Facilitation and spatial summation in neurons concerned with epileptiform afterdischarge in the isolated cerebral cortex of the cat.

Abstract

The relationships between epileptiform afterdischarges (EAD) and surface-positive burst responses recorded from neuronally isolated slabs of cerebral cortex were studied in 23 cats. The results suggest that a specific population of neurons participating in an EAD are facilitated by the afterdischarge activity. In their facilitated condition they can respond to weak electrical stimuli which had been ineffective previous to the EAD. The response of the activated neurons resembles the epileptiform bursts recorded toward the end of an afterdischarge; continued application of the weak stimuli at rates of from 0.5 to 2.0 per second can sustain the epileptiform activity for periods of up to 20 min. The initial epileptiform afterdischarge activity, and the sustained epileptiform bursts which can be evoked by the weak stimuli, are transmitted across an isolated cortical slab by a system of neurons which is distinct and separate from the neuronal networks which transmit the surface-positive burst response across the same slab.