Parallel cone Bipolar to On-β Ganglion Cell Pathways in the Cat Retina: Spatial Responses, Spatial Aliasing, and Spatial Variance

An important issue in understanding the retina is finding candidate functional roles for different cell pathways and the details of their anatomy and physiology. We consider various spatial properties of the three main cone $\Longrightarrow$ cone biopolar cell $\Longrightarrow$ on-$\beta$ ganglion cell pathways in the cat retina and possible roles for the particulars of their anatomy. The cone bipolar cells in these pathways have distinct morphologies and modest differences in their convergence, divergence, densities, and synaptic weighting; and it is unclear whether the pathways differ in their spatial properties in some other manner. Since differences in spatial processing of cells are best studied on a system-wide level, we developed the multirate filter-based method of retinal modeling, a technique for relating the anatomy of multiple cell layers to its systemic effects. We demonstrate: (i) despite the anatomic distinctions between the three main cone bipolar cell pathways, their spatial responses are essentially identical; (ii) despite the spatial averaging in the pathways, there is essentially no filtering of the non-aliasing signal components after the cone layer; (iii) instead, this averaging combined with prefiltering by the eye's optics and cone gap junctions prevents spatial aliasing; and (iv) the averaging and prefiltering combined allow cell responses to be similar despite significant cell-to-cell anatomic differences.