Photoreceptor regulation of spatial visual behavior

PURPOSE. To better understand how photoreceptors and their circuits support luminancedependent spatial visual behavior. METHODS. Grating thresholds for optokinetic tracking were measured under defined luminance conditions in mice with genetic alterations of photoreceptor activity. RESULTS. The luminance conditions that enable cone- and rod-mediated behavior, and the luminance range over which rod and cone functions overlap, were characterized. The AII amacrine pathway was found to support low-resolution and high-contrast function, with the rod–cone pathway supporting high-resolution and low-contrast function. Rods alone were also shown to be capable of driving cone-like spatial visual function, but only when cones were genetically maintained in a physiological dark state. CONCLUSIONS. The study defined how luminance signals drive rod- and cone-mediated spatial visual behavior and revealed new and unexpected contributions for rods that depend on an interaction between cone and rod systems.