THE ROLE OF THE CEREBELLO-THALAMO-CORTICAL PATHWAY IN SKILLED MOVEMENT

Studies of lesions of the primate cerebellum leave little doubt that t he cerebellum is necessary for the execution of smooth and accurate mo vements. How the cerebellum fulfills this role at a neuronal level rem ains unknown. It is likely that the cerebellum exerts the same effect on a number of different efferent targets. In order to influence volun tary movement, a major output from the cerebellum projects to the moto r cortex via the cerebello-thalamo-cortical (CTC) pathway. By examinin g neuronal activity in the cerebellar thalamus, and comparing this wit h activity recorded from its connections with the deep cerebellar nucl ei and motor cortex, conclusions can be made regarding cerebellar func tion. Current data does not support a role for the CTC pathway in the initiation of movement or the control of trans-cortical reflexes. Also , the evidence does not support the hypothesis that the cerebellum pre vents terminal movement oscillations by predictively sending a message to the antagonist muscle to brake the movement. The available literat ure supports the Eccles theory that during normal movement, the CTC pa thway receives a form of efference copy from the motor cortex and comp ares this message with that derived from peripheral afferents about th e actual progress of the movement. However, there is not a significant degree of kinematic information passing through this pathway in the c ourse of a voluntary movement. Therefore the actual site of comparison or error-detection in this system awaits further elucidation.