Perirhinal cortex projections to the amygdaloid complex and hippocampal formation in the rat

The differential efferent projections of the perirhinal cortex were traced by using anterograde and retrograde tracing techniques. The dorsal bank cor tex (area 36) projected lightly to the lateral entorhinal cortex and more s trongly to the lateral, posterolateral cortical, and posterior basomedial a mygdaloid nuclei and amygdalostriatal transition zone. The ventral bank (do rsolateral entorhinal cortex) projected to the lateral entorhinal cortex, d orsal subiculum, and subfield CA1 and mainly targeted the basolateral amygd aloid nucleus. Corticocortical projections from the dorsal and ventral bank s targeted different cortical areas. The fundus of the rhinal sulcus (area 35) projected to both lateral and medial entorhinal cortices, ventral subic ulum, lateral and basolateral nuclei, and amygdalostriatal transition zone. Corticocortical projections targeted areas projected to by both dorsal and ventral banks and also by second somatosensory area, first temporal cortic al area, and striate cortex. Neurons projecting to the lateral nucleus were distributed in all layers of the dorsal bank, wheras those projecting to C A1 and subiculum were found in superfical layers (mostly layer III) of the ventral bank. Projections to the basolateral nucleus arose from superfical layers (mostly layer II) of the fundus and deep layers of the ventral bank. Furthermore, projections to the amygdala mostly arose from rostral levels, whereas hippocampal projections primarily originated caudally. The rat per irhinal cortex is heterogeneous in its efferent connectivity, and distinct projections arise from the dorsal and ventral banks and fundus of the rhina l sulcus. The widespread cortical connectivity of the fundus suggests that only this part of the perirhinal cortex is similar to area 35 of the primat e brain. (C) 1999 Wiley-Liss, Inc.