Organization of the somatosensory cortex in elephant shrews (E. edwardii)

Abstract

The superorder Afrotheria consists of a diverse group of mammals, including elephants, hyraxes, dugongs, sea cows, aardvarks, tenrecs, golden moles, and elephant shrews. Recent studies suggest this clade diverged from other placental mammals 100 million years ago and thus may represent the sister group to the remaining placental mammals. Despite this important taxonomic position, relatively few studies have investigated cortical organization in these species. Here we present results of an investigation of the somatosensory cortex in the Cape elephant shrew (Elephantulus edwardii). Using multiunit electrophysiological recording techniques, we identified a topographic map of the elephant shrew's body in a location and orientation consistent with the primary somatosensory cortex (S1). The elephant shrew's elongated snout, extensive facial vibrissae, and long tongue accounted for a large portion of the somatosensory representation, located in a relatively rostral area of cortex. Evidence for an additional somatosensory area, presumed to be secondary somatosensory cortex (S2), was found just lateral to S1. Visual and auditory responsive areas were also identified and the extent of visual cortex appeared to be quite large in these highly visual mammals. Despite the elephant shrew's exceptionally well-developed eyes, ears, and vibrissae, there were no anatomical correlates to sensory areas, or body part representations (e.g., barrels), that could be identified in the flatted cortex.