Columnar organization of spatial phase in visual cortex

Images are processed in the primary visual cortex by neurons that encode different stimulus orientations and spatial phases. In primates and carnivores, neighboring cortical neurons share similar orientation preferences, but spatial phases were thought to be randomly distributed. We discovered a columnar organization for spatial phase in cats that shares similarities with the columnar organization for orientation. For both orientation and phase, the mean difference across vertically aligned neurons was less than one-fourth of a cycle. Cortical neurons showed threefold more diversity in phase than orientation preference; however, the average phase of local neuronal populations was similar through the depth of layer 4. We conclude that columnar organization for visual space is not only defined by the spatial location of the stimulus, but also by absolute phase. Taken together with previous findings, our results suggest that this phase-visuotopy is responsible for the emergence of orientation maps.