P14-25 Effects of evoked pain on the muscle action potential obtained by direct muscle stimulation

S190 Methods: Pain and tactile thresholds were studied using IES and transcutaneous electrical stimulation (TS), respectively, in ten healthy volunteers before, and 1 h, 3 h, and 5 h after a local anesthesia with lidocaine. Cortical potentials evoked with IES and TS were also studied in 12 healthy volunteers before and 5 h after the anesthesia. Results: Although the local anesthesia had no effect on the evoked potentials or the tactile threshold for TS, it markedly increased the pain threshold and almost abolished the evoked potentials for IES. Conclusion: These results suggest that IES is a sensitive tool for detecting functional changes of cutaneous A-delta fibers. P14-22 Trigemino-cervical system imbalance in patients with cervicogenic and posttraumatic headaches E.A. Kuznetsova1 , E.Z. Yakupov1 1 Department of Neurology, Neurosurgery and Medical Genetics, Kazan State Medical University, Kazan, Russia Objective: To elucidate neurophysiological mechanisms of different forms of chronic secondary headaches and, in particular, to evaluate involvement of trigemino-cervical system in pathogenesis of cervicogenic (CH) and posttraumatic headaches (PH). Methods: 30 patients with CH aged 11 72 years old and 40 patients with chronic PH aged 10 77 years old were included into study. 30 healthy subjects aged 18 76 years old presented the control group. Neurophysiological methods included short-latency somatosensory evoked potentials (SEP) on median nerve stimulation, trigeminal evoked potentials (TEP), blink reflex (BR) and stimulative EMG of masticatory muscles. All neurophysiological investigations were performed with the use of standard techniques. Statistical methods included Fisher exact test and correlation analysis with Pearson criterion. Results: The statistical analysis revealed increase of the following SEP parameters in patients with CH in comparison with healthy controls: N9N13 (p < 0.01), N9-N20 (p < 0.01), N9-N11 (p < 0.001), N20-P23 (p < 0.05) and P23 latency increase (p < 0.05). The present study showed the tendency to TEP latencies decrease, increase of early BR component R1 duration (p < 0.05) and latency decrease of late component R2 (p < 0.05) ipsilaterally in patients with CH. According to the results of stimulative EMG of masticatory muscles the tendency to latency decrease and increase of M-response duration (p < 0.05) on temporalis muscle stimulation were observed. In patients with chronic PH statistical analysis showed increase of P23-N30 (p < 0.05), the trend to TEP latencies decrease and latency decrease of BR late component (p < 0.05). Conclusion: The present study demonstrated conduction delay in somatosensory pathway predominantly on spinal level in patients with CH and cortical level in patients with PH as well as increase of reflex irritability of trigeminal system predominantly on brainstem nuclei level in both groups of patients. According to the obtained results, complex therapy of chronic secondary headaches is recommended, including neuroprotective and vasoactive therapy and anticonvulsants in case of trigeminal system involvement. P14-23 Functional dissociation of lateral and medial pain systems during sleep. A study with intracranial recordings in humans H. Bastuji1 , S. Mazza2 , C. Perchet1 , M. Frot1 , F. Mauguiere1 , M. Magnin1 , L. Garcia-Larrea1 1 INSERM, U 879 (Central Integration of Pain), Claude Bernard University, IFNL, France, 2 Lumiere University Lyon 2, Study of Cognitive Mechanisms Laboratory (EMC), Bron, France The present study aimed to detect and quantify, using intracerebral recordings, sleep-related changes in the activity of nociceptive generators in the suprasylvian opercular (SII), posterior insular and mid cingulate cortices. We recorded intracerebral laser evoked potentials in 10 epileptic patients scheduled for functional surgery. Sequences of thermal laser stimuli at pain threshold were delivered over the radial territory during (i) wakefulness, (ii) sleep stage 2, (iii) and paradoxical (REM) sleep. The cortical responses in opercular and insular cortices were attenuated to a similar extent in sleep stage 2 and paradoxical sleep as compared with waking; conversely, in the mid cingulate the cortical response was significantly more depressed in paradoxical sleep than in stage 2, and virtually disappeared during paradoxical sleep in 4 cases. In accordance with previous results (Frot et al 08), the electrophysiological

