PROJECT SUMMARY The overall goal of this proposal is to understand the role of interactions between the receptive field center and surround in encoding motion signals in sparsely expressed retinal ganglion cells of the macaque monkey retina. Studies of primate retinal ganglion cell physiologies have largely been limited to 5 dominantly expressed types. This proposal will contribute to our understanding of three poorly understood and sparsely expressed ganglion cell types: the broad thorny, the ON smooth monostratified, and the OFF smooth monostratified. These three types will be characterized in terms of center-surround interactions that contribute to each ganglion cell’s functional output. The proposed research has two specific aims: 1) To determine whether surround motion facilitates spiking outputs of smooth monostratified ganglion cells. I will record synaptic inputs and spiking outputs of smooth monostratified ganglion cells to measure ganglion cell sensitivity when a motion stimulus is presented to the surround. I will test the specific hypothesis that despite showing a traditionally suppressive surround to stationary spots, the smooth monostratified cell’s spiking output is facilitated by motion in the surround. 2) To determine whether center and surround interact to create selectivity for object motion in the broad thorny ganglion cell. I will measure synaptic inputs and spiking outputs of the broad thorny ganglion cell to determine whether motion in the broad thorny surround is suppressive to all visual inputs except object motion. My experiments will test the specific hypothesis that surround motion makes the broad thorny sensitive to differential motion.