The global pattern of cytochrome oxidase stripes in visual area V2 of the macaque monkey

In primate visual area V2, histochemical staining for Cytochrome oxidase (CO) reveals a tripartite pattern of densely labeled thick and thin stripes separated by pale interstripes. This modularity is believed to be related to functionally distinct processing streams that course through the hierarchy of visual areas. Here, we studied the overall pattern of CO stripes in V2 of the macaque monkey, using tissue that had been physically unfolded and flattened prior to histological sectioning. CO stripes were identified on the basis of their physical dimensions and on their differential immunoreactivity for the monoclonal antibody Cat-301. We observed several distinctive features of compartmental organization in V2. The most prominent was a dorso-ventral asymmetry in the stripe pattern, occurring in the majority of cases studied. In dorsal V2, most stripes measure ~10 mm in length and run roughly orthogonal to both the posterior and anterior borders of V2. In contrast, many stripes in ventral V2 have a curved or oblique trajectory, and some extend up to 20 mm in length. Stripes following a curved trajectory often become nearly parallel to the anterior border of V2. These differences imply an asymmetry in how the visual field maps onto dorsal versus ventral stripes. Occasionally, thin stripes fail to alternate 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 ~110 mm in length, ~900 mm² in surface area, and that it contains ~28 complete sets of stripes (one thick, one thin and two interstripes), yielding an average of ~4 mm per set of stripes. The maximum width of ventral V2 (13-14 mm) exceeds that of dorsal V2 (10 mm), and there is a consistent narrowing of V2 in the region of foveal representation (3-5 mm).