Ipsilateral and bilateral EEG activity from the hippocampus.

Using scalp and depth electroencephalography (EEG), we examined the relationship between the surface EEG activity and abnormal EEG discharges in the ipsilateral hippocampus in order to study the neuronal connection between the two cerebral regions. Ictal EEG was divided into 4 groups: 1) unitempo-ipsilateral-bifrontal slow waves, 2) unitempo-ipsilateral-bilateral slow waves, 3) bilateral slow waves, and 4) bilateral slow waves with repetitive spikes. Abnormal depth EEG activity in the hippocampus was classified into paroxysmal discharges and recruiting rhythms. Ictally and interictally, repetitive sharp waves or spikes in the unilateral hippocampus were associated with sharp waves or spikes in the ipsilateral temporal region. These findings suggest that the ipsilateral projection of seizure activity originating in the unilateral hippocampus is dependent upon the function of the subiculum.