How Do Functional Maps in Primary Visual Cortex Vary with Eccentricity?

It is important to understand whether functional maps of primary visual cortex (V1) are organized differently at the representation of different eccentricities. By using optical imaging of intrinsic signals, we compared the maps of orientation and spatial frequency (SF) preference between central (0-3 degrees ) and paracentral (4-8 degrees ) V1 in the prosimian bush baby (Otolemur garnetti). No differences related to eccentricity were found for orientation selectivity or magnitude between central and paracentral V1. We found, however, that cardinal orientations were overrepresented in central but not in paracentral V1 and that isoorientation domain size tended to be smaller in the central representation. We demonstrated that spatial frequency was represented continuously across V1, and that the map of SF preference exhibited eccentricity-dependent variations, with more territory devoted to higher SFs in central than in paracentral V1. Although there were no spatial relationships between orientation domains and cytochrome oxidase (CO) blobs or interblobs, CO blobs tended to prefer lower SFs than interblobs. Taken together with previous research, our data indicate that functional domains in V1 show eccentricity-related differences in organization and also support the idea that different maps (with or without specific geometrical relationships) are organized for adequate coverage of each feature in visual space.