MOVEMENTS ELICITED FROM PRECENTRAL GYRUS OF ADULT CHIMPANZEES BY STIMULATION WITH SINE WAVE CURRENTS

Abstract

The precentral gyri of 3 adult chimpanzees were explored with the 60 c.ps. sine wave current. The movements elicited were interpreted as activation of discrete motor nuclei of the cranial and spinal nerves and of parts of these nuclei; of groups of motor nuclei within the spinal cord which innervate extensor or flexor sheets of skeletal muscles; and of brain stem integration systems. Certain of the co-innervations suggest cortical selection of nuclear groups, such that use patterns were elicited. The most frequently elicited movements of skeletal muscles were those of the digits, flexion of the lateral four and adduction of the first. Isolated movements of 2nd or 5th fingers were rare; those of the 3rd and 4th fingers did not occur. Different loci for antagonistic movements at the joints were obtained. Vocalization, a light whistle, and salivation were produced in one chimpanzee. The postcentral gyrus responded without previous facilitation. The liminal strength of the stimulating frequency for area 4 (arm and leg) was higher (0.22 to 2.0 mA.) than for the face area (largely area 6) (0.2 to 1.5 mA.). A single point on 2 of these precentral gyri was stimulated with a range of double vibrations (5 to 1440 c.p.s.) of the sinusoidal current. 90 c.p.s. was the optimum frequency for each of these points. The frequencies eliciting movements which in their timing, sequence, and smoothness resembled those characteristic of the unanaesthetized animal were those in the neighborhood of the optimum.