Postnatal maturation of subcortical projections from the prefrontal cortex in the rhesus monkey.

Orbital and dorsolateral prefrontal lesions were performed on a series of rhesus monkeys at 2, 6, or 24 months of age. The consequent degeneration in the efferent pathways from these cortical regions to the caudate nucleus, the dorsomedial nucleus of the thalamus and adjacent structures was studied at 5- and 15-day survival times by a modification of the Nauta-Gygax method for tracing degenerating fibers. Following dorsolateral lesions, considerable numbers of black-impregnated degenerating fibers were found in the parvocellular division of the dorsomedial nucleus and in the fiber bundles of the internal capsule and the subcallosal fasciculus at all ages.