Mouse visual cortex is a complex network comprising the primary visual cortex (V1) and several higher- order visual areas. Although these visual cortical areas are believed to contribute differentially to perception and behavior, our understanding of their role in visual processing is still unclear.
Mouse V1, along with the higher visual areas LM and RL, contains a substantial visuotopic representation of the binocular field of view. Binocular neurons in the visual cortex combine signals from left and right eye images. The small differences between these images, called binocular disparities, provide the visual system with critical information for depth perception. In primates, disparity selectivity is differentially processed across visual cortical areas. To test whether such specializations also exist in rodents, we characterized binocular disparity in V1 and in areas LM and RL of the anesthetized mouse. We employed a dichoptic stimulation protocol, using oriented gratings presented at varying interocular phases as well as random dot stereograms.
We found that disparity processing is highly distributed across neurons in areas V1, LM, and RL, but with clear differences in preferred disparities: area RL contains a higher fraction of neurons selective to near disparities compared to V1 and LM, indicating that RL is specialized for processing visual objects at close distance to the mouse. Preference for near disparities in RL was evident using both gratings and random dot stereograms for stimulation, and it was also observed in awake animals. Since recent data show that most neurons in mouse RL respond to both visual and whisker stimulation, we speculate that this area might contain a multimodal representation of the immediate space in front of the animal.