Connections of inferior temporal areas TE and TEO with medial temporal- lobe structures in infant and adult monkeys

Abstract

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 connections between inferior temporal cortex and medial temporal-lobe structures in infant and adult monkeys. Inferior temporal cortical areas TEO and TE were injected with WGA conjugated to HRP and tritiated amino acids, respectively, or vice versa, in 1-week-old and 3-4-yr-old Macaca mulatta, and the distributions of labeled cells and terminals were examined in both limbic structures and temporal-lobe cortical areas. In adult monkeys, inferior temporal-limbic connections included projections from area TEO to the dorsal portion of the lateral nucleus of the amygdala and from area TE to the lateral and lateral basal nuclei; inputs to both areas TEO and TE included those from the lateral, lateral basal, and medial basal nuclei of the amygdala and to area TE from the accessory basal nucleus. Additional limbic inputs to both areas TEO and TE arose from the posterior portion of the presubiculum. In infant monkeys, we found, in addition to these adultlike connections, a projection from area TEO to the lateral basal nucleus of the amygdala. Inferior temporal cortical connections in adult monkeys included projections from area TEO to area TE and, in turn, from area TE to area TG and perirhinal area 36, as well as from area TE back to area TEO; inputs to both areas TEO and TE included those from area TG, perirhinal areas 35 and 36, and parahippocampal areas TF and TH. All of these adultlike connections were also observed in infant monkeys, but, in addition, the infants showed projections from area TE to perirhinal area 35 as well as to parahippocampal areas TF and TH, and from area TEO to area TF. Moreover, in infants, the projection from area TE to perirhinal area 36 was considerably more widespread than in adults, both in areal extent and in laminar distribution. The results therefore indicate the existence of projections in infant monkeys from inferior temporal areas to the amygdala, perirhinal cortex, and parahippocampal cortex that are either totally eliminated in adults or more refined in their distribution. Both elimination and refinement of projections thus appear to characterize the maturation of axonal pathways between the inferior temporal cortex and medial temporal-lobe structures in monkeys.

Topographic organization of the reciprocal connections between the monkey entorhinal cortex and the perirhinal and parahippocampal cortices

“…The perirhinal cortex receives inputs from unimodal visual areas in the temporal lobe (Suzuki and Amaral, 1990;Webster et al, 1991;Martin-Elkins and Horel, 1992) as well as presumed polysensory information from areas including the parahippocampal cortex and cingulate cortex (Suzuki and Amaral, 1990). These anatomical findings have been confirmed by electrophysiological studies in the monkey which found that cells in the perirhinal cortex respond to polysensory stimuli (Desimone and Gross, 1979).…”

Schizophrenia, neurodevelopment and corpus callosum

“…22,23 Animal studies have shown that cortical connections develop through phases of exuberant growth, followed by partial regression. Initially both long-and local axonal branches are formed in excess and, subsequently, massive elimination of axonal branches takes place [24][25][26][27][28][29][30][31][32][33] (see also Innocenti 34 for a review). This regressive phase is concomitant with synaptogenesis, which eventually leads to the overproduction of synapses that are subsequently deleted.…”

“…Finally, it is tempting to assume that connections in the association areas, in particular the prefrontal, temporal and cingulate areas, might follow similar developmental rules as in the primary visual areas; however only a handful of studies exist to indicate that this might indeed be the case. 32,40,72 Lessons from the past and future directions…”

Formation of mnemonic neuronal responses to visual paired associates in inferotemporal cortex is impaired by perirhinal and entorhinal lesions.

“…After training with 12 pairs of pictures, single units were recorded from the inferotemporal cortex of the monkeys as the control. By injecting a grid of ibotenic acid, we unilaterally lesioned the entorhinal and perirhinal cortex, which provides massive direct and indirect backward projections ipsilaterally to the inferotemporal cortex.…”

“…There is strong evidence that IT cortex receives direct and indirect backward projections from the perirhinal and entorhinal cortex (10)(11)(12)(13). The hypothesis for the role of the backward connections predicts that the lesion of the perirhinal and entorhinal cortex would impair the formation of the associative code for pictures in the IT cells.…”