Regional differences in the cat caudate nucleus as to the effectiveness in inducing contraversive head-turning by electrical stimulation.

An attempt was made to re-examine regional differences in the cat caudate nucleus as to the effectiveness in inducing contraversive head-turning by electrical stimulation and to analyze the time course of head-turning quantitatively. In 5 of the total 9 cats, the right sensorimotor cortex and its surrounding areas had been ablated chronically. While the awake, unrestrained cat maintained a stable standing posture facing forward, stimulation was applied systematically to various points in and around the caudate nucleus with a movable stimulating electrode. Trains of stimulating current pulses of less than 300 microA were given, mostly at a rate of 100 Hz for 5 s. In most experiments in which stimulation was given to the side of the intact cerebral cortex, stimulation of caudal portions of the head of the caudate nucleus was effective in inducing contraversive head-turning, but that of its rostral portions was ineffective. In experiments on the side of chronic cortical ablation, similar results were obtained. These results suggested that head-turning induced by stimulation of the caudate nucleus was brought about not by the activation of the corticofugal fibers from these cortical areas by a current spreading to the internal capsule, but by the activation of caudate neurons. Hence, it was demonstrated that there were regional differences in the cat caudate nucleus as to the effectiveness in inducing head-turning. The mean of the shortest latencies of the onset of head-turning for individual stimulation points was 396 ms (S.D., 210 ms) for the side of the intact cerebral cortex, and 454 ms (S.D., 289 ms) for the side of the cortical ablation. Statistically, there was no significant difference between them. Therefore, it was further revealed that the elimination of the sensorimotor cortex did not affect the caudate-induced head-turning in terms of the latency of its onset.