Akio Ikeda

IFCN standards for digital recording of clinical EEG

Marc R. Nuwera*, Giancarlo Comib, Ronald Emersonc, Anders Fuglsang-Frederiksend, Jean-Michel Guerite, Hermann Hinrichsf, Akio Ikedag, Fransisco Jose C. Luccash, Peter Rappelsburgeri University of California, Los Angeles, CA, USA University of Milan, Milan, Italy Neurological Institute, Columbia University, New York, NY, USA Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark University Catholique Louvain, Brussels, Belgium Otto von Guericke University, Magdeburg, Germany Kyoto University, Kyoto, Japan Hospital I Albert Einstein, Sao Paolo, Brazil Institute of Neurophysiology, Vienna, Austria

Primary somatosensory cortex is actively involved in pain processing in human

We recorded somatosensory evoked magnetic fields (SEFs) by a whole head magnetometer to elucidate cortical receptive areas involved in pain processing, focusing on the primary somatosensory cortex (SI), following painful CO(2) laser stimulation of the dorsum of the left hand in 12 healthy human subjects. In seven subjects, three spatially segregated cortical areas (contralateral SI and bilateral second (SII) somatosensory cortices) were simultaneously activated at around 210 ms after the stimulus, suggesting parallel processing of pain information in SI and SII. Equivalent current dipole (ECD) in SI pointed anteriorly in three subjects whereas posteriorly in the remaining four. We also recorded SEFs following electric stimulation of the left median nerve at wrist in three subjects. ECD of CO(2) laser stimulation was located medial-superior to that of electric stimulation in all three subjects. In addition, by direct recording of somatosensory evoked potentials (SEPs) from peri-Rolandic cortex by subdural electrodes in an epilepsy patient, we identified a response to the laser stimulation over the contralateral SI with the peak latency of 220 ms. Its distribution was similar to, but slightly wider than, that of P25 of electric SEPs. Taken together, it is postulated that the pain impulse is received in the crown of the postcentral gyrus in human.

Electrocorticogram–electromyogram coherence during isometric contraction of hand muscle in human

OBJECTIVEnTo clarify how the primary sensorimotor and supplementary motor areas are involved in the generation of the rhythmicity of electromyogram (EMG) activity during continuous muscle contraction.nnnMETHODnWe analyzed the coherence between subdurally recorded cortical electroencephalograms (EEG) and EMGs of the contralateral wrist extensor muscle during continuous isometric contraction in 8 patients with medically intractable epilepsy.nnnRESULTSnIn all subjects, a significant coherence between the primary motor area (M1) and EMG was observed at the peak frequency of 15+/-3 Hz (means+/-SD). In the primary somatosensory area (S1) of 7 subjects and the supplementary motor area proper (SMA proper) of 4 subjects, significant coherence with EMG was observed at 12+/-5 and 15+/-4 Hz, respectively. The time lags revealed by cross-correlogram were 10+/-3, 7+/-1 and 22+/-8 ms in the M1, S1 and SMA proper, respectively, with the EMG lagging in all areas.nnnCONCLUSIONnThese findings suggest that the rhythmic activity in the SMA proper, as well as in the S1 and M1, is related to the generation of the rhythmicity of EMG activity.

Abnormal contingent negative variation in writer's cramp.

OBJECTIVEnTo investigate the physiological abnormality in writers cramp, a focal dystonia which specifically affects writing.nnnMETHODSnWe recorded brain potentials that precede hand and neck movements (contingent negative variation or CNV) in 11 patients and 11 age-matched normal subjects. A 1000 Hz tone burst (S1) was delivered to the right or left ear in random sequence, and 2 s after, a 2000 Hz tone burst (S2) was delivered to both ears simultaneously. For the response task to S2, the subjects were instructed to extend their fingers ipsilateral to the ear to which S1 was given in one experiment or to rotate the head to the side of the S1 presentation in another. All the patients had symptoms in the right hand only, and performed both tasks normally. CNV amplitudes were compared between normals and patients using unpaired t test.nnnRESULTSnThey showed normal CNV for neck movement but significantly decreased CNV amplitudes for movements both in the affected and unaffected hands.nnnCONCLUSIONSnOur findings suggest that motor programming is specifically abnormal for the affected body part, including the asymptomatic contralateral limb, and that the clinical symptom may result from a deficient compensatory mechanism for abnormal motor programs or subroutines.

Pre-movement gating of short-latency somatosensory evoked potentials.

Somatosensory evoked potentials (SEPs) are reduced in amplitude during movement (gating). The mechanism involves central gating of afferent input and competition from other afferents activated by the movement. We distinguished these two by giving 11 normal subjects a warning sound followed 1 s later by an electric stimulus to the right median nerve at the wrist. The latter served both as a cue to start a finger movement and as stimulation to evoke SEPs. Gating effects were widespread in frontal (N30) and central (N60) areas, but were also seen, albeit to a lesser extent, in the recordings at P3 (P30). Since finger movement began after the stimulus, such gating must have been purely central in origin, presumably reflecting motor preparation.

