ACTIVATION OF PYRAMIDAL TRACT NEURONS BY IPSILATERAL CUTANEOUS STIMULI

Abstract

About 70[degree]/o of the pyramidal tract neurons isolated in the post-cruciate cortex of chloralose-decamethonium-anesthetized cats were reliably driven by stimuli applied to either side of the body. Nearly half of them responded to electrical stimulation of each of the foot pads. Some also responded to auditory and visual stimuli. Many other post-cruciate neurons not identified as pyramidal tract neurons had bilateral peripheral fields. Such elements were most often found in the deeper layers of the cortex. Ipsilateral unit responses consistently had longer latencies than did responses elicited by stimulating the homologous contralateral skin area. The number of spikes per discharge and the maximum repetitive frequency followed faithfully were also significantly less for ipsilateral than for contralateral responses. Multiunit recording from the bulbar pyramids also revealed responses to ipsilateral stimuli [long dash]the latency always being longer than that of responses to contralateral stimuli. Multiunit recording often revealed early and late components of both ipsilateral and contralateral responses. The early ipsilateral component was abolished by section of the corpus callosum. Late components of ipsilateral and contralateral responses persisted after section of the corpus callosum, the anterior and posterior com-missured, and the massa intermedia. It was suggested that late com-ponents are mediated by a slowly conducting ascending path projecting to both hemispheres. The late ipsilateral pyramidal response does not depend on either somatosensory area II or the association area of Amassian.