Somatotopic organization of raccoon dorsal column nuclei

Abstract

Abstract Somatotopic organization was demonstrated by means of microelectrode mapping studies of three somatic sensory nuclear regions in the raccoon medulla. Projections of peripheral receptive fields in the cuneate‐gracile nuclear complex occur iteratively in rostro‐caudal columns. These projections are organized into a detailed 3‐dimensional pattern, in contrast to the more diffuse intermingling of such projections in the spinal dorsal roots and columns. This indicates that afferent fibers are re‐sorted before synaptic termination. In the extensive representation of the volar hand, there are distinct subnuclei, delineated by intervening fiber laminae, each containing the projections from one of the forepaw digits. Units in the external‐cuneate nucleus responded only to stimulation of deeperlying tissues in anterior body regions. These projections were also somatotopically organized. Retrograde degeneration studies indicated that some cells, in that region where cuneate‐gracile adjoins external‐cuneate, may project through both the ipsilateral cerebellar peduncles and the contralateral midbrain. The spinal trigeminal nucleus adjoining the cuneate‐gracile complex displayed many characteristics similar to those of the latter. Neighboring, although anatomically distinct, regions contained projections from neighboring peripheral receptive fields.