The hyperexcitable neuron: microelectrode studies of the chronic epileptic focus in the intact, awake monkey

The activity of single neurons in the chronic cortical epileptogenic focus in monkeys rendered epileptic by the intracortical injection of alumina cream was studied by extracellular recording over a number of days while the intact animals were awake. The activity of units in homologous cortex of normal control monkeys was also studied. In the normal preparation, fewer cells were spontaneously active, the discharge frequency was lower, and the discharge pattern was more irregular. Within the chronic epileptic focus, action potentials were smaller, and the unit activity was characterized by the occurrence of regular, autonomous, high-frequency bursts of three to twelve spikes. Synchronous unit-burst activity was noted. In contrast to previous observations in acute experimental preparations, long trains of tonic, high-frequency discharge were not observed, and propagating seizures were relatively infrequent.