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

Star-nosed moles have a well-developed somatosensory cortex with multiple cortical areas representing the behaviorally important tactile star. In each of three cortical representations, the 11 mechanosensory appendages from the contralateral nose are represented in a series of dark cytochrome oxidase modules. Here the connections of this complex cortical network were explored with injections of the neuroanatomical tracer wheat germ agglutinin conjugated 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 representation (S1) of the star allowed us to determine the topography of local cortical connections and the projection and termination sites of corresponding interhemispheric connections. The results revealed precise topographic corticocortical connections reciprocally interconnecting the S1 star representation with its counterparts in S2 and in a third representation (S3) unique to star-nosed moles. Callosal connections from a widespread area of the contralateral hemisphere terminated primarily in the septa between cytochrome oxidase dark modules and in areas of cortex surrounding the star representations. However, midline structures of the star represented in S1 and S2 exhibited a high level of callosally labeled cells and terminals. This included label both within septa and within the centers of cytochrome oxidase dense modules representing midline appendages.