The somatotopic pattern of afferent projections from the digits to the spinal cord and cuneate nucleus in macaque monkeys.

The somatotopic patterns of terminations in the spinal cord and cuneate nucleus of afferents from the digits of macaque monkeys were determined by the transganglionic transport of a mixture of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) and free horseradish peroxidase (HRP). Injections placed in either a single digit or in various combinations of digits indicate that terminations from the digits are located medially in the superficial laminae of cervical segments 5-7 in the dorsal horn. Each digit has a distinct zone of terminations, and inputs from D1-D5 terminate in order in a rostrocaudal sequence. In the cuneate nucleus, afferents from single digits are ventrally situated and organized into rostrocaudally elongated columns of label. In the pars rotunda of the cuneate nucleus, the representations of the digits appear to be offset from one another with D1 represented most laterally, and the other digits represented in order progressively more medially. In portions of the cuneate nucleus rostral and caudal to the pars rotunda, the projections from the digits are more diffuse and overlap one another.