Abstract. To investigate the contributions of amacrine cells (AC's) to red-green opponency, a linear computational model of the central macaque retina was developed based on a published cone mosaic. In the model, AC's of ON and OFF types receive input from all neighboring midget bipolar cells of the same polarity, but OFF AC's have a bias toward M-center bipolar cells. This might arise due to activity-dependent plasticity because there are midget bipolar cells driven by S cones in the OFF pathway. The model midget ganglion cells receive inputs from neighboring AC's cells of both types. As in physiological experiments, the model ganglion cells showed spatially opponent responses to achromatic stimuli, but they responded to cone isolating stimuli as though center and surround were each driven by a single cone type. Without AC input, L and M cones contributed to both the centers and surrounds of model ganglion cell receptive fields. According to the model, the summed AC input is red-green opponent even though individual AC's are practically unselective. A key prediction is that GABA and glycine depolarize L OFF and M ON central midget ganglion cells; this may be reflected in lower levels of the chloride transporter KCC2 in their dendrites.
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