Connectional Evidence for Dorsal and Ventral V3, and Other Extrastriate Areas in the Prosimian Primate, <i>Galago garnetti</i>

Abstract

Previously we described patterns of connections that support the concept of V3 in small New World marmoset monkeys, three species of larger New World monkeys, and two species of Old World macaque monkeys. Here we describe a pattern of V1 connections with extrastriate visual cortex in Galago garnetti (also known as Otolemur garnetti) that demonstrates the existence of a V3 in a strepsirhine (prosimian) primate. Injections of fluorochromes or cholera toxin subunit-B (CTB) in V1 labeled cells and terminals in retinotopically matched regions in V2, V3, DL (V4), and MT. Labeled axon terminations were more focused primarily in middle layers of cortex, likely representing ‘feedforward’ input from V1, whereas labeled cells were more widespread and found in both superficial and deeper cortical layers, indicative of feedback projections. Averaged across injections, V3 had the third largest percentage of labeled cells (11%), following only V2 (47%) and the middle temporal area (MT; 19%). The dorsolateral area (DL, or V4; 9%) also contained a relatively large number of retrogradely labeled cells. These results indicate that V2, V3, DL (V4), and MT are retinotopically connected with V1, and provide major sources of feedback. Other extrastriate areas were less densely connected to V1, and there was no clear indication of labeled terminals. Inferotemporal cortex (IT) provided nearly 7% of feedback connections, whereas the dorsomedial area (DM) contributed about 3%. The remaining areas that have been proposed for galago extrastriate cortex, MTc, MST, FST, LPP and VPP, each accounted for about 1% or less of the total number of labeled cells. Thus, six extrastriate areas, V2, MT, V3, DL (V4), IT, and DM provide over 96% of visual cortex projections to V1. These areas also provide most of the projections to V1 in New and Old World monkeys.

The case for a dorsal V3 in the ‘third-tier’ of primate visual cortex: a reply to ‘the case for a dorsomedial area in the primate ‘third-tier’ visual cortex’

“…The view presented in the Rosa et al's commentary is based on retinotopic maps from Rosa's group and connection patterns from Angelucci's group, with all of the work being conducted in marmoset monkeys. As we presented in the original review not only does a large body of anatomical and mapping data in several species other than marmoset support the Lyon & Connolly interpretation of a V3d [2][3][4][5][6][7][8][9][10][11][12][13][14][15], the original work that led Jon Kaas and me to the re-interpretation of a V3d in place of DM was with marmosets as well [16].…”

“…In summary, it seems likely that differences in the localization of the outer border of dorsal V2 is the primary reason for the very different conclusions regarding V3d and DM following the analysis of connection patterns [6][7][8]16,24]. Even while more anatomical studies would certainly help in evaluating whether or not there is a DM or a V3d immediately adjacent to the outer border of dorsal V2, the preponderance of evidence from imaging of retinotopic maps in monkeys and humans [1] is overwhelmingly in favour of V3d.…”

Pulvinar contributions to the dorsal and ventral streams of visual processing in primates

“…In early studies from our laboratory, we did not recognize V3 and included the territory of V3 in other visual areas (see Kaas and Lyon, 2001). However, now we feel that the issue is largely resolved (Lyon, 2007), as a series of anatomical studies provided strong evidence for V3 (including ventral and dorsal halves) in prosimian galagos (Lyon and Kaas, 2002a) four species of New World monkeys 2002b;Lyon, et al, 2002) and Old World macaque monkeys (Lyon and Kaas, 2002c). V1 and V2 both have connections that associate them with both the dorsal and ventral visual streams, but more of their outputs are directed into the ventral stream (Kaas, 2004a).…”

Functional and cortical adaptations to central vision loss

“…Although the primary visual cortex (V1) receives feedback connections from higher visual areas (Girard et al, 2001;Lyon & Kaas, 2002), its spatial organization is closely tie to the afferent inputs from the retino-geniculate pathway. Brain-lesion and brain-imaging studies have demonstrated a retinotopic organization in V1 (e.g.…”