Published on Mon Jul 26 2021

Inseparable color and form in mouse visual cortex described by random pooling from rods and cones

Rhim, I., Nauhaus, I.

Recent investigations of the mouse ventral retina demonstrate that rod and cone responses are combined to detect changes between UV and green light. An important question is how the spatial representations of both color and brightness contrast are transformed by downstream circuits.

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Abstract

An image projected onto the retina is composed of local contrasts in color and brightness, both of which can aid in any visual perception task. Recent investigations of the mouse ventral retina demonstrate that rod and cone responses are combined to detect changes between UV and green light, thus providing a new model for color vision. An important question is how the spatial representations of both color and brightness contrast are transformed by downstream circuits. Its known that SF tuning of brightness contrast is sharpened at the level of mouse primary visual cortex, yet color contrast is untested. Here, we presented sinewave gratings that drive one of four axes of rod and cone contrast space, including brightness contrast (rod+cone) and color contrast (rod-cone). We find that V1 neurons are tuned to higher spatial frequencies of brightness contrast than color contrast, and are most responsive to color at the lowest spatial frequencies. These results are consistent with a model of single-opponency between rods and cones, but do not match its classic description. The data can instead be described by a simple model of convergent ON and OFF inputs to V1, which randomly pool discrete quantities of each photoreceptor class. Unlike classic depictions of single-opponency, this model requires minimal constraints on the circuit, accounts for our observed bandpass spatial frequency tuning of rod and cone isolating contrast, and is consistent with recent studies showing unselective pooling from photoreceptors in the retina.