Segregation and convergence of functionally defined V2 thin stripe and interstripe compartment projections to area V4...

The organization of projections from V2 thin stripes and interstripes to V4 was investigated using a combination of physiological and anatomical techniques. The compartments of V2 were first characterized, in vivo, using optical recording of intrinsic signals. Multiple anterograde tracers were then injected into different V2 compartments. The distribution of labeled axons was analyzed in tangential or horizontal sections including V4. A small iontophoretic injection, either in a thin stripe or an interstripe, labeled a large primary and several secondary foci in V4. The primary foci from the thin stripe and interstripe were spatially segregated by a gap of approximately 1 mm. Furthermore, less dense regions within the primary foci were often 'filled-in' by secondary foci from the opposite V2 compartment. When two injections were made both at interstripes, their projections to V4 were almost entirely overlapping. These anatomical patterns indicate that segregation and convergence of intercortical pathways are both important features of V4 organization. Furthermore, the size of cortical modules increases considerably from the blobs of V1, through the stripes of V2, to the afferent domains of V4.