Cerebellar output: motor and cognitive channels.

The input to the cerebellum has long been known to originate from widespread regions of the cerebral cortex including the frontal, parietal and temporal lobes. The output of the cerebellum, however, was thought to project mainly to the primary motor cortex. Recent anatomical observations have challenged this view. It is now apparent that cerebellar output goes to multiple cortical areas, including not only the primary motor cortex, but also areas of premotor and prefrontal cortex. In fact, there is growing evidence that each of the areas of cerebral cortex that project to the cerebellum is also the target of cerebellar output. The cerebellar output to individual cortical areas originates from distinct clusters of neurons in the deep nuclei which we have termed `output channels'. The individual output channels to the cortical areas we have examined display little or no overlap. Physiological recordings in awake trained primates indicate that neurons in different output channels appear to be involved in distinct aspects of behavior, and in both motor and cognitive functions. These observations indicate that the cerebellar influence on the cerebral cortex is more extensive than previously recognized.