Synaptic organization of the cerebello-thalamo-cerebral pathway in the cat. I. Projection of individual cerebellar nuclei to single pyramidal tract neurons in areas 4 and 6.

The neural connections of the dentate (DN) and the interpositus (IN) nuclei to the motor cortex and area 6 were investigated by recording intracellular postsynaptic potentials from fast and slow pyramidal tract neurons (PTNs) in the anesthetized cat. Localized stimulation of DN and IN produced di- or polysynaptic EPSPs in fast and slow PTNs in the "forelimb area" of the motor cortex and area 6. The effects of stimulation of the two cerebellar projections were essentially the same, although some regional difference of their relative strength was noted. In these cortical areas, the majority of fast and slow PTNs received convergent inputs from both DN and IN. By examining the interaction of DN- and IN-evoked EPSPs, spatial facilitation and occlusion at the level of the thalamus were demonstrated. Therefore, it was concluded that at least a portion of the convergence of the dentate and the interpositus inputs occurred at the level of the ventrolateral nucleus of the thalamus.