Intracellular recordings from chronic epileptogenic foci in the monkey

Abstract

Extracellular and intracellular recordings were obtained from neurons of chronic alumina epileptogenic foci in monkey cortex during focal epileptiform discharges. In 30 of 55 neurons alterations in the frequency of spike discharge occurre during interictal surface epileptiform waves. Intracellular recordings revealed that spontaneously occurring slow membrane depolarization and hyperpolarizations resembling augmented synaptic potentials were closely associated with surface epileptiform waves. Depolarizations generated bursts of spikes similar to those characteristically seen in extracellular recordings from the alumina focus. A few cells were primarily inhibited during each interictal surface discharge. No distinct abnormalities of synaptic or spike activities were noted in the impaled neurons. The discharge patterns of involved neurons were similar qualitatively to those of acute epileptogenic foci; however, the amplitude of surface epileptiform discharges and intracellularly slow membrane events were smaller and the proportion of neurons involved in epileptogenesis was lower in the chronic focus. These differences may result from the more diffuse nature of the chronic alumina focus. The intracellular data are discussed in relation to proposed mechanisms of burst generation in neurons of the chronic epileptogenic focus.