Spatial limits of epileptogenic cortex: its relationship to ectopic spike generation.

In order to investigate if ectopic spike generation was ubiquitous in and specific generation was ubiquitous in and specific to epileptogenic cortex, a method was devised to determine the limits of such an area based on a well-accepted physiologic characteristic of epileptogenicity. The limits of the penicillin-induced epileptogenic cortex were defined in terms of a retinal activation field; this is a circumscribed area whose stimulation by light evokes a characteristic cortical epileptiform wave. All lateral geniculate nucleus (LGN) neurons manifesting ectopic spike generation during interictal epileptiform waves had receptive fields within the activation field. During organized seizures, ectopic spike generation was observed in neurons with receptive fields outside the activation field. Because of these findings it was concluded that ectopic spike generation is a characteristic and specific feature of epileptogenic cortex and that it is a characteristic of the epeleptogenic process rather than a peripheral event related entirely to the direct effect of penicillin on neurons.