Motor functions of cerebellum and basal ganglia: the cerebellocortical saccadic (ballistic) clock, the cerebellonuclear hold regulator, and the basal ganglia ramp (voluntary speed smooth movement) generator.

Abstract

A theory of the motor functions of the cerebellum and the basal ganglia is presented. It is based on the following observations: The functional interpretation starts from the fact that rapid (saccadic, ballistic) movements cannot be regulated continuously but rather they must be preprogrammed. In case of complete recruitment of motoneurons the energies needed for different movements must be translated into different burst durations of motoneurons. For the calculation of these durations the starting and end positions must be taken into account. Therefore afferent information from mechanoreceptors are required for this preprogramming. On the other hand, slow smooth movements of voluntary speed may be regulated continuously by feedback. In the production of ramp movements the main point is integration-in the technical sense. The conclusion is that the function of the cerebellar cortex is to calculate the burst duration for rapid preprogrammed movements, a discontinuous function. On the contrary, the function of the cerebellar nuclei is to hold the positions reached by rapid movements precisely, a continuous regulation. The function of the basal ganglia (the strio-nigro-pallidum) is to generate slow smooth movements of voluntary speed, i.e. from the technical point of view, the basal ganglia function as a ramp generator.