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

Area of Science:

• Neuroscience
• Visual Cortex Research
• Primate Brain Studies

Background:

• The secondary visual cortex (V2) is crucial for visual processing in primates.
• Understanding V2's functional organization is key to deciphering visual pathways.
• Cytochrome oxidase (cytox) staining reveals structural stripes in V2, but their functional significance requires investigation.

Purpose of the Study:

• To map the functional architecture of the macaque secondary visual cortex (V2).
• To correlate 2-deoxy-d-glucose (DG) uptake patterns with cytox stripes under specific visual stimuli.
• To investigate the presence of orientation columns and color processing in V2.

Main Methods:

• Injected 14C-2-deoxy-d-glucose (DG) into macaque monkeys during presentation of visual stimuli.
• Compared DG uptake patterns with cytochrome oxidase (cytox) stripe locations.
• Utilized multiple animals and compared DG effects of different stimuli within the same hemisphere.

Main Results:

• DG uptake revealed consistent, robust functional architecture in V2, independent of cytox stripe clarity.
• DG patterns were predominantly columnar, extending from white matter to the cortical surface, with highest contrast in layers 3B/4.
• Evidence confirmed orientation columns in V2, spaced approximately 1.6 times further apart than in V1, and identified color processing within thin cytox stripes.

Conclusions:

• The functional architecture of V2 is consistently present and columnar, with orientation columns and specific color processing.
• V2 exhibits distinct functional organization compared to V1, particularly regarding laminar differences and orientation column spacing.
• DG mapping provides a robust method for studying functional organization in V2, complementing cytox staining.