D. 2.2) and 12 controls (mean age 10.6, S.D. 1.5). E E G was recorded for 20 rain with closed eyes with a 17-channel system, the electrodes were placed according to the 1 0 / 2 0 system. Spectral analysis by common F F T of all 4 sec epochs free of artifacts. Imaging of absolute and relative power of 6 frequency bands, non-parametric statistics (two-tailed Wilcoxon test). Neuropsychological tests (d2, Hawik-R, Conners-Skala). Hyperactives showed an increase in absolute and relative delta activity in frontal and parietal areas. Two subgroups could be differentiated among the hyperactives. The first group showed significant differences in all frequency bands in comparison to the controls. The other showed no significant differences in any frequency band. The severity of the E E G changes correlated with the neuropsychological findings.

GERMAN EEG SOCIETY

44. Relationship between electrical and mechanical activity of single motor units in neurogenic and myopathic lesions. - Th. Vogt and W.A. Nix (Department of Neurology, University Hospital, Mainz) A group of patients with neurogenic disorders (anterior horn cell diseases and peripheral nerve lesions) were examined using the m a c r o - E M G technique combined with spike triggered averaging of single motor unit force. Normal values established with this method demonstrate a close relationship between twitch force and size of m a c r o - E M G potential. In peripheral nerve lesions, twitch force and potential size are increased by reinnervation and the relationship with the electrical macro-signal remains undisturbed. Anterior horn cell diseases however show a dissociation of muscle force and electrical activity. A disturbed correlation of muscle twitch and motor unit action potential was also seen in a few patients with myopathic lesions.

45. Analysis of fatigue in mitochondrial myopathies. - K. Wohlfarth, A. Konstanzer, M. Schubert, S. Zierz and R. Dengler (Bonn) In mitochondrial myopathies a frequent complaint of patients is weakness and fast fatigability of muscles. We studied 20 patients with histologically and biochemically proven diagnosis by applying a fatigue test. Pre- and posttetanic c o m p o u n d muscle action potentials (CMAPs) and twitch contractions (TCs) following supramaximal stimulation of the ulnar nerve were assessed in the adductor pollicis muscle before and after the test. C M A P and T C amplitude and TC half-relaxation times were measured. The test consisted of 20 min intermittent isometric muscle contraction. In 15 controls and 8 patients pretetanic C M A P amplitudes were reduced by 20% and TCs by 30% maximum. T e n patients showed reduced TCs by 3 0 - 7 0 % and normal CMAPs. In 2 patients there was a pronounced reduction of both C M A P and T C amplitudes by more than 40%. In most patients increased half-relaxation times were found. The following conclusions are possible. A selective decrease of TCs could be caused by a metabolic dysfunction of muscle cells. Prolonged half-relaxation times can be explained similarly. The combined TC and C M A P reduction may be due to an additional neuro-muscular component.

46. Muscular contraction in myotonic dystrophy. - U. Dillmann, G. Kriimer, W.A. Nix and H.C. Hopf (Department of Neurology, University Clinics, Mainz) We examined isometric twitches of the adductor pollicis muscle after stimulation of the ulnar nerve in 27 healthy subjects and 12 patients with myotonic dystrophy. W e used single and double pulse stimulation with intervals of 0.4-180 msec. In normal controls the maximal twitch force showed a more than linear summation with a m a x i m u m with short intervals. In myotonic dystrophy the degree of the more than linear s u m m a t i o n was much higher than in the control group. T h e maximal potentiation was reached with shorter stimulus intervals. In addition the refractory period of the muscle was significantly shorter than in controls. With short stimulus intervals the contraction velocity of the second twitch was slower than that of the single twitch in the control group. This so-called early depression was absent in patients. Our findings confirmed the experimental findings and may be attributed to altered Ca kinetics in myotonic dystrophy.

47. How many motor units are necessary to diagnose a neuropathic or myopathic process? - J. Strempel, H. Feistner, T.F. Miinte and H.-J. Heinze (Neurologische Klinik mit Klinischer Neurophysiologie, Medizinische Hochschule, Hannover) Buchthal d e m a n d e d to record several M U A P s from at least 20 M U s to assess a muscle measuring duration and to a lesser extent amplitude and phase count. Fulfilling Buchthal's requirement is

9P difficult in clinical routine, because it is very time consuming and patients might lack the ability to cooperate. E M G diagnosis therefore often has a qualitative instead of a quantitative character. Modern E M G machines and computerized E M G analysis justify a new discussion on the above question. With a computerized E M G analysis system developed by us for clinical routine usage we determined normal values under standardized recording conditions for a variety of M U A P parameters of different muscles. In a group of 60 healthy persons we looked at the n u m b e r of M U s with abnormal M U A P parameters. This allows to state a threshold of abnormal M U s to be observed in neuropathic and myopathic muscles. For all muscles studied we could show that they can be judged as pathologic if more than 2 out of 7 M U s have abnormal M U A P parameters.

48. Does automatic interference pattern analysis replace quantitative single motor unit potential evaluation in everyday EMG? A.C. Nirkko, F.X. GIocker, K.M. R6sler and C.W. Hess (NeuroIogische Universit~itsldinik, Inselspital, Bern, Switzerland) U p to date, quantitative single motor unit potential analysis (quantitative E M G ) has been considered the most sensitive electrophysiological method to assess chronic neuromuscular dysfunction. Modern E M G equipment now enables quantitative interference pattern analysis according to Willison. We have so far examined a total of 18 muscles on 11 patients with both methods simultaneously, using a Viking II system (Nicolet). Mean potential duration deviation from normal was compared to the results of Willison analysis evaluated according to St~lberg. In 13 muscles agreement of results was found (5 normal, 6 neurogenic, 2 myopathic). In 4 of the other 5 muscles, conventional evaluation yielded normal results while interference pattern analysis was abnormal (1 neurogenic and 3 myopathic). In ! case interference pattern analysis was normal and m e a n potential duration was neurogenic. In no case, the two methods yielded contradictory results. Interference pattern analysis is simple, fast and reproducible, since it does not depend much on the patient's cooperation and is independent of the subjective assessment of the examiner. Our preliminary results indicate that this method is a valuable addition to quantitative E M G and sometimes seems to be even more sensitive.

49. Quantitative analysis of the interference pattern in myogenic and neurogenic lesions. - H. Feistner, B. Frank, T.F. Miinte, J. Strempel and H.J. Heinze (Neuroiogische Klinik mit Klinischer Neurophysiologie, Med. Hochschule, Hannover) Methods of interference pattern analysis such as the Willison method have nowadays been integrated into commercially available E M G machines. Besides the t u r n s / s e c this method provides the m e a n amplitude of the recorded activity pattern. The t u r n s / s e c can be taken as correlating with the degree of polyphasia while the m e a n amplitude can be used as a rough estimate for the differentiation of myogenic and neurogenic lesions. Since it does not provide any information on the distribution of amplitudes its diagnostic value is limited. Therefore we developed and 'extended computerized Willison analysis' that permits the determination of additional statistical parameters. From the distributions of the amplitudes and inter-peak latencies this method allows the calculation of the median of these parameters. To clinically validate this method, patients with myopathic as well as lower motor neuron disease were examined while exerting a defined force. The various parameters of the extended Willison analysis of the patients were compared to those of normal controls. It was found that the median of the amplitude distribution, its 10th and 90th percentiles and the median of the inter-peak latencies were more sensitive in the detection of lesions than the classical parameters.

10P 50. Computer assisted analysis of the surface EMG during bicycle ergometry in neuromuscular disease. - U. Mielke, J. Walle and K. Schimrigk (Universifiitsnervenklinik, Neurologie, H o m b u r g / Saar)

Surface EMG of bicycling is an appropriate method to describe the disturbances of motion in neuromuscular disease. It may reveal alterations of recruitment as well as duration and displacement of the activity related EMG intervals. The overall EMG activity related to certain periods of a movement is calculated by integration of the rectified signals, while the position of the EMG peaks and the frequency of the signals are not exactly determined. Therefore we chose an algorithm for the registration of amplitudes and intervals of the non-rectified EMG. The primary signal is recorded from 8 channels and digitized by a fast 8 bit AD converter. Signals are recorded from 8 channels over a period of 6 sec with a frequency of 14 kHz. Data processing is performed by a 6800/8 Motorola CPU. An average amplitude pattern is calculated from the mean values of 6 activity cycles at constant work load and cycling velocity. Frequencies are determined by turns analysis. Computer assisted analysis of amplitudes and turns seems to be reliable in detecting deviations of the movement pattern in neuromuscular disease. 51. Lambert-Eaton syndrome. High frequency stimulation versus test with single shocks. - R. Dengler (Department of Neurology, University of Bonn, Bonn)

The Lambert-Eaton syndrome is a presynaptic disorder of the neuromuscular junction. Supramaximal nerve stimulation typically evokes small muscle compound potentials which increase, at least, by a factor of two with high frequency stimulation (20 Hz, 5 sec). Alternatively, supramaximal shocks before and after maximal muscle contraction can be used. The diagnostic reliability of the latter approach, however, is not clear. We could recently compare the two tests in 3 patients. One patient could not tolerate high frequency stimulation but revealed a 2.7-fold amplitude increase in the abductor V muscle after contraction. The other two patients showed a more than 3-fold increase of the potential amplitude with both tests in the ext. digitorum brevis muscle and with single shocks in the abd. digiti V muscle. If the test with single shocks does not yield a relevant potential increase, the application of high frequency stimulation appears not very promising and may be restricted to cases with strongly suspected diagnosis. 52. Results of the derivation of cortical somatosensory and early acoustical evoked potentials in children. - G. Mattigk and K.-H. Daute (Universit~its-Kinderklinik, Jena)

The special diagnostic relevance of cortical somatosensory and early acoustical evoked potentials as a sage, non-invasive examination method in pediatric neurology is given by the fact that they cannot, in principle, be influenced by sleep or by drugs affecting the central nervous system. These evoked potentials were investigated for 35 children between the ages of 6 and 17, for whom there were no anamnestic or clinical indications of neurological or otological diseases. The latencies of the P15 and N20 of the N. medianus as well as those of the N30 and P40 of the N. tibialis show significant dependencies on the height of the children. Influence of gender could be demonstrated merely for the latency of the N30 of the N. tibialis in the form of longer latencies in boys than in girls which were independent of b~'dy size. The small standard deviations of the latencies as well as the narrow standard limits of the amplitudes of the early acoustical evoked potentials too, show the high degree of intra- and interindividual stability of these evoked potentials from infancy onwards.

SOCIETY PROCEEDINGS 53. Evoked potentials in brain tumors during childhood. - U. Neirich, G. Jacobi and J. Seeger a (Frankfurt, and a Wiesbaden)

We registered evoked potentials in 81 children treated for brain tumors. At time of diagnosis there were 2 newborns, 3 infants, 20 children, 43 school-aged children and 10 young adults. We saw 14 medulloblastomas, 16 cerebellar tumors, 10 brain-stem tumors, 24 suprasellar tumors, 3 tumors of the thalamus, 3 pinealis tumors, 7 tumors of the cerebral hemispheres, 1 meningosarcoma, 2 central tumors in neurofibromatosis. At the time of diagnosis we registered auditory evoked brain-stem potentials in 56 children, early somatosensory evoked potentials in 37 children, visual evoked potentials in 49 patients. During the follow-up period we controlled AEP in 52 patients, SEP in 41 patients and VEP in 45 patients. The AEP showed pathological findings as interpeak latency delay, prepontine and pontine, and deformed configuration of different waves. In 24 cases the AEP were normal. Alterations of SEP were seen in 34 cases, normal findings in 26 cases. We saw hemisphere differences in cervico-cortical latencies, in the configuration of potentials and in the magnitude of amplitudes with either diminished or giant cortical potentials. VEPs were normal in 38 cases, showed mostly slight abnormalities in 23 patients with differences in amplitudes, delay of latency and abnormal potential configuration. 54. Pathologically increased early VEP components in children with migration disorders of CNS and with neuronal ceroid lipofuscinosis. - J. Kohler and F. Hanefeld (G6ttingen)

Visual evoked potentials (VEP) are an important tool in the diagnosis of CNS inflammatory and degenerative diseases like encephalomyelitis disseminata and leukodystrophies. In these disorders pathological changes of VEP with delayed latencies and depressed amplitudes are found. In addition, pathologically increased amplitudes within the regular time frame (main positivity at 100-120 msec) are described for disorders with increased cerebral excitability like myoclonus epilepsies and MERRF syndrome. However, pathological elevated early waves of the cortical VEP, exceeding 15 ~V approximately 55 msec after stimulation, are rather uncommon. These high voltage early components are found in children with neuronal ceroid lipofuscinosis followed by reduced or missing late VEP components - a pattern highly significant for this disorder. On the other hand children with lissencephaly demonstrate high voltage early components, too, followed by late components with high amplitude and delayed latency. This pattern was recorded in 6 out of 14 patients, in two of them repeatedly without age dependent changes. This might be explained by an abnormal cell density in the fourth cortex layer due to incomplete migration to higher layers. 55. Multimodal evoked potentials used in the documentation of peroxisomal neurometabolic diseases. - J. Kohler, C. Korenke and F. Hanefeld (G6ttingen)

Peroxisomal disorders are characterized by a metabolic deficiency in degrading very long chain fatty acids and are transmitted by an autosomal recessive or X-chromosomal inheritance. The sex-linked disease shows a widespread age distribution at onset and diverse neurologic symptoms like cerebral movement disorders, spinal tract lesions, polyneuropathy, and neuropsychologic alterations. Elevated very long chain fatty acids (VLCFA) in plasma are a significant diagnostic indicator. Multimodal evoked potentials can demonstrate the site and progression of lesions at or even before the onset of clinical symptoms. Visual and auditory evoked potentials (VEP, AEP) reveal abnormal latencies before any loss of perceptual functions.

GERMAN EEG SOCIETY Three of 11 VLCFA patients remained free of clinical symptoms. Their metabolic disorder was discovered because of affected siblings. Seven had abnormal VEP and 5 abnormal AEP including 1 asymptomatic child in each group. Somatosensory evoked potentials (SSEP) are more sensitive than the peripheral neurography as nerve conduction velocity is slowed late in the clinical course. Just 4 patients showed reduced NCV, none of them was free of symptoms. In contrast the SSEPs were delayed in all but 1 patient, an asymptomatic child. 56. Prognostic value of ABR in nearly drowned children. - G. v. Czettritz and H.M. Weinmann

Between 1988 and 1991 19 nearly drowned children (1.7-10.5 years) were delivered to the Intensive Care Unit (Kinderklinik Technische Universit~it Miinchen). Seven patients died, 4 survived with neurological sequelae of different grades (including apallic syndromes). Eight had no detectable abnormalities. The registration of auditory brain-stem responses proved to be a reliable prognostic tool especially in the acute phase during which EEG and neurological assessment is unreliable due to necessary sedation and relaxation. ABRs are also of great value in ascertaining brain death. In 5 of the 7 children who died ABRs were initially present, expiring during the following days. One child showed no ABR at admission, in another ABRs were severely alterated; the latter died due to acute cardiac failure. In the 4 children with neurologial deficits ABRs were either unaltered or only slightly disturbed. All children without neurological deficits exhibited normal ABRs in the follow-up examination. No child with initially lacking ABRs survived. 57. Visual evoked activity: retinal and cortical processing in patients with visual field defects. - W. Skrandies a and K.P. Leipert b (a MPI fiir Physiol. und Klin. Forschung, Bad Nauheim, and Physiologisches Institut, Justus-Liebig-Universit/it, Giessen, and b Univ.-Augenklinik, TU Miinchen, Munich)

Recordings of retinal and cortical potentials permit to localize steps of information processing in the afferent visual pathway. Alterations of components of the cortical VEP may be caused by physiological or pathological changes in the retina. Thus, the recording of luminance and pattern ERGs helps to arrive at conclusions about the localization of defects (see also Skrandies, Z. EEG EMG, 1991). We examined more than 20 patients with visual field defects where we correlated the electrophysiological activity of the photoreceptor-pigment epithelium complex (EOG), distal (scotopic and photopic luminance ERG) and proximal structures of the retina (pattern ERG) and the cortical VEP with clinical data (perimetry, neurological and ophthalmological examinations, computer tomography, neurosurgery data). Marked differences in electrical activity were obtained with retinal and central lesions: long-standing lesions of the optic nerve and optic chiasm were followed by changes in retinal activity presumably caused by retrograde degeneration. On the other hand, adult patients with cortical lesions displayed normal retinal activity. In addition, the consequences of therapeutic intervention could be documented by ERG and VEP recordings. 58. Visual evoked potentials in the diagnosis of uveitis. - W. T6njes, U. Mielke, M. Hermes, G. Holzer and B. Bastian a (Universitfitsnervenklinik, Neurologie, and a Universitiitsaugenklinik, Homburg/Saar)

Inflammatory diseases of the uveal tract may be accompanied by inflammatory reactions of the brain or even may be a symptom of a cerebral disease. We examined whether visual evoked potentials can show a cerebral involvement in uveitis. Fourteen patients with uveitis

liP (12 male, 4 female, aged 19-55 years) underwent the following examinations: VEP, MRI, and lumbar puncture. In four patients with normal VEP, neither CSF nor MRI revealed pathological changes. Two patients had only decreased amplitudes of VEP, one of them showed inflammatory CSF changes. In 3 cases VEP could not be evoked in one eye. In one of these patients MRI was suspicious of white matter lesions. Five patients had prolonged latency of VEP. Three of them had inflammatory changes in CSF, one of them white matter lesions. In 1 case CSF and MRI were pathologic. Visual evoked potentials seem to have a high sensitivity in showing cerebral lesions in uveitis. 59. Use of visual evoked potentials in the follow up of pseudotumor cerebri. - D. Timmann, A. Delcker and P.M. Faustmann (Essen)

Normal visual evoked potentials (VEP) have been described in pseudotumor (PC). In most cases patients without reduced visual acuity have been tested (Rizzo et al., Acta Neurol. Belg., 1984, 84: 57-63; Soerensen et al., Arch. Neurol., 1985, 42: 150-168; Verplanck et al., Neurology, 1988, 38: 1789-1792). We recorded VEP from 2 patients with severe loss of vision due to PC, 1 patient with unusual cranial nerve involvement. Case 1: 24-year-old, overweighted female presenting with headache, blurred vision (OD 6/120, OS 6/20), bilateral papilledema. CCT, MRI, arteriography, CSF were normal, CSF opening pressure 50 mm Hg, VEP (P100) latencies: right 148 msec, left 128 msec; after repeated lumbar punctures: right 115 msec, left 108 msec, visual acuity bilateral 6/6. Case 2: 17-year-old, overweighted female presenting with headache, vomiting, blurred vision (reduced to finger counting), bilateral papilledema, Vlth nerve palsy left, facial palsy (left), trigeminal affection (sensory/left, motor/right), hypoglossal palsy (right), paresthesia of the right hand. CCT, MRI, arteriography, CSF were normal. CSF opening pressure 60 mm Hg, VEP (flashlight) latencies: right 176 msec, left 166 msec; after repeated lumbar punctures, treatment with acetazolamide and cortisone: right 150 msec, left 140 msec, visual acuity OD 6/20, OL 6/12. The VEP latencies were clearly delayed (normal range + 3 S.D.: 111 msec). They changed corresponding to the clinical course: normalized in case 1, decreased in case 2. 60. VEP mapping in the course of a patient with multiple intracranial dural fistulae. - H.C. Hansen, St. Zschocke, H.J. Freitag, H. Goossens-Merkt, A. Arlt and K. Kunze (Neurological Univ. Clinic, Hamburg-Eppendorf)

A patient with pulsating tinnitus had multiple intracranial dural fistulae that were identified and embolized using a micro-catheter. There were small subdural hemorrhages in the vicinity of the parieto-occipital fistulae, more on the left side. Neurological examination showed no abnormal findings. Routine EEG disclosed only minimal left low amplitude parieto-occipital theta activity. Mapping of pattern evoked visual responses (derivation against linked earlobes) showed initially a clear hemisphere asymmetry with later and smaller responses over the left side (125 vs. 118 msec) indicating involvement of the retrochiasmatal projections. After embolization of the fistulae the patient was free of tinnitus and had a symmetrical evoked response regarding components N2, P2 and N3 with larger amplitudes. We obtained another recording of this patient 8 weeks later when due to return of tinnitus the question of recanalization arose. The VEP maps again showed symmetrical activation over the parieto-occipital region. As predicted, angiography proved no recurrence of fistulae, so further management aimed at other causes of tinnitus in this case.

