THE ROLE OF RETINAL BIPOLAR CELL IN EARLY VISION - AN IMPLICATION WITH ANALOG NETWORKS AND REGULARIZATION THEORY

A linear analogue network model is proposed to describe the neuronal c ircuit of the outer retina consisting of cones, horizontal cells, and bipolar cells. The model reflects previous physiological findings on t he spatial response properties of these neurons to dim illumination an d is expressed by physiological mechanisms, i.e., membrane conductance s, gap-junctional conductances, and strengths of chemical synaptic int eractions. Using the model, we characterized the spatial filtering pro perties of the bipolar cell receptive field with the standard regulari zation theory, in which the early vision problems are attributed to mi nimization of a cost function. The cost function accompanying the pres ent characterization is derived from the linear analogue network model , and one can gain intuitive insights on how physiological mechanisms contribute to the spatial filtering properties of the bipolar cell rec eptive field. We also elucidated a quantitative relation between the L aplacian of Gaussian operator and the bipolar cell receptive field. Fr om the computational point of view, the dopaminergic modulation of the gap-junctional conductance between horizontal cells is inferred to be a suitable neural adaptation mechanism for transition between photopi c and mesopic vision.