DESCRIPTION: The ultimate goal of the study is to contribute to the understanding of the function of the basal ganglia in movement control. The precise knowledge of the circuitry of the basal ganglia is important for both theoretical and practical application to the study of basal ganglia disorders. The purpose of this proposal is to achieve the following two specific aims. The first specific aim is to substantiate my hypothesis that cortical signals are transmitted to the basal ganglia output nuclei, the entopeduncular nucleus and the substantia nigra pars reticulata, through two different nuclei, the neostriatum and the subthalamic nucleus. The investigators will examine whether stimulation of the sensorimotor cortex induces, in basal ganglia output nuclei, a disynaptic excitation which is mediated through the subthalamic nucleus, and a disynaptic inhibition which is mediated through the neostriatum. The second specific aim is to test my hypothesis that the globus pallidus is the control center of the basal ganglia in that the globus pallidus converges inputs from the neostriatum and the subthalamic nucleus and the output of the globus pallidus controls the activity of the entire basal ganglia. The investigator's studies, as well as those of others, have demonstrated that the globus pallidus integrates inputs from the neostriatum and the subthalamic nucleus. The globus pallidus also projects heavily to the neostriatum and the basal ganglia output nuclei, the entopeduncular nucleus and the substantia nigra pars reticulata. The investigators study will focus on the effects of pallidal projections to the neostriatum and the entopeduncular nucleus. This study will characterize physiological properties and the role of pallidal projections to the neostriatum and the entopeduncular nucleus. At the end of the proposed projects, they will be able to offer an anatomical and physiological basis for explaining how the activity of GP neurons influence other basal ganglia nuclei. The methods for the proposed study include: unit recording, intracellular recording and staining in both anesthetized animals and brain slice preparations.