12P Our results show that, despite difficulties in interindividual comparisons of VEP mapping, this method can be useful in intraindividual assessment of cases with parieto-occipital lesions. 61. Evoked potentials as a useful diagnostic instrument in alcohol withdrawal syndrome. - K. Schr6der-Rosenstock, H. Busch and G. Priill (Giessen)

The application of evoked potentials is well known to show harmful effects in chronic alcoholics, even though they have not become routine. Recording evoked potentials in the state of alcohol withdrawal in patients has not been done up to now. In the therapy of alcoholics the so-called detoxication is the first condition. The withdrawal syndrome is treated very differently - more than 130 drugs and drug combinations - without generally accepted instructions. Qualified criteria are missing in the evaluation of treatment studies. In a psycho-neurophysiological survey of alcohol withdrawal syndrome visual evoked potentials and brain-stem potentials were recorded in various intervals to the beginning of abstinence. Hyperexcitability in withdrawal, as known from animals, could be confirmed by shortened latencies respectively increased amplitudes of evoked potentials. Otherwise hyp0reactive potentials were recorded in the state of alcohol intoxication in the beginning of abstinence. The latencies of the visual evoked potentials showed a remarkable reactivity. We expect that evoked potentials are an appropriate instrument in the prognosis of alcohol withdrawal and may help to identify risk patients, such as with seizures or delirium tremens, earlier. On this basis treatment of withdrawal syndrome will be optimized. 62. Scalp potentials preceding self-initiated saccades to visual targets. - W. KIostermann, D. K6mpf, W. Heide, T. Seyfert and B. Wauschkuhn (Neurologische Klinik der Medizinischen Universifiit zu Liibeck, Liibeck)

In 8 healthy adults, we studied scalp potentials (time constant 5 sec) preceding self-initiated saccadic eye movements of 12°, at first to a fixed visual target in the right hemifield, then to the remembered target position in the dark. Like other investigators, we found the presaccadic negativity (PSN) maximal at the vertex, and more prominent over the contralateral (C3) than over the ipsilateral (C4) hemisphere. The amplitude was the same for voluntary saccades to visual and remembered targets. According to its localisation on the scalp, the PSN could reflect activity of the supplementary motor area, especially the supplementary eye fields, and also the frontal eye fields. The PSN preceded the saccade by 1000 msec in the visual condition and by 700 msec in the dark. A marked PSN over the parietal cortex was only present in the visual condition, more pronounced over the contralateral hemisphere. This might reflect directed visual attention. In contrast to the PSN, the amplitude of the presaccadic positivation (PSP), that preceded the saccade by 60-130 msec, was identical in both conditions and at both the central and parietal electrodes, thus not being influenced by target presence. 63. Asymmetries of vestibular and optokinetic nystagmus following unilateral posterior parietal lesions. - W. Heide (Neurolog. Universithtsklinik, Liibeck)

In 8 patients with localized postischemic unilateral lesions of the posterior parietal cortex (intraparietal sulcus), we recorded horizontal optokinetic (OKN) and vestibular nystagmus using DC electrooculography. An optokinetic full-field stimulus with constant angular velocities of 30, 60 and 90°/sec was presented for 30 sec each. Vestibular stimulation was performed on a rotatable chair in the dark, applying velocity steps of 90°/sec (within 1 sec) and sinusoidal rotation (amplitude + 90°/sec, frequencies 0.04, 0.08 and 0.2 Hz). Four patients had mild spontaneous nystagmus with the fast phases beating contralaterally. In 3 cases, OKN gain was more than

SOCIETY P R O C E E D I N G S 20% lower with ipsiversive than with contraversive stimulation; furthermore, the gain of the vestibulo-ocular reflex was elevated (1.01.11) with ipsilateral and reduced (0.67-0.93) with contralateral rotation, despite equal caloric responses of both labyrinths. This vestibular asymmetry, which has never been described after cortical lesions in man, recovered rapidly in 1 case where the lesion had occurred recently, whereas the OKN asymmetry persisted. In accordance with analogous findings in the monkey we conclude that the posterior parietal cortex is important not only for OKN and pursuit eye movements, but also for direction-specific modulation of vestibular functions. 64. Disturbances of saccadic eye movements after frontal and parietal lesions. - T. Mergner, D. Braun and H. Weber (Freiburg)

Patients with unilateral frontal or parietal lesions were presented with 4 stimulus conditions using a 2 x 2 design (temporal gap versus overlap between fixation point and target presentations; one target with random location versus two simultaneously appearing lights). Percentages of anticipatory, express (reflex-like), and regular saccades, time and direction errors as well as mean latencies were compared across (i) normal controls (Ns), frontal lobe patients with lesion in the frontal eye fields (FEF), and frontal non-FEF patients, as well as across (ii) Ns, parietal lobe patients with lesions in and outside the dorsolateral region. Results; (i) FEF patients showed a release of express saccades with ipsilateral preponderance (gap). However, suppression of express saccades by overlap was normal. Both FEF and non-FEF patients showed decreased percentages of contralateral anticipatory saccades, but normal ranges of direction and time errors. (ii) Patients with dorsolateral parietal lesions showed decomposed patterns of their saccadic reaction time histograms, increased percentages of time and direction errors, and decreased percentages of express and anticipatory saccades. These effects had a contralateral preponderance. Our results suggest that frontal lesions impair mainly the volitional control over saccade initiation, whereas dorsolateral parietal lesions impair mainly the selection and coding of the visual target. 65. The "posterior" INO. Electrophysiological evidence for the existence of a prenuclear abduction paresis. - F. Th6mke and H.C. Hopf In 5 patients with unilateral and 5 patients with bilateral abduction paresis, masseter and blink reflex changes indicated rostral pontine or midbrain lesions ipsilateral to the paretic or the more severely affected eye. Clinical signs such as contralateral monocular elevation paresis (1 patient), vertical gaze paresis (1 patient), and ipsilateral superior oblique paresis (2 patients) also pointed to a midbrain location. The existence of an uncrossed connection between the paramedian pontine reticular formation (PPRF) and the oculomotor nucleus has been demonstrated anatomically and physiologically. This connection runs in close vicinity but clearly separated from the medial longitudinal fasciculus. Inhibition arising from PPRF neurons is mediated via this connection to ipsilateral medial rectus motoneurons. A localized lesion of this connection at the rostral pontine or midbrain levels causes impairment of inhibition of the ipsilateral medial rectus muscle. This results in abduction paresis of the ipsilateral eye despite normal excitation of the lateral rectus muscle. 66. Topographic analysis of early median nerve stimulated SEPs results improving normative values. - H. Buchner, T. Waberski, I. Ludwig and A. Ferbert (Aachen) The cortical median nerve SEPs are characterized by a high inter- and intraindividual variability of latencies and amplitudes causing a lack in detecting abnormalities. The aim of our study was

GERMAN EEG SOCIETY to improve the technique of recording and analyzing the SEP used in the routine laboratory. The SEPs were recorded in 50 normal subjects using 18 electrodes placed at or midway between 1 0 / 2 0 locations with a contralateral ear-lobe reference. Additionally, Fz referenced recordings from C P 3 / 4 and the spinous process C7 were done. T h e location of the amplitude maxima varies intra- and also interindividually. As an example, the N20 amplitude maxima after right side stimulation were found at P4 (33 x ), CP (10 x ), O (5 x ), or T ( 2 x ) . The latencies of the peaks vary between the different electrode positions. As an example, the N20 latency was significantly longer at P than at CP (0.4_+0.5 msec). T h e intraindividual variability can be reduced and the routinely used method improved by recording the SEPs from at least 4 positions: CP, P, Fz and F. 67. On the age dependence of cortical SEP interpeak latencies by posterior tibial and peroneal nerve stimulation. - J. Eckert and W. Emser (Abt. f. klin. Neurophysiologie, Universitfit Giittingen, G6ttingen, and Caritas-Krankenhaus, DUlingen/Saar) Scalp-recorded somatosensory evoked potentials (SEP) to posterior nerve and peroneal nerve stimulation were studied in 77 healthy volunteers, 20-60 years of age. In a two-tailed U test there was no significant age difference between the sex groups. The posterior tibial nerve was stimulated in the usual m a n n e r at the ankle, peroneal nerve stimulation was performed at the retinaculum extensorum. Cortical SEPs were recorded at Cz' against a frontomedian reference. For both nerves the following peaks were measured: N33, P40, N50, P60 and N75. Interpeak latencies (IPL) (N33-P40, P40-N50, N50-P60, P60-N75, N33-N50, P40-P60, N50-N75) were calculated. In both sex groups the age dependence of the IPLs was examined using a linear regression model. W h e r e a s the earlier IPLs (N33-P40, P40N50, N33-N50) expressed only minor age-dependent changes, the later cortical IPLs (N50-P60, P60-N75, N50-N75) increased with advancing age. With the exception of N50-N75 by peroneal nerve stimulation, female IPLs showed a greater average increase with age than male IPLs. For IPL P40-P60 of both nerves we found age-dependent changes only in the female group. The results suggest sex-dependent age changes of the cortical generators of these peaks, especially in the sensible association area. 68. Perception of motion and the motion aftereffect: DC potentials as electrophysiological correlates. - E. AItenmiiller, T. Autenrieth and J. Kahrs (Tiibingen) The perception of motion and the motion aftereffect (MAE) is believed to be correlated with activation and inhibition of motion-detecting neurons in occipital and parietal brain areas. In order to obtain an electrophysiological correlate of these neuronal processes in h u m a n s we recorded in 30 subjects cortical D C potentials during the viewing of a rotating high-contrast logarithmic spiral (10 sec) and during the subsequent M A E (7 sec). Control conditions were the viewing of the spiral without rotation or with oscillations on its axis at 1 Hz (no MAE). The 3 stimuli were presented randomly. During the rotation of the spiral but not during the control conditions a significant increase of surface-negative D C potential occurred bilaterally over occipital and parietal cortical areas. Surprisingly, the M A E yielded no occipito-parietal positivation, but an additional bilateral frontal activation which could not be explained by ocular artifacts. T h e results indicate that D C potentials reflect occipitoparietal activation during continuous motion but not the subsequent inhibition of motion-detecting neurons. The role of the frontal activation remains unclear and may be explained by additional cognitive processes not primarily related to visual processing. (Supported by the D F G (SFB 307/B8).)

13P 69. Global-local processing in unilateral brain-damaged patients: electrophysiological evidence for perceptual left/right asymmetry. - H.J. Heinze, T.F. Miinte, M. Matzke, G. Dorfmiiller a and H. Dietz a (Departments of Neurology, and a Neurosurgery, Medical School Hannover, Hannover) In recent years, the processing of hierarchical stimuli has become a central issue in the study of h u m a n visual perception and attention. According to the global precedence hypothesis, visual pattern processing proceeds form the more global to the more local level. Other studies, however, challenged various aspects of the global precedence hypothesis. Rather, studies in brain-injured patients suggest that the processing of global and local information is determined by separate, parallel mechanisms. To date, mechanisms of global/local processing were inferred from behavioral experiments. In the present study, E R P s and behavioral parameters were recorded from unilateral brain-lesioned patients and matched controls. Reaction time analysis basically replicated previous findings suggesting that global information processing is more affected by right hemisphere lesions and local information processing is more affected by left hemisphere lesions. ERPs revealed marked differences in the posterior negativities to global/local level processing as an index of perceptual left/right asymmetries of hierarchical letter processing. The results support the hypothesis that global and local information is processed by different neural mechanisms that act in parallel or at least with a similar time course. 70. Cortical DC potentials during simple and paradoxical visual motion stimuli. - D. Patzwahl, J. Zanker, E. Altenmiiller and W. Kriechbaum (Tiibingen) During motion stimuli cortical DC potentials were recorded over occipital, occipito-parietal and frontal cortical areas. The trials consisted of 3 sec lasting left and right moving stimuli patterns followed by 3 sec pause without motion. Subjects viewed (a) counterphase flicker of checkerboard and random dot patterns, (b) moving random dot patterns and (c) moving bars with different texture motion: no motion of the texture elements ('drift balance'), object and their texture elements moving in the same ('Fourier motion') or in opposite direction ('theta motion'). The averaged DC potentials of 8 subjects showed similar activation patterns. Over frontal cortical areas a short lasting positivation occurred 250-500 msec after motion onset. A triphasic potential occurred over occipital an occipitoparietal cortical areas: in most subjects a negativation (250-300 msec) was followed by a positivation with its maximum at 350-550 msec and a subsequent sustained negativity until the motion stopped. A direction specific activation over the left and right cortical hemispheres occurred during the viewing of object motion (condition c). These results indicate that cortical DC potentials can reflect neural processing of motion information. 71. Task difficulty influences cortical activation patterns during mental arithmetics. - E. AItenmiiller, M. Zwing, J. Kahrs and W. Krieehbaum (Tiibingen) Cortical DC potentials were recorded in 34 right-handed subjects during mental arithmetics requiring the addition of two 2-digit or two 3-digit numbers. Easy (e.g. 22 + 39) and difficult (e.g. 379 + 438) tasks were presented randomly. Shifts of cortical DC potential during mental arithmetics were evaluated using an adaptive single trial analysis with duration of each trial corresponding to the time subjects needed to process the respective task. Easy and difficult addition tasks yielded left-hemispheric lateralization over frontal and central brain regions in 75% of the subjects: over parietal brain regions left- and right-hemispheric lateralizations were equally probable. Difficult tasks caused significantly larger negative DC potentials over all left-hemispheric brain regions and over the right pari-

14P etal region when compared to easy tasks. In contrast, the inter-electrode correlation was markedly higher during the processing of easy arithmetic tasks. The results demonstrate that during mental arithmetics left-hemispheric dominance is not as pronounced as during language processing. The increase of left-hemispheric activation during difficult mental arithmetics may be due to additional predominantly verbal cognitive processes. (Supported by the DFG (SFB 307/B8).)

72. Cortical DC potentials during language processing: follow-up studies in normal subjects and in patients with aphasia. - G. Marckmann, C. Thomas, E. AItenmiiller and H. Uhl (Tiibingen) In 15 normal subjects and in 10 patients with aphasia due to left-hemispheric lesions, cortical DC potentials were recorded during language processing from frontal, central, temporal and parietal electrodes. Subjects had to search as many synonyms as possible to acoustically presented nouns. DC shifts of single trials were analyzed and classified according to polarity, lateralization and amplitude of DC potential. All normal subjects showed left frontal dominance with almost identical absolute values (/~V) in the follow-up examinations; in contrast, activation over parietal and temporal electrodes differed intraindividually in subsequent measurements. Patients with pronounced aphasic deficits revealed variable activation patterns: left frontal dominance, bilateral activation or right frontal dominance occurred. Occasionally, right frontal dominance shifted towards the left hemisphere along with clinical recovery. From the results we conclude that in normal subjects the frontal lateralization of DC potentials provides the most reliable criterion to assess speech dominance. The change of the frontal hemispheric lateralization along with clinical recovery in patients with aphasic symptoms documents functional compensation. (Supported by the DFG (SFB 307/B8).)

73. Sex differences in cortical activation patterns during language processing: a DC potential study. - E. Altenmiiller, H. Pf'afflin and J. Kahrs (Tiibingen) In 30 female and 30 male right-handed subjects cortical DC potentials were recorded from frontal, central, temporal and parietal electrodes during language processing: subjects had to search synonyms to acoustically presented nouns with either concrete (e.g., house, tree) or abstract (e.g., haste, thesis) semantical content. DC shifts were analyzed during the stimulus presentation (2 sec) and the mental search for synonyms (4 sec) and were compared to a baseline determined from a 3 sec prestimulus interval. About 90% of female and male subjects yielded left-frontal dominance during processing of concrete or abstract semantic material. Only females showed a significant left-hemispheric dominance over temporal regions and a stimulus specific biparietal activation during processing of concrete semantic material. Furthermore, interelectrode correlation was significantly higher in females during the processing of concrete semantic material. From the results we conclude that female subjects show a more stimulus-specific activation pattern including parietal association areas when processing concrete verbal material. The higher inter-electrode correlation in females may reflect a more homogeneous activation pattern due to interindividually similar cognitive strategies. (Supported by the DFG (SFB 307/B8).)

74. Human DC scalp potentials during the perception of self-motion. - K. B6tzel (Dept. of Neurology, Klinikum Grosshadern, Munich) During vestibular stimulation of a human subject a negative going DC scalp potential with maximum at the Cz electrode has been reported previously. It is still questionable if this represents neurophysiological correlates of rotation or unspecific arousal. We addressed this question by rotating subjects in light and in darkness, by eliciting the phenomenon of circular vection and by

SOCIETY PROCEEDINGS using different control paradigms. DC EEG was recorded from midline electrodes and averaged off-line. We found a negative DC potential with maximum at parietal electrodes and with maximal steepness and amplitude with rotation in light. Under rotation in darkness a steep increase of negativity was seen but the amplitude was lower than with rotation in light. With circular vection the slope of the increasing negativity was less than under the other conditions. In control experiments a small increase in negativity was seen and attributed to unspecific arousal. The observed negativity parallels with the sensation of rotation under different stimulus conditions the features of time constant of increase and amplitude and therefore is likely to be the correlate of visuo-vestibular and somatosensory integration during the perception of self-rotation. 75. Is averaging really necessary? - A. Hufschmidt, C.H. Liicking and J. Niemann (Freiburg) Averaging is still the standard method to improve the low signalto-noise ratio of event-related brain electrical activity. Very often, especially in studies of slow brain potentials, the shape of the potential is relatively unimportant, and the experimenter's interest is focused on the amplitude of a potential shift within a known time period. In this situation, we suggest that it may be useful to abandon averaging altogether and evaluate the single trials instead. As an example, this type of analysis is demonstrated on a slow potential study of a tracking task. In every second trial, visual control is interrupted during a pre-fixed period of some seconds ("test interval") in the middle of the trial. Subjects are asked to continue their movement during this gap. As a first step in evaluation, the mean DC level during the test interval is computed for every trial. Control values are obtained by measuring the DC levels during the same period in trials with continuous visual feedback. Thus, the first step yields one row of numeric values for every experimental condition, with each single reading corresponding to one trial. In a second step, the two classes are compared by a statistical test. 76. The compound P300-40 Hz response of the human brain. - E. Ba§ar a, C. Ba§ar-Eroglu b, T. Demiraip c and M. Schiirmann a (a Institute of Physiology, Liibeck, b Institute of Medical Psychology, Liibeck, and c Department of Physiology, Istanbul Faculty of Medicine, Capa, lstanbui, Turkey) In our earlier studies we have shown that the so-called "middle latency response" of the human auditory evoked potential reflects the 40 Hz wave packet elicited in the first 100 msec following the stimulus (Ba§ar et al., Int. J. Neurosci., 1987, 33: 103-117). By using omitted stimuli in a P300 paradigm a significant 40 Hz response with a delay of 300 msec following the omitted stimuli was recorded in the hippocampus of the cat brain (Ba§ar-Eroglu and Ba§ar, Int. J. Neurosci., in press). Accordingly, we extended our analysis by searching for 40 Hz cognitive potentials in human event-related potential recordings by means of odd-ball and omitted stimulus paradigms. Our preliminary results show that it is possible to record 40 Hz wave bursts in frontal, parietal and vertex derivations with a delay of approx. 250-400 msec depending on the paradigm and recording location. The delayed 40 Hz response is a weak signal often masked by other activities and is often accompanied by the P300 potential. The compound P300-40 Hz human response shows enormous intraindividual and interindividual fluctuations. 77. Significance of dipole calculations of EEG and EPs in psychiatry. - T. Dierks, K. Maurer and W.K. Strik (Universit~it Wiirzburg, Wiirzburg) Studies of EEG in psychiatric diseases were only to some degree of significance since the choice of reference influences the descrip-

G E R M A N E E G SOCIETY tion of the 2-dimensional distribution of frequencies on the scalp. Furthermore existed the problem of alpha inflation when evaluating multichannel recordings statistically. The calculation of equivalent dipoles on the other hand allows a 3-dimensional description of electrical currents in the brain. Additionally dipole calculations permit an efficient and sensible way of data reduction. In the case of EPs studies using multichannel recordings have been presented only in recent years. The previously used 1-2-channel recordings were not very useful in their physiological meaning and the multichannel recorded EPs have the same problems as the multichannel E E G recordings. Only since methods for reference independent evaluation of EPs (Lehmann and Skrandies 1980) had been developed and applied in psychiatry sound statements regarding brain functions have been possible (Dierks et al. 1990). The possibility by different methods to calculate equivalent dipoles in EPs allows for the first time the connection between their components and anatomical structures. Our investigations of dipole calculation of spontaneous E E G with the help of F F r approximation show significant differences between psychiatric diseases as well as the influence of psychopharmacologic drugs. 78. Calculation of equivalent dipoles of spontaneous EEG by FFT approximation and of AEP-P300 before and after application of benzodiazepines and their antagonists. - T. Dierks, W. Engelhardt and K. Maurer (Universit/it Wiirzburg, Wiirzburg)

Results of investigations of conventional E E G and qEEG are difficult to interpret in a physiological way due to the influence of the reference. Calculation of dipoles is independent of reference and therefore more suitable for a physiological interpretation of results. In the present study we investigated the influence of midazolam and flumazenil on electrical brain activity. In 11 healthy young subjects dipoles were calculated by FFT approximation (Lehmann and Michel 1990). Measurement was done before and after application of midazolam (0.2 m g / k g b.w.) and flumazenil (1 mg). At the same time the acoustic evoked P300 was measured. Additional testing and monitoring included SKT, d2 test, reaction time, vigilance scoring, blood pressure, heart rate, and O 2 saturation. The EEG generators for alpha and especially for beta activity were significantly more frontally localized after application of midazolam, the change of localization into frontal regions was reversed after flumazenil application. The P300 was reduced in amplitude and prolonged in latency and reacted more sensibly to drug influence compared to psychometric tests. The results show compared to the conventional EEG that different anatomical structures may participate in the E E G generation before and after application of benzodiazepines. Correlations with PET imaging of benzodiazepine receptors is possible. P300 results showed that allocortical structures are influenced by drug application. 79. The effects of lesions of the auditory cortex on long-latency auditory evoked potentials and the P300. - H. Knott, K. Niemann, A. Ferbert a and D.G. von Keyserlingk (Institute of Anatomy, a Clinic of Neurology, Aachen University of Technology, Aachen)

Not only for the N100, but also for the P300 the auditory cortex is of special importance (NS.~it~inen and Picton 1987; Knight et al. 1989). The effects of vascular lesions of the auditory cortex on the N100, however, remain controversial. Michel et al. (1980) were unable to record any N100 from patients with bilateral temporal lobe lesions. Others (Woods et al. 1984) reported normal responses in such patients. These discrepancies may result from the variable extent of the lesions. A digital brain atlas gives the opportunity to exactly locate and compare the lesions in the CT scan series. With the help of the atlas 16 patients with unilateral lesions of the auditory cortex were identified. These patients and 16 healthy agematched controls were investigated in an auditory oddball paradigm.

