Functional anatomy of the second visual area (V2) in the macaque

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Abstract
To study the functional organization of secondary visual cortex (V2) in the primate, 14C-2-deoxy-d-glucose (DG) was injected while macaque monkeys were shown specific visual stimuli. Wherever possible, patterns of DG uptake were compared with the position of dark and light cytochrome oxidase (cytox) stripes (Tootell et al., 1983). Often, the DG effects of 2 different stimuli were compared in the same hemisphere to eliminate ambiguities inherent in between-animal comparisons. Data were obtained from a large number of animals in conjunction with related DG studies in area V1 (primary visual of striate cortex). The following conclusions were reached: (1) in some macaque monkeys, dark cytox stripes were faint or absent. Although this could conceivably be due to poor staining technique, some evidence suggests that the lack of enzyme stripe pattern in real. In all animals, including those that showed poor or no cytox staining evidence of stripes, the functional architecture revealed by the DG was consistently present and robust, (2) Uniform gray stimuli produce a relatively uniform pattern and minimal stimulus-related DG uptake. (3) Eye movements per se produce some uptake in the V2 stripes. (4) Very generalized visual stimulation conditions (e.g., binocular stimulation with a grating of varied orientation and varied spatial frequency) produce a pattern of uptake that is greatest in both sets of dark cytox stripes and lighter in the light cytochrome stripes. (5) In both the DG and cytox results, the V2 "stripes" are more accurately described as stripe-shaped collections of patches. (6) In almost all cases, DG patterns were columnar in shape, extending from white matter to cortical surface. The boundaries of the columns were most sharply defined, and the contrast was highest, in layers 3B/4, becoming slightly more blurry and lower in contrast in other layers. Laminar differences between DG patterns in V2 were almost negligible, compared with the profound laminar differences in macaque V1. (7) There is no DG evidence for, and much against, the possibility of an ocular dominance architecture in V2. (8) There are orientation columns in macaque V2. DG-labeled orientation columns are spaced further apart than those in V1, by a factor of about 1.6, but the columns are not correspondingly wider. (9) Spatially diffuse variations in color produce high uptake confined, at least largely, to the thin cytox stripes. (10) There is evidence for spatially antagonistic color surrounds in color cells in the thin stripes. (11) In general, achromatic gratings of low luminance contrast (.apprx. 8%) produce faint-to-medium DG uptake confined in thick V2 stripes, and little or no stimulus-driven DG uptake outside the thick V2 stripes. Since such stimuli stimulate magnocellular but not parvocellular LGN cells, this suggests that V2 receives input mainly from parvocellular rather than magnocellular channels, except for the magnocellular-derived input to the thick V2 stripes. (12) Variations in the spatial frequency of achromatic, sinusoidal gratings produce corresponding variations in the DG patterns from V2 (see also Tootell et al., 1983). Binocular stimulation with a grating of low (.apprx. 1.5 c/deg) spatial frequency at all orientations produces high DG uptake on every dark cytox stripe. Comparable stimulation with a high (.apprx. 6.5 c/deg) spatial frequency produces isolated columns of high uptake, often aligned along the light cytox interstripes.