Cortical myoclonus. Sensorimotor hyperexcitability

Cortical or cortical reflex myoclonus is characterized by abnormally enlarged cortical somatosensory evoked potentials (giant SEPs), which most likely reflect pathologically hyperexcitable sensorimotor cortex. To clarify the pathogenesis of myoclonus of cortical origin, we simultaneously recorded SEPs and whole head somatosensory evoked magnetic fields (SEFs) following electric stimulation of the median nerve at the wrist in six patients with cortical myoclonus. N20m and enlarged P30m were observed in all patients and were localized at the posterior bank of the central sulcus (Brodmann area 3b of the primary somatosensory cortex). In addition, P25m and N35m components of SEFs were recognized in five and four patients, respectively. P25m component, that is, the magnetic counterpart of P25 in EEG, was the earliest cortical component showing enhancement in patients. Multidipole analysis combined with magnetic resonance imaging (MRI) coregistration revealed that the generators of P25m were in the precentral gyrus in four patients and in the postcentral gyrus in one patient. The second SEFs around 200 msec after the single stimulus were recorded in three patients at area 3b (repetitive SEFs); two of whom showed negative as well as positive myoclonus. The importance of motor cortex for the generation of cortical reflex myoclonus was thus demonstrated. The pathologic features of SEFs suggest abnormal excitability of primary sensorimotor cortex.

Serial processing of the somesthetic information revealed by different effects of stimulus rate on the somatosensory-evoked potentials and magnetic fields.

In order to evaluate information processing in the somatosensory cortex, the effect of two different stimulus rates was investigated by simultaneously recording somatosensory-evoked potentials (SEPs) and magnetic fields (SEFs) in nine healthy adults. During electric stimulation of the median nerve at the wrist, SEFs were recorded with the helmet-shaped whole-head coverage magnetometer array with 122 first-order planar gradiometers while SEPs were simultaneously recorded from seven scalp positions. Interstimulus intervals (ISIs) of 0.9 s and 4 s were compared. In all subjects, N20 as well as its magnetic counterpart, N20m, was clearly demonstrated over the contralateral somatosensory area. Subsequent deflections around 80-200 ms did not make any clear peak and were smaller than those at 20-60 ms (P30m, P40m, N50m and P60m). After 200 ms, SEFs were negligible, whereas SEPs had larger amplitude than those of shorter latencies, constituting a peak around 250 ms (P250). Both SEF and SEP deflections later than 40 ms were decreased in responses at the shorter ISI; this diminution was most prominent for P250. Therefore, it is concluded that the tangential currents in the somatosensory cortex (area 3b) mainly contribute to responses during the first 200 ms after the stimulus, whereas the radially oriented currents (most likely in the crown of the postcentral gyrus) take over for subsequent information processing.

Movement-related cortical potentials associated with voluntary relaxation of foot muscles.

OBJECTIVEnIn our previous study of movement-related cortical potential (MRCP) in association with the voluntary relaxation of the hand muscle, Bereitschaftspotential (BP) was maximal at the vertex and symmetrically distributed, and Negative Slope (NS) was maximal over the contralateral central region. In order to clarify the generator sources of MRCP with voluntary muscle relaxation, we recorded MRCP in association with voluntary relaxation of the foot.nnnMETHODSnMRCP in association with plantar flexion of the foot caused by voluntary relaxation of the tibialis anterior muscle was recorded in 10 normal subjects.nnnRESULTSnThe BP started at about 1.7 s before the onset of the muscle relaxation, followed by NS starting at about 650 ms before it. Both were maximal at the vertex and symmetrically distributed. There was no additional EEG activity in the lateral frontal areas, which are presumably located over the primary negative motor areas (PNMA).nnnCONCLUSIONSnIt is concluded that the voluntary muscle relaxation, similarly to the voluntary muscle contraction, involves the cortical preparatory activity at least in the primary motor area (M1) and probably the supplementary motor areas (SMAs). There is no evidence to suggest that the PNMA is also active prior to the voluntary muscle relaxation.

Cortical mechanisms underlying point localization of pain spot as studied by event-related potentials following CO2 laser stimulation in man

Abstractu2002To elucidate cortical mechanisms underlying point localization of a pain spot, we investigated event-related potentials (ERPs) while using a CO2 laser beam to apply a pain stimulus to the hand dorsum in 16 healthy men. The stimulus spot (pain spot) was shifted for each stimulus, while the subject was requested to identify the stimulated spot as accurately as possible and to use a pointer in the non-stimulated hand to indicate the corresponding spot on a figure of a hand that was projected onto a screen (localization condition). For the control condition, the subject pointed to a single predetermined spot, regardless of the location of the stimulation (control motor task condition). Electroencephalograms were recorded from 21 electrodes, referenced to the linked earlobes, and were averaged time-locked to the stimulus onset for each task separately. Under the control rest condition (neither point localization nor motor task), only two early components (N2 and P2) were recorded. During the control motor task condition (no point localization), in addition to N2 and P2, a steep negative-going slope was recorded at the fronto-central region. Exclusively during the localization condition, a positive peak (647 ms, 5.6 µV for the left and 634 ms, 5.7 µV for the right hand stimulation) was identified; this was maximal at the midline centro-parietal area and distributed symmetrically over the scalp. It is suggested that the late positive component detected exclusively during the localization task is related to the somatotopic point localization of the pain spot. From the distribution of this ERP, the task most likely involves bilateral activation of the superior parietal cortices.

Somesthetic function of supplementary motor area during voluntary movements.

To clarify the somesthetic functions of the supplementary motor area (SMA), we recorded the cortical potentials following the median nerve electric stimulation directly from the SMA and investigated the modulation caused by voluntary movements in two patients with intractable SMA seizures. The evoked potentials over the SMA consisted of positive (61.5ms) and negative (100.0 ms) peaks, which were enlarged by voluntary movements of the stimulated hand. The present finding is in strong contrast with the attenuation (gating) of the response at the primary sensorimotor area (SM1) and suggests that the voluntary movements differently modulate the somatosensory functions of SMA and SM1.