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The earliest stages of cortical visual processing in areas V1 and V2 of the macaque monkey contain internal subdivisions ('blobs' and 'interblobs' in layer 4B in V1; thin, thick and interstripes in V2) that are selectively interconnected and contain neurons with distinctive visual response properties. Here we use anatomical pathway tracing to demonstrate that higher visual areas, V4 and the ventral posterior inferotemporal cortex, each contain anatomical subdivisions that have distinct input and output projections. These findings, in conjunction with others, suggest that modularity and multistream processing within individual cortical areas are widespread features of neocortical organization.

Nature 371, 151-154 (1994) EDITING of the opening sentence of the first paragraph of this Letter introduced a misleading error: the internal subdivisions given in parentheses should correctly read: "('b\obs\ 'interblobs' and layer 4B in VI; 'thin', 'thick' and 'interstripes' in V2)".

V2 is a visual area of the macaque monkey which is at the second level in a recently proposed hierarchy of cortical visual areas1. Histochemical staining for cytochrome oxidase (CO) in V2 reveals a pattern of alternate thick and thin CO-rich stripes separated by CO-sparse interstripes2,3. These subregions receive distinct inputs from neurones in CO-rich and CO-sparse zones arrayed within the superficial layers of V1 (refs 4,5). Are output projections from V2 to higher visual areas also segregated? Using an anatomical double-label paradigm, we have now demonstrated that V2 cells projecting to two of its major target areas, MT and V4 (refs 6, 7), are arranged in stripe-like clusters which are largely segregated from one another and which are closely related to the pattern of CO stripes. Concomitant electrophysiological recordings from V2 indicate that groups of cells having similar receptive field properties are clustered within the subregions defined by these anatomical techniques.