This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Rapid eye movements called saccades remain accurate throughout life despite changes in the brain and the eye muscles brought about by growth, injury and aging. This year we published several observations that implicate the cerebellum in this motor adaptation or learning. First, the cerebellum receives a signal that reports by how much and in what direction saccades, which shift the direction of gaze, are in error. Second, when we stimulate electrically the pathway that delivers this error information to the cerebellum, we are able to cause gradual changes in both the amplitude and direction of saccades, which mimic those produced when there is a real saccade dysmetria. Third, when there is such an error, it causes a concomitant change in the activity of Purkinje cells, which provide the output of the cerebellum. In many P-cells, the changes in activity were appropriate to produce the changes in saccade amplitude that would cause a reduction of the saccade error. Finally, we have made pharmacological injections into this saccadic cerebellum and the preliminary findings suggest that different cerebellar cells are involved in increasing and decreasing saccade amplitude. We feel these results converge on the proposal that the learning of other precision behaviors, e.g., finger pointing, probably also involve similar cerebellar mechanisms.