Cortical cells projecting to the dorsal column nuclei of rhesus monkeys.

Corticals cells projecting to the dorsal column nuclei (DCN) of Rhesus monkeys have been identified after unilateral or bilateral injection of horseradish peroxidase (HRP) into the dorsal medulla. HRP-positive neurons identifiable as the source of cortico-DCN projections were pyramidal cells in layer V whose largest diameters ranged from 12--31 micron. Cortico-DCN neurons were concentrated in the trunk, fore- and hindlimb regions of area 4 and of SI, and to a lesser extent in SII. This distribution is comparable to the topographical distribution of cortico-DCN neurons in cats. However, cortico-DCN neurons in monkeys are also numerous in at least part of the supplementary motor cortex and in area 5. The results suggest that cortical neurons in several different cytoarchitectonic areas may exert direct control upon cells in the DCN and that the functional role of cortic-DCN projections ought not be view as a simple "feedback" system.