Topographic patterns of v2 cortical connections in a prosimian primate (Galago garnetti)

Abstract

Topographic patterns of cortical connections of the second visual area (V2) were examined in a lorisiform prosimian primate (Galago garnetti). Up to five different tracers were injected into dorsal and ventral V2. Tracers included wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) and up to four fluorochromes. Tracer injections consistently labeled neurons and terminals in primary visual cortex (V1), V2, the middle temporal area (MT), and the dorsolateral visual area (DL). Labeled neurons were also found in other proposed extrastriate areas such as the dorsomedial visual area (DM), dorsointermediate area (DI), middle temporal crescent (MTc), medial superior temporal area (MST), ventral posterior parietal area (VPP), and caudal inferotemporal cortex (ITc), but these connections were more variable and less dependent on the retinotopic position of injection sites in V2. Areal boundaries were identified by differences in cytochrome oxidase (CO) and myelin staining. We conclude that V2 cortical connections in prosimian galagos are similar to those in simian primates, suggesting that prosimians and other lines of primate evolution have retained several visual areas from a common ancestor that relate to V2 in similar ways. Architectural features of striate and extrastriate areas in prosimian galagos are similar to simian primates, with notable exceptions such as stripes in V2, which appear to be less differentiated in galagos.