Mgp. Rosa et Lm. Schmid, VISUAL AREAS IN THE DORSAL AND MEDIAL EXTRASTRIATE CORTICES OF THE MARMOSET, Journal of comparative neurology, 359(2), 1995, pp. 272-299
To define the number and limits of the visual areas in the primate ext
rastriate cortex, the visuotopy of the dorsal convexity and medial wal
l was studied by electrophysiological recordings in five marmosets ana
esthetised with sufentanil and nitrous oxide and paralysed with pancur
onium bromide. We identified five visuotopic representations in and ar
ound the densely myelinated zone between visual area 2 (V2) and the po
sterior parietal cortex. Most of the densely myelinated zone is formed
by the homologue of the owl monkey's dorsomedial area (DM); thus, we
also termed this area DM in the marmoset. Within DM, the lower quadran
t representation is continuous, with central vision represented latera
lly, peripheral vision medially, the horizontal meridian caudally, and
the vertical meridian rostrally. In contrast, the upper quadrant repr
esentation is split, with the central portion represented at the later
al edge of DM on the dorsal surface, and the periphery along the midli
ne. Two other visual field representations, corresponding to the dorso
intermediate area (DI) and to a new subdivision termed the dorsoanteri
or area (DA), are also densely myelinated but can be distinguished fro
m DM based on the separation of the bands of Baillarger and visual top
ography. In addition, a homologue of the medial visual area (M) was id
entified. Our results reveal a highly complex visuotopy in primate cor
tex, with local discontinuities in representation and borders between
areas that are often not coincident with either the horizontal or the
vertical meridian. The topography of the dorsal extrastriate cortex in
the marmoset strongly suggests that both visual area 3 (V3) and the p
arietoococipital area (PO) of other primates are portions of a single
visuotopic representation, DM, and calls into question the existence o
f visual areas with partial or quadrantic representations of the visua
l field. (C) 1995 Wiley-Liss, Inc.