Posters activation to noxious stimuli occurred simultaneously in the operculoinsular and mid cingulate cortices. However, the differential behaviour of these two areas during sleep substantiates the hypothesis that they represent two parallel processes with different functional significance. Intensity coding and stimulus localization, supported by the lateral operculo-insular system, seem to be partially inhibited to a similar extent during both stage 2 and paradoxical sleep, while mid cingulate processes related to fast attentional orienting and avoidance behaviour appear to be exceptionally depressed during sleep and may virtually disappear during the paradoxical (REM) phase. P14-24 Development of a cortical electrophysiological response to noxious stimulation in human infants L. Fabrizi1 , R. Slater1 , A. Worley2 , J. Meek3 , S. Olhede4 , S. Boyd2 , M. Fitzgerald1 1 Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK, 2 Clinical Neurophysiology, Great Ormond Street Hospital for Children, London, UK, 3 Neonatal Intensive Care Unit, Elizabeth Garrett Anderson and Obstetric Hospital, University College London Hospital, London, UK, 4 Statistical Science, University College London, London, UK Objective: To describe age related changes in scalp potentials evoked by clinically essential noxious heel lances in human infants. Noxious stimulation of infants 35 39 weeks postmenstrual age (PMA), evokes specific cortical neuronal activity at the vertex (nERP). However the infant cortex undergoes significant structural and functional changes between 28 and 46 weeks PMA and this may affect processing of noxious stimulation at a cortical level. Methods: nERP was defined from EEG epochs (n = 23) recorded following noxious heel lances at electrodes CPz of 18 term infants (37 46-week PMA) using Principal Component (PC) Analysis. The weights of the defined nERP were calculated in equivalent EEG epochs (n = 63) at 16 electrode positions from 44 infants (28 46-week). The influence of PMA on the weight of the nERP was then assessed with a linear regression. This was compared to the influence of the PMA on the occurrence of deltabrushes in the same EEG epochs. Delta-brushes (a distinctive EEG pattern of premature infants normally evoked by sensory stimulation) were identified adopting wavelet time-frequency analysis. Results: nERP consisting of a positive deflection at 460 ms poststimulation was identified (1-way ANOVA, p = 1.7×10 5 ). The associated PC weights had a significant increasing linear trend with respect to PMA at CPz/Cz (0.008 and 0.006 week 1 ; p < 0.05). Delta-brushes were evoked following noxious stimulation in all the youngest and in only 20% of the oldest infants. Conclusions: The nociceptive specific component increases with PMA. Our results are consistent with a less-specialized response to noxious stimulation in the younger infants, possibly reflecting a relatively immature organization of the functional neuronal networks of the cortex. P14-25 Effects of evoked pain on the muscle action potential obtained by direct muscle stimulation L. Duez1 , E. Qerama1 , A. Fuglsang-Frederiksen1 , T. Staehelin Jensen2 Department of Neurophysiology, Aarhus University Hospital, Aarhus, Denmark, 2 Danish Pain Research Center, Aarhus University Hospital, Denmark

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Objective: The purpose of this study was to investigate the influence of experimental pain on amplitudes obtained by direct muscle stimulation (DMS). We hypothesized that the DMS amplitude would decrease after muscle pain due to muscle fiber in-excitability. Methods: We induced pain by intramuscular infusion of hypertonic saline in 40 young men. Ten subjects were infused with isotonic saline and served as controls. The infusions were given distal to the motor endplate region on the brachial biceps muscle of the dominant arm in a doubleblind manner and controlled by a pump. Pain was recorded by a visual analog scale (VAS). A stainless steel sub dermal stimulation-electrode and an anode were placed in the distal third of the muscle, one cm distal to the motor point region. The recording needle was placed three cm distal from this site. A stimuli-response curve of the amplitudes from DMS was obtained by stimulating 0.5 ms at 10, 30, 50, 70 and 90 mA. Results: The amplitudes from DMS without induced pain increased from 6.02 (±3.97) at 10 mA to 13.95 (±4.44) at 90 mA. The increase was

