Primate Visual Cortex

Few regions in the brain have received as much attention and scrutiny as the visual cortex, whose structural and functional organization provides an ideal model for understanding cerebral cortex in general. Binocularity in the visual system further permits experimental manipulations of a single eye input with the other eye serving as a useful internal reference point. In the last century, the visual cortex has consistently been used as a fertile testing ground for virtually every new neurobiological technique and innovation. As a result, much of its anatomical, neurochemical, and functional organizations have been examined. Of special significance is the discovery by Hubel and Wiesel (1968) of ocular dominance columns, orientation columns, and the exquisite system of functional modules in the primate striate cortex. Our understanding of the visual system has reached new heights over the last decade, with new techniques based on brain metabolism, enzyme histochemistry, immunohistochemistry, voltage-sensitive dyes, and brain imaging having been applied rigorously to the study of the visual cortex (e.g., Kennedy et al., 1976; Wong-Riley, 1979b; Horton and Hubel, 1981; Hendrickson et al., 1981; Tootell et al., 1982, 1988a–e; Hockfield et al., 1983; Horton, 1984; Carroll and Wong-Riley, 1984; Wong-Riley and Carroll, 1984a,b; Livingstone and Hubel, 1984a; Hendry and Jones, 1986; Blasdel and Salama, 1986; Wong-Riley et al., 1989a,b; Ts’o et al., 1990; Beaulieu et al., 1992). In this chapter, I will concentrate on cytochrome oxidase, and review what this endogenous metabolic marker has revealed about the primate visual cortex. The species on which most of the studies are based is the macaque monkey, but other primate species including man will be described when appropriate. A comparative study with other mammalian species has been reported previously (Wong-Riley, 1988).