Organization of somatosensory cortex and distribution of corticospinal neurons in the eastern mole (Scalopus aquaticus).

The somatotopic organization of somatosensory cortex of the eastern mole (Scalopus aquaticus) was explored with multiunit microelectrode recordings from middle layers of cortex. The recordings revealed the presence of at least parts of two systematic representations of the body surface in the lateral cortex. One of the representations appears to be primary somatosensory cortex (S1), and it contained cytochrome oxidase dark regions, separated by light septa that formed isomorphs with some body parts. The rostral portion of this presumptive S1 cortex contained a face representation with a series of barrel-like cytochrome oxidase dark ovals that corresponded to the vibrissae on the snout. In caudolateral S1, light septa outline the palm and digits of the forepaw. Cortex caudal to S1, in the expected region of auditory cortex, responded to vibration, suggesting a modification of auditory cortex. Injections of wheat germ agglutinin-horseradish peroxidase into the cervical enlargement of the spinal cord revealed two dense foci of cortical cells that project to the spinal cord. The focus medial to the face region in S1 may correspond to primary motor cortex (M1). The second focus was coextensive with the somatosensory representation of the forelimb and the trunk in S1. The dense corticospinal projections from the forelimb representation of S1 and motor cortex may reflect sensorimotor specializations related to digging behaviors in moles.