Characteristics of Dentate Neuronal Discharge in a Simple and a Choice Reaction Time Task in the Monkey

Abstract

A role for the lateral cerebellar system (hemisphere and dentate nucleus) in the planning, initiation and execution of movement is suggested by its connectivity: it receives input from the associative regions of cerebral cortex and projects to the precentral motor cortical areas (Allen and Tsukahara, 1974). In a recent study, we found that the discharge of dentate neurons, occurring well in advance of movement, does not specify the subsequent direction of movement in a simple reaction time (RT) task (Chapman et al., 1986). This is in marked contrast to, for example, motor cortex where the large majority of neurons, in this same task, are directional (Lamarre et al., 1980, 1981, 1983). It was, furthermore, difficult to reconcile these observations with those of other investigators who have reported a large proportion of direction-sensitive responses in dentate (Thach, 1970; Harvey et al., 1979; Stein, 1978; cf. Thach et al., 1982). It was suggested that the relative absence of direction-dependent discharge in this previous study might be explained by nature of the task used — a simple RT situation, with no preparatory period, in which the GO signal did not specify the desired direction of movement.