Amygdaloid connections with posterior insular and temporal cortical areas in the rat.

The connections of the amygdala with the insular and temporal cortices were examined by injecting wheat germ agglutinin conjugated to HRP (WGA-HRP) into the rat cortex. Following injections into the posterior agranular insular area (AIp) or perirhinal cortex (PR), bands of labeled neurons extending across nuclear boundaries were observed in the amygdala. These neuronal bands involved cells in the lateral, basolateral, and basomedial nuclei as well as the periamygdaloid cortex. Other nuclei of the corticomedial amygdala and the ventral endopiriform nucleus also exhibited retrogradely labeled cells. Anterograde label was observed in nuclei containing labeled neurons and in the central nucleus. Injections into gustatory, somatosensory, and auditory neocortical areas located dorsal to AIp and PR labeled small numbers of cells in the lateral and basolateral nuclei. Injections into AIp, PR, and, to a lesser extent, dorsally adjacent neocortical areas produced both retrograde and anterograde labeling in the contralateral amygdala. The main nuclei with contralateral insular and temporal projections are the basomedial nucleus, ventral endopiriform nucleus, and nucleus of the lateral olfactory tract. The contralateral central nucleus and to a lesser extent the lateral nucleus exhibited anterograde labeling. The pattern of retrograde labeling seen with injections at different rostrocaudal levels of the AIp-PR continuum indicates that amygdalocortical projections to these areas exhibit an overlapping topographical organization. Comparison of the results of this study with findings on amygdaloprefrontal cortical efferents suggests that amygdaloid projections to the entire fronto-insulo-temporal mesocortical field are topographically organized.