The visual parietal areas in the macaque monkey: current structural knowledge and ignorance

Classic and current parcellations of the posterior parietal cortex are reviewed. Whereas earlier studies relied on subjective observation of cortical cytoarchitecture, present parcellations are mostly based on connectional and physiological criteria. These criteria have led to the identification of five areas in the intraparietal sulcus with alleged visual function: VIP, MIP, PIP, AIP, and LIP. Other visual parietal areas are 7a, in the lateral parietal surface, and, in the medial parietal wall, 7m, and V6A. Present knowledge of the dimensions, boundaries, and connections of the various visual parietal areas is uneven: whereas LIP, 7a, and 7m have been extensively explored in anatomical and physiological studies, only scant information is available for most of the intraparietal areas. It is suggested that future studies address the anatomical and functional parcellation of the posterior parietal cortex using manifold objective means of study that allow comparison by independent researchers.