The overall goal of the proposed research is to determine the neural circuitry of the largest ganglion cell class of the primate retina, the midget cells. Midget ganglion cells project to the parvocellular layers of the lateral geniculate nucleau (LGN) and are necessary for red/green color vision and spatial acuity. Despite the large role they play in visual perception, our understanding of the midget system's circuitry is limited. A new in vitro preparation of the macaque retina will be used to identify midget ganglion cells and record their light response. The proposed research has two specific aims: (1 ) To measure and model the spatial receptive fields of midget ganglion cells across the retina. The hypothesis that midget cells near the fovea receive their excitatory input from a single cone only will be directly tested. The first detailed description of midget cell surround size and strength as a function of eccentricity will also be provided. (2) To determine the retinal mechanism for red/green spectral opponency in midget ganglion cells. The relative strengths of L- and M-cone inputs to the receptive field center and surround of midget ganglion cells will be measured. Two competing hypotheses for red/green opponency will be directly tested: the cone type-specific hypothesis, which states that a pure L- or M-cone input is transmitted to both receptive field center and surround; and, the cone type-mixed hypothesis, which states that red/green opponency arises by a differentiai weighting of random L- and M-cone inputs to center and surround.
