Cerebellar outputs in non-human primates: An anatomical perspective using transsynaptic tracers

Abstract

Important insights into cerebellar function can be gained from an anatomical analysis of cerebellar output. Recent studies using transsynaptic tracers in nonhuman primates demonstrate that the output of the cerebellum targets multiple nonmotor areas in the prefrontal and posterior parietal cortex, as well as the motor areas of the cerebral cortex. The projections to different neocortical areas originate from distinct output channels within the cerebellar nuclei. The neocortical area that is the main target of each output channel is a major source of input to the channel. Thus, a closed-loop circuit represents the fundamental macro-architectural unit of cerebro-cerebellar interactions. The outputs of these circuits provide the cerebellum with the anatomical substrate to influence the control of movement and cognition. Similarly, it has been shown that discrete multisynaptic loops connect the basal ganglia with motor and nonmotor areas of the cerebral cortex. Interactions between cerebro-cerebellar and cerebro-basal ganglia loops have been thought to occur mainly at the level of the neocortex. More recently, neuroanatomical studies demonstrate that the anatomical substrate exists for substantial interactions between the cerebellum and the basal ganglia in both the motor and nonmotor domains. These data, along with the revelations about cerebro-cerebellar circuitry, provide a new framework for exploring the contribution of the cerebellum to diverse aspects of behavior.