Cerebellum lesions and finger use

We tested monkeys, patients, and normal control human subjects in a task that requires skilled use of the fingers. Animals and patients with lesions of the cerebellum, particularly of the cerebellar hemispheres, were severely impaired in retrieving raisins from small holes (monkeys) or shifting beads from place to place through a series of such holes, using the index finger alone or in apposition (humans). As they descend through the pontine nuclei, pyramidal tract fibres give off a collateral to pontine cells. The axons of pontine cells, in turn, project to the cerebellar cortex, where they terminate as mossy fibres. We suggest that the corollary discharge from pyramidal tract fibres to the cerebellum via the pontine nuclei is required for skilled, co-coordinated, simultaneous or sequential movements.