Transient subcortical connections of inferior temporal areas TE and TEO in infant macaque monkeys.

As part of a long-term study designed to examine the ontogeny of visual memory in monkeys and its underlying neural circuitry, we have examined the subcortical connections of the inferior temporal cortex in infant monkeys and compared them to those previously described in adult monkeys (Webster et al. [1993] J. Comp. Neurol. 335:73-91). Inferior temporal areas TEO and TE were injected with wheat germ agglutinin conjugated to horseradish peroxidase and tritiated amino acids, respectively, or vice versa, in 1-week-old (N = 6) and 3-4-year-old (N = 6) Macaca mulatta, and the distributions of labeled cells and terminals were examined in subcortical structures. Although the connections of inferior temporal cortex with subcortical structures were found to be similar in infant and adult monkeys, several projections appear to undergo refinement during development. Quantitative analysis showed that 1) whereas the projection from TE to the superior colliculus is consistent (5 of 5 cases) and widespread in infants, it is less reliable (2 of 7 cases) and limited in areal extent in adults; 2) although the projections from TE to nucleus medialis dorsalis and the tail of the caudate are present in infants and adults, they are reduced in adults; and 3) TEO receives input from the dorsal lateral geniculate nucleus in both infants and adults, but the number of cells giving rise to this projection is lower in adults. There was also a suggestion that TE projects to nucleus paracentralis in infants (2 of 5 cases) but not in adults (0 of 7 cases). No differences between infants and adults were apparent in other subcortical connections, including those with the pulvinar, reticular nucleus, claustrum, and putamen.