Optical imaging of functional organization of V1 and V2 in marmoset visual cortex.

Using optical imaging of intrinsic cortical signals, we examined the functional organization of visual cortical areas V1 and V2 of the marmoset (Callithrix jacchus). Previous studies have reported that adult marmosets do not have ocular dominance columns (ODCs); however, recent studies have called this into question. Using optical imaging methods, we examined whether ODCs could be detected in adult marmosets. We found evidence for functional ODCs in some marmosets but not in others. The activation patterns, when present, were relatively weak and appeared as a mosaic of irregular bands or islands. Consistent with studies in other New World monkeys, these data suggest the presence of ODC variability within the marmoset population. Orientation maps in V1 revealed iso-orientation domains organized in semicontinuous bands oriented orthogonal to the V1/V2 border, a pattern unlike that in Macaque monkey. The presence of directional preference maps in V1 was also suggested. In V2, similar to V2 in Macaque monkeys, stripe-like regions of orientation selectivity overlay the pale cytochrome oxidase regions of V2; zones not selective for orientation overlay the cytochrome thin stripes. However, unlike Macaques, we did not observe clear evidence for orientation maps overlying thick cytochrome oxidase stripes. In sum, our data suggest that significant organizational differences exist between the organization of V1 and V2 in the marmoset and that of Old World primates. Implications for the establishment of functional ocular dominance columns, the coestablishment of multiple featural maps, and cortical magnification factors are discussed.