High-sensitivity rod photoreceptor input to the blue-yellow color opponent pathway in macaque retina

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Abstract
It has been thought that blue-yellow color opponent cells in the primate retina receive little input from rods. Here, the authors report that rod and cone signals are multiplexed in blue-yellow cells and that this may be the source of the blue hue bias in night vision. Small bistratified cells (SBCs) in the primate retina carry a major blue-yellow opponent signal to the brain. We found that SBCs also carry signals from rod photoreceptors, with the same sign as S cone input. SBCs exhibited robust responses under low scotopic conditions. Physiological and anatomical experiments indicated that this rod input arose from the AII amacrine cell–mediated rod pathway. Rod and cone signals were both present in SBCs at mesopic light levels. These findings have three implications. First, more retinal circuits may multiplex rod and cone signals than were previously thought to, efficiently exploiting the limited number of optic nerve fibers. Second, signals from AII amacrine cells may diverge to most or all of the ∼20 retinal ganglion cell types in the peripheral primate retina. Third, rod input to SBCs may be the substrate for behavioral biases toward perception of blue at mesopic light levels.

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