INFLUENCES OF THE VISUAL CORTEX UPON POSTEROMEDIAL THALAMUS IN THE CAT

Abstract

Experiments were carried out on cats under chloralose anesthesia to investigate the influence of the visual cortex upon visual responses elicited in a posteromedial thalamic region comprised of the centrum medianum and adjacent structures which has been previously reported to respond to light, sound, and somesthetic stimulation. Short latency (4ms) responses are found in this region to electrical stimulation of the visual cortex, indicating the presence of a pathway through which cortical control could be exerted. Modifying the excitability of the visual cortex by drugs (strychnine, KC1) or local cooling produces specific alterations of thalamic responses to light, leaving those to sound or somatic stimulation unchanged, suggesting that the state of excitability of the visual cortex has a specific influence on occurrence and strength of visual responses in those medial thalamic regions.