THE HYPER-EXCITABLE NEURONE. MICROELECTRODE STUDIES OF CHRONIC EPILEPTIC FOCI IN MONKEY

Abstract

Microelectrode studies of 300 single neurones in experimental cortical epileptic foci in the monkey are reported. The epileptic foci were prepared by the sterile injection of alumina cream into the sensorimotor cortex. Within the epileptic focus, a majority of the cells were found to be spontaneously active in contrast to normal cortex. Their activity is characterized by the occurrence of autonomous, high frequency bursts during the interseizure period and varying patterns of gross hyperactivity during a spontaneous, propagated seizure. Inter-seizure may consist of long trains of discharges at the rates of 100-400/second. During the onset of a spontaneous seizure, a very high frequency decremental discharge at rates up to 1000/second may occur. There is no constant relationship between the background slow waves recorded either from the pial surface or from the depths and the hyperactive discharge of the unit in the epileptic focus. Nothing was observed to suggest that the cortical "spikes" characteristic of the epileptic eeg represent a summation of unitary discharges. As judged by the amplitude of the discharges, the cells involved in the hyperactivity appear to be of small or intermediate size. During a seizure, massive dendritic potentials are generated. Some of the mechanisms which may result in the observed synchrony of these potentials are discussed. It is concluded that the capacity for sustained autonomous discharge is a fundamental property of the epileptic neurone. This appears most likely to result from abnormalities in the dendritic arborizations of the neurone.