Projections from V1 to lateral suprasylvian cortex: an efferent pathway in the cat's visual cortex that originates preferentially from CO blob columns.

ABSTRACT

The patchy pattern of retrograde labeling produced by injections of anatomical tracers into the lateral suprasylvian (LS) visual area was compared to the cytochrome oxidase (CO) blobs in cat visual cortex. Following large injections of anatomical tracers in LS, retrograde labeling formed an irregular lattice of patches with a spacing of slightly less than 1 mm in area 17, and slightly greater than 1 mm in area 18. By comparing labeling in alternate serial sections, patches of LS-projecting cells in both areas were found to align with CO blobs. The conclusion of alignment between CO blob columns and patches of LS-projecting cells was confirmed by a quantitative analysis which showed a significant correlation between the local density of LS-projecting cells in reconstructions of charted cells and the intensity of CO staining in the CO-reacted sections. As for areas 17 and 18, labeling in other afferent areas of LS was also patchy with a spacing on the order of 1 mm except for area 19 where we found patches of LS-projecting cells with a larger spacing, roughly 2 mm. No matching fluctuations in CO density could be discerned in area 19, however. In conjunction with recent evidence that CO blob columns in cats receive strong input from Y-cells of the lateral geniculate nucleus (Boyd & Matsubara, 1996; Shoham, et al., 1996), these data support the hypothesis (Shipp & Grant, 1991) that the patches of LS-projecting cells correspond to Y-cell input columns. As a relationship between the CO architecture and certain classes of efferent cells has previously been shown in primates, these findings show new similarities between CO blobs in different mammalian species.