Abstract
The organization of extrastriate visual cortex in macaque monkeys has been open to several interpretations. While many proposals include a V3, V3 takes various forms including that of a dorsal V3 representing the lower visual quadrant only, but with the ventral V3 region included in another visual area, VP, because of lack of evidence for ventral V1 connections with ventral V3. As V3 was originally defined by connection patterns of V1, we reconsidered these connections after making large injections of the sensitive neuroanatomical tracers cholera toxin subunit-B (CTB), and fluorochromes into ventral or dorsal V1. The injections were made by approaching from the caudal pole of visual cortex where we exposed the upper and lower banks of the calcarine sulcus by gentle pressure from a cotton swab. In a total of four rhesus macaques (Macaca mulatta), eight injections in dorsal V1 (representing the lower visual quadrant; marked by the upper bank of the calcarine) labeled lower quadrant locations in dorsal V2 and dorsal V3, and seven injections in ventral V1 (representing the upper visual quadrant; marked by the lower bank of the calcarine) similarly labeled upper quadrant regions in ventral V2 and ventral V3. The results suggest that macaques have a V3 that is a mirror reversal of V2 in retinotopic organization. This V3 is about half the width of V2, and it includes both dorsal and ventral halves, with ventral V3 in place of VP. Injections in dorsal or ventral V1 also labeled DL(V4), DM(V3a), MT, and inferotemporal cortex.
Supported by NEI Grant EY 02686 and NRSA Training Grant 5T32 EY07135.