Specificity of cortico-cortical connections in monkey visual system.

When the primate primary visual cortex, area 17, is stained for the mitochondrial enzyme cytochrome oxidase, it shows a striking polka-dot pattern (cytochrome oxidase blobs). Area 18, the second visual area, shows a cytochrome-oxidase pattern of coarse alternating thick and thin stripes running perpendicular to the 17-18 border and separated by lighter (interstripe) regions. Here we show that the thin cytochrome oxidase stripes, and possibly also the thick stripes, in area 18 receive projections specifically from the blobs in area 17, and that the interstripe regions of 18 receive projections from the interblob matrix of area 17. This indicates a specificity of cortico-cortical connections far exceeding the demands of topographical mapping. Together with our physiological results, it suggests that within the pathway from area 17 to area 18 different kinds of information may be handled separately and in parallel.