Cortical afferents of the perirhinal, postrhinal, and entorhinal cortices of the rat

Abstract

We have divided the cortical regions surrounding the rat hippocampus into three cytoarchitectonically discrete cortical regions, the perirhinal, the postrhinal, and the entorhinal cortices. These regions appear to be homologous to the monkey perirhinal, parahippocampal, and entorhinal cortices, respectively. The origin of cortical afferents to these regions is well-documented in the monkey but less is known about them in the rat. The present study investigated the origins of cortical input to the rat perirhinal (areas 35 and 36) and postrhinal cortices and the lateral and medial subdivisions of the entorhinal cortex (LEA and MEA) by placing injections of retrograde tracers at several locations within each region. For each experiment, the total numbers of retrogradely labeled cells (and cell densities) were estimated for 34 cortical regions. We found that the complement of cortical inputs differs for each of the five regions. Area 35 receives its heaviest input from entorhinal, piriform, and insular areas. Area 36 receives its heaviest projections from other temporal cortical regions such as ventral temporal association cortex. Area 36 also receives substantial input from insular and entorhinal areas. Whereas area 36 receives similar magnitudes of input from cortices subserving all sensory modalities, the heaviest projections to the postrhinal cortex originate in visual associational cortex and visuospatial areas such as the posterior parietal cortex. The cortical projections to the LEA are heavier than to the MEA and differ in origin. The LEA is primarily innervated by the perirhinal, insular, piriform, and postrhinal cortices. The MEA is primarily innervated by the piriform and postrhinal cortices, but also receives minor projections from retrosplenial, posterior parietal, and visual association areas.

The rat perirhinal cortex: A review of anatomy, physiology, plasticity, and function

“…Within area 36, the dorsal and ventral subregions make up the rostral region (with the ventral subregion sometimes protruding more rostrally than the dorsal subregion) and the posterior subregion is located caudally, bordering the postrhinal cortex. These three subregions are distinct from each other in that cells in layers II-V of the dorsal subregion are organised radially whereas cells in the same layers of the ventral subregion show no particular orientation and layers V and VI are narrower in the dorsal subregion (Burwell and Amaral, 1998b;Burwell, 2001). The posterior subregion differs from the rostral subregions of area 36 due to the presence of round, medium-sized cells throughout layers V and VI and the absence of a bilaminated layer VI (Burwell, 2001).…”

“…Finally, based on cortical input to either area, the perirhinal cortex receives markedly greater levels of input from various cortical areas compared to the ventral temporal association area, i.e. the ventral temporal association area receives no input from the piriform but receives more somatosensory and auditory input and lower levels of input from the insular and entorhinal cortices (Burwell and Amaral, 1998b).…”

“…2a;Saper, 1982;Deacon et al, 1983;Wyss and Van Groen, 1992;Burwell and Amaral, 1998b;Haberly, 2001;Naber et al, 2001a,b;Majak and Pitkä nen, 2003;Jones and Witter, 2007). Out of these cortical areas, a number project to both areas 35 and 36 of the perirhinal cortex including the cingulate, parietal, piriform, insular and auditory cortices (Saper, 1982;Deacon et al, 1983;Wyss and Van Groen, 1992;Burwell and Amaral, 1998a,b;Haberly, 2001;Naber et al, 2001a,b).…”

“…Out of these cortical areas, a number project to both areas 35 and 36 of the perirhinal cortex including the cingulate, parietal, piriform, insular and auditory cortices (Saper, 1982;Deacon et al, 1983;Wyss and Van Groen, 1992;Burwell and Amaral, 1998a,b;Haberly, 2001;Naber et al, 2001a,b). In contrast, the precentral, prelimbic and periamygdaloid cortices project to area 35 only (Deacon et al, 1983;Majak and Pitkä nen, 2003) and the visual association cortex projects to area 36 only (Burwell and Amaral, 1998b). Many of the projections also show topographic organisation which vary depending on the pathway, some show rostralcaudal or ventral-dorsal topographical gradients whereas others project to a particular region of the perirhinal cortex alone (see below for a more detailed description of these topographies).…”

“…The cingulate cortex projection originates in the dorsal anterior region in layers II/III and V and projects to the caudal regions of both areas 35 and 36 (Deacon et al, 1983;Burwell and Amaral, 1998b) predominantly in the deep layers of the perirhinal cortex (Jones and Witter, 2007). Similarly, the prelimbic cortex projects caudally but terminates only in area 35 (Deacon et al, 1983) mainly in the deep layers of area 35 but with a small amount of projections terminating in superficial layers (Sesack et al, 1989;Jones and Witter, 2007).…”