Cortical connections of the middle temporal and the middle temporal crescent visual areas in prosimian galagos (Otolemur garnetti)

Abstract

While considerable progress has been made in understanding the organization of visual cortex in monkeys, less is known about the visual systems of prosimians. The middle temporal visual area (MT), an area involved in motion perception, is common to all primates. We placed injections of tracers in MT and just caudal to MT in cortex expected to be the MT crescent (MTc), an area previously identified in monkeys but not in prosimians. We analyzed the patterns of projections in sections of the flattened cortex and used sections stained for cytochrome oxidase (CO) and myelin to identify the borders of MT, MTc, middle superior temporal (MST), superior temporal sulcus (FST), and V1 and V2 and to identify possible subdivisions of these areas. As in owl monkeys, MTc is a belt around most of MT that consists of a single row of CO-dense patches in a CO-light surround. Injections placed in MT revealed connections with V1, V2, V3, FST, MST, MTc, dorsomedial, dorsolateral (DL), posterior parietal cortex, and inferotemporal (IT) cortex. Injections localized to MTc displayed a slightly different pattern of connections with more involvement of DL and IT cortex, though other aspects, including patchy connections with V1 and V2, were similar to MT connections. The results indicate that prosimian galagos have an MT area with connection patterns that are similar to those in New and Old World monkeys. The MTc, initially described in owl monkeys, is present in galagos and is likely to be a common component of primate visual cortex. Anat Rec, 290:349-366, 2007. 2007 Wiley-Liss, Inc.

Organization of the posterior parietal cortex in galagos: II. Ipsilateral cortical connections of physiologically identified zones within anterior sensorimotor region

“…Among other areas, primary auditory (A1) and middle temporal visual (MT) areas were easily recognized by their dense myelination and CO-dark appearance (Krubitzer and Kaas, 1990). Visual areas V1 and V2 were also easily recognized by their characteristic CO and myelin patterns, demonstrating blobs in V1 and in most favorable sections stripes in V2 (Lyon and Kaas, 2002; Kaskan and Kaas, 2007). In favorable sections, area DM has been distinguished from PPC as more densely myelinated.…”

“…The visual inputs to PPC come from visual areas well defined in galagos, including areas MT (Kaskan and Kaas, 2007), MST, V3, DM (Beck and Kaas, 1998), V2 (Collins et al, 2001), and other less well-understood and more associative areas. Based on our previous (Fang et al, 2005) and unpublished observations, the caudal half of PPC that is unresponsive to ICMS receives most of the inputs from visual cortex and relays it to the anterior excitable PPC.…”

Differential Expression Patterns of occ1-Related Genes in Adult Monkey Visual Cortex

“…As ISH for occ1 -related genes showed characteristic expression patterns in the visual circuit, we also examined their ISH in a distinct area of the primate visual system, the middle temporal visual area (MT), which is a highly myelinated compartment and the center of motion processing in the visual dorsal pathway (Kaskan and Kaas 2007). However, the expression patterns of occ1 -related genes in MT were similar to those in extrastriate visual cortex and did not show clear demarcation with surrounding areas (Fig.…”

Organization of the posterior parietal cortex in galagos: I. Functional zones identified by microstimulation

“…Moreover, patterns of label after injections of tracers in the middle temporal visual area (MT) and narrow middle temporal crescent area (MTc) bordering MT suggest that both areas also have connections with posterior PPC (Wall et al, 1982; Krubitzer and Kaas, 1990; Kaskan and Kaas, 2007). Thus, there are probably four or more visual areas that distribute visual information to the posterior half of PPC in galagos.…”