Common projection of the motor cortex to the caudate nucleus and the cerebellum.

1. Stimulation of the caudate nucleus (Cd) was found to evoke early mossy fibre (MF) and late climbing fibre (CF) responses in fairly wide areas of the cerebellar cortex in cats. Points capable of eliciting the cerebellar responses were situated exclusively in the head portion of the nucleus. These responses showed a close resemblance to those induced by stimulation of the medial part of the anterior sigmoid gyrus (ASG) both in their contours and in their distributions. 2. There was a remarkable interaction between the Cd- and the medial ASG-induced field potentials in the pontine nuclei. When conditioned by the Cd stimulation at significantly short time intervals, the field potentials evoked by the medial ASG stimulation were more remarkably suppressed than those by the lateral ASG stimulation. 3. Field potentials or extracellular unitary activities in the inferior olive elicited by the Cd stimulation were closely related to those evoked by the medial ASG stimulation both in their responsiveness and in their topographical localizations. 4. When the cortical motor area had been ablated 10--14 days previously, the Cd stimulation elicited no responses in the cerebellar cortex. 5. From these findings, it was indicated that the Cd receives collaterals of the cortico-pontine and/or the cortico-olivary axons that originated almost exclusively from the neurones in the medial ASG (area 6). This suggested the existence of a common innervation of the basal ganglia and the cerebellar systems by the premotor area of the cerebral cortex.