15P The potentials were recorded at C3, Cz, C4 and Pz. As compared with the controls the patients showed a significant ( P < 0.01) reduction of the amplitude of the N100 and the P300 at C3 and Cz. 80. P300, psychopathological and neuropsychological parameters in schizophrenia. - G. Eikmeier and E. Lodemann (Essen)

The reduced P300 amplitude is a robust biological phenomenon in schizophrenia. The present study tried to clarify whether P300 latency is prolonged in schizophrenics and whether the changes of P300 are correlated with clinical or neuropsychological variables. Therefore in 15 schizophrenic patients ERPs were recorded during a 2-tone discrimination task in the acute phase and after remission. Clinical symptoms were rated by BPRS, SANS, InSka and FBF3. Four neuropsychological tests (Benton test, ZSY, LGT 1/3, LPS 6) were performed. Ten controls were studied in the same manner. We could not find an influence of neuroleptic treatment on P300 amplitude or latency. The 2-way A N O V A (group x time, repeated measurements) showed a significantly reduced P300 amplitude and a significantly prolonged P300 latency, the interaction between the main factors 'group' and 'time' was not significant. In the acute phase we found no relation between P300 amplitude or latency and clinical or neuropsychological parameters. In the remitted state P300 amplitude was correlated negatively with the negative syndrome of schizophrenia and positively with the performance in two of the neuropsychological tests (ZSY, LGT 1/3). 81. Visual P300 in infarction of the middle cerebral artery (MCA) distribution. - A. Taghavy and H. Hamer (Erlangen)

We examined 24 patients (62.0_+ 18.3 years) with infarction in the territory of MCA and compared them with a patient norm (53.4 _+ 11.0 years; n = 11). Diagnosis was made clinically and in all cases at least one CCT was performed. 54% showed areas of hypodensity in CCT of different degrees and 46% only moderate cerebral atrophy. Visual P300 potentials were derived simultaneously from O1 and O2 to Fz (Cz was ground) in an "odd-ball paradigm" (A: 16 * 16 caskets; B: 64 * 64). No significant interhemispheric differences in latencies and amplitude (healthy versus affected side) were found in comparison with the norm (larger versus smaller amplitude/latency). The averaged potentials between O1 and 02, however, showed a significant diminution of the patients' amplitude N250/P300 (7.3 +_3.4 /xV) in comparison to the norm (9.7 + 3.2 /zV; P < 0.05) and an increase of latencies of N250 and P300 ( P < 0.005). The group with atrophy behaved so more prominently. In one case of complete infarction of the MCA the amplitude of the affected side was 50% diminished supporting the hypothesis that components of P300 complex are generated in temporal lobe. The P300 potentials reflect cognitive disorders in infarction of MCA territory independently of side and more so when generalized cortical atrophy is present. 82. N400: interaction of expectancy and semantic relatedness. - T.F. Miinte, U. Stiegemann and H.J. Heinze (Neurologische Klinik mit Klinischer Neurophysiologie, Med. Hochschule, Hannover)

The N400 component of the ERP is sensitive to a variety of language variables. The present study examined the interaction between expectancy and semantic relatedness. Word-pairs (ISI 1000 msec) were visually presented. The first stimulus of a pair constituted a category name (e.g., bird), while the second stimulus could either be (1) an expected exemplar of the category (e.g., bird-robin, 20%), (2) an expected exemplar of another category (e.g., weapon-lake, 20%), (3) an unexpected exemplar of another category (e.g., bird-lion, 5%), (4) an unexpected exemplar of the category (e.g., weapon-pistol, 5%), or (5) a non-word (e.g., bird-narg, 50%).

16P Twelve healthy subjects were given a lexical decision task. The results showed no effect of expectancy on the ERP between word 1 and word 2. For unrelated second stimuli no N400 was observed for expected stimuli. For unexpected related stimuli only a small N400 was seen. It is concluded that these results are compatible with a post-lexical process integrating information from semantic and non-semantic sources as underlying N400. 83. N400 to grammatical incongruencies: the underlying process. T.F. Miinte, S. Schuchardt and H.J. Heinze (Neurologische Klinik mit Klinischer Neurophysiologie, Med. Hochschule, Hannover)

Semantic mismatches elicit an N400 component of the ERP in 1-word or sentence contexts. A similar negativity to grammatical incongruencies would significantly reduce the number of possible explanations for N400. Simple short stories were presented word by word (ISI 800 msec) to 12 healthy subjects. Within the stories, there were grammatically, semantically and orthographically incongruent stimuli. ERPs to the semantic incongruencies showed a typical N400. The grammatical incongruencies were associated with a similar negativity of smaller amplitude, while the orthographical mismatches showed a completely different ERP. It will be argued that an N400 to grammatical incongruencies is consistent with the view that N400 reflects some (post-lexical) process, that checks the coherence of a text according to a variety of criteria. 84. The relationship between cognitive deficits and quantitative liver function in early portal-systemic encephalopathy (PSE). - C.F.A. Kiigler, J. Petter, A. Taghavy, G. Wensing, E. Lotterer, W.E. Fleig and E.G. Hahn (Erlangen)

Pattern flash elicited P300 potentials were applied to 88 patients with chronic liver disease to investigate a possible relationship between subtle cognitive deficits and quantitative liver function in early PSE. According to the clinical testing for PSE and the type of liver disease the patients were subdivided into NC: with chronic, non-cirrhotic liver disease (n = 34); CI: clinically non-encephalopathic cirrhotics (n = 46); and C2: clinically encephalopathic cirrhotics (n = 8). While the PFP300 amplitudes remained unchanged, the N250 as well as PFP300 latencies were significantly longer in CI (N250: 305.2 + 27.3 msec; PFP300:379.5 _+36 msec) and C2 (N250: 339.9_+ 33.3 msec; PFP300: 426.4 _+40.6 msec) than in NC (N250: 268.7_+ 12.4 msec; PFP300:336 + 23.4 msec). Hepatic metabolic function (GEC, AAT) was significantly reduced in patients with abnormal PFP300 test results. These findings were confirmed by significant inverse correlations between the latencies of the PFP300 complex and parameters of hepatic metabolic function (GEC: r = - 0 . 6 1 ; AAT: r = - 6 1 ; P <0.02), but not LBF or the degree of portal-systemic shunting (BA). The PFP300 potentials are especially appropriate for quantifying early PSE. Their inverse correlation with GEC and ABT may indicate that reduced metabolic function rather than reduced liver blood flow or increased portal-systemic shunting may be of primary pathogenic relevance in early PSE. 85. The basis of akinesia. - A. Hufschmidt, J. Wiesenfeldt and C.H. Liicking (Freiburg)

The expression of akinetic symptoms varies from patient to patient. This applies not only to the general motor disability, but also to the relative severity of single symptoms. This clinical experience suggests that akinesia is a syndrome rather than a single symptom, being composed of a number of largely independent basic disturbances. The hypothesis is verified by a study of multiple motor functions on groups of parkinsonian patients and elderly normal subjects.

SOCIETY P R O C E E D I N G S Subjects passed a test battery including reaction times, movement times, diadochokinesis, and visuo-manual tracking. Parkinsonian patients were also assessed clinically by the Unified Rating Scale, and a Mini-Mental Status examination was taken. As expected, parkinsonian patients did significantly worse on all tests of motor function. However, there were great interindividual differences of the test profiles. These were studies by a factor analysis, assuming that tests which correlate closely are under the common influence of the same underlying pathogenetic factor, whereas others vary independently because they are linked to different basic disturbances. The analysis reveals 5 factors which are interpreted according to the functional significance of the motor tests on which they load. 86. Pathophysiologicai mechanisms of chorea. - J. Noth (Essen)

It is still open to question whether similar pathophysiological mechanisms underlie choreatic movement disorders of various etiology. In benign familial chorea, for instance, no morphological or metabolic deficits can be discerned within the striatum, while patients in the early stages of Huntington's disease (HD) show striatal atrophy and reduced glucose utilization within the striatum. This is caused by degeneration of striatal neurones projecting to the lateral globus pallidus. It is thought that the decline of these GABA and enkephalin containing neurones leads to diminished activity in the subthalamic nucleus and finally results in disinhibition of thalamocortical projections, which causes the choreatic movements. Subtle neurophysiological investigations have uncovered specific sensorimotor deficits in early HD patients and even in asymptomatic offspring, such as slowing of voluntary movements and decline in cortical SEP amplitudes. These changes are not caused by the choreatic movements themselves. At these early stages of HD, neuropathological abnormalities are confined to the striatum, It may therefore be speculated that the pathological outflow from the striatum inhibits the somatosensory transmission either at the thalamic or at the cortical level. SEP recordings obtained in an animal model of HD (quinolinic acid lesions of the striatum) support this hypothesis. (Supported by the DFG (SFB 200).) 87. Reciprocal inhibition in spasmodic torticollis. - G. Deuschl, F. Heinen, C. Seifert and C.H. Liicking (Freiburg i. Br.)

Idiopathic focal dystonias like spasmodic torticollis, blepharospasm and writer's cramp are the most frequent dystonic diseases. Their origin is unknown and neurologic routine examinations usually show normal findings. The unifying clinical abnormality is slow movement or abnormal postures caused by sustained cocontractions of antagonist muscles. An important spinal reflex pathway opposing involuntary cocontractions is reciprocal inhibition between antagonist muscles which can be formally tested with H reflex techniques. Following electrical radial nerve stimulation nerve flexor muscles display 3 separate phases of inhibition. We investigated 13 patients with spasmodic torticollis who showed significantly less inhibition in the second and third phase than normal controls. This was found in both arms of the patients. This abnormality is most likely due to alterations of the supraspinal control of these reflex pathways and appears to indicate bilateral CNS abnormalities outside of the region of clinical disease. Similar abnormalities have already been described in patients with writer's cramp. Thus a common abnormality in patients with focal dystonia may exist but the detailed physiological mechanisms are not yet clear. 88. Motor unit discharges in tremor. - R. Dengler (Bonn)

The discharge pattern of motor units in tremor is characterized by two changes, the synchronization of discharges of different MUs and the occurrence of so-called double discharges, i.e., discharges of

GERMAN EEG SOCIETY the same M U with short interval. Synchronization can be seen in routine EMG. More detailed analysis using cross-correlograms of the discharge times reveals that the most frequent intervals between the M U s range from 0 to 50 msec. Thus, the synchronization seems not very close. It is caused by oscillations in neuronal networks induced by pacemaker systems or by oscillations in reflex loops. Double discharges show intervals from 20 to 80 msec inversely correlated to the tremor intensity. They are associated with a more-than-linear summation of the M U twitches with short interval which is preserved with tremor frequencies of 4 - 6 Hz. This m e c h a n i s m plays an important role in the development of high tremor amplitudes. Basis of the tremor is the synchronization of MUs, the double discharges exert an additional effect as tremor amplifiers.

89. Cerebellar disorders: neurophysiological findings. - K. Wessel a, N. Mai b, R. Verleger a and D. K6mpf a (a Department of Neurology, Medical University of Liibeck, and b Department of Clinical Neuropsychology, General Hospital, Miinchen-Bogenhausen)

The integration of the cerebellum into motor control via open and closed loops is well described by experimental work. T h e neurophysiological possibilities of investigating disorders of motor function in patients with cerebellar diseases are limited. On the one hand mechanical m o v e m e n t s can be registered. Regarding this the results of our posturographic investigations and microcomputer aided registrations of finger forces and finger m o v e m e n t s in a homogenous group of well documented patients with cerebellar atrophy and olivo-ponto-cerebellar atrophy are presented. Direct registration of neuronal activity in the h u m a n cerebellum is not possible. Therefore we employed the non-invasive neurophysiological method of recording the readiness potential (Bereitschaftspotential) for research in the pathophysiology of cerebellar diseases in man. The comparison of patients suffering from cerebellar atrophy with a group of agematched healthy controls showed an earlier onset and a lack of topographical differentiation of the Bereitschaftspotential in the patient group, whereas control persons showed maximal amplitudes of the Bereitschaftspotential at Cz and C3. These results indicate that cerebello-cortical pathways play a role in the generation of the Bereitschaftspotential. It is possible that patients with C A try to compensate for their motor deficits by a longer and more extended cortical activation preceding voluntary movements.

90. The M2 stretch reflex response of active human muscle is mediated by different mechanisms at different joints. - A.F. Thilmann, R. T6pper, M. Schwarz, S.J. Fellows and J. Noth (Neurologische Klinik, Alfried Krupp-Krankenhaus, Essen)

Imposed stretch of voluntarily activated h u m a n muscle results in a reflex response consisting of short latency (M1) and longer latency (M2) components. As the m e c h a n i s m of the M2 response is still under discussion, the present study tested the hypothesis that the M2 response is evoked via a transcortical reflex pathway. For this purpose, stretch reflexes were obtained from the first dorsal interosseus (FDI), biceps brachii (BB), triceps brachii (TB) and triceps surae (TS) muscles in normal subjects and patients with Huntington's disease (HD). As expected, all H D patients showed selective loss of FDI M2 responses with good M1 components. In all other muscles tested clear M2 reflexes were evoked in all H D patients, without qualitative difference to the normal control group. Using Huntington's disease as a pathophysiologic model with pure supraspinal lesions, this study shows that the M2 responses in the muscles under study are evoked by different mechanisms. It is concluded that longer latency stretch reflex components are mediated over

17P supraspinal pathways only in muscles, such as those of the hand, whose functions are normally directly under cortical control. 91. Answers on muscle stretch of the human upper arm during elbow motion and its functional meaning. - D. Limbeck and P.-W. Sch6nle (G6ttingen) While the biceps brachii or the triceps brachii, respectively, was performing an elbow motion, it was suddenly stretched by a torque motor. The 8 normal volunteers should answer this perturbation by a corrective motion as short as possible. As a result some persons reached the target gradually from one side and others were overshooting and had to reposit the forearm. In most cases the monosynaptic stretch reflex (M1 burst) was negligible. The greatest part of the answer was contributed by voluntary activity (M3 burst). The significance of the long-latency reflex (M2 burst) varied from person to person. It seemed M2 could effectively limit the displacement in some cases, but additional M3 activity was necessary for complete compensation. On average the angle of displacement and the components MI, M2 and M3 were proportional to the displacement impulse, whereas the time of correction was nearly constant. The magnitudes of the 3 components were quite variable under the same conditions. This variability could either be explained by a great influence of a central set on the reflex bursts or by a great inaccuracy of the servo mechanism. 92. H reflexes and facilitated F waves by hemispastics. - D. Miiller and R.D. Koch (Magdeburg) In normal individuals the H reflex may be elicited especially in the calf muscles, by posttetanic potentiation or by using averaging techniques in other muscles. In newborns and patients with neurological central disorders H reflexes may appear and replace F waves in small muscles of hand and foot. We investigated 52 patients with hemiplegic syndrome and registered late potentials by electrical stimulation from the m. abd. dig. V and m. ext. dig. brevis. We found H reflexes and "facilitated" F waves on the hemiplegic side more in hand muscles than in foot muscles. Only 19% had " n o r m a l " late potentials. In conclusion, late potentials in small muscles of hand and foot are a more consistent basis for a test of spasticity than classic H reflexes in calf muscles. 93. The diagnostic significance of H reflex and F wave studies in SI radiculopathy. - H. Lohner, B. Kukowski and K.-P. Sch~ifer (Abteilung f'dr Klinische Neurophysiologie, Universit~it Giittingen, G6ttingen) We compared several neurophysiological parameters with clinical symptoms in patients with the diagnosis of S1 root compression. According to a standardized protocol, we measured the nerve conduction velocity of the sural and tibial nerves. The F wave latency was recorded from the abductor hallucis muscle and the amplitude and latency of the soleus H reflex were determined for both sides. Furthermore we performed needle electromyography in gastrocnemius, gluteus maximus and paraspinal muscles. The F wave latencies remained normal in most cases even when spontaneous activity was found in the S1 myotome. The most common changes of the soleus H reflex were unilateral absence or a reduction of amplitude, in a few cases prolonged latency, as well. W h e n compared with physical examination, there was a strong correlation of abnormal H reflex with absent or diminished ankle jerk. In conclusion, the soleus H reflex and the F wave failed to provide additional information not detected by physical examination and needle electromyography in the evaluation of S1 radiculopathy.

