The accurate generation of voluntary movements involves neuronal processing related to attention, learning, memory, expectation and planning. Motor systems therefore, are an excellent model to address questions related to perceptual and cognitive processing. The overall goal of my research program is to understand the role of the basal ganglia (BG) and superior colliculus (SC) in target selection for saccadic eye movements. In this application we are focused on the relationship of one output nucleus of the BG, the substantia nigra pars reticulata (SNr) to the SC and their combined role in processing events related to choosing a goal for a saccadic eye movement. A central question in cognitive neuroscience is how visual stimuli are identified as objects for perceptual processing or as goals for movements. We propose that in addition to the role of the BG movement initiation, the BG also actively regulate the information processing occurring within target structures to select goals for movements. Here we propose to use the BG-SC pathway and eye movements as a model system to study this broader movement control issue. As a first step toward exploring the role of the BG as an active player in the sensorimotor events leading to voluntary movements, we will focus on the output pathway from the SNr to the SC. The Specific Aimof this proposal is to determine whether extrinsic inhibitory inputs to the SC arising from the SNr can influence the response field (RF) properties of SC neurons. Four experiments are proposed to accomplish this aim: 1) Measure the location tuning of SC neurons in a Go/No-Go task to test the hypothesis that position information in the SC is altered when a monkey chooses to make a saccade; 2) Measure the contrast sensitivity of SC neurons and determine whether contrast information is altered when a monkey chooses to make a saccade, 3) Electrically stimulate the SNr during the visual, delay and cue periods of the Go/No-Go task to test the hypothesis that increases in SNr activity increase the inhibition on SC neurons and alter the position and contrast sensitivity of SC neurons; 4) Reversibly inactivate the SNr with muscimol, a GABA agonist, and measure the position and contrast tuning of SC neurons to test the hypothesis that decreases in SNr inhibition alter SC neuronal properties. Our overarching hypothesis is that the inhibitory drive to the SC provides a biasing signal to the SC to regulate cortical information transmitted directly to the SC for the selection of targets that lead to saccadic eye movements.