Physiological and anatomical evidence for a discontinuous representation of the trunk in S-I of tree shrews.

Microelectrode mapping methods revealed that the representation of the body surface in the first somatosensory area of cortex, S-I, of the tree shrew is unique in that only the ventral trunk was found in the usual location of the trunk representation in cortex of the dorsolateral surface of the cerebral hemisphere. Instead, the dorsal trunk was found as an extension of the representation of the posterior leg in cortex on the medial wall. The separation of the representation of the trunk occurs along a line that is counter to the orientation of the dorsal root dermatomes, so that S-I of the tree shrew clearly cannot be characterized as a serial representation of dermatomes. Anatomical studies of connections support the conclusion that the representation of the trunk is split in S-I. Both the representation of the dorsal trunk on the medial wall of the cerebral hemisphere and S-I of the dorsolateral surface were found to project to S-II when horseradish peroxidase was injected into S-II.