18P 94. Neurophysiological evaluation of sensorimotor functions of the distal leg: comparison of evoked cortical potentials following electrical and mechanical stimulation, long-latency muscle responses and transcranial magnetic stimulation. - C. Thomas, H. Ackermann and J. Dichgans (Department of Neurology, University of Tiibingen, Tiibingen) Twenty-two patients with localized lesion of the central nervous system (unilateral cerebral ischemia, cervical myelopathy, spinal tumor, familial spastic paraplegia) underwent neurophysiological evaluation of sensorimotor deficits of the distal leg. Functional methods using muscle stretch as a stimulus, i.e., long-latency muscle responses and cortical potentials evoked by dorsiflecfion of the foot, were compared with transcranial magnetic stimulation and somatosensory evoked cortical potentials following electrical stimulation of the posterior tibial nerve. The functional neurophysiological methods yielded no diagnostic superiority with respect to the procedures using artificial, i.e., magnetic and electrical stimulation. However, in most cases of missing compound motor action potentials following transcranial stimulation or missing electrically evoked cortical potentials the long-latency muscle responses still allowed quantitative assessment of sensorimotor functions. 95. Production of individual early and medium cortical responses upon tibialis stimulation with varying frequencies in spatial-temporal dispersion and desynchronization. - A. Simi~ (Ludwigshafen) Tibialis stimulation was effected by individual supraliminal rectangular impulses (1-5 Hz) by bipolar surface electrodes placed at ankle. The deducing electrodes were placed over C'z, according to the international 10-20 system and switched to a fronto-median reference (Fz). In order to register the impact of individual impulses of varying frequencies at constant intervals, an expansion of the time-frame from 100 msec to 1000 msec was necessary. During stimulation one stimulus-free interval of at least 2 sec had to be kept up between the individual impulses. After the stimulation of individual impulses with different frequencies, 7 respective individual cortical responses, led from the scalp, were superposed on peak P40 after 5-fold wave extension of the early and medium cortical component and visually evaluated. During the investigation l0 healthy probands were stimulated with 100 individual 1 Hz impulses at the ankle, and for each person 100 individual cortical responses were deduced and registered. After 5-fold wave extension of the early components, the amplitudes were visualized according to their dimension and statistically evaluated. During two separate treatments, series of 50, 100, 150 and 200 stimuli of varying frequencies were applied to the same proband in waking condition and in sleeping condition. 96. Quantitative assessment of motor function of the hand in patients with discrete lesions of the upper motor neurone. - K.M. Stephan and V. H6mberg (Diisseldorf) The study of writing is well suited for the detection of deficits in fine motor functions of the hand, because graphomotoric movements have a n u m b e r of invariant characteristics: writing time, for instance, is nearly constant even if the size of the letter varies (isochronism). A further characteristic is rhythmicity of movements. In patients with basal ganglia disease disturbances of the 'isochronism principle' as well as a reduction in the maximal frequency of the power spectrum obtained after F F T can be observed. T h e aim of this study was to assess writing disturbances in patients with minimal clinical deficits of the upper motor neurone. These data were compared with results of clinical observations and electrophysiological parameters (SSEP and MEP). Patients with clinically apparent paresis have marked disturbances of the 'isochronism principle,' and an obvious shift of the maximal F F T frequency. Even in patients with only mild deficits and

SOCIETY P R O C E E D I N G S normal results in electrophysiological testing, subtle disturbances can be observed. Different grades of disturbances are not only obvious in patients with different stages of illness, but may also vary in patients over time. Therefore this method can be used for the assessment of progress in rehabilitation. 97. Impaired temporalis reflex in whiplash injury. - M. Keidel, P. Rieschke and H.C. Diener (Department of Neurology, University of Essen, Essen) The purpose of the study was to demonstrate experimental evidence of a brain-stem dysfunction following whiplash injury. 50 patients (f: 29, m: 21, 2 = 27.6 years, S.D. = 8.5) with acute cervicocephalic syndrome with post-traumatic headache, tension of neck and shoulder muscles and neck stiffness, but without neurological deficits or bone injury of the cervical spine, were investigated within a m e a n of 4.7 days after the acceleration accident. Data were compared to normal subjects (n = 35; age: ~ = 29.2 years; S.D. = 7.7). The early and late (exteroceptive) brain-stem mediated suppression (ES1 and ES2) in the S E M G of the right temporalis muscle was elicited by ipsilateral stimulation of the nervus V / 2 + 3. The mean of 10 responses was calculated per subject. The following significant abnormalities were found in patients: shortened duration of ES2 with delayed onset and premature ending; diminished ratio of ES2:ES1 and E S 2 : ' D of IE' (D of I E = d u r a t i o n of interposed preceding E M G activity). No significant differences were evident for the onset of ES1, D of IE or the ratio ES1 :D of IE. Our results confirm the findings of a reduced ES2 in muscle tension headache of other origin. We conclude that a neuronal dysfunction in the reflex circuit is due to acceleration forces imposed during whiplash. 98. Myoelectrical activation pattern of m. biceps brachii in neurological patients. - H.Ch. Seholle, S. Popp, Ch. Anders and N.P. Schumann (Jena) The surface E M G of m. biceps brachii of healthy subjects and patients with neurological syndromes (e.g., spastic hemiparesis) was monopolarly recorded by using a 16-channel E M G system. Based on defined parts of these E M G curves, parameters of spectral E M G power were calculated by m e a n s of Fast Fourier Transformation. Using these values of spectral E M G parameters and a linear interpolation technique, E M G maps were processed (topographical pattern of myoelectrical activation). Depending on the posture of upper extremities (90 ° flexions by the elbow joint during supination, pronation as well as neutral position of forearm) in healthy subjects the E M G activation patterns were changed. In patients with spastic paresis the variance of these patterns was higher, but the "basis pattern" could also be found in some patients with strong paresis. These diagnostic possibilities could be used to quantify therapeutic effects. 99. Dependency of body stabilization and body height. - W. Berger, M. Trippel and M. Discher (Freiburg i. Br.) Recent investigations have shown a developmental change in correcting E M G responses following perturbations during stance and gait in children with an increase of extensor E M G activity and decrease of coactivafion. The study reported here should analyze the height dependency of stance stabilization by excluding age dependent changes. This was done by perturbing subjects of different height at the back (level of center of gravity) standing on a force measuring platform. E M G activity of the leg muscles and biomechanical parameters were recorded. The following results were obtained: small subjects showed larger displacements at the ankle joint. This resulted in larger E M G responses and a stronger coactivation of lower leg muscles. M o m e n t a of increasing strength resulted in a larger increment of both ankle joint displacement and gastrocnemius E M G responses in the smaller

GERMAN EEG SOCIETY subjects. It is supposed that proprioceptive information from the impact site of the m o m e n t u m is responsible for the generation of the EMG. 100. Correlation of different doses of intrathecal baciofen with monoand polysynaptic reflexes. - J. Dressnandt, A. Konstanzer, I. Trender and B. Conrad (Neurologische Klinik der Technischen Universit~it, Munich) T h e aim of this study was to investigate whether there is a correlation between the dose of intrathecal baclofen and the change in the elicitability of mono- and polysynaptic reflexes. In 4 patients with para- or tetraspasticity because of multiple sclerosis baclofen was applied intrathecally from an implanted p u m p through a subcutaneous catheter. The dose of the continuously given baclofen was increased stepwise. Every 24 h after the last dose change records were m a d e of: H reflex and repetitive (3 Hz) stimulation by stimulating the tibial nerve and measuring the compound muscle action potential (CMAP) of the m. soleus; cutaneo-muscular flexor reflex by stimulating the plantar foot. With increasing doses of baclofen the amplitude of the H reflex decreased. The flexor reflex was elicitable even under higher doses and vanished later than the H reflex. During repetitive stimulation an increment of the C M A P amplitudes could be seen before starting the intrathecal baclofen therapy which showed normal values soon after baclofen was given. We conclude that the recording of these reflexes yields easily available parameters for the evaluation of sufficient baclofen therapy in spasticity. 101. lntrathecal baclofen therapy in generalized tetanus: longitudinal investigations of somatosensory and transcranial motor evoked potentials. - L. Englisch, T. Dreyhaupt and P.W. Sch6nle (Abt. Klinische Neurophysiologie der Universit~it G6ttingen, Giittingen) The G A B A agonist baclofen has been well known in the therapy of spasticity for many years. The main effect depends on presynaptic inhibition of motoric Ia fibers; an effect on spinal interneurons is under discussion. In cases of severe spasticity intrathecal application of baclofen is possible. Several patients suffering from generalized tetanus have improved upon intrathecal baclofen application. They required less neuromuscular blocking agents and shorter terms of controlled ventilation. We report the results of somatosensory and transcranial motor evoked potentials from a patient suffering from generalized tetanus and treated with baclofen intrathecally. In both somatosensory and transcranial motor evoked potentials we found minor changes in latency hut a striking reduction of amplitude, which returned to normal upon discontinuation of baclofen application. These findings suggest that the pharmacological action of baclofen is a complex mechanism, which exceeds sole modulation of central motor efferents, even if the drug is applied on a spinal level. 102. Electrophysiological assessment of motor pathways to masticatory muscles. - U. Tiirk, K.M. R6sler, J. Mathis and Ch.W. Hess (Neurologische Universit~itsklinik, Inselspital, Bern, Switzerland) The recording of muscle c o m p o u n d action potentials (CMAPs) from masticatory muscles is difficult, since most of them are covered with muscles innervated by n. facialis, which may h a m p e r measurements by volume conducted activity. Only m. pterygoideus medialis is situated directly beneath a body surface, and with an enoral surface electrode C M A P s can easily be recorded. We studied this recording technique for assessment of masticatory motor pathways in 13 patients with a unilateral peripheral facial palsy, where the side-to-side comparison allowed an estimate of volume conducted activity from facial muscles.

19P Electrical stimulation of the trigeminal nerve beneath the zygomatic arch, and magnetic stimulation of the motor cortex were performed. L a t e n c i e s / a m p l i t u d e s on the side of facial palsy were 1.25 m s e c / 2 . 9 5 mV with peripheral stimulation, and 5.96 m s e c / 0 . 8 3 m V with cortical stimulation, respectively. The respective values for the non-paretic side were 1.29 m s e c / 3 . 3 8 mV and 6.47 m s e c / 0 . 7 2 mV. The shapes of the potentials were similar on both sides, and the statistical side-to-side comparison showed significant correlations of the parameters. Thus, our recording technique was barely influenced by volume conducted activity from facial muscles, allowing for a reliable m e a s u r e m e n t of latencies and amplitudes from masticatory muscles. 103. SSEP of the genitofemoral nerve - normal values. - U. Mielke, H.-J. Streb, W. Tiinjes and M. Grundmann (Universitfitsnervenklinik, Neurologie, Homburg/Saar) Sensory conduction velocity of the n. genitofemoralis is difficult to assess in clinical routine. In 20 healthy persons the somatosensory evoked potentials (SSEP) of the n. genitofemoralis were investigated by m e a n s of scalp recordings ( C z / F p z ) after surface stimulation of the inguinal region. Multilevel recordings of the tibial nerve served as control values. The primary cortical response has a typical w shape with a relatively constant P1 peak. Mean values (x+S.D.) of the P1 latencies are 31.3 msec_+5.6 with a lateral difference of 1.2_+0.8. The mean amplitude N 1 / P I is 0.82 /zV+0.8. In 5 patients suffering from typical pain latencies were markedly prolonged on the clinically affected side, in 2 cases no responses at all were evoked. SSEP recordings of the n. genitofemoralis seem to be appropriate to detect peripheral lesions. 104. Uremic neuropathy during chronic intermittent hemodialysis indications of a two-phasic development. - M.J. Hilz, D. Claus, G. Riisl, E. Hofmann, R.B. Sterzel a and B. Neund6rfer (Departments of Neurology and a Nephrology, University of Erlangen-Nuremberg, Erlangen) To evaluate the influence of chronic intermittent hemodialysis on uremic neuropathy, 2 groups of hemodialyzed uremic patients were investigated twice. The mean interval between the 1st (I) and 2rid investigation (II) was 85 weeks. Mean times of dialysis of group A (n = 25) were 2.8 weeks (I) and 65 weeks (II), of group B (n = 32) 252 weeks (I) and 325 weeks (II). Clinical symptoms of neuropathy, 5 sensory and motor conduction velocities, electromagnetic vibratory thresholds (Somedic AB) at the malleoli, warm and cold perception thresholds (Marstock method) at the malleoli and the volar wrists were determined. Comparison of group A0) vs. A(H ) and A(i ) vs. Ba) showed the most significant changes of symptoms: in the longer dialyzed patients neuropathy was more frequent, conduction velocities were impaired more frequently and severely ( P < 0.05), whilst warm and cold thresholds, i.e., small fiber function, had improved. Comparison of group A(n ) vs. B01 ) and B(I ) vs. B(H ) did not reveal such significant changes. Altogether, in uremic neuropathy large nerve fiber function seems to worsen whilst small fibers ameliorate during the 1st and 2nd year of hemodialysis; later on, a probable steady state between chronic renal failure and intermittent detoxication seems to prevent further significant changes of uremic neuropathy. 105. Incidence of polyneuropathies in Hodgkin's disease - a retrospective study of delayed therapeutic damages. - B. Frank a, C. Bokemeyer b, H. Feistner a, j. v. Rhee b, A. Schrader b, H.-J. Schmoll b and H.J. Heinze a (a Neurologische Klinik mit Klinischer Neurophysiologie, and b Onkologische Klinik, Medizinische Hochschule Hannover, Hannover) This study aims at assessing the incidence of chemotherapy related polyneuropathy in patients treated for Hodgkin's disease. To

20P this end we retrospectively examined 76 patients (mean age 32, range 18-74) neurologically and neurophysiologically. T h e patients had been treated by the oncology service between 1965 and 1988. They were in full remission, no tumor had recurred during the last 2 years. 28% of the patients had only received radiation therapy, 16% had only undergone chemotherapy, while the majority (56%) had received both. Three patients were excluded for diabetes. The mean follow-up time was 96 (27-243) months. Besides motor and sensory NCV of the upper and lower extremities, latency of the F wave was determined and the small foot muscles were examined by EMG. 19 patients showed pathological neurophysiological results. 13 were qualified as having an axonal polyneuropathy, one showed an affection of the myelin sheath and 5 showed a combined damage. In 11 of the 27 patients who showed symptoms and signs of a polyneuropathy on neurological examination a polyneuropathy was corroborated by neurophysiological results. 106. Malignant tumour of the psoas: another cause of meralgia paraesthetica. - G. Amoiridis, J.C. Wiihrle, I. Grunwald and H. Przuntek (Bochum) Meralgia paraesthetica (MP) is a mononeuropathy involving the lateral femoral cutaneous nerve (LFCN) which consists of sensory fibres of L 2 and L 3 roots. MP is most commonly caused by entrapment of the nerve at the site where it pierces the inguinal ligament or the fascia lata. However, more proximal lesions of the LFCN or its roots result in the same clinical picture. Apart from spinal stenosis and pelvic inflammatory disease the reported aetiologic factors were benign or temporary. Diagnosing another case of MP we found a malignant t u m o u r of the psoas, not previously reported as a cause. We discuss the use of sensory nerve conduction study, somatosensory evoked potentials and diagnostic nerve block to detect the site of the lesion. This appears of major importance, as causes located above the inguinal ligament can bear a more serious prognosis than the ones below. In our opinion neurophysiological investigations will not be necessary if the properly placed diagnostic nerve block is successful; however, if it fails, these techniques will give important diagnostic clues towards the localization of the lesion. 107. Follow-up examination of electrophysiologieal parameters of the operated carpal tunnel syndrome. - E. Lang, D. Claus and B. Neund6rfer (Erlangen) There is no follow-up examination of the electrophysiological parameters before and at fixed time invervals after surgical treatment of the carpal tunnel syndrome (CTS). Those data may provide information about the regeneration of the thick myelinated nerve fibers, in order to examine their etiological significance for the clinical symptoms at the ipsi- and contralateral hand. In 24 patients with CTS (20 women, 4 men, age 54.4_+ 10.5 years) the distal motor latency (DML) and the orthodromic sensory nerve conduction velocity (SNCV) of the median and ulnar nerves were examined bilaterally before and 1, 3, 6 and 12 m o n t h s after surgical treatment of the CTS. 77% of improvement of the D M L measured after 12 m o n t h s took place in the first postoperative month. In contrast, the ipsilateral SNCV of the median nerve increased continuously and differed not significantly from the baseline value before 6 m o n t h s postoperatively. At the contralateral hands the amplitude of the potential of the abductor pollicis brevis muscle increased continuously, the D M L and SNCV did not change significantly. 108. The significance of distal motor latency after carpal tunnel surgery. - S.A. Rath, G. Antoniadis, U.M. Mauer, H.J. Klein and H.-P. Richter (Department of Neurosurgery, University of UIm, UIm) The distal motor latency (DML) is a very important electrophysiological p a r a m e t e r in the diagnosis of the carpal tunnel syndrome

SOCIETY P R O C E E D I N G S (CTS). In a retrospective study of 1420 primary CTS operations, the postoperative D M L was evaluated in 239 cases. On patients with good clinical results, an average D M L improvement of 0.95 msec after 2 weeks and of 2.33 msec after 1 year could be observed. The individual improvement was directly proportional to the preoperative prolongation of the DML. Patients with recurrent carpal tunnel syndrome presented in spite of clinical deterioration with improved electrophysiological findings in 9 cases out of 17. In 7 patients with unchanged complaints an increase of D M L was seen in 4 cases and a decrease in 2 cases. In 23 patients with postoperative reflex sympathetic dystrophy an improved D M L from 1.0 up to 3.3 msec was found, whereas a deterioration occurred only in 6 cases. In conclusion, the postoperative distal motor conduction time does not seem to be a helpful criterion in the diagnosis of cases with poor results after CTS surgery. 109. Clinical and eleetrodiagnostic long-term results of carpal tunnel syndrome operations. - W.F. Haupt, A. Sehop, G. Wintzer and J. L6ttgen (Neurological and Surgical University Hospitals, Cologne) Clinical and electrodiagnostic long-term follow up examinations were performed on a collective of 60 patients who had been operated on a total of 86 hands for carpal tunnel syndrome. The minimal follow up period was 2 years, the m e a n 5.5 years. Clinical examinations included standardized and graded testing of motor, sensory, pain, and trophic functions. The standardized electrodiagnostic evaluation included E M G as well as motor and sensory NCV. The results demonstrated an impressive overall improvement in 86% of the cases. The motor, sensory and trophic findings showed comparable rates of improvement. Also, electrodiagnostic findings demonstrated the same development. The treatment results were highly dependent on the preoperative duration of signs but not on their severity. Concomitant diseases such as obesity, hypertension, thyroid and renal diseases had no significant influence on prognosis. In the case of diabetes, however, we found a markedly poorer prognosis. The long-term results following carpal tunnel surgery prove to be equally favorable for the global assessment as well as for the individual specific functions tested and are reflected by electrodiagnostic findings. Concomitant diseases with the exception of diabetes do not affect the prognosis. 110. Facial nerve palsy after removal of acoustic neuromas: an electrophysiological study. - W. Jenni, K.M. R6sler, U.D. Sehmid, R. Seiler and Ch.W. Hess (Neurologische und Neurochirurgische Universitfitskliniken, Inselspital, Bern, Switzerland) Facial nerve function in patients with acoustic neuromas was examined clinically and electrophysiologically before, during and 6 or more months after surgery ( m e a n 849 days). For neurography, the nerve was stimulated electrically at the stylomastoid fossa and transcranially by magnetic stimulation. Intraoperatively, the nerve was stimulated within the cerebellopontine cistern. The nasalis muscle response was recorded. 37 patients were identified with a clinically evident facial palsy after surgery (in 17 patients mild to moderate, in 20 patients severe palsies). Preoperatively, no neurographic side-to-side differences were found in these patientes. Six or more months later, amplitudes were 46.5%/46.9% (electrical/magnetic stimulation; P < 0.05) and latencies were 108.5%/119.7% (electrical stimulation; P > 0.05/magnetic stimulation; P < 0.05) as compared to the contralateral side, indicating severe axonal damage. These results were compared with those of intraoperative nerve stimulation. If the nerve was stimulated near the brain-stem and a response in m. nasalis was absent after tumor removal, the long-term prognosis was unfavorable (60% severe palsies). Presence of a response in m. nasalis, however,

G E R M A N E E G SOCIETY was a good prognostic factor, since in 61% a slight to moderate palsy and in only 6% a severe facial palsy developed. 111. Traumatic lesions of the brachial plexus - clinical, neurophysiological and MRI findings. - B. Frank, H. Feistner and H.J. Heinze (Neurologische Klinik mit Klinischer Neurophysiologie, Medizinische Hochschule Hannover, Hannover)

Traumatic lesions of the cervico-brachial plexus are common sequelae after motorbike accidents. We examined 12 men (age 18-32 years) with a posttraumatic lesion of the brachial plexus and compared the clinical and neurophysiological findings with the results of MRI studies of the cervical spine with regard to damages of the cervical roots. Besides the E M G examination of the paravertebral muscles (C5-D1) sensory and motor NCV as well as SEP were recorded. MRI scans were done using sagittal, axial and coronal slices. In 10 patients the neurophysiologically suspected lesion of one or more cervical roots was corroborated by MRI. In 2 patients there were no positive MRI findings of root evulsion in spite of definitively pathological neurophysiological results (pathological spontaneous activity in paravertebral muscles, no cortical components of the SEP). It has to be suspected that in these 2 patients a tearing of the roots was responsible for the neurophysiologically seen damage. The results show that a thorough neurophysiological examination suggesting an evulsion of the cervical roots can be verified by an MRI examination of the cervical region. 112. Does botulinum toxin affect peripheral nerve function? - D. Dressier a and R. Benecke b (8 Dyskinesia Clinic, Psychiatry Department, Georg-August-University, Giittingen, and b Neurology Department, Heinrich-Heine-University, Diisseldorf)

Botulinum toxin (BT) has now been used for some time to treat dyskinesia with remarkable success. Increasing clinical experience with its use did not reveal major side effects. Animal experiments, however, indicate centripetal BT transport along peripheral nerves. We sought to investigate whether this p h e n o m e n o n can affect peripheral nerve function. For this purpose the distal motor latency (DML) to the orbicularis oculi muscle was studied in 6 patients who received BT injections into this muscle for treatment of blepharospasms or hemifacial spasms. Magnetic facial nerve stimulation at a site between the nerve root entry zone and the porus acousticus internus was performed with a Novametrix Magstim 200 and its 9 cm diameter coil placed over the ipsilateral side of the head. D M L m e a n s before BT injections ranged from 3.55 msec (S.D. 0.21 msec) to 4.08 msec (S.D. 0.21 msec). Between 25 and 43 days after BT injections D M L m e a n s ranged from 3.55 msec (S.D. 0.23 msec) to 4.00 msec (S.D. 0.15 msec). At the same time the compound muscle action potentials decreased to between 11% and 4% of their original values. Therapeutic use of BT does not seem to affect the peripheral nerve function thus indicating a site of BT action solely at the cholinergic synapse. 113. Differences between evoked potentials due to stimulation of AI3 or A~ fibers of the radial nerve. - R.-D. Treede and V. Kunde (Institute of Physiology, UKE, Hamburg)

Evoked potentials due to activation of nociceptive A 6 fibers in the radial nerve have been compared with those following activation of A/3 fibers in the median nerve (EEG J., 1988, 70: 429-441). We now investigated potentials following stimulation of radial nerve A/3 fibers. Radial nerve A/3 fibers were activated by electrical stimuli at the wrist ( 4 × threshold), A 6 fibers by laser stimuli at the dorsal hand (15 m J / m m 2 ) . For comparison, the median nerve was stimulated

