MOVEMENT-RELATED ACTIVITY IN THE PALLIDO-THALAMO-CORTICAL LOOP

Unitary activities of thalamic and pallidal neurons were studied in aw ake monkeys which were trained to lift a lever with their wrist moveme nts in response to visual stimuli. Thalamic neurons with pallidal inpu t (GP-thalamic neurons) projecting to the motor cortex showed movement -related activity, and were located mainly in VLo. Neurons in the caud o-ventral part of the globus pallidus which received motor cortical in put via the putamen also showed movement-related activity. On the othe r hand, GP-thalamic neurons projecting to the supplementary motor area frequently showed delay-related activity during delayed go/no-go disc rimination task. Neurons in the rostro-dorsal part of the globus palli dus which received input from the supplementary motor, premotor and pr efrontal areas frequently showed delay-related and cue-related activit y. These findings suggest that the cortico-strio-pallido-thalamo-corti cal loop could be divided at least into two distinct 'motor' and 'asso ciation' loops. The motor loop appears to convey movement-related acti vity and exert relatively direct influence on the movement control thr ough the cortico-spinal pathway. The function of the association loop remains to be investigated.