Cerebellar nuclear activity in relation to simple movements.

Single unit activity in the fastigial, interpositus and dentate cerebellar nuclei was recorded in relation to simple elbow flexion and extension movements in two macaque monkeys. In common with proximal muscle activity, 94% of the task-related neurons had qualitatively similar discharge patterns for both directions of forearm movement. In many cases the flexion and extension discharge was virtually identical, but some cells had a distinct directional bias. The very few neurons which were directionally specific were located in the dentate and interpositus. Two had tonic activity well correlated to elbow angle. Task-related changes in discharge rate occurred earliest in dentate and latest in fastigial, but almost always during the period of concomitant proximal and elbow EMG changes. Correlations of phasic activity with movement velocity were uniformly weak. Many eye movement-related neurons were encountered in the fastigial, dentate and y-group nuclei. Fastigial eye cells, both bursting and tonic, tended to be highly direction specific, whereas dentate eye cells were usually omnidirectional and variable. For both arm and eye cerebellar cells, the directional preferences of phasic and tonic discharge, in the same neuron, could be opposed to one another.