21P electrically. Evoked potentials were recorded with 15-27 scalp electrodes (bandpass 0.5-200 Hz). Latencies and amplitudes were determined from C4'-Fz. The topographies of early components following electrical stimulation of the radial and the median nerve were comparable. However, radial nerve stimuli were perceived as less intense ( P ~ 0.01), led to smaller amplitudes and a longer N20 latency, in spite of equal average stimulus intensities (5 _+2 mA). The evoked potential following laser stimulation of the radial nerve territory began at about 150 msec with a negativity that was maximal in lower temporal leads. None of the components after A/3 fiber activation corresponded in topography to the earliest A 6 fiber potential. 114. The measurement of sympathetic skin response: a diagnostic method to assess vegetative disorders. - U. Kirchh6fer (Erfurt)

Vegetative disorders are one of a number of neurologic diseases. T h o u g h a fact known for more than 100 years, its objectification represents a problem which has not been completely solved until today. M e a s u r e m e n t s of the sympathetic skin response offer a routine, non-invasive method allowing the assessment of the sympathetic part of the vegetative nervous system. A group of 60 test persons was formed to create own standard values of the latencies for sympathetic skin responses and to check their dependency on age and sex. We also compared different types of stimulus production. Both the electric and the acoustic stimulus production can be r e c o m m e n d e d for routine applications. In 20 test persons we additionally stimulated electrically the infra-umbilical skin and registered the responses from hands and feet. Here, too, latencies at the feet were found to be longer than those at the hands. We examined a group of 40 diabetics and 20 alcoholics suffering from clinically confirmed polyneuropathy to find out responses. Thus we were able to prove that disorders occurring in the sympathetic part of the vegetative nervous system can be recognized by the m e a s u r e m e n t of sympathetic skin responses. 115. Stimulated NIR flowmetry: a method for functional testing of vasomotor nerve fibers. - G. Reichel, F. Rieger and U. Kirchh6fer

In order to investigate the function of vasomotor nerve fibers, we developed a method which measures changes of the pulse-synchronous volume variations of the microcirculation after stimulation of sympathetic nervous system. We employed the near infrared (NIR) flow rate m e a s u r e m e n t method. Acoustic stimuli were used to produce sympathetic excitation waves. Microcirculation variations were assessed by means of the variable part of the reflected infrared light. Registrations were made from fingers and toes. The variations of the N I R intensity curves, which were induced by stimulation of the sympathicus, and the autocorrelograms of these curves were assessed. To do this, we introduced a vasoconstriction coefficient (VC) correlating the variable portions of the reflected N I R activity from 2 equal time windows before and 3 sec after stimulation. To assess the autocorrelograms quantitatively, the amplitudes of the 2 n d - 5 t h waves were correlated with the 1st amplitude. This relative value shows the variations of the periodic part in the N I R signal. A sympathetic excitation wave reduces the periodic part. In healthy persons, the pulse-synchronous amplitude of the N I R signal decreases after stimulation by almost one third to 68.1+15.2%, with the VC being > 0.2. 116. A simple method for measurement of heart rate variations in autonomic polyneuropathy. - H.-J. Braune (Marburg)

A quick and practicable method is described for the measurement of respiratory heart rate variation by using the equipment of an

22P ordinary E M G machine. The built in software for analysis of threshold triggered single motor unit potentials renders possible the measurement of the longest and the shortest QRS interval of the electrocardiogram over a period of 8 heart beats. Longer periods are not appropriate since with longer data collecting time the test becomes more prone to be artificially biased by single extremely short or long QRS intervals. The quotient longest/shortest QRS interval is derived. It is shown that a cutoff value of 1.06 reliably separates normals and patients with heart rate rigidity in autonomic polyneuropathy. 117. Visual evoked phenomena and quantitative EEG: correlative studies in human neuropharmacology. - W.G. Sannita (Center for Neuroactive Drugs, Inst. of Neurophysiopathology, University, and Center for Cerebral Neurophysiology, CNR, Genova, Italy, and Dept. of Psychiatry, SUNY, Stony Brook, NY, USA)

Neuroactive drugs administered systemically to humans affect the visual system electrophysiology consistently with findings in animal and in in vitro models. Substantial retina/visual cortex analogies allow inference from retinal to cortical drug action; comparable, stimulus-dependent electrophysiological phenomena are evoked in humans and in animal experimental models upon application of similar stimuli; stimulus-related evoked potentials are reliably recordable in man in multiple pre- and postdrug control designs, and have defined relationships with age and sex. Normative data are available. Effects on retinal and visual cortex electrophysiology are described for virtually all compounds used in psychiatry though classifications comparable to those based on E E G estimates are not yet available. Experimental and human evidence is provided of differential sensitivity of distinct retinal/cortical evoked phenomena a n d / o r components to modifications of GABAergic and dopaminergic systems and of correlations with CNS disorders such as dopamine-dependent Parkinson's conditions. Quantitative E E G and visual (luminance modulation) cortical potential data after anticholinergic drug administration are presented to exemplify drug-induced effects on the visual electrophysiology independent from E E G effects and to indicate Ach-related effects in man of possible application in the study of pharmacological aspects of aging and dementia. 118. Non-linear EEG dynamics: the dimensionality of human's sleep EEG. - J. R6schke (Department of Psychiatry, University of Mainz, Mainz)

The daily experience of the electroencephalographer dealing with sleep has shown that the time history of the E E G during a certain sleep stage is not predictable over a longer time period. In this sense the unpredictability of the sleep E E G might be a basic feature of its stochastical character. On the contrary, in recent years it has become clear that non-linear dynamical systems are able to generate so-called "deterministic chaos." One attempt to characterize the dynamics of a chaotic system is to calculate the dimensionality of its attractors in phase space. This number estimates the complexity and the degrees of freedom of the investigated system. Our results have shown that the deeper the sleep the lower the dimensionality of the E E G varying between D2 = 4.30 (stage IV) and D2 = 6.20 (stage REM). In normal healthy subjects the influence of lorazepam does not alter the dimensionality of slow wave sleep but that of stages II and REM. In schizophrenia a significant decrease of the EEG's dimensionality was observed, too. Taken together, the evaluation of the dimensionality of the sleep E E G during different sleep stages is an additional tool to get better insight into brain function and sleep regulation.

SOCIETY P R O C E E D I N G S 119. Classification for map landscapes, and generator Iocalisations for EEG frequency bands. - D. Lehmann (Neurology Dept., University Hospital, Ziirich, Switzerland)

Multichannel ERP and EEG produces large amounts of data. The necessary data reduction must preserve the relevant characteristics of the data. The landscapes of ERP maps can be classified using the locations of the centroids of the positive and the negative measurements as descriptors. The descriptors define segments of constant landscapes (ERP "components") of the map series. Typically, the segment borders coincide with the maxima of the curve of "global map dissimilarity" and with the minima of the curve of "global field power." Effects of medication are measured as changes of map landscape. Effects on the topography of EEG frequency bands are assessed by modelling the power maps with a single dipole generator (in terms of phase angles) for each frequency. The result is a potential map for the entire EEG epoch for each frequency; this map can be conventionally modelled using a single dipole source (in terms of amplitudes), or can be assessed numerically using the landscape descriptors. A massive reduction of the space-time continuum of a map series using a measure of complexity (fractal dimensionality) yields a single value concerning all channels and all time points of the map series; this measure can also detect subtle drug effects.

120. Towards a systematic theory of artificial neural networks. - R. Rojas (Berlin)

The application of artificial neural networks (ANN) for the solution of certain problems in the fields of pattern recognition, robotics, speech recognition, etc., has increased dramatically in the last years. We are witnessing in fact the "renaissance" of a research area that was almost abandoned in the seventies. One of the primary goals of current research is to systematize and to extend the theory of ANN. The first impression that researchers willing to employ neural networks get, is that there are too many models but an imprecise theory. The models are used more as "black-boxes" which somehow produce some results. We try to show which is the relation between several ANN models and how the theory could be systematized. We discuss also some recent results that promise to put the theory of ANN on a more solid foundation. 121. Brain electric source analysis: ways towards source imaging of EEG and evoked potentials. - M. Scherg (Munich, and New York, NY, USA)

Spatio-temporal multiple dipole source analysis was introduced for the analysis of evoked potentials in order to separate the dynamic source activities which overlap at the scalp (Scherg and von Cramon 1985, 1986; Scherg 1990). Similarly, in the diagnosis of partial epilepsy, the overlap of multiple source processes underlying seizure onset or interictal spikes must be resolved. Recent advances make the imaging of E E G and MEG source activities also feasible for the ongoing EEG and MEG by analysis in the frequency domain or using covariance matrices. Multiple dipoles can act as inverse operators to image the ongoing source activity. Non-coherent dipolar source processes can be detected and localized by scanning the brain using the MUSIC algorithm (multiple signal classification; Mosher et al. in press). However, multiple dipole models are superior in detecting source activities which are more widespread or correlated, e.g., between hemispheres. To illustrate these new methods, analyses of simulated data, somatosensory evoked potentials and magnetic fields and of interictal spike data are presented.

G E R M A N E E G SOCIETY 122. Classification of EEG and clinical data with neural networks. B. Kliippel (Kassel)

The first part starts with a general introduction into the mode of working with neural networks without detailed analysis of the resulting mathematical and computer science problems. Main keywords like "learning," "working phase," "relaxation," "network topology" and "learning rule" will be explained using practical examples. Short case studies will exemplify the practical use of neural networks. Furthermore the different principles of neural networks and other intelligent classification schemes (e.g., classical artificial intelligence) will be compared. The emphasis lies on the advantages and disadvantages of both methods with respect to analyzing E E G data. The advantages of neural networks will be shown based on the hardware of today (PC and workstation systems) as well as estimating the near future (first special hardware). The second part gives an outline of some first impressions from a current project on classification of E E G data. Empirical results about the network parameters and various preprocessing will be presented with respect to this project. 123. Neurometric subtyping of psychiatric patients. - E.R. John and

L.S. Prichep (New York, NY, USA) In neurometric QEEG, univariate and multivariate features are extracted from 2 min of 19-channel artifact-free resting E E G for Gaussianity, are regressed, and Z transformed to estimate abnormality relative to a normative database. Using t tests between groups to select subsets of sensitive variables, dichotomizing discriminant functions have been constructed which separate normals from groups of patients with depression, schizophrenia, dementia and a number of other DSMIIIR diagnostic categories with high and independently replicable accuracy. A merged set of 26 variables was constructed, comprised of the variables most useful in these various discriminant functions. Using this merged discriminating variable set, cluster analysis was carried out on a sample of 742 normal subjects and patients in 8 DSMIIIR categories, divided into balanced split-half groups. The resulting clusters displayed two interesting features: (1) patients in each of the major DSMIIIR categories were divided among 3 or more clusters, containing patients with the same clinical symptoms but different pathophysiological profiles; (2) most clusters contained substantial proportions of patients with several different DSMIIlR categories, displaying different clinical symptoms but similar profiles of pathophysiology. In several instances, evidence of differential response of subtypes to various treatments is emerging. Implications will be discussed. 124. Classification of psychotropics based on multi-lead multifrequency CEEG model. - T.M. Itil, K.Z. Itil and E. Eralp

(Tarrytown, USA) For more than 2 decades, we have been classifying psychotropic drugs based on multi-frequency E E G but by recording from only one area of the brain. While this classification was sufficient for most psychotropics developed based on "classic" pharmacology models, we faced difficulties to classify drugs developed according to new biochemical, and especially receptor models. In our recent quantitative pharmaco-EEG (QPEEG[R]) studies, we established that multi-lead, multi-frequency CEEG analysis is definitely superior to a single lead CEEG data collection and analysis. The new methodology includes 16-19-lead data collection. The data are analyzed simultaneously using both power spectrum and period analyses, each with 20 frequency bands (2 delta range, 4 theta range, 6 alpha range and 8 beta range). Pre-drug data are compared with post-drug data in each area of the brain based on t statistics. Thus, to establish drug effects, we obtain 19 sets of t profiles for 1, 2, 3 etc. h post-drug administration for each subject, for each time

23P period. Each of these t profiles of the new drug is compared with the 19 t profiles of HZI's data base psychotropic drug groups (anxiety relievers, mood elevators, CNS depressants, vigilance enhancers or cognitive activators). The "similarity coefficient" of each area of the brain is used for the purpose of brain mapping. 125. On the dimensionality of pharmaco-EEG data. - W.M. Herrm a n n (Berlin)

The basic dimensions of a power spectral analysed E E G are: (a) frequency components (e.g., 63 primary frequency classes: 0.5-32.0 Hz, Af = 0.5 Hz); (b) localisations (e.g., 28 EEG leads for mapping); (c) persons (person types) (e.g., 64 persons); (d) dynamics (e.g., 75 primary segments, 4 sec each). To keep these investigations to 3 dimensions (modes) the primary segments were averaged. Both cluster and factor analyses suggest the following secondary variables: (a) 6 frequency bands: delta F = 0.5-6.0; theta F = 6.0-8.5; alpha I F = 8.5-10.5; alpha 2 F = 10.5-12.5; beta l F = 12.5-18.0; beta 3 F = 21.0-32.0; (b) 4 localisation areas: frontopolar, frontocentral, temporal and parieto-occipital; (c) 2 main person types and several other types: alpha types and low voltage type. The other person types cannot be described with sufficient accuracy because of their low incidence. In several experiments these secondary variables led to a better discrimination: (a) frequency bands: large effects could be shown in one band while in the neighbouring band there were low effects; (b) localisation: fronto-central effects were opposite of occipital; (c) person types: opposite reaction of different types. The conclusion of these findings is that beside the frequency components the localisation as well as person types have to be considered to obtain more differentiated and precise information on drug effects. 126. Event related potentials as predictors of individual response to psychoactive drugs. - U. Hegeri (Berlin)

Event related potentials are a promising tool for identifying those neurophysiological characteristics which are underlying the enormous variability in the clinical responses to psychoactive drugs. It has been reported that the intensity dependence of sensory evoked potentials is related to the antimanic or antidepressive response to lithium in patients with affective psychoses. Patients with a steep amplitude/stimulus intensity function (ASF) show a better clinical response than those with a fiat ASF slope. We studied whether or not a steep ASF slope is also related to a favourable outcome to prophylactic lithium medication. In a retrospective pilot study lithium reponders were characterized by steeper ASF slopes of the auditory evoked N 1 / P 2 component than non-responders. This result was confirmed in a replication study. First results of the prospective study concerning the predictive quality of the ASF slope indicate that patients with flat ASP slopes have a less favourable outcome to lithium prophylaxis than patients with steep ASF slopes. The data are, however, still not sufficient for a final conclusion. Since lithium is discussed to act via central serotonergic effects, it is of theoretical importance that there are several direct and indirect arguments for a steep ASF slope of auditory evoked potentials being an indicator of low central serotonergic neurotransmission. 127. Complexity measures of multichannel EEG: local and global correlation exponents. - I. Dvo[fik (Laboratory for Applied Mathematics and Bioengineering, Prague Psychiatric Center, Prague, Czech Republic)

A new approach to EEG analysis was introduced recently that brings new parameterization of multichannel EEG. This approach stems from the theory of deterministic chaos.

24P

SOCIETY P R O C E E D I N G S

The methodology of this theory results in estimations of the measures of complexity of the EEG. The signal is regarded as a projection of the trajectory in the state space characterizing the time course of the brain activity. Complexity m e a s u r e s classify the studied processes according to their positions on a scale between the constant process and the white noise. Correlation exponent is the most popular of these complexity measures. It can be calculated in two ways from the multichannel EEG. Either we estimate the local correlation exponent of a single channel E E G or we estimate the global correlation exponent of E E G for more channels together. The value of local correlation exponent for healthy subjects varies between 4 and 8. It is lower for states with closed eyes and higher for states with open eyes. In the case of epilepsy this value falls under 3 or even 2, on the contrary in the case of anesthesia it grows to 9. Global correlation exponent is around 5 or 6 for healthy subjects and also falls down in the case of epilepsy. 128. Spontaneous and evoked EEG in the assessment of analgesics. - B. Bromm (Institute of Physiology, University Hospital Eppendorf, Hamburg) Analgesic effects, unspecific alterations of vigilance, plasma levels and side effects of 26 analgesics, opioids, NSAIDs and others, are reviewed. Pain was induced by intracutaneously applied electrical shocks; target variables were the pain ratings, late cerebral potential components and stimulus induced power in the delta frequencies; in addition the spontaneous EEG, the auditory evoked potentials, reaction times and mood scales were used to separate analgesic effects from unspecific vigilance decreasing effects. Doses corresponded to the 2-fold minimal clinical dose r e c o m m e n d e d by the drug companies. Comparisons based on placebo-controlled, double-blind, crossover studies with h o m o g e n e o u s samples of healthy males result in the following statements: (1) High correlations (r ca. 0.6) exist between subjective pain ratings and pain related cerebral potential components. (2) Even higher correlations exist between analgesic-induced pain relief and decrease of pain related cerebral potentials. (3) Strongest effects were observed u n d e r opioids, such as meperidine and flupirtine. (4) Even the so-called peripherally acting analgesics, such as aspirin or acetaminophen, revealed clear effects on the CNS variables. (5) On the average, the pharmacodynamics of the analgesics in the E E G parameters correspond to their different pharmacokinetics; in case of the NSAIDs the individual variations are too large to achieve significant correlations between plasma levels and effects. (Supported by D F G (Br 310/15, 16,1-3).) 129. The spectral dynamics V. Albrecht, J. H6nig, Applied Mathematics Center, Prague, Czech

and its application in pharmaco-EEG. M. Palus and I. David (Laboratory for and Bioengineering, Prague Psychiatric Republic)

T h e method of spectral dynamics of E E G (SD) was introduced recently to follow drug induced changes in E E G spectra. The SD is based on the concept of distance between the predrug and the postdrug spectra. Plotting distances between the predrug and the postdrug spectra against time of spectra m e a s u r e m e n t s yields the spectral kinetic profile of the drug. The shape of the spectral kinetic plot is then parameterized similarly as the plasma kinetic curve, e.g., its modality, time location of the maximum distance from the basal, the half-time of the m a x i m u m distance etc. are estimated. The spectral dynamic profile is either the plot of spectral distances against drug concentration in the blood or plot of results of some performance test, e.g., CFF or tremorometry, against the spectral distances. The spectral dynamic profile usually conforms a loop in the state space. There is no natural distance in the space of E E G spectra thus the choice of the distance formula plays a crucial role. Besides the well known Lp distances, distances minimizing the statistical variance are investigated at present. Simultaneously, the

SD sensitivity to detect a change in E E G spectrum was compared with the classical approach based on frequency band analysis. 130. Do neurophysioiogical prognostic evaluation Wessel, G.P. Huss, H. of Neurology, Medical

tests contribute to the diagnosis and of late onset cerehellar ataxias? - K. Briickmann and D. K6mpf (Department University of Liibeck, Liibeck)

Twenty-one patients diagnosed as suffering from autosomal dominant or idiopathic late onset cerebellar ataxia were investigated clinically, by m e a n s of neurophysiological tests (BAEP, blink reflex, SEP, MEP, VEP) and CT scan. The study included an initial investigation and a follow-up examination on average 25.3 months thereafter (minimal 8, maximal 36). Patients could be divided into 4 groups: (1) patients with pure cerebellar ataxia (CA) after a course of 5 years minimum, (2) patients with pure cerebellar ataxia, who exhibited pathological neurophysiological tests on occasion of the last examination, (3) patients who upon initial examination clinically presented with pure cerebellar ataxia, but according to the last examination developed a multisystem disorder, (4) patients with multiple system atrophy (mostly olivo-ponto-cerebellar atrophy) presenting additional non-cerebellar signs of involvement. The main point of this paper is, that individuals who according to clinical criteria were initially classified as CA but finally developed a multisystem disorder, already presented pathology in the neurophysiological tests on occasion of the initial examination (group 3). The increasing frequency of pathology in the several neurophysiological tests together with the progression of the disease is obviously of prognostic significance. The results demonstrate, that neurophysiological tests performed at regular intervals are of diagnostic and prognostic value in late onset cerebellar ataxia. 131. Down's syndrome: comparison to healthy subjects and to AIzheimer's disease. - P. Vieregge, R. Verleger, H. Schulze-Rawa and D. K6mpf (Neurological Clinic, Medical University of Liibeck, Liibeck) Event-related potentials of 15 DS subjects (22-42 years) were compared to 7 patients with Alzheimer's disease (DAT; mean age: 67 years), 18 young (YH) and 20 old healthy subjects (mean age: 25 and 67 years). An auditory oddball and a visual 'push-wait' task were applied. Results: (a) Oddball: reaction times and N2b and P3 latencies were later in DS than in the YH but did not differ from DAT. The DS had special features: both with targets and non-targets, a positive shift appeared at Fz and Cz in the first 200 msec, overlapping the ensuing N2b, whereas P3 was large but had its focus at Cz instead of Pz. (b) Push-wait task: reaction times, N2 and P3 latencies were prolonged compared to YH and did not differ from DAT. Unlike the other groups, P3 amplitudes were larger to ' p u s h ' than to 'wait' and had the same centrally focussed topography to both stimuli. Most conspicuous in DS was the slow frontocentral positive shift that may also be responsible for reducing N2b's amplitude and for modulating P3's topography. Disregarding that shift, latencies were similar for DS and D A T subjects. 132. Topographically different response of EEG sleep activities to GABAergic sleep modulation by flunitrazepam - relationship to regional distribution of BZD receptor subtypes? - W. Scheuler, C. Pastelak-Price and St. Kubicki (Dept. of Clin. Neurophysiology, Universit~itsldinikum Rudolf Virchow, Berlin) We performed spectral analysis to study if the various activities react homogeneously to a GABAergic modification of sleep regulation or show regional differences which might be related to particular systems. In a double-blind, randomized cross-over design 12

