Separation of different interictal discharge patterns in acute experimentally induced epileptic foci of the rat in vivo.

Epileptic discharge patterns in an acute experimental model of epilepsy were analyzed. Epileptic foci were induced by epicortical application of penicillin on the rat motor cortex in vivo. Patterns with regular 1/s discharges, patterns with irregular discharges of about 0.5/s as well as compound patterns comprising discharges with intervals of about 300 ms could be differentiated by means of interval histograms and autocorrelation functions. These patterns occurred in an ordered sequence indicating that the different rhythms are activated by a progressive enlargement of the focus and duration of focal activity. The experiments suggest that different interictal discharge patterns can occur within the same brain regions and are not specific for a certain etiology; instead they seem to represent 'resonance' frequencies characteristic for the brain tissue which are disclosed under pathophysiological conditions.