Controversial issues in visual cortex mapping: Extrastriate cortex between areas V2 and MT in human and nonhuman primates

The visual cerebral cortex of primates includes a mosaic of anatomically and functionally distinct areas processing visual information. While there is universal agreement about the location, boundaries, and topographic organization of the areas at the earliest stages of visual processing in many primate species, i.e., the primary (V1), secondary (V2), and middle temporal (MT) visual areas, there is still ongoing debate regarding the exact parcellation of cortex located between areas V2 and MT. Several parcellation schemes have been proposed for extrastriate cortex even within the same species. With the exception of V1, V2, and MT, these schemes differ in areal borders, areal location, neighboring relations, number of areas, and nomenclature. As a result, most anatomical and physiological studies of these areas have been carried out following one or another scheme, in the absence of any general agreement. This situation is inevitably hampering our understanding of the function and evolution of these visual areas. The goal of this special issue is to provide a critical review and evaluation of the literature on the most controversial issues regarding the parcellation of extrastriate cortex, to identify the main reasons for the controversy, and to suggest critical future experimental approaches that could lead to a consensus about the anatomical and functional identity of these areas.