G E R M A N E E G SOCIETY healthy subjects with physiological N R E M alpha activity (5 female, 7 male; 21-55 years, median 30 years) were given placebo or 1 mg flunitrazepam, respectively. Spectral analysis of 16-channel all-night sleep EEG was performed aimed at defined sleep activities: delta (0.5-2 Hz), alphaj (7-9 Hz), alpha 2 (9-11 Hz), sigma 1 (11-13 Hz) and sigma 2 (13-15 Hz). Repeated measures analysis of variance was done. We observed sleep stage and sleep cycle dependent differences in the topographic reaction. A power density increase dominated in the frontal regions for the alpha 2 and sigma I frequency band whereas a decrease was emphasized in the posterior regions for the delta and alpha I bands. These findings indicate clear functional differences on regional sleep activity systems; the responses might be related to the topographic distribution of benzodiazepine receptor subtypes omega 1 and omega 2. (This project was supported by the Deutsche Forschungsgemeinschaft.) 133. Digital EEG recording: pitfalls and benefits. - H. Hinrichs (Neurologische Klinik mit Klinischer Neurophysiologie der Medizinischen Hochschule Hannover, Hannover)

To benefit from digital E E G recording techniques, a careful design is necessary considering the basic laws of digital signal processing. Among these are the adequate selection of the sampling rate, sampling procedure and bandwidth of the anti-aliasing filter. In addition, the resolution on the digital side has to match the features of the preceding analog amplifier. Disregarding these rules may lead to irregular or distorted signals. On the other hand, digital storage of the E E G is simple and cheap using commercial mass-storage devices such as hard disks or optical disks. An exact reproduction of the signal can be performed directly on the PC. There are further advantages of the digital technique: arbitrary filtering can be done without any phase distortion (e.g., notch filter); a change in the technical recording parameters, like sensitivity, time constant etc., may be simulated without really modifying the raw data. The same signal may be repeatedly evaluated applying various recalculated montages. Any kind of analysis is possible directly from the digital signal. Including source coding algorithms, a data compression by an amount of 80% can be achieved. 134. Digital long-term EEG acquisition unit with amplification near the electrodes. - J. Strempel, H. Hinrichs, E. Redmer and G. Reefmann (Neurologische Klinik mit Klinischer Neurophysiologie, Medizinische Hochschule Hannover, Hannover)

Various clinical questions require long-term EEG registration allowing free patient movement. Special cassette recorders restrict the possibilities of computerized analysis of the recorded E E G due to the limited quality of signal reproduction (noise, bandwidth) and the need for expensive replay recorders. Therefore we developed an E E G acquisition unit featuring: preamplification near the electrodes to reduce artifacts; digitization after antialiasing filtering; source coding to reduce the data rate; storage of digitized and compressed signal in semiconductor memory. The prototype records 8 channels with a sampling rate of 166.6 Hz and a resolution of 1 /xV. Controlled by a microprocessor, data are stored using D R A M modules. 40 MB of storage is needed for a 24 h registration. Coding results in a 63.4% reduction of storage capacity. For future developments Flash-EPROM modules are to be preferred. 135. Options and attributes of the digital EEG and its paperless registration. - U. Walter, P. Jacobi and U. Kfihler (Walter Graphtek GmbH)

The usual E E G writes the E E G signals in bipolar or monopolar devalidation with the writing systems analog on paper. The digital E E G uses the same E E G amplifier, but leads the EEG signals only

25P monopolarly against the reference electrode. The program switching is made in the computer and allows great flexibility. We investigated the exactness and evaluation possibilities of digitalized EEGs. During recor:ling all raw data are stored. That means, every single signal of each electrode is stored without limitation of the dynamic (72 dB = 12 bit). A chosen derivation is simultaneously shown on the screen. High amplitude signals, which are limited in the usual EEG through the writing system, can now be recorded and displayed without distortion. It is also possible to display or print the EEG or another chosen time section in another time scale or another filtering. At the same time the E E G can be watched in any devalidation, in order to enable a better judgement. 136. Intracranial EEG recording by means of an intraarterial catheter. - L. Dieterle, P. Stoeter, A. Meyer and N. Prey (Abt. fdr Neurologie und Abt. f'ur Neuroradiologie im St. Elisabethenkrankenhaus, Ravensburg)

Intracranial EEG recordings were carried out by means of insulated Seeker-10 guide wire° (Rehaforum Medical). These guides wires were covered with a continuous teflon coating leaving only the distal (20 mm) and proximal parts unprotected. In the course of an external carotid angiography by patients with meningiomas in order to embolise the supplying blood vessels the guide wires were introduced intracranially into the frontal or parietal branch of the middle meningeal artery. The potentials, recorded from the surface of the temporal lobe, had been 2-4 times higher than the simultaneously registered extracranial EEG. This technique is able to record depthE E G and brain-stem potentials. 137. Distribution functions and normative values of parameters of the spontaneous EEG. - R. Laudahn, E. Scharein and B. Bromm (Institute of Physiology, University Hospital Eppendorf, Hamburg)

The placebo sessions of a database for analysis of pharmacologic effects of spontaneous EEG were used to investigate the distribution functions and to determine normative values of the following EEG parameters: total power, absolute and relative power of standard frequency bands delta (1-4 Hz), theta (4-7 Hz), alpha 1 (7-10 Hz), alpha 2 (10-12 Hz), beta~ (12-20 Hz) and beta 2 (20-30 Hz), Q1, median, Q3 and edge frequency (95% percentile), as well as frequency and amplitude of peaks of the power spectra. In addition, the absolute and relative power of 0.5 Hz frequency ranges from 1 to 30 Hz were analysed. The E E G recordings (Cz versus linked earlobes, bandpass 0.1-30 Hz) were collected from 207 healthy male medical students, 20-30 years of age. The duration of the recording session was 2-4 h. 240-560 artefact free E E G segments of 5 sec with randomised intervals of 10-20 sec were available for each session. The distribution functions of these E E G parameters differ from gaussian distribution, documented by the values of skewness and kurtosis. Some of the investigated parameters had up to 3 modi, due to subgroups with different spectra, e.g., the median frequency with maxima at 2.5 Hz, 5.5 Hz, and 8.5 Hz. The only parameter with a gaussian distribution was edge frequency. (Supported by DFG (Br 310/16-3).) 138. Computerized EEG evaluation versus visual evaluation under clinical routine conditions. - H. Hinrichs a, H. Feistner a and G. Ferber b (a Neurologische Klinik mit Klinischer Neurophysiologie der Medizinischen Hochschule, Hannover, and b Sandoz-AG, Basel, Switzerland)

During recent years we have developed a system for an automatic evaluation of both E E G background activity and intermittent activ-

26P ity. Based on spectral analysis, several parameters such as bandpower values and location measures are derived and fed into a couple of statistical procedures to determine the type of E E G activity as well as asymmetries and dysrhythmic activity. Intermittent patterns (parenrhythmia, alpha spindles, artifacts) are recognized by m e a n s of classical pattern recognition techniques and classified with the aid of an expert system. The complete result is summarized in a report. To validate the system we compared a sample of 200 visually evaluated E E G s from our neurological department with the corresponding computer generated reports. Concerning background activity, the a g r e e m e n t between visual and computerized classification was in the range of the interrater reliability. Especially in the case of asymmetries, a considerably higher consistency was observed with the computer. The validity in analysing intermittent activity was slightly less satisfying. The reason for this is that the various types of grouped E E G patterns lack a unique and consistent definition. 139. Influence of stimulation frequency on SEP components in the 5 0 - 2 5 0 msec latency range. - G. Adler (Central Institute of Mental Health, Mannheim) The influence of stimulation frequency on the somatosensory evoked potential (SEP) components N60, P100, N140 and P200 was assessed in healthy, right-handed subjects (6 men, 4 women; age: 2 0 - 4 , years). SEPs were elicited by stimulation of the median nerve at the wrist with rectangular pulses having a duration of 0.1 msec. Stimulus intensity was adjusted to achieve a clearly visible twitch of the t h u m b (approx. 10 mA). The investigation was carried out at stimulation frequencies of 0.2/sec, 0 . 5 / s e c and 1/sec. SEPs were recorded from F3, F4, C3 and C4, using linked electrodes on the mastoids as reference. 100 sweeps of 500 msec duration (including 100 msec pre-stimulus baseline) were recorded for each stimulation frequency and either stimulated side in a frequency range of 1-100 Hz. Recordings were repeated once or twice to assure the reproducibility of the wave form obtained. At increasing stimulation frequency, the amplitudes of the SEP components investigated decreased. Amplitude decrease was stronger for the late SEP components (N140, P200) than for the earlier ones (N60, P100). Amplitude decrease at increasing stimulation frequency was stronger for stimulation of the right median nerve than for stimulation of the left one. 140. A method for the correction of the DC drift in continuous EEG recordings for evoked potentials. - G. Dirlich, B. Gerull, M. Scherg and M. Heuser-Link (Max Planck Institute for Psychiatry, Munich) At our lab for evoked potentials a recording and data analysis technique has been developed and tuned to the requirements of routine clinical studies which allows the continuous DC recording of 32 channels at sampling frequencies up to 2 kHz. Prior to the computation of evoked potentials by event related averaging several types of disturbances can be eliminated from the data in order to enhance the signal-to-noise ratio. Besides physiological sources of disturbances, e.g., eye blinks, eye m o v e m e n t s and body movements, is the so-called D C drift a well known source of disturbances in DC recording: the junction between the metallic electrode and the living tissue gives rise to potential differences that can be large relative to the evoked potential and in addition can drift with time (Regan 1989). We describe the drift by discussing qualitative and quantitative aspects of D C data, we demonstrate the e n h a n c e m e n t of signal quality that can be achieved by correcting the D C drift, and we present a locally operating heuristic method for the correction of the DC drift based on statistical concepts. This m e t h o d is part of the signal quality improving procedures utilized at the lab.

SOCIETY P R O C E E D I N G S 141. Extracting a representative mean of evoked potentials by using a time-warping algorithm. - G. Schneider, H. Buchner, G. Artmann and G. Hennig (Ilmenau, Aachen) A simple averaging is not generally applicable for creating interindividual representative wave forms (grand-average) of evoked potentials. Different latencies cause a change in morphology and lower amplitudes. By using the time-warping technique mean values of latencies and amplitudes are computed. A software for time warping was created and tested on multichannel recorded SEPs. The grand average and the time-warp mean of multi-channel recorded SEPs from 11 subjects were computed. The median dipole source model was chosen for comparison. The dipole source analysis of the time-warp m e a n revealed the major sources in accordance to the median dipole source model. Source localization on the grand average was not possible. The time-warping algorithm was suitable to compute physiological representative evoked potential means. 142. Evaluation and correction of artifacts in multichannel evoked potential measurements: new aspects of brain electric source analysis. - H. Buchner, I. Ludwig, M. Scherg and P. Berg (Aachen, Munich, and Konstanz) Artifacts bias evoked potential scalp maps or source analysis, for example dipole localization. Therefore, quantitative evaluation and correction of artifacts are desirable. Using somatosensory evoked potential data, we describe a new method, based on brain electric source analysis (Scherg 1990), to remove artifacts from multichannel recordings. Artifacts present in the pre- and poststimulus interval may be distinguished from signals in the poststimulus interval as follows. Applying bandpass filtering and singular value decomposition (SVD), the spatial components underlying the activity in the prestimulus interval can be quantitatively defined. Large weighting coefficients at isolated electrode sites determine artifactual channels, which can be excluded from further analysis. However, the more general approach treats each spatial component vector of the SVD like an additional source in the multiple dipole source model of the poststimulus epoch. The interferences of the artifact/noise components with the brain source components were studied quantitatively by varying the n u m b e r of artifact components in the analysis. T h e new method substantially improved estimates of source activities and locations. 143. The human frequency-following response (FFR): normal variability and relation to the click-evoked brain-stem response. M. Falkenstein, J. Hoormann and J. Hohnsbein (Dortmund) The frequency-following response (FFR) was recorded from 20 h u m a n subjects (11 female and 9 male) in order to study the normal variability of the response and its dependence on age and sex. Particular regard was paid to the frequency function of the FFR. Moreover the relation of the F F R to the click-evoked brain-stem response (BER) was analyzed. The F F R latency was 6.4 msec and frequency invariant, the amplitude was maximal (385 nV) for stimulus frequencies around 350 Hz, with considerable interindividual variance of the best frequency and the shape of the frequency function. In the F F R to low-frequency stimuli large second harmonics were seen. A weak age effect, but no sex effect was found for the F F R amplitude, which was in contrast to the age and sex effects found for the BER. The interindividual amplitude variances of the F F R and the B E R waves were in the same range, whereas the latency variance was larger for the FFR. There were no correlations between F F R and B E R latencies. Significant correlations were found between the amplitudes of the F F R and of B E R waves lI, III and IV, but not of waves V and VI. The results do not favor the

G E R M A N E E G SOCIETY

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hypothesis that the colliculus inferior is the major source of the scalp-recorded human FFR. 144. Somatosensory evoked potentials during moderate hyperthermia. - H. Strenge, W. Schmidt-Bojahr and J. Hedderich (Kiel)

The effects of moderate whole-body hyperthermia on the cervical and cortical somatosensory evoked potentials (SEP) were studied in healthy male subjects, aged 22-32 years. They were immersed in hot water and heated to a median rectal temperature of 39.0°C. Serial SEPs to median nerve stimulation were recorded during cooling at intervals of 0.1°C. The general wave form and the amplitudes did not systematically change. For a I°C drop there was a median latency increase of 2.6-3.7% in cervical and 1.5-7.4% in cortical SEP components. In individual cases significant latency delays of cervical N13 and cortical N20 could already be observed at differences of 0.2 ° and 0.5°C respectively. All other components showed significant latency changes at temperature intervals of 0.6-0.8°C. 145. Neurographie im Volumenleitermodell. Buchner und A. Ferbert (Aachen)

Ch. Rathmer, H.

By title only. 146. Disturbances of color perception in Parkinson's disease. - W. Kuhn, R. Steinberg, T. Biittner, A. Heinz, M. Langkafel, L. Voss, D. Bulgaru and H. Przuntek (Department of Neurology, St. Josef-Hospital, Bochum)

Abnormal visual functions have been observed in Parkinson's disease (PD) by measuring contrast sensitivity and visual evoked potentials. In previous studies a close connection between dopaminergic deficiency and visual dysfunction has been demonstrated. Under treatment with lisuride i.v. a patient of our hospital with malignant neuroleptic syndrome reported a red line instead of a red point stimulus. This misperception normalized by reducing the dose of lisuride. Similar observations have been made in parkinsonian patients under dopaminergic treatment. For the investigation of this phenomenon we developed a computer aided assessment of color perception. Different colored horizontal bars were divided into 60 vertical lines and were presented on a monitor in a flickering way (8 Hz). The monochromatic lines enlarged discontinuously and fusion to the original bars was complete after 10 sec. The point of fusion had to by announced by the patient. We investigated 80 patients with PD and 59 controls. By measuring different color items, a significant faster fusion time could be observed for dark green. The relationship between dopaminergic deficiency, drug treatment and disturbance of color perception in PD has to be discussed. 147. Brain electric source analysis (BESA) in search of effects on late auditory evoked potentials after intravenous application of neuropeptide hormones and cortisol. - M. Heuser-Link, G. Dirlich, A. Hartmann and L. Vogl (Max Planck Institute for Psychiatry, Munich) We investigate the impact of hormones on late auditory evoked potentials. At our lab DC data are continuously recorded on 32 channels at a sampling rate of 500 Hz. The evoked potentials computed from these data by event related averaging are analyzed by the brain electric source analysis (BESA) method (Scherg 1990). This method is based on a spatio-temporal model of few electrical dipoles. It allows, in principle, a separation and identification of the macroscopic electrical activity of the activated brain regions, i.e., the intracranial electrical generators. At present, findings concerning possible impacts of the neuropeptides corticotropin releasing hormone (CRH), adrenocorticotropin (ACTH) and cortisol are still controversial in the literature. In particular, influences on the N100, on the mismatch negativity (MMN) and on the P3a are debated. We performed a clinical study with 10 healthy male adults in order to

identify effects of the hormones mentioned above and to assess possible divergencies between their effects. The presence of effects on latencies and amplitudes of the potentials, and moreover on the likelihood of alpha-EEG activity, the frequency of eye blinks and their phase relationship to the stimulus have been observed. 148. Specific effects of xanthine derivatives on central neurons. - I. Moraidis, D. Bingmann and Z. Liu (Institut f'ur Physiologie, Essen) An overdose of methylxanthines like theophylline and caffeine may lead to epilepsies in patients. It is often assumed that this epilepsy is due to an unspecific rise of neuronal excitability. To test this assumption, effects of various xanthine derivatives on central neurons of guinea pigs were studied electrophysiologically in in vitro experiments. In hippocampal CA3 neurons the xanthine derivative theophylline led to periodically occurring paroxysmal depolarizations (PD; 5 - 6 0 / m i n ) when the bath concentration of this drug exceeded 0.1 mmol/1. Theophylline is known to have a high affinity towards adenosine receptors. Derivatives of lower affinity induced PD sequences only at higher concentrations. Thus, the threshold concentration of caffeine amounted to 0.2 mmol/l, that of theobromine 0.5 mmol/1. The epileptogenic effect was present only in distinct neuronal populations. Caffeine caused PD sequences in 104 out of 112 CA3 neurons, but only in 5 out of 37 CA1 neurons. Granule cells (n = 19) being presynaptic to CA3 neurons as well as neocortical neurons (n = 11) did not generate epileptic discharges even when the caffeine concentration of the bath was elevated to 10 mmol/l. The findings indicate that methylxanthines induce epilepsies through a specific blockade of adenosine receptors only in a subpopulation of central neurons. 149. Reduction of the glutamate and GABA reactions by pentylenetetrazol in oocytes of Xenopus laevis after injection of rat brain RNA. - P. BIoms a,b, M. Madeja a, U. Musshoff a, F. Spener b and E.-J. Speckmann a,c (a lnstitut for Physioiogie, b Institut fiir Biochemie, c Institut fiir Experimentelle Epilepsieforschung, Universit~it Miinster, Miinster) Interactions between the epileptogenic agent pentylenetetrazol (PTZ) and the excitatory neurotransmitter glutamate (Glu) and the inhibitory neurotransmitter GABA, respectively, were investigated in Xenopus oocytes. For the expression of transmitter receptors RNA was prepared from rat brain (guanidine/lithium chloride method after Cathala et al., DNA, 1983, 2) and injected into oocytes (75 ng/cell). The active substances (PTZ: 5-100 mmol/l; Glu: 200 /zmol/l; kainate: 50 /.Lmol/l; quisqualate: 50/zmol/1; GABA: 200 ~ m o l / l ) were administered systemically. Membrane currents were recorded with a conventional voltage clamp technique (Vh: --50 mV). On simultaneous application with PTZ in increasing concentrations (5-100 mmol/1) the Glu reaction was reduced and finally completely suppressed (reduction to 60-0% of the initial value). PTZ exerted analogous effects on the reactions of the agonists of Glu subreceptors kainate and quisqualate. Additionally, a reduction of the GABA reaction (to 60-15% of the initial value) by PTZ (5-100 m m o l / l ) was observed. The experiments show that the epileptogenic agent PTZ can reduce both the reaction to the excitatory transmitter Glu and the reaction to the inhibitory transmitter GABA. 150. DNQX and CNQX block transmission of somatosensory evoked potentials in the rat thalamus. - F. Block, M. Schwarz a and K.H. Sontag (MPI Exp. Medicine, Giittingen, and a Dept. Neurology, Univ. Essen, Essen) The transmission of cortical somatosensory evoked potentials (SEPs) is supposed to be mediated via non-N-methyl-D-aspartate

