Distribution of the central terminals of cutaneous primary afferents innervating a small skin patch: the existence of somatotopically inappropriate projections.

High frequency microstimulation was used to stimulate primary afferents innervating a small area of skin. The action potentials invading the central branches of group II afferents were observed in unaveraged and averaged recordings within somatotopically characterized regions of the dorsal horn. Results show that some afferents project to areas of the dorsal horn in which dorsal horn neurons have receptive fields distant from that of those afferents. Such afferents must therefore be considered as having somatotopically inappropriate projections to the dorsal horn. These projections are rostrally and/or caudally displaced from the somatotopically appropriate region.