INTRINSIC CORTICAL CONNECTIONS IN MACAQUE VISUAL AREA V2 - EVIDENCE FOR INTERACTION BETWEEN DIFFERENT FUNCTIONAL STREAMS

Area V2 of macaque visual cortex represents an important but poorly un derstood stage in visual processing. To provide a better understanding of the region,we studied the organization of its intrinsic cortical c onnections by making focal (200-300 mu m) iontophoretic microinjection s of the tracer biocytin. Alternate tissue sections were tested for bi ocytin, cytochrome oxidase (CO), or Cat-301 immunoreactivity to locali ze biocytin label relative to the three stripelike compartments that c haracterize this area. Biocytin-labeled pyramidal neurons of layers 2/ 3, and, to a lesser extent, layer 5, provided laterally spreading axon projections that terminated in discrete patches (250-300 mu m diamete r), primarily in layers 1-3. Any injected locus in V2 projected to 10- 15 similarly sized patches, up to 4 mm from the injection site, and di stributed in an elongated field orthogonal to the stripe compartments. We noted prominent patchy connections within, as well as between, ind ividual compartments, perhaps reflecting functional substructures with in stripes. Each stripe compartment projected to all three compartment s but with different relative frequencies; CO-rich compartments projec ted mainly to other CO-rich compartments (75%), whereas CO-poor compar tments projected equally to CO-rich and CO-poor compartments. Wetheref ore emphasize the existence of substantial interconnections among all three V2 compartments. As further evidence for crosstalk between visua l channels, we also noted an input to the V2 ''thick'' CO stripes from V1 cells in layer 4A as a distinct population in addition to the neur ons of layer 4B. Thus, the CO stripe architecture may not be a marker for strictly segregated parallel visual pathways through V2. (C) 1994 Wileg-Liss, Inc.