The medial parietal occipital areas in the macaque monkey

Abstract

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.

Topographic organization of the “third tier” dorsomedial visual cortex in the macaque

“…This region has been traditionally assigned to PO/V6, usually being combined with a lower quadrant representation in the parietooccipital sulcus to form a complete representation of peripheral vision (Fig. 1; Colby et al, 1988; Neuenschwander et al, 1994; Gamberini et al, 2015). However, as illustrated in Figures 4 and 7, this lower quadrant representation can be seen as a straightforward continuation of V3d.…”

“…Thus, in order to avoid multiplication of names, we favor retaining the designation V6, with the provision that this area is not separated from V2 by a strip of V3d, as proposed previously (e.g. Gamberini et al, 2015).…”

“…The rectangle shows the region magnified on the right. Right : diagrammatic representation of the model we test in this paper (Ungerleider and Desimone 1986; Colby et al 1988; Gattass et al 1988; Gamberini et al 2015), according to which the cortex rostral to dorsomedial area V2 contains 2 areas, V3d (blue) and PO (or V6, pink), each with a distinct representation of the lower visual field. The question mark indicates the possibility that another area, PIP, may separate V3d from PO/V6.…”

Spatiotopic coding during dynamic head tilt

“…In fact, the first evidence for spatiotopic coding came from single-cell recoding in the monkey, showing that neurons in V6 have spatial tuning invariant with gaze position (Galletti et al 1993), later also reported in the ventral intraparietal cortex (VIP) by Duhamel et al (1997). Subsequently, the same group showed that V6 is organized in a retinotopic fashion, with individual cells showing a sensitivity to the real motion of objects in allocentric coordinates (Gamberini et al 2015). Even in the primary visual cortex, V1, the selectivity has been shown to modulate to some extent with gaze (Celebrini et al 2009;Durand et al 2010).…”

Topographic Organization of the 'Third-Tier' Dorsomedial Visual Cortex in the Macaque

“…1). Although proposals regarding the boundaries of PO/V6 continue to evolve (Gamberini et al, 2015), it is generally agreed that receptive fields of neurons in this region emphasize peripheral vision. Moreover, models proposed by various groups converge on the idea that PO/V6 encompasses a representation of the lower quadrant in the parietooccipital sulcus, as well as a representation of the upper visual field on the mesial surface of the hemisphere.…”