28P (non-NMDA) types of receptor (Klockgether, J. Physiol., 1987, 394: 455) within the ventrobasal thalamic nucleus (VB). To verify this assumption the effect of microapplication of the specific non-NMDA antagonists, 6,7-dinitroquinoxaline-2,3-dione (DNQX) and 6-cyano7-nitroquinoxaline-2,3-dione (CNQX), and the specific NMDA antagonist (-)-2-amino-7-phosphonoheptanoate (AP7) into the VB on the amplitude and latency of cortical SEPs were measured. SEPs were recorded from the somatosensory cortex of phentobarbitalanaesthetized rats, in response to single shock stimulation of the contralateral forepaw. Microinjection of the non-NMDA antagonists DNQX and CNQX into the VB resulted in a decrease in amplitude and an increase in latency of early cortical SEPs. These changes were: (1) dose-dependent over the range from 0.1 to 1.0 nmol; (2) specific for non-NMDA receptors: coadministration with AMPA, an agonist at the non-NMDA receptor, prevented these changes, whereas coadministration with NMDA did not. Furthermore, microapplication of the specific NMDA antagonist AP7 alone did not affect SEPs; (3) site-specific: injections of DNQX and CNQX into thalamic nuclei adjacent to the VB did not influence the amplitude or latency of early cortical SEPs. 151. NMDA and non-NMDA receptors are involved in the transmission of visual evoked potentials in the rat thalamus. - M. Schwarz a, F. Block and K.H. Sontag (MPI Exp. Medicine, G6ttingen, and a Univ. Essen, Essen)

Within dorsal lateral geniculate nucleus (DGL) of the thalamus transmission of visual input to the cortex is critically dependent on excitatory amino acids acting on N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Whereas the importance of NMDA receptors has been established by the use of specific antagonists such as (-)-2-amino-7-phosphonoheptanoate (AP7), our understanding of the role of non-NMDA receptors was hampered by the lack of antagonists. Since the discovery of quinoxalinediones selective antagonists at the non-NMDA receptor are now available. The present study investigated the effect of microapplication of the specific non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) and the specific NMDA antagonist AP7 into the DGL on the amplitude and latency of visual evoked potentials (VEPs). VEPs were recorded from the primary visual cortex of phentobarbitalanaesthetized rats, in response to single light flashes. Injection of DNQX and AP7 into the DGL resulted in a decrease in amplitude and an increase in latency of early VEPs. These changes were: (1) dose-dependent (DNQX 0.01-1.0 nmol; AP7 0.5-5 nmol); (2) receptor-specific: the effect of DNQX was prevented by coadministration with AMPA, an agonist at the non-NMDA receptor, but not with NMDA; the effect of AP7 was prevented by NMDA, but not by AMPA. 152. Abnormalities of somatosensory evoked potentials in the quinolinic acid model of Huntington's disease. - M. Schwarz, F. Block b, K.H. Sontag b, R. T6pper a and R.J. Noth a (Dept. Neurology, Univ. Essen, a Alfried-Krupp-Hospital, Essen, and b MPI Exp. Medicine, G6ttingen)

One of the very early neurophysiological signs in Huntington's disease (HD) is a diminution of amplitude of early somatosensory evoked potentials (SEPs) recorded over the parietal cortex of HD patients. On the basis of indirect evidence this diminution in amplitude of SEPs has not been attributed to the profound neuronal damage in the striatum, hut rather to the mild atrophy in the dorsal column/lemniscal somatosensory system. The present study investigates whether (1) the quinolinic acid (QA) animal model of Huntington's disease (HD) mimics the diminution of SEP amplitudes and (2) QA lesions confined to the striatum are sufficient to induce these SEP abnormalities. Two weeks after unilateral intrastriatal injection of QA (240 nmol) or the solvent SEPs were recorded with chronically

SOCIETY PROCEEDINGS implanted electrodes from the somatosensory cortex or the ventrobasal thalamus (VB) of lightly phenobarbital-anaesthetised rats, in response to single shock electrical stimulation of the contralateral forepaw. Whereas intrastriatal injection of solvent did not influence SEPs, striatal QA lesion significantly reduced the amplitude of short-latency cortical SEPs by about 40% without affecting the latency. In contrast, SEPs recorded from the VB were unchanged after QA lesion. Careful histological examination after intrastriatal injection of QA revealed no evidence for cell damage outside the striatum. 153. Modality-dependent features of evoked potentials in the frequency domain: a comparison of human scalp recordings and cat intracranial recordings. - M. Schiirmann, T. Demiralp, C. Ba§ar-Eroglu and E. Ba§ar (Institute of Physiology, Medical University, Liibeck)

According to a working hypothesis published earlier (Ba§ar, EEG Brain Dynamics, Elsevier, Amsterdam, 1980), we consider evoked potentials (EPs) as stimulus-induced EEG rhythmicities. Accordingly, it is advantageous to analyze EPs in the frequency domain. We used this approach to compare auditory and visual EPs. In 11 healthy volunteers EEG-EPograms (EEG preceding/EEG following the stimulus; 2 sec each; Ba~ar 1980) were recorded. Averaged EPs were transformed to the frequency domain - by an FFT - to compute amplitude frequency characteristics (AFCs). Digital filtering permitted a combined time and frequency domain approach, Vertex EPs: AFCs computed from auditory and visual EPs showed marked differences: dominant maxima were at around 6-8 Hz in the auditory case and about 8-10 Hz in the visual case. Occipital EPs: alpha responses to visual stimuli were marked, but alpha responses to auditory stimuli were of low amplitude. This was also observed in intracranial visual cortex recordings in cats. Prestimulus EEG: we compared auditory and visual EEG-EPograms - both occipital recordings - and observed higher prestimulus alpha power in the visual case (6 out of 11 subjects). In summary, frequency domain analysis demonstrates modalitydependent features of alpha activity in brain responsiveness to external stimuli. (Supported by DFG grants Ba-943/1-1 to C.B.-E. and Ba-831/5-1 to E.B.) 154. Phosphate concentration increases in the extracellular space of the cerebral cortex during generalised epileptic seizure activity as monitored by in vivo microdialysis sampling. - A. Lehmenkiihler a, j. Kolb b, D. Scheller b F. Tegtmeier b, T. Peters b and E.-J. Speckmann a,c (a Institut ffir Physiologie der Universitfit Miinster, Miinster, b Institut fiir Experimentelle Medizin, Janssen Research Foundation, Neuss, and e Institut ffir Experimentelle Epilepsieforschung der Universitfit Miinster, Miinster)

Seizure activity leads to severe disturbances of the cellular ionic microenvironment in the brain. In the present study seizure-related changes of interstitial phosphate levels were measured by intracerebral microdialysis sampling. A microdialysis probe (Carnegie Medicin, Stockholm) was lowered into the motor cortex of anaestbetised and artificially ventilated rats. The probe was perfused with a phosphate-free artificial cerebrospinal fluid at a flow rate of 2 izl/min. 20 /~1 fractions were continuously collected and inorganic phosphate determined according to P.P. VanVeldhoven and G.P. Mannaerts (Anal. Biochem., 1987, 161: 45-48). At a probe distance of about 300 /~m, a microelectrode was inserted (tip at a cortical depth of 1000 /zm) to measure DC potential shifts. Generalised tonic-clonic seizures were induced by i.p. injection of pentylenetetrazol (120-240 mg/kg) and monitored as periodically recurring negative DC potential shifts. With the occurrence of epileptic discharges phosphate concentration within the dialysate fractions increased continuously and reached

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a maximum after 50-60 rain which was 4-7-fold higher than the resting level. 155. Effect of the epileptogenic agent pentylenetetrazol on a cloned voltage-gated potassium channel (oocyte, Xenopus laevis ). - M. Madeja a, M. Stocker b, U. M u s s h o f f a, O. Pongs b a n d E.-J. Speckmann ax (~ lnstitut for Physiologie, Universit~it Miinster, Miinster, b Lehrstuhl for Biochemie, Universitfit Bochum, Bochum, and ~ Institut fiir Experimentelle Epilepsieforschung, Universitfit Miinster, Miinster) In order to study the functional significance of potassium currents in epileptogenesis, the effect of the convulsant pentylenetetrazol (PTZ) on a cloned potassium channel was investigated. RCK1 potassium channels were expressed in oocytes of Xenopus laecis after injection of in vitro transcribed R N A (0.3-1.0 ng/oocyte) from RCK1 c D N A sequence (Stiihmer et al., E M B O J., 1989, 8: 3235). M e m b r a n e currents were studied with the 2-electrode voltage-clamp technique. Holding potential was - 8 0 inV. C o m m a n d potentials (Vc) ranged between - 70 and + 10 m V (duration 2 sec). P T Z in concentrations of 0.1, 1, 10, 50 and 100 m m o l / l was applied for up to 300 SeC.

With depolarizing Vc slowly inactivating outward currents were elicited (n = 18). The amplitude of the currents was 0.4-1.6, 2.4-6.0 and 8.0-11.5 ,aA at Vc of - 5 0 , - 3 0 and - 1 0 mV. With application of P T Z the outward current was enhanced in the potential range between - 5 0 and - 4 0 mV and was decreased in the potential range more positive than - 3 0 mV. With P T Z concentrations above 50 m m o l / I the inactivation of the current increased. All effects of P T Z depended on the concentration of the drug and were completely reversible.

156. Sequential expression of functional glutamate subreceptors in individual oocytes of Xenopus laevis after injection of RNA from rat brain. - U. Musshoff, M. Madeja, P. Bloms and E.-J. Speckmann (Institut fiir Physiologie, Miinster) Injection of rat brain R N A into oocytes of Xenopus laevis led to the expression of glutamate receptors. To get further information about the development of functional differentiation of this receptor type the latencies of expression of glutamate subreceptors in individual oocytes after injection of R N A were measured. R N A was isolated from rat brain and injected into oocytes by pressure (75 ng/cell). M e m b r a n e currents were measured using conventional voltage clamp technique. Ligands were administered at the following concentrations (in izmol/1): kainate (KA) 50; a-amino3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) 100; quisqualate (QA) 50; N-methyl-D-aspartate ( N M D A ) 100. After injection of R N A the same cells were tested daily for sensitivity to the ligands. T h e development of the sensitivity for the agonists showed a time-course which was different for the various agonists ( + = sensitivity for the agonist): Time after injection

KA

6 h

1 day 2 days 3 days 4 days 5 days

+ + + + +

AMPA

QA

NMDA

_

_

m

+ + + +

+ + + +

+

The K A response was reduced markedly by simultaneous application of A M P A . This was also true for the first day when an A M P A reaction was not detectable. N M D A and n o n - N M D A receptors can be clearly differentiated by their delay of expression. The n o n - N M D A receptors KA and A M P A were obviously not separated.

157. Effects of intracellularly and extracellularly applied lead on action potentials of identified neuronal individuals (buccal ganglia, Helix pomatia). - M.N. Said a, N. Binding a, U. Witting a, U. Altrup c and E.-J. Specklnann b,c (a lnstitut f'ur Arbeitsmedizin, b Institut f'ur Physiologie, and c Institut fiir Experimentelle Epilepsie-Forschung, Universit~it Miinster, Miinster) Lead is known to be responsible for several types of neurotoxicity. The present investigations aim to contribute to further analysis of possible mechanisms underlying the clinical manifestations. The experiments were performed on the identified neurons B1, B2, and B3 of the buccal ganglia of HelLr pomatia. Changes in m e m b r a n e potential were measured with conventional techniques. Lead (PbCl 2) was applied extracellularly (0.01 and 0.02 retool/l) or intracellularly with pressure ejection (0.17 retool/l). (A) Extracellularly applied lead caused (i) a decrease in the amplitude and (ii) an increase in the duration of the action potentials (AP). (iii) After washing out of the substance these effects were not completely reversible. (B) Intracellularly applied lead (i) caused a little decrease in the duration of the AP, (ii) abolished the effects of extracellularly applied lead, and (iii) reduced the widening of the AP by cobalt (CoClz, 5 m m o l / l ) or tetraethylammonium (TEA-CI, 10 m m o l / l ) . (C) Intracellularly applied calcium (CaC1 z 1 tool/l) exerted similar effects as described for intracellular lead. A possible interpretation of the results is that lead exerts its effects by interaction with calcium dependent processes.

158. Low MgZ+.induced epileptic field potentials in hippocampus: increase of the antiepileptic effects of verapamil with elevated extracellnlar K + concentration. - M. Pohl a, H. Straub b and E.-J. Speckmann b,c (~ Fyziologick~ fistav (~SAV, Prague, Czech Republic, b Institut fiir Physiologie and c Institut fiir Experimentelle Epilepsieforschung, Universitfit Miinster, Miinster) Verapamil has been shown to depress low Mg2t-induced epileptic field potentials (EFP) in the hippocampus (Pohl et al., Eur. J. Neurosci., 1991). The aim of the present investigations was to compare the antiepileptic effects of verapamil in neurons with normal and decreased m e m b r a n e potentials. Therefore, the study was performed with normal and elevated K + concentrations of the Mg 2+free artificial cerebrospinal fluid (CSF). Experiments were carried out on 36 slices (400-500 p~m) from guinea pig hippocampus. The effects of verapamil (40 and 60 tzmol/l) were compared in Mg2+-free CSF containing 4 (normal) and 8 m m o l / I K +. W h e n the K + concentration was elevated (i) the latency of abolition of EFP became significantly shorter and (ii) the depressive effects of verapamil were maintained significantly longer during the washing period. This prolongation was abolished when normal K + CSF was used for washing out following verapamil acting in elevated K + CSF. These observations show that the efficacy of the calcium antagonist is strongly enhanced with elevated e~tracellular K + concentration. It may be assumed that this effect is coupled with te decrease of m e m b r a n e potential.

159. Application of confocal microscopy to investigate the development of morphological changes during epileptic activity. - A. Schulze-Bonhage a, U. Altrup a, E.-J. Speckmann a,b and W. Wittkowski c (a Institut fdr Experimentelle Epilepsieforschung, b lnstitut fur Physiologie, and c Institute fur Anatomie der Universitfit Miinster, Miinster) Epileptic activity has often been discussed to cause structural changes of the neurons involved. In the present study, structure and function of single neurons in the intact tissue are investigated in parallel by the combination of intracellular recordings and the use of an inverted confocal laser scanning microscope.

30P A perfusable experimental chamber with a coverslip bottom is inserted in a central notch of a table constructed for an inverted microscope. This table with microelectrode holders attached can be driven by an x/y stepper motor during intracellular recordings. Impaled neurons are stained with the fluorescent dye Lucifer Yellow. Optical sections inside the tissue placed on the coverslip bottom can be obtained at a maximal depth of 100 /~m with a lateral resolution of less than 1 p.m. First experiments were carried out on identified neuronal individuals in the buccal ganglia of Helix pomatia and on neurons of hippocampal slices of the guinea pig. After induction of epileptic activity, the following morphological changes could be observed: the development of multiple constrictions and of small processes, local or extended swellings of dendritic segments, the appearance of single vacuoles, and the extrusion of intracellular material.

160. Evoked field potentials in the visceral ganglion of Helix pomat/a: the effect of acetylcholine (ACh). - A. Schiitt-lshizawa and E. Ba§ar (Institute of Physiology, Medical University, Liibeck)

The electrically evoked compound field potentials of the isolated ganglion resemble visual evoked potentials (EPs) of cat surface EEG. Methods of analyses based on systems theory were used: Fourier transform for frequency analysis and root-mean-square (RMS) voltage of digitally filtered signals for quantification. ACh at 10 4-10 -3 M selectively enhances the 4-15 Hz as well as the 30-70 Hz components of the EPs, but at 10 -2 M shows a tendency of suppression. Stimulation causes 50% damping of prestimulus activities facilitated by ACh (a late part of evoked activity). The neuronal system may change its state of intrinsic activity by damping of oscillation when exogenous stimulus is given. The results observed in the present ganglion model imply particP pation of ACh in activating these frequency channels for processing electrical signals even in a small population of diverse, connected cells. The 3.5-8 Hz, 8-13 Hz and 40 Hz responses are consistently elicited in acoustical or visual EPs in cats and humans (Ba§ar, EEG-Brain Dynamics. Elsevier, Amsterdam, 1980). The ACH-induced selective increase of the 4-15 and 30-70 Hz responses, which may be comparable to theta-alpha combined rhythm and 40 Hz rhythm in the mammalian EEG, respectively, may be possible evidence for what may happen in the neuronal assemblies of the cholinergic system during the course of arousal in higher animals.

161. Influence of muscimol microinjections into the fastigii nuclei on posture and eye movements in monkeys. - A. Straube, R. Kurzan, Ch. Helmchen and U. Biittner (Dept. of Neurology, University of Munich, Klinikum Grosshadern, Munich)

There is no good knowledge about the effect of lesions in the fastigial nuclei in monkey and man. Beside a control on body posture recent results from single unit recordings suggest a role also in the control of eye movements. Nothing is known about the pharmacological mechanisms involved. Therefore we injected after localisation of the fastigial nuclei by single unit recordings 1 /zg muscimol or 1 p.l lidocaine 1% and investigated the effects on eye movements by magnetic search coil registration and on body posture by video registration. After rostral muscimol injections there was a tendency to fall to the ipsilateral side, which was compensated rather quickly, without any limb ataxia or oculomotor disturbances. More caudal injections induced a reduction of the smooth pursuit gain of about 30% towards the contralateral side without any ataxia. The vestibulo-ocular reflex did not change. The influence on saccades was not investigated in this study. The results indicate a specific role

SOCIETY PROCEEDINGS of the caudal fastigial nucleus also in the generation of a smooth pursuit signal. 162. The role of scalp EEG in epilepsy Surgery. - H. Liiders (Bethel)

Evaluation with invasive electrodes is frequently essential to define with precision the localization of an epileptogenic focus in candidates for surgery of epilepsy. Invasive electrodes, however, are only necessary in a selected number of patients. On the other hand, evaluation with scalp electrodes is an indispensable procedure which provides the following essential information. (a) It establishes if the spells are actually of epileptic nature and an analysis of the seizure symptomatology helps identifying the location of the epileptogenic zone. (b) Analysis of the spatial distribution of the interictal spikes permits subdivision of the focal epilepsies into the following 4 groups: (1) unilateral mesio-temporal epilepsies which frequently do not require any additional invasive recordings; (2) bilateral mesiotemporal epilepsies which usually require recordings with depth electrodes; (3) unilateral neocortical epilepsies which usually require evaluations with epidural, subdural and/or foramen ovale electrodes; (4) bilateral neocortical epilepsies which usually are not suitable surgical candidates. (c) Analysis of ictal scalp recordings usually complements the results obtained in the analysis of the interictal activity. 163. Compound P300-40 Hz response in the eat brain. - C. Ba§arEroglu a, E. Ba§ar, F. Schmielau a and U. Schramm c (a Institute of Medical Psychology, Liibeck, b Institute of Physiology, Liibeck, and c Institute of Anatomy, Liibeck)

Physiological correlates of cortical 40 Hz oscillations recently gained tremendous importance. One of the main questions is whether 40 Hz oscillations have only cortical origin. The purpose of this paper was to analyze subcortical 40 Hz components. Our experiments were performed with 9 freely moving cats with chronically implanted intracranial electrodes. As stimulation, we used 1000 msec bursts of 2 kHz tone with an intensity of 80 dB SPL. The tones were presented repetitively with intervals of 2.5 sec and every fifth tone was omitted. Our results showed that the hippocampal P300 response has a frequency content with prominent theta and 40 Hz enhancement (P < 0.001), especially in lower pyramidal layer (CA3) recordings. Furthermore, analysis in the frequency domain showed that the 40 Hz component of P300 in the reticular formation was also enhanced. These results indicate that the 40 Hz response is not only a cortical pattern. Moreover, the P300 is accompanied by a 40 Hz response and it appears to be also a universal building block of brain responsiveness. Additionally we will discuss the relation between 40 Hz response and cognitive function. (Supported by DFG grant (Ba-943/1-1 and Schm 428/5-1).) 164. Localization and lateralization of supplementary motor seizures (investigation with surface and epidural peg electrodes). - H. Holthausen, A. Sakamoto, H.-J. Meencke, S. Noachtar and H. Liiders (Epilepsy Center, Bethel)

Supplementary motor seizures are characterized by their sudden onset, short duration, occurrence predominantly during sleep and motor signs including tonic posturing of contralateral and ipsilateral proximal limbs. Consciousness is frequently well preserved. For the purpose of presurgical evaluation we investigated 8 patients who had typical supplementary motor seizures. (A) Clinical signs. All 8 patients had tonic seizures involving proximal muscle groups of both arms with variable involvement of trunk and legs. Focal clonic seizures were recorded in 1 patient only. Versive eye movements initially or during the evolution of the

GERMAN EEG SOCIETY seizures were seen in 5 patients. Consciousness was preserved during all seizures in 5 patients. (B) E E G findings. Six patients had interictal and ictal epileptiform changes. O n e patient had interictal and 1 patient ictal changes only. In 5 patients these changes were pointing to the supplementary motor region. In 3 patients changes were seen more diffusely. (c) Lateralization. We felt that reliable lateralization of seizures was possible in 2 patients only. Interictally their E E G s showed sharp waves fronto-central and contralateral to the side of focal tonic (and focal clonic in 1 case) seizures; ictal recordings revealed low amplitude fast activity over the same region. 165. Simultaneous depth and surface electrode recording of temporal lobe seizures. - A. Ebner, I. Tuxhorn and H. Liiders O n e of the main objectives of the presurgical evaluation of patients with mesiotemporal epilepsy is the correct lateralization of the epileptogenic zone. Scalp E E G recordings not infrequently will show a bilateral ictal pattern as the initial ictal change and thereby not permit correct lateralization of the epileptogenic zone. In patients with temporal lobe epilepsy who had prolonged simultaneous E E G monitoring with bilateral temporal depth and scalp electrodes, bilateral ictal slow waves at the scalp were associated with unilateral ictal spikes at the mesial depth electrodes. These rhythms were synchronous suggesting that a strictly unilateral epileptogenic focus was causing the diffuse bilateral surface ictal pattern. The analysis of the voltage distribution of this ictal pattern suggests that a highly synchronized unilateral mesiotemporal focus may determine the bilateral surface distribution by a far-field generator mechanism. The orientation of the mesiotemporal generator, which may be assumed to be a dipole, would determine the surface E E G distribution of its far-field effect. A more anterolaterally oriented dipole (radial orientation with respect to the temporal convexity) would generate a correctly lateralized ictal event on surface electrodes, whereas a more anteromedially oriented dipole would be reflected as a bilateral frontotemporal change on the surface. 166. Electrocorticographic observations of pharmacological and physical activation of the epileptic focus - a comparison of 5 methods. - A. Hufnagel and C.E. EIger (Dept. of Epileptology, University of Bonn, Bonn) Specific responses of the epileptic focus following application of 5 different activational methods were assessed in 179 medically intractable epileptic patients. T h e aim was to obtain additional information about the focus location in the process of presurgical evaluation. Pharmacological activation was achieved by intracarotidally applied amobarbital (n = 52; 104 tests), methohexital anesthesia (n = 27; 54 tests) or propofol anesthesia (n = 20; 40 tests). In addition, cortical electrical stimulation (CES) (n = 32, 32 tests) and transcranial magnetic stimulation (TMS) (n = 48; 60 tests) were performed. Data analysis was generally based on electrocorticographic registrations via chronically implanted subdural electrodes. T h e following responses of the epileptic focus were observed (percentages of the cohort involved): (1) seizure induction; amobarbital = none, methohexital = none, propofol = 5%, CES = 31%, TMS = 6%; (2) induction of epileptiform activity; amobarbital = 62%, methohexital = 89%, propofol = 25%, CES = 81%, TMS = 60%; (3) suppression of spontaneous epileptiform activity: amobarbital = 12%, methohexital = none, propofol = 50%, CES = 25%, TMS = 33%. The best correlation with the spontaneous epileptogenic status was observed during a deep methohexital-induced narcosis (100 mg i.v.). Conclusively, electrocorticographic registration following application of (intracarotid) amobarbital, high doses of methohexital or during CES and TMS contribute valuable and in part unique data about the location of the primary epileptic focus.

