THE GLOBAL PATTERN OF CYTOCHROME-OXIDASE STRIPES IN VISUAL AREA V2 OFTHE MACAQUE MONKEY

In primate visual area V2, histochemical staining for cytochrome oxida se (CO) reveals a tripartite pattern of densely labeled thick and thin stripes separated by pale interstripes. This modularity is believed t o be related to functionally distinct processing streams that course t hrough the hierarchy of visual areas. Here, we studied the overall pat tern of CO stripes in V2 of the macaque monkey, using tissue that had been physically unfolded and flattened prior to histological sectionin g. CO stripes were identified on the basis of their physical dimension s and on their differential immunoreactivity for the monoclonal antibo dy Cat-301. We observed several distinctive features of compartmental organization in V2. The most prominent was a dorso-ventral asymmetry i n the stripe pattern, occurring in the majority of cases studied. In d orsal V2, most stripes measure similar to 10 mm in length and run roug hly orthogonal to both the posterior and anterior borders of V2. In co ntrast, many stripes in ventral V2 have a curved or oblique trajectory , and some extend up to 20 mm in length. Stripes following a curved tr ajectory often become nearly parallel to the anterior border of V2. Th ese differences imply an asymmetry in how the visual field maps onto d orsal versus ventral stripes. Occasionally, thin stripes fail to alter nate with thick stripes but instead occur next to one other, separated only by interstripes. In the three most complete reconstructions, we found that unfolded V2 is similar to 110 mm in length, similar to 900 mm(2) in surface area, and that it contains similar to 28 complete set s of stripes (one thick, one thin and two interstripes), yielding an a verage of similar to 4 mm per set of stripes. The maximum width of ven tral V2 (13-14 mm) exceeds that of dorsal V2 (10 mm), and there is a c onsistent narrowing of V2 in the region of foveal representation (3-5 mm).