Control Mechanisms in Cortical Epileptogenic Foci*

ELECTROPHYSIOLOGICAL investigations of cellular activities in cortical epileptogenic foci produced by strychnine,2,3local freeze lesions,4,5and penicillin application6-9have revealed that the population of neurons in the area of focal surface epileptiform discharge is a heterogeneous one in terms of its behavior during surface paroxysmal discharges. (In order to avoid confusion in terminology, surface epileptiform discharge or surface paroxysmal discharge will be used throughout to refer to interictal focal epil-eptiform spikes. The term spike or unit spike will always refer to the neuronal action potential.) Intracellular records in such foci show that in most neurons excitatory events, ie, large depolarization shifts (DSs) and repetitive unit firing, accompany surface epileptiform activity; some neurons, however, are inhibited during the surface discharge.2,3,5,8,9The role of inhibited neurons in a region of focal epileptogenesis and the relationship of such cells to the neuronal population responsible for generation of the surface