Identification and localization of functional subdivisions in the visual cortex of the adult mouse.

We investigated the anatomical characteristics of the mouse visual system through in situ hybridization for the neuronal activity marker zif268. Our main goal was to delineate the full extent of the cortical region processing visual information and additionally to identify the monocularly and binocularly driven subregions therein. We therefore analyzed the neocortex of monocularly and binocularly enucleated mice versus visually stimulated control mice. These visual manipulations revealed eye-specific parcellations at the neocortical level. In binocularly enucleated mice we detected an unambiguous lateral border between visually driven and nonvisual cortex based on the clear deprivation-induced reduction in zif268 expression in the first. However, medially a transition zone of intermediate intensity was found between primarily visual, that is V1 and multimodal retrosplenial cortex. Also in monocularly enucleated mice, the visual cortex contralateral to the deprived eye clearly displayed distinct regions of lower signal than the ipsilateral cortex. Yet interspersed between these regions of basal activity we could clearly identify a zone of high activity spanning the V1-V2L border. A second zone of higher activity was noticeable near the medial border of visual cortex. Comparison with binocularly enucleated mice indicates the presence of both binocular input as well as nonvisual input in this medial cortical region and thus confirms the transitional nature of the recently described rostromedial areas.