Microstimulation of movements from cerebellar-receiving, but not pallidal-receiving areas of the macaque thalamus under ketamine anaesthesia

The motor thalamic areas receiving input from the globus pallidus (VA) and the cerebellar nuclei (VL) appear to have different roles in the generation and guidance of movements. In order to further test these differences, we used electrical stimulation to map the ventro-anterior and ventro-lateral n uclei of the thalamus in three ketamine anaesthetised monkeys. Movements we re readily evoked from VL at currents of down to 10 mu A. The movements wer e typically multijoint, and stimulation could evoke arm and trunk or arm an d facial movement at the same current threshold. Evoked arm movements often involved multiple joints, with or without finger movements. Facial movemen ts included the lips, tongue, jaw, eyebrows and, occasionally, the eyes. Th e thalamic map was topographic, but complex with at least two separate regi ons related to arm movement. Very few sites within the VA could stimulate m ovement, even at high currents. We therefore suggest that the cerebellar pr ojections to motor regions of the cortex, which pass through the VL thalami c nuclei, have a different relationship and are closer to movement executio n than the projections from basal ganglia via the ventro-anterior nucleus.