PROLONGED STIMULATION OF BRAIN IN AWAKE MONKEYS

Abstract

The effects of repeated and continuous stimulation of the brain were studied in 10 monkeys with permanently implanted electrodes. Stimulation was applied to some monkeys by a small transistor timing device, attached to a collar, while they were completely free as members of a colony. Results were as follows: Stability of cerebral points through time was demonstrated. Repeatable effects were also demonstrated while the animals formed part of a group. Evoked motor activity in some cases resembled spontaneous movements; it did not affect the social behavior of the colony. Lasting modifications of spontaneous electrical activity and pattern of evoked after-discharges were produced by long periods of stimulation. Continuous stimulation revealed quick fatigue (in seconds) in the motor cortex; slow fatigue (in minutes) in some areas of the putamen and hypothalamus, while in another area of the hypothalamus there was no fatigue after 72 hr. of continuous stimulation. Long-lasting rebound was observed after cessation of prolonged stimulation of the hypothalamus. Simultaneous stimulation of 2 areas of antagonistic action (contraction and dilatation of the pupil) canceled their effects by producing a dynamic equilibrium which persisted for minutes without fatigue. In no case did prolonged stimulation of the brain cause visible histological damage.