Cerebello- and pallido-thalamic pathways to areas 6 and 4 in the monkey.

Projections from the cerebellar nuclei (CN) and the internal segment of the globus pallidus (GPi) to areas 6 and 4 via the thalamus were examined electrophysiologically in monkeys. In addition to the well-known pallido-thalamo-cortical projection to area 6, some thalamic neurons with CN input were found to project to area 6. Seventeen neurons in VLc, area X and the dorsal margin of VPLo were activated antidromically by stimulation of supplementary motor or premotor areas, and orthodromically by CN stimulation. Twelve neurons in area X and the medial part of VPLo were found to receive CN input and to project to the arcuate premotor area (APA). Four neurons in the VLo-X border region which were identified to project to APA were inhibited by GPi stimulation.