29th International Congress of Clinical Neurophysiology linear. Hypertonic saline induced a significantly higher peak VAS than isotonic saline. The pain evoked by hypertonic saline resulted in a greater decrease in amplitude than in the control group. The decrease after induced pain was from 37% to 44%, whereas the decrease in the control group was from 13% to 24%. Conclusions: DMS with increasing current resulted in a linear increase in amplitude of the action potentials. Pain evoked by infusion of hypertonic saline resulted in a decrease in the amplitude of action potentials obtained by DMS. This may be due to an effect on the muscle fiber excitability indicating that the induced pain had a peripheral effect. P15. EEG (1) P15-1 Real-time and training-free control of a prosthetic arm using human electrocorticograms T. Yanagisawa1,2 , M. Hirata1 , Y. Saitoh1 , H. Kishima1 , T. Goto1 , R. Fukuma2,3 , H. Yokoi4 , Y. Kamitani2,3 , T. Yoshimine1 1 The Department of Neurosurgery, Osaka University, Osaka, Japan, 2 ATR Computational Neuroscience Laboratories, Kyoto, Japan, 3 Nara Institute of Science and Technology, Nara, Japan, 4 Department of precision engineering, University of Tokyo, Tokyo, Japan Objective: Cortical control of a multi-jointed prosthetic device can be applied to restore upper limb function for amputees and paralysed persons. Although it has been demonstrated with populations of neurons in the motor cortex, some problems has been pointed out for clinical use; (1) the technical difficulties in maintaining stable long-term recordings, (2) the clinical risk with invasive recording, (3) the need for extensive training for users. Electrocorticogram (ECoG) is one of the candidates of a clinically feasible BMI signal having superior long-term stability with lower technical difficulty and lower clinical risk compared to spike recordings. Here we demonstrate a system that permits a person to control a prosthetic arm using ECoG signals without any prior training. Methods: Three patients with subdural electrodes over their sensorimotor cortices performed three to five types of simple upper limb movements following a sound cue to train the two decoders which predicted the timing and the type of movement based on a linear support vector machine (SVM). The power modulations of some frequency bands (2 200 Hz) during movements were used as the input features to the decoders. The decoding performances with the features were compared among frequency bands. With the trained decoder, a novel ECoG signals were analyzed on line to control a prosthetic arm by a patient’s intention to move their arms without any external cues. Results: Among the frequency bands, the gamma-band power was the most informative feature to infer the upper limb movements. With the trained decoders, the movement parameters were accurately decoded from ECoG signals in real-time. Notably, patients succeeded to control the prosthetic arm without any prior training. Conclusions: Our ECoG based BMI system paves the way towards the development of clinically feasible BMI that can be stably used in daily lives without any extensive efforts of the patients. P15-2 Functional integration of the brain after detection of rare target stimuli a depth EEG study M. Brazdil1 , J. Janecek2 , R. Roman3 , P. Jurak2 , J. Chladek2 , P. Daniel1 , J. Halamek2 1 Brno Epilepsy Center, Masaryk University, Czech Republic, 2 Institute of Scientific Instruments, Academy of Sciences, Brno, Czech Republic, 3 Department of Physiology, Masaryk University, Brno, Czech Republic Functional integration refers to the interactions among multiple specialized neuronal populations, and how these interactions depend upon context. In terms of functional connectivity, it has been repeatedly defined as correlations between spatially remote neurophysiological events. To investigate inter-areal integration at the optimal mesoscopic scale we computed dynamic cross-correlations in pairs of human depth EEG signals. Five intractable epileptic patients undergoing depth electrode recordings prior to their surgical treatment participated in the study. A visual oddball task with the presentation of rare (target) and frequent stimuli was completed by the subjects. Simultaneously intracerebral macro-EEG signals were collected (a total of 456 brain sites). In each subject, the cross-correlations in 3364 12100 contact pairs were examined in two frequency ranges (1 45 Hz, 55 95 Hz) and the

