The medial parietal occipital areas in the macaque monkey

The number, location, extent, and functional properties of the cortical areas that occupy the medial parieto-occipital cortex (mPOC) have been, and still is, a matter of scientific debate. The mPOC is a convoluted region of the brain that presents a high level of individual variability, and the fact that many areas of mPOC are located within very deep sulci further limits the possibility to investigate their anatomo-functional properties. In the present review, we summarize the location and extent of mPOC areas in the macaque brain as obtained by architectural, connectional, and functional data. The different approaches lead to a subdivision of mPOC that includes areas V2, V3, V6, V6Av, and V6Ad. Extrastriate areas V2 and V3 occupy the posterior wall of the parieto-occipital sulcus (POs). The fundus of POs and the ventralmost part of the anterior wall of the sulcus are occupied by a retinotopically organized visual area, called V6, which represents the contralateral part of the visual field and emphasizes its periphery. The remaining part of the anterior wall of POs is occupied by two areas, V6Av and V6Ad, which contain visual as well as arm reaching neurons. Our analyses suggest that areas V6 and V6Av, together, occupy the cortical territory previously described as area PO. Functionally, area V6 is a motion area particularly sensitive to the real motion of objects in the animal's field of view, while V6Av and V6Ad are visuomotor areas likely involved in the visual guidance of arm movement and object prehension.