ORGANIZATION OF CONNECTIONS BETWEEN THE AMYGDALOID COMPLEX AND THE PERIRHINAL AND PARAHIPPOCAMPAL CORTICES IN MACAQUE MONKEYS

Neuroanatomical studies in macaque monkeys have demonstrated that the perirhinal and parahippocampal (PRPH) cortices are strongly interconne cted with the hippocampal formation. Recent behavioral evidence indica tes that these cortical regions are importantly involved in normal rec ognition memory function. The PRPH cortices are also interconnected wi th the amygdaloid complex, although comparatively little is known abou t the precise topography of these connections. We investigated the top ographic organization of reciprocal connections between the amygdala a nd the PRPH cortices by placing anterograde and retrograde tracers thr oughout these three regions. We found that there was an organized arra ngement of connections between the amygdala and the PRPH cortices and that the deep (lateral, basal, and accessory basal) nuclei of the amyg daloid complex were the source of most connections between the amygdal a and the PRPH cortices. The temporal polar regions of the perirhinal cortex had the strongest and most widespread interconnections with the amygdala. Connections from more caudal levels of the perirhinal corte x had a more discrete pattern of termination. Perirhinal inputs to the amygdala terminated primarily in the lateral nucleus, the magnocellul ar and parvicellular divisions of the basal nucleus, and the magnocell ular division of the accessory basal nucleus. Return projections origi nated predominately in the lateral nucleus, the intermediate and parvi cellular divisions of the basal nucleus, and the magnocellular divisio n of the accessory basal nucleus. The interconnections between the amy gdala and the parahippocampal cortex were substantially less robust th an those with the perirhinal cortex and mainly involved the basal nucl eus. Area TF was more strongly interconnected with the amygdala than w as area TH. Input from the parahippocampal cortex terminated predomina ntly in the lateral half of the parvicellular division of the basal nu cleus but also to a lesser extent in the magnocellular division of the basal nucleus and the lateral nucleus. Return projections originated predominantly in the magnocellular division of the basal nucleus and w ere directed almost exclusively to area TF. (C) 1996 Wiley-Liss, Inc.