The Retinotopy of a Prosimian (Bush Baby) Pulvinar

Abstract

The pulvinar nucleus in primates has connections with all known visual cortices, yet little is known about its functions. To clarify the functional organization of pulvinar, a few studies have investigated its visuotopic maps in simians using electrophysiological methods. These studies consistently showed two maps, but the organization of these maps were reported to differ between the New and Old World simians. In this study we investigated the visuotopy of the prosimian bush baby (Otolemur garnettii) pulvinar, as prosimians are considered closer to the common ancestors of New and Old World primates. We used single electrode extracellular recording to determine the retinotopy of the lateral (PL) and inferior (PI) subdivisions of the pulvinar and compared the visuotopic maps to bush baby pulvinar chemoarchitecture. Three subdivisions, the lateral central (PIcl), medial central (PIcm) and medial (PIm) inferior pulvinar, were identified in bush baby PI, using myelin, acetylcholinesterase and cytochrome oxidase staining. We found two visuotopic maps which covered PL and PIcl, a dorsal map in dorsal PL and a ventral map in PIcl and ventral PL. Both maps had a lateral upper field representation and a medial lower field representation. Their central vision representations were found on the postero-medial side of the border between the two maps. The global features of the visuotopic maps, including location, orientation of the central-peripheral and upper-lower field axes, appeared similar between bush baby and the Old World macaque monkey but different from the New World cebus monkey. Using reconstructed 3D models of these maps, however, we found details that differed between bush baby and those reported in macaque monkey. These differences included: 1) the first order representation of the dorsal map, 2) the central vision representation as a point and 3) the vertical meridian representation on a curve in bush baby but not in macaque. Meeting abstract presented at VSS 2013