Retinal circuits driving a non-image forming visual behavior

Outer retinal circuits that drive non-image forming vision in mammals are unknown. Rods and cones signal light increments and decrements to the brain through the ON and OFF pathways, respectively. Although their contribution to image-forming vision is known, the contributions of the ON and OFF pathway to the pupillary light response (PLR), a non-image forming behavior, are unexplored. Here we use genetically modified mouse lines, to comprehensively define the outer retinal circuits driving the PLR. The OFF pathway, which mirrors the ON pathway in image-forming vision, plays no role in the PLR. We found that rods use the primary rod pathway to drive the PLR at scotopic light levels. At photopic light levels, the primary and secondary rod pathways drive normal PLR. Importantly, we find that cones are unable to compensate for rods. Thus, retinal circuit dynamics allow rods to drive the PLR across a wide range of light intensities.