Submillimeter fMRI reveals a layout of dorsal visual cortex in macaques, remarkably similar to New World monkeys

Abstract

The macaque dorsal occipital cortex is generally thought to contain an elongated third visual area, V3d, extending along most of the rostral border of area V2. In contrast, our submillimeter retinotopic fMRI maps (0.6-mm isotropic voxels, achieved by implanted phased-array receive coils) consistently show three sectors anterior to V2d. The dorsal (mirror image) sector complies with the traditional V3d definition, and the middle (nonmirror image) sector with V3A. The ventral (mirror image) sector bends away from V2d, as does the ventrolateral posterior area (VLP) in marmosets and the dorsolateral posterior area (DLP) in owl monkeys, and represents the entire contralateral hemifield as V3A does. Its population-receptive field size, however, suggests that this ventral sector is another area at the same hierarchical level as V4d. Hence, contrary to prevailing views, the retinotopic organization of cortex rostral to V2d differs substantially from widely accepted models. Instead, it is evolutionarily largely conserved in Old and New World monkeys given its surprisingly similar overall visuotopic organization.