The relationship between V6 and PO in macaque extrastriate cortex.

The cerebral cortex of three macaque monkeys, electrophysiologically studied in chronic preparations in order to recognize functionally the medial parieto-occipital area V6, was reconstructed using the software CARET. Locations of cells recorded from area V6 (n = 553) and from neighbouring cortical areas V2/V3 and V6A (n = 1341) were displayed on surface-based reconstructions of individual brains, and on a surface-based atlas of the macaque cerebral cortex. Results show that area V6 occupies the ventral part and fundus of the parieto-occipital sulcus, as well as the ventral part of the precuneate cortex. V6 borders areas V2/V3 posteriorly and laterally, and area V6A anteriorly. The visualization of individual cases on a common template (atlas), and the use of atlas datasets, allowed us to compare data coming from different individuals and different laboratories. In particular, a comparison of the location and extent of the medial parieto-occipital areas V6 and PO indicates that area PO occupies different locations according to different authors but in general includes parts of both areas V6 and V6A. We therefore suggest that the term V6 is a more appropriate designation of the visuotopically-organized area located on the anterior wall of the parieto-occipital sulcus.