Photoreceptor regulation of spatial visual behavior.

Purpose: To better understand how photoreceptors and their circuits support luminance-dependent 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.