31P 167. Comparison of foramen ovale and subdural strip electrodes in presurgical epilepsy evaluation. - P. Schiller, H. Stefan, U. Neubauer a and H. Schulemann a (Depts. of Neurology and a Neurosurgery, Centre for Presurgical Evaluation and Epilepsy Surgery, University Erlangen-Niirnberg, Erlangen) For presurgical focus localization in epilepsy, invasive E E G techniques are often used. We compared foramen ovale (FO) and subdural strip (SD) electrodes. In 34 patients, FO electrodes were placed bilaterally. The side-effect most often seen was pain due to trigeminal nerve irritation However, in no patient the investigation had to be interrupted. Other side-effects were: continuous hypaesthesia (3), paresis in chewing muscles (1), braking of electrodes (1 intracranial, 2 extracranial), bleeding in extracranial tissue (1), dislocation (3). In 1 patient a brain-stem lesion was seen probably due to the FO electrode. Twenty-three of these patients had additional 2-8 4/8-contact SD electrodes (19 on both sides, 4 on one side) in frontal lateral/basal a n d / o r temporal lateral position. The discomfort due to pain was less intense, only 2 patients suffered dysaesthesia in the region of the drill-hole. In 1 patient a spontaneous dislocation was seen. Bleeding or infections were not seen. Twenty patients had a temporal focus: 11 could be localized only with FO electrodes. In 9 a combination of FO and SD electrodes was used: 5 had a temporo-mesial ictal onset, 3 a temporo-lateral, 1 a shift of onsets. In 7 patients that came out as frontal lobe epilepsies, FO electrode did not show false positive results. 168. Localization of epileptogenic foci with frequency and raw potential EEG mapping. - B. Schiiler, Th. Schlegel and H. Stefan (Dept. of Neurology, University Erlangen-Niirnberg, Erlangen) In 17 patients a computerized analysis (Brain-star, Schwind, Germany) of scalp E E G was performed during presurgical evaluation. Thirty epochs without artifacts of 2 sec duration were selected visually (sample rate 256 Hz, 0.5-100 Hz). Frequency maps for the delta, theta, alpha and beta bands were calculated. In addition, epileptiform activity was averaged (7-44 averages) for a raw potential analysis. In 6 cases, a foramen ovale or sphenoidal electrode was used as trigger. In d e l t a / t h e t a band, 8 patients showed a focus in correct localization, 3 in wrong localization, 1 did not show focal slowing. In 3 cases, interpretation was equivocal due to fronto-temporal localization, in 2 due to slowing on contralateral side, too. In alpha and beta bands, 10 showed a correct localization, 2 a wrong one and 1 a doubtful one. Four did not show clear abnormalities. Raw potential analysis had different results when phase reversal of a dipolar pattern was seen as correct localization or simply the maximal amplitude of the spike. The first method had the following results: correct 9, false 7, ambiguous 1. The data for the second evaluation are: correct 10, false 3, ambiguous 4. Thus, analysis of beta band gave most reliable results which is hardly possible by visual evaluation. 169. Chemosensory evoked potentials in epilepsy. - T. Hummel, P. Schiiler, H. Stefan and G. Kobal (Erlangen) Olfactory function can be assessed by m e a n s of chemosensory evoked potentials (CSEP) which have proved throughout recent years to be a useful tool in clinical diagnosis of smell disorders. The aim of the study was to birhinally investigate olfactory function in patients with epilepsy of the temporal lobe in order to test the hypothesis that olfactory stimulation ipsilateral to the focus is processed differently to contralaterally applied stimuli. Fourteen patients were investigated, 8 patients with left temporal lobe epilepsy and 6 patients with right temporal lobe epilepsy. Localization of epileptical loci was carried out by m e a n s of clinical investigation,

32P scalp surface EEG, intracranial EEG, and NMR. Investigation of the trigeminal system was performed by the use of carbon dioxide, a substance reported to exclusively activate fibers of the trigeminal nerve. The olfactory system was tested using vanillin and hydrogen sulfide as stimuli. Stimulus duration was 200 msec (interval approximately 40 sec). CSEPs were recorded from 5 positions. CSEP latencies after left-side stimulation were prolonged in patients with leftsided epileptical foci. In contrast, in patients with a right-sided focus, CSEP latencies were prolonged when the right nostril had been stimulated. These findings were less pronounced after stimulation of the trigeminal system. 170. Epilepsia partialis continua with unilateral cortical dysplasia a case report. - G. Hefner, C.E. Elger, W. Entzian a and G. Kersting b (Clinic for Epileptology, a Clinic for Neurosurgery, b Institute of Neuropathology, University of Bonn, Bonn)

The 8-year-old patient, after a normal development during infancy, had the first seizure - a left sided partial seizure - in her 4th year. Simultaneously, a slowly progredient left hemiparesis developed. Beside partial seizures, left sided hemi-grand-mal or secondary generalisations developed additionally. The M R T showed no abnormalities. Notwithstanding therapeutic intervention with various anticonvulsants, the epilepsy developed progressively with an intermittent and finally a continuous epilepsia partialis continua left. The patient appeared mentally retarded. Neuropsychological testing was not possible. A renewed examination with imaging techniques now showed a discrete right hemiatrophy. Subsequent to a presurgica[ evaluation a functional hemispherectomy was performed. Postoperatively no more seizures were seen. The hemiparesis was not aggravated. The postoperative mental development was positive. Histology showed a cortical dysplasia with unstructured cortex and without Betz cells in the precentral gyrus. The case report demonstrated that cortical dysplasia can lead to a late manifestation of neurological disturbances and epileptic seizures. 171. Hemispheric lateralization of cortical DC potentials in left handers - two case reports. - C. Thomas, E. AItenmiiller and H. Uhl (Tiibingen)

In left-handed subjects sodium amytal tests revealed left hemispheric speech dominance in the vast majority of cases. Nelson et al. Brain Cogn., 1990, 14: 92) found no hemispheric lateralization in E R P s during a language comprehension task in left-handers. Our evaluation of cortical DC potentials during speech processing revealed a right hemispheric activation in 22% of left-handers (AItenmiiller, Int. J. Neurosci., 1989, 47: 1). We report a marked right hemispheric speech dominance in 2 exemplary cases. A 46-year-old familial left-hander suffered from complex seizures with speech arrest due to a right temporal angioma. A 21-year-old female with strongly right-handed relatives had a slight right-sided hemiparesis due to a perinatal left hemispheric stroke. DC potential shifts in frontal, central, temporal and parietal leads were analyzed during acoustic presentation of a noun and mental search for synonyms. In both cases right fronto-central activation could be demonstrated in the stimulus period as well as in the task period. From these results we conclude: (1) fronto-central lateralization of DC potentials during language processing reflects hemispheric dominance for language. (2) The activation pattern of the patient with infantile cerebral palsy may be a result of cortical plasticity in early childhood. (Supported by the D F G (SFB 307 B8).) 172. The dynamics of EEG and saccades during therapy with carbamazepine and diphenylhydantoin. - K.P. Hoffmann, G. Miihlau, C. Miiller, R. Both, M. Jahns and W. Zahlten (Jena)

In our study on the dynamics of E E G activity and saccadic eye movement parameters patients with partial epilepsy were included.

SOCIETY PROCEEDINGS During pharmacological therapy patients were given carbamazepine or diphenylhydantoin. The patients were examined before therapy, 3 weeks after the maximal drug dose and 2, 4, 8 and 12 weeks later. The E E G was analysed by computer. Simultaneously plasma concentration was determined and saccadic eye movements were recorded. The saccadic parameters measured were reaction time, duration, peak velocity and overshoot. Time series analyses of the dynamics of various parameters like m e a n frequency of the alpha peak at the E E G power spectrum and peak velocity of saccades are very important to detect the pharmacological influence. The correlations of all parameters were calculated. These examinations show a possible way to objectify side effects during the pharmacological therapy by using neurophysiological methods. 173. Undesired enhancement of phenprocoumone effect by carbamazepine. - C. Fritz and H.-J. Braune (Marburg)

A 47-year-old female patient who had been suffering from cerebral venous thrombosis was treated with p h e n p r o c o u m o n e over the course of 6 m o n t h s in order to prevent further thrombotic complications. U n d e r a dosage of 5 - 7 x 3 m g / w e e k the prothrombin time was within therapeutic range. In addition, the patient had to be treated with carbamazepine for symptomatic epilepsy (2X400 mg retard/day). This resulted in a rapid rise of prothrombin time which made adjustment of the phenprocoumone dosage necessary. An intensification of coumarin effects by carbamazepine has so far not been reported. We conclude that patients with such a combination therapy should be followed up very carefully. 174. Fundamentals and principles of magnetoelectroencephalography. - H. Stefan (Department of Neurology, University Erlangen-Niirnberg, Erlangen)

Electrophysiological investigations provide the basis for a deeper pathophysiological understanding of neuronal activity. Besides elect r o e n c e p h a l o g r a p h y (EEG), recently m a g n e t o e n c e p h a l o g r a p h y (MEG) has become available for functional diagnosis. Magnetic fields in the nervous system are less influenced than electric fields because of different conductivities of the various body tissues. This fact provides the main aspect of the established assumption that magnetoencephalographic records are suitable for the localization of generators of spontaneous and evoked activity. Fundamentals and methods are demonstrated for the recording of electrophysiological p h e n o m e n a in M E G and E E G in information processing and their computed analysis. 175. A new encephalomagnetic effect in static magnetic fields. - L. von Klitzing (Dept. Clin. Res., Medical University, Liibeck)

Alterations of power density calculated from E E G data in static magnetic fields point to a shift from the genuine isotropic distribution of encephaloelectric charge transports to an anisotropic state that m e a n s the charge movements become an orientation. Because of the physical law that each electrical charge movement induces a magnetic event we fixed coils at the head surface for detecting these possible encephalomagnetic fields. By this method we sampled data from corresponding points of the two hemispheres (e.g., P3 and P4 position, corresponding to the international 10-20 system) with altered power densities in some frequency bands when switching the field vector twice between two epochs of data sampling. By special methods we are able to discriminate between artificial (by movements) and true signals. 176. Enzephalomagnetischer Effekt im statischen Magnetfeld. - L. von Klitzing (Med. Universitfit zu Liibeck, Liibeck)

By title only.

GERMAN EEG SOCIETY 177. About the significance of influences of static magnetic fields on evoked potentials and spontaneous EEG of man. - L. von Klitzing (Dept. Clin. Res., Medical University of Liibeck, Liibeck) In the last years there were some reports about influences of magnetic field on biological systems, especially on encephaloelectrical signals. The main problem is to separate true signals from artifacts, produced by m o v e m e n t s of the whole detecting system, like electrodes or cables. W h e n generating somatosensory evoked potentials the n. medianus is stimulated and movements of the t h u m b or the arm are possible. By this the whole body of the test person may be moved synchronously by each stimulus. W h e n the time of this periodical movement is short in comparison to the stimulus sequence, the phase angle of the artificial signal related to the trigger point ( = stimulus) has to be the same during the whole experiment. By Fourier Transformation we tested the frequency and time domains of the averaged SEPs. Because of shifting phase angles of the separated frequency components we are sure that the altered SEPs in static magnetic fields are true signals. Furthermore we analysed the spontaneous E E G by the same method, averaged by ECG R wave trigger. Corresponding to the results before, we found shifting angles, too. Our conclusion is that the encephaloelectric effects in static magnetic field are real events. 178. The "contingent magnetic variation" (CMV). First finding~ with a multichannel system. - J. Vieth, P.B.C. Fenwick a, p. Grummich, J. Lumsden b, H. Kober, G.W. Fenton ¢, E. Weise, H. Pongratz and A. Daun (Erlangen, a London, UK, b Crowthorne, UK, and ~ Dundee, UK) The magnetic "contingent negative variation' (CMV) was recorded from 5 subjects with a 37-channel m a g n e t o m e t e r (Siemens Krenikon ®) in a shielded room. the G o / N o - g o paradigm was: a warning tone and test tone presented with an interval of 3.5 sec via an airline headphone. The Go stimulus was 2 kHz, and the No-go 1 kHz. To avoid white noise, with Go trials a button press was required and with No-go trials button pressing must be inhibited. There were major similarities of the CMV and the CNV. As would be expected, a dipole-like pattern of the magnetic field m a p was seen for the auditory evoked response. The fields of the C M V were complex suggesting deep sources and multiple distributed generators. First results using the single current dipole allow us to suggest for the early C M V component an occipital accumulation of dipoles and for the late component a frontal one. Further modelling procedures using the distributed source solution are in progress in collaboration with Ioannides. 179. Induced theta and alpha rhythmicities in magnetoencephalographic recordings. - E. Rahn a, K.B. Mikkelsen b, K. Saermark b and E. Ba§ar a ( a Institute of Physiology, Liibeck and b The Technical University of Denmark, Lyngby, Denmark) We measured auditory evoked magnetic fields (AEFs) with 15 subjects by m e a n s of a 7-channel squid system (stimulus: 1 kHz tone burst at 60 dB H L intensity, 1 sec duration). For each channel position the frequency content of the averaged A E F was computed with the help of FFT. The maxima of the amplitude frequency characteristics (AFCs) in temporal locations were focussed at 5 - 7 Hz or 9-10 Hz, sometimes forming a complex 5-15 Hz response. Pronounced changes in frequency distribution within the channel array could be observed. Transient evoked responses revealed a rhythmicity in the 10 Hz range corresponding to a prominent alpha peak in the A F C or a damped theta rhythmicity corresponding to the theta maximum in the AFC. A n u m b e r of single sweeps also showed without digital filtering - oscillatory alpha or theta wave forms in accordance with the AFCs. Evoked potentials (EPs) can be con-

33P ceived partly as stimulus-induced coherent activity of some generators of the spontaneous E E G rhythms (Ba~ar 1980). In this study some neuromagnetic ex~dence of stimulus-induced theta and alpha rhythmicities of the braJn is presented. We are inclined to consider this magnetic rhythmic activity as closely related to the resonance p h e n o m e n a observed in EP experiments. (Supported by D F G grant Ba 831/5-1.) 180. Cortical landmarks: a left-right comparison. - K. Niemann, H. Knott and D.G. von Keyserlingk (Institute of Anatomy, Aachen University of Techv.ology, Aachen) The interpretation of electrophysiological and neuromagnetic data of the cortex is closely related to brain topography. Cerebral structures like fissures can be registered from formaline-fixed brain specimens using a 3D ,ligitizer. Thus information about their 3-dimensional variation car: be gathered. For the registration, 20 brain specimens were cut medio-sagittally and oriented in the ACPC reference system. 19 sul,:i were registered in their complete depth. A left-right comparison in the same brain is enabled by a reflection of the digitized points throagh the midsagittal plane. The variation was analysed in a 3 - d i m e n s ' m a l voxel space. We already used similar algorithms for the implc,nentation of a 3-dimensional computer-resident brain atlas. The course of the sulci can be projected onto deliberately chosen planes. In a medio-sagittal projection the angle between the intercomm~ssural line and the central sulcus was 56.5 ° (S.D. = 6.8) on the left md 55.8 ° (S.D. = 7.4) on the right side. The respective values for the superior temporal sulcus were 27.2 ° (S.D. = 4.8, left side) and 26.5 ° tS.D. = 6.2, right side). Side differences were significant at the 0.01 Ic~:el only for the sylvian fissure (29.0 °, S.D. = 5.9, left side; 33.2 °, S . D = 7.2, right side). 181. Multichannel magnetoneurography of evoked brachial plexus activity. - G. Curio, S.N. Ern~ a, R. Koetitz a, j. Scheer a, D. Stollfuss a, p. Aust and C. Schumacher (Abt. f. Neurologie, Klinikum Steglitz, Freie Universit/it Berlin, and a Physikalisch-Technische Bundesanstalt, Institut Berlin, Berlin) Magnetic compound action fields (CAF) of the brachial plexus have been detected by sequential single channel m e a s u r e m e n t s (Curio et al., E E G J., in press). For clinical operation, rapid data acquisition and reliable channel positioning are mandatory. First experiences with a planar 37-channel magnetometer, operated in the Berlin magnetically shielded room, show: (1) At 10-13 msec after electrical nerve stimulation at wri~-,t, CAFs (about 100 IT) were detected above the upper thoracal quadrant (6000 averages; 6 stimuli/sec, intensity 5 - 2 0 mA, width 0.1 mscc; recording bandwidth 6-500 Hz, 2 kHz ADC, system noise 5 fT/H~/~-). (2) Muscle twitches contingent upon suprathreshold stimulation did not introduce relevant artefacts. (3) Upon stimulation of median, ulnar or radial nerves. CAFs with different peak amplitudes were seen propagating toward the spine. (4) Plexus CAFs did not show a symmetric dipolar field distribution probably related to the geometry of the thoracal volume conductor and the fanning out of the activated nerve fibers within the plexus. (5) Clinical perspectives comprise improved detection and localization of nervous malfunction, e.g., in case of plexus trauma or suspected thoracic outlet syndrome. 182. Examinations of biomagnetic fields in unshielded environment. - K.-P. Hoffmann, R. Both, M. Jahns, G. Miihlau and H. Nowak (Jena) An intracellular current produces a biomagnetic field. This magnetic field can be sensed by a detection coil made of superconducting wire. The sensor is a S Q U I D coupled to a second order gradiometer. A 1- and a 5-channel system are used. After amplifying the signals are digitized and stored for further computer evaluation and display.

34P In unshielded environment it was possible to record the magnetic fields during eye movements and to detect saccades. With a 5-channel system the epileptical activity of a patient from the left temporal lobe was measured. The triggered crosscorrelation functions from E E G and M E G were calculated. After an electrical median nerve stimulation of the wrist a somatosensory evoked potential and simul-

SOCIETY PROCEEDINGS taneously the magnetic fields were recorded. The visually evoked magnetic fields were measured after averaging of 128 responses on brief flashes of light. Isofield maps over the occipital region were drawn. The results show that it is possible to measure various magnetic fields in unshielded environment. The future of biomagnetism strongly depends on the development of clinical applications.