Learning of fast and stable hand movement and cerebro-cerebellar interactions in the monkey.

Monkeys were trained to lift a lever by wrist extension in response to a light stimulus and changes of premovement cortical field potentials were observed during the training period with electrodes which had been chronically implanted in various cortical areas. The purpose of the study was to follow changes in potentials mediated by cerebro-cerebellar neuronal circuits as fast and stable hand movements were attained during later stages of motor learning. As compared to initial stages of an operantly conditioned movement in response to the light stimulus, further training shortened reaction times gradually over several weeks, and this was associated with gradual increases of premovement superficial thalamo-cortical (T-C) responses in the contralateral forelimb motor area. Since the T-C responses are known to depend at least in part on impulses from the neocerebellum, it is suggested that the neocerebellum--superficial T-C projection--motor cortex system is gradually recruited during motor learning and that this in turn contributes to fast and stable movements.