Several studies indicate that the frontal cortical and associated basal ganglia circuitry may be involved in relatively abstract aspects of motor control rather than mechanics of movement. This proposal is based on the general hypothesis that frontal cortical and basal ganglia circuitry are specifically involved in the learning of motor sequences. The studies will employ a serial reaction time task where one portion of a sequence of movements is kept constant while the others vary randomly. Over several trials, humans demonstrate learning for the constant portion of the sequence without explicit awareness of the learning. Three specific aims are outlined. The first will determine if there are neurons in motor and mesial premotor areas that discharge for specific sequences regardless of the limb used to perform the task. The hypothesis is that there will be neurons with an abstract representation of motor sequences that do not depend upon the motor apparatus used to execute the task. The second specific aim will determine if monkeys with bilateral lesions of the GPi are specifically impaired in learning new motor sequences. It is hypothesized that pallidotomy will disrupt learning of new motor sequences but will not disrupt performance of previously learned sequences. The third specific aim will be to determine if pallidotomy will affect neural correlates of sequence learning in primary motor cortex and dorsal and mesial premotor cortex. It is hypothesized that pallidotomy will slow or eliminate the development of sequence-related neural discharge, whereas discharge related to overlearned motor sequences will remain unchanged.