Enhanced slow waves at the periphery of human epileptic foci

Experimental epilepsy foci are surrounded by an enhanced inhibition zone. We looked for evidence of peripheral inhibition in human epilepsy foci by analyzing the waveforms of discharges. The sharp-wave of an epileptic discharge is thought to reflect EPSP synchronization, and the subsequent slow-wave to reflect inhibition. Ratios of amplitudes of the sharp- and slow-waves in human EEGs may show how excitatory and inhibitory processes relate to discharge spread implicating peripheral inhibition in human epilepsy, too.

In electrocorticography from 10 adult patients we compared amplitudes of sharp-waves and of slow-waves and their ratios in each electrodes as a function of their distance from the highest sharp-wave electrode.

Sharp-wave amplitude decreases as a function of electrode distance from the highest sharp-wave electrode, but the slow-wave voltage exhibits a slight increase. The ratio slow-wave/sharp-wave increases several-fold within 2-3 cm from the highest sharp-wave electrode.

In human cortex epileptic discharges at the periphery of a focus exhibit a prevalent slow-wave consistent with a possible local enhanced inhibition.

Waveform analysis of electrocorticography epileptic discharges suggests the presence in human neocortex of surround inhibition, a basic mechanism limiting the spread of epileptic activity, long studied in experimental models.