S191 time evolution of post-stimulus cross-correlations was evaluated (targets versus frequents). Significant fluctuations of inter-areal correlations were detected after the stimuli in a number of investigated pairs. In both examined frequency ranges the cross-correlations changed after targets more often than after frequents. In the lower frequency range, an increase of correlations after targets prevailed in all the subjects; in the gamma range a predominant decrease of correlations was observed. Interestingly, dynamics of post-stimulus changes differed obviously inter-areal couplings of oscillatory activities in lower frequencies were generally less stimulus-locked than changes in the gamma range. An intracranial EEG and direct measures of event-related synchronization (ERD) using depth electrodes play crucial roles in the study of local synchronous oscillations in the brain. This pilot study has indicated that standard mathematical analysis of depth EEG signals might be favorably used for the study of inter-areal synchronous neural oscillations too. Our data further support the hypothesis that slower oscillations are more involved in long-range synchrony, and possibly involved in the coordination of faster oscillations in functionally related but spatially segregated areas. P15-3 Modulation of corticomuscular coherence by afferent stimulation varies with the intensity and nature of the stimulus V.M. McClelland1 , K.R. Mills1 Department of Clinical Neurophysiology, King’s College Hospital, London, United Kingdom 1

Objective: The correlation within the frequency domain between rhythmic activity in the electro-encephalogram (EEG) and electromyogram (EMG) is known as corticomuscular coherence (CMC). CMC is reduced when afferent feedback is blocked, but the role of afferent inputs in modulating CMC remains uncertain. In earlier studies investigating CMC modulation, subjects performed a dynamic motor task, making it difficult to differentiate effects of a changing voluntary command from those of the changing afferent input. The purpose of this investigation was to examine the effects of transient peripheral stimuli on CMC during a maintained motor task. Methods: 14 healthy adults performed a simple key grip motor task with the dominant hand.EEG from sensorimotor cortex and EMG from two intrinsic hand muscles were recorded. In 5 subjects, graded single pulse electrical stimuli (1.0 2.5 times perceptual threshold (T)) were applied to the dominant index finger. In 12 subjects a pulsed lateral mechanical displacement was applied to the gripped object. A short time FFT was used to estimate dynamic changes in CMC. Results: CMC between sensorimotor cortex EEG and intrinsic hand muscle EMG was detected between 14 36 Hz. Electrical stimuli above 2.0T produced a reduction in the background 14 36 Hz CMC, followed by a rebound increase of CMC in this frequency range. This increase outlasted any reflex evoked cortical activity and continued up to 2.5 seconds poststimulus. The depth of CMC modulation varied with stimulus intensity. The mechanical stimulus, although much smaller than the electrical stimulus, produced a similar pattern of modulation of CMC. Conclusions: The novel finding that modulation of CMC varies with stimulus intensity provides further evidence that CMC is influenced directly by afferent information. The observation that very small, but physiologically relevant mechanical stimuli modulate CMC supports the hypothesis that CMC is physiologically important and suggests a role in sensorimotor integration. P15-4 How human face is special: dominant perception during binocular rivalry Y. Kume1 , K. Ogata1 , S. Tobimatsu1 1 Department of Clinical Neurophysiology, Neurological Institute, Faculty of Medicine, Graduate School of Medical Sciences, Kyushu University, 3 1 1 maidashi, Fukuoka 812 8582, Japan To investigate the speciality of human face recognition, we evaluated the psychophysical perception and induced EEG oscillations during binocular rivalry in which a human face, a monkey face or a house were presented to each eye. Ten normal healthy subjects participated in this study. The rivalrous stimulus consisted of superimposed two pictures from three categories, including “human face”, “monkey face” and “house”. They were separately defined by red and green luminance variation. The luminance and contrast were the same for each stimulus. Subjects viewed