Color columns in macaque VI: Two novel color systems are revealed by intrinsic optical imaging

We examined the spatial organization of color processing in the primate visual cortex. and focused on 4 questions: (i) Is there a spatial structure in VI that differentiates isoluminant color stimuli from otherwise-similar luminance stimuli? (ii) Is there a spatial structure that discriminates between color stimuli of different hues, even in the presence of luminance contrast? (iii) How do the tuning properties of the various cortical networks depend on stimulus contrast? (iv) What is the relationship between the color-processing structures and the already-familiar columnar organization, such as ocular dominance columns, orientation patches, and the cytochrome oxidase blobs? We imaged the striate cortex of anesthetized, paralyzed macaque monkeys stimulated with drifting gratings of various orientations and spatial frequencies Extensions of principal components analysis enable us to achieve sensitive, robust, and quantifiable detection of spalial activity patterns. Our results indicate the presence of two closely related color-processing columnar systems one responds preferentially to isolummant stimuli of all colors, while the other distinguishes between stimuli that are identical in mean luminance and contrast, but differ only in hue The two systems have different characteristic spatial scales, with the isoluminance-detecting system being a spatial subset of the hue-detecting system Neither of these systems bears a clear relationship with the ocular dominance columns and neither is spatially related to the cytochrome oxidase blobs Finally, the various cortical columnar systems such as the ocular dominance columns, the color columns, and the orientation patches, have strikingly different contrast response functions, suggesting separate processing by the diverse neural networks that coinhabit the same conical area.