Abstract. Cone-specific responses are generated by midget ganglion cells in primates, despite the electrical coupling of L and M cones and the unselective connections of inhibitory neurons. Lebedev and Marshak (2006) proposed a model of the central macaque retina that reconciled these findings. OFF amacrine cells (ACs) receiving synapses from all bipolar cells (BPs) but with a bias toward those receiving input from M cones were a key feature of that model. Here we demonstrate how this bias might develop due to activity-dependent synaptic plasticity. Our model consists of 1) array of cones, 2) array of OFF BPs that each receive input from one cone and 3) OFF ACs that receive input from all BPs within their dendritic fields. A series of random, colored stimuli were presented (stimulation of M and S cones being slightly correlated), and the weights of synapses from BPs to ACs were modified using a physiologically plausible, Hebbian-like learning rule depending on the membrane potentials of the presynaptic and postsynaptic neurons. As a result, excitatory synapses from BPs with input from M cones were strengthened, and the magnitude of the effect depended on the local S cone density. These interactions would occur only in the OFF pathway because there are no ON midget BPs receiving input from S cones.
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Last Update: August 30, 2006