DESCRIPTION:(adapted from applicant's abstract) The long-term goal of the present project is to understand the neural substrates underlying motoric choices. In picking one of the many identical apples from a tree for example, the nervous system must choose whether to pick an apple on the right or left, up or down, whether to use the right hand or left hand, and whether to grasp the apple with a power grip or to pinch the stem. These choices have more to do with movement to be executed than the apple to be picked. Here we advance the novel hypothesis that the same cortical areas, in particular the PMV, SMA, that participate in selecting movements based on external and internal cues also participate in choosing among multiple equivalent movements particularly when perceptual and motivational factors are evenly balanced. Put simple, if all the apples are equal, motoric factors will influence the subjects movement choices. Because the striatum receives partially overlapping projections from PMv and SMA, as well as dopaminergic inputs signalling events predictive of a desirable reward, we hypothesize that striatal neurons also participate in motoric choices. We propose to study the related processes of movement selection and motoric choice by having subjects select movements specified by external cues on some trials (no-choice), while on other trials the subjects will have a choice between equally appropriate movements, unbiased by perceptual or motivational factors. We will examine our hypotheses with the following specific aims. (1) Do neuronal populations in the Pmv, SMA, and the striatum participate in the choices of which hand to use and on which side the responses are made? (2) Do neuronal populations in the PMv, SMA, and the striatum also participate in other non-lateralized choices, such as up and down, and pinch and power grasp? (3) How does reversible inactivation or microstimulation of the PMv, SMA, and striatum bias motoric choices? (4) How do the partially overlapping cortico-striatal projections from the PMv and SMA correlate with striatal regions participating in motoric choices?