Keijiro Koseki

The synchronization between brain areas under motor inhibition process in humans estimated by event-related EEG coherence.

To investigate the functional connection of brain areas under motor inhibition, the event-related coherence (ERCoh) of the electroencephalogram (EEG) was calculated for 10 subjects who were asked to perform a visual discrimination (GO/NO-GO) task. The subjects were instructed to push (GO) or not to push (NO-GO) a micro-switch according to different visual stimuli. Twenty-one-channel scalp EEGs were recorded and the surface Laplacians were calculated at F3, F4, C3, C4, P3 and P4 using the source derivation method. The time-courses of the inter- and intra-hemispheric coherence were calculated using the fast Fourier transform for each condition (GO or NO-GO), and were compared statistically between the two conditions. The results suggest that the ERCoh under the NO-GO condition consisted of two components; alpha band synchronization between bilateral frontal areas and theta band synchronization among bilateral frontal, central and parietal areas. It is likely that the former is related directly to the decision not to move, and the latter is related to the motor inhibition process.

EVENT-RELATED DYNAMICS OF THE GAMMA-BAND OSCILLATION IN THE HUMAN BRAIN : INFORMATION PROCESSING DURING A GO/NOGO HAND MOVEMENT TASK

To investigate the gamma band activity relating to the discrimination process and motor behavior in the human brain, the event-related dynamics of the EEG spectrum was calculated during the visual GO/NOGO hand movement task and a control task (the visual element of the GO/NOGO task only) in eight subjects. The subjects were instructed to push (GO) or not to push (NOGO) a microswitch according to different visual stimuli and 21-channel scalp EEGs were recorded. The time courses of the power spectra after the stimuli were calculated using the fast Fourier transform for each condition (GO, NOGO and the control task), and were compared statistically between the conditions. The results suggested that a high gamma band oscillation, occurring at the frontal and left parieto-occipital areas at around 90 ms after the stimuli, relates to the discrimination process. Under the GO condition, this oscillation continued until 140 ms, and a subsequent oscillation occurred over the motor areas at around 200 ms, which seemed to be related to the motor action. On the other hand, under the NOGO condition, a low gamma band oscillation occurred in the central area at around 230 ms, which seemed to be related to the inhibition process.

The time course of interhemispheric EEG coherence during a GO/NO-GO task in humans

Event-related coherence of the EEG was calculated for 10 subjects performing a visual discrimination GO/NO-GO task. The subjects were instructed to push (GO) or not to push (NO-GO) a button according to visual stimuli. Twenty-one-channel scalp EEGs were recorded and the surface Laplacian was calculated using the source derivation method. The time courses of the coherence between F3 and F4, C3 and C4, and P3 and P4 were calculated using the fast Fourier transform for each task and were compared between conditions. Statistical analysis showed that coherence in the NO-GO condition became significantly higher than that in the GO condition between F3 and F4. The synchronization between bilateral dorsolateral frontal areas might therefore play an important role in the motor inhibition process.

Estimation of Electrical Sources of Interictal Spikes in FrontalLobe Epilepsy with the Dipole Tracing of the Scalp-Skull-Brain Head Model: Comparison with Temporal Lobe Epilepsy.

cryptogenic BECT more clearly than did EEG, in terms of localization and current moment of the dipoles. Epileptic discharges in idiopathic BECT appear to be generated by synchronous activation of a larger neuronal population than those in cryptogenic BECT and SPE. Our earlier study on children with RD in 1992 showed that those with sylvian seizures had a benign outcome regardless of the presence of organic background in pathoetiology, whereas those with an organic background and complex partial seizures without sylvian seizures had an outcome as unfavorable as that of other SPEs. This shows that RD is not a hallmark indicating benignancy of partial epilepsy in children. It is likely that there is a wide spectrum of clinical expression among children with RD. It is possible that MEG can elucidate this spectrum.

Estimation of Electrical Source Generators of Diffuse Slow Spike and Wave Complex in Lennox‐Gastaut Syndrome

In Lennox-Gastaut syndrome, some of the electrophysiological manifestations such as diffuse slow spike and wave complexes and rapid rhythms were observed on scalp EEG.4 These findings might reflect the various pathophysiological bases of Lennox-Gastaut syndrome, but the precise mechanisms for generation of diffuse slow spike and wave complex are still unclear. To estimate the locations of the electrical sources of diffuse slow spike and wave complex, a new computer-aided method called dipole tracing method was a ~ p l i e d . ~ ~ In this method it is assumed that the brain is embedded in an infinite homogeneous conductor, and that only one dipole is elicited, which is calculated from the active potential distribution on scalp EEG.

Language-Related Potentials in Temporal Lobe Epilepsy Before and After Surgical Treatment

Purpose: Temporal lobectomy has contributed to treatment for medically intractable epilepsies. However, influence of the surgical treatment on cognitive function is not still clear, especially from the electrophysiological viewpoint. N400, an event related potential (ERP) named for its negative polarity and peak latency of 400 ms, is reported to be an electrophysiological sign of neural activities associated with semantic priming in language perception. In the present study, ERPs are applied to evaluate the cognitive function of temporal lobe epilepsy before and after temporal lobectomy.

2610 Time course of inter-hemispheric coherence during GO/NO-GO task

Eiici Naito’ , Miya Muroi’, Ryuta Kwashima3, Michikazu Matsumuro4 We investigated neuronal mechanisms of the interference between Counting and Reading by reaction time (RT) and ERP. For the first session, subjects performed Counting and Reading separately. There was no delay of RT of incongruent condition in both trials. Disturbance factors that one stimulus has two kinds of information solely did not cause the interference. Next, the subjects performed two types of tasks which contained both trials randomly, so that they had to decide in every trial which one they should perform according to the visual cue. In Prior-task condition the cue was presented before the numerals, and in Same-task condition it was presented at the same time. RT of both trials in incongruent condition delayed under the Same-task condition, and that of Counting trials delayed under the Prior-task condition. The ERP showed hybrid patterns between typical waveform of Counting and Reading. The result also indicated interference might occur at multiple stages of the processing.