Areal and callosal connections in the somatosensory cortex of the star-nosed mole

Star-nosed moles have a well-developed somatosensory cortex with multiple c ortical areas representing the behaviorally important tactile star. In each of three cortical representations, the 11 mechanosensory appendages from t he contralateral nose are represented in a series of dark cytochrome oxidas e modules. Here the connections of this complex cortical network were explo red with injections of the neuroanatomical tracer wheat germ agglutinin con jugated to horseradish peroxidase (WGA-HRP). The main goal was to determine the connection patterns of the somatosensory areas that represent the star . Injections of tracer made in or around the primary somatosensory represen tation (S1) of the star allowed us to determine the topography of local cor tical connections and the projection and termination sites of corresponding interhemispheric connections. The results revealed precise topographic cor ticocortical connections reciprocally interconnecting the S1 star represent ation with its counterparts in S2 and in a third representation (S3) unique to star-nosed moles. Callosal connections from a widespread area of the co ntralateral hemisphere terminated primarily in the septa between cytochrome oxidase dark modules and in areas of cortex surrounding the star represent ations. However, midline structures of the star represented in S1 and S2 ex hibited a high level of callosally labeled cells and terminals. This includ ed label both within septa and within the centers of cytochrome oxidase den se modules representing midline appendages.