Perirhinal and postrhinal cortices of the rat: A review of the neuroanatomical literature and comparison with findings from the monkey brain

Abstract

KEY WORDS: parahippocampal, entorhinal polysensory cortex, memory, hippocampal formation,This review is prompted by recent findings that the perirhinal and parahippocampal cortices in the monkey brain are important components of the medial temporal lobe memory system. Given the potential importance of the comparable rcgions 1 0 niemory function in rhe rat brain, it is surprising that so little is known about their neuroanatomy. In fact, there are no comprehensive studies of the borders, cytoarchitecture, or connections of the cortical regions surrounding the posterior portion of the rhinal sulciis in the rat. This review is meant to summarize the current state of our knowledge regarding these regions in the rat brain. Based on existing data and our own observations, a new terminology is introduced that retains the term perirhinal cortex for the rostral portion of the region and renames the caudal portion the posirhi!,ind cortex. Issues of continuing uncertainty are highlighted, and information gleaned from the monkry literature is used to predict what anatomical traits thc rat perirhinal region might demonstrate upon further examination. To the extent possible with available data, the similarities and differences of the rat and monkey perirhinal, postrhinal, and parahippocampal regions are evaluated. (Fig. 1B).The entire region was located more caudally than inRose. This is because the rostrally adjacent area 13 (insular cortex) extended Farther caudally, substantially beyond the caudal limit of the underlying claustrum. As

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

“…There are a number of anatomical differences (Burwell et al, 1995;Burwell and Amaral, 1998a,b;Pitkä nen et al, 2000;Burwell, 2000Burwell, , 2001) and functional differences (Norman and Eacott, 2005) existing between the two areas and it has been suggested that the rat postrhinal cortex is homologous to the monkey parahippocampal cortex (Burwell et al, 1995;Burwell, 2000). Therefore, we follow Burwell's classification (2000) and distinguish between the perirhinal and postrhinal cortices as two distinct anatomical regions in the rat brain.…”

“…Area 35 completely lacks layer IV while area 36 does have layer IV but it appears to be less well defined particularly in the medial portions of the cortex compared to other neocortical areas (Burwell et al, 1995). Brodmann's areas 35 and 36 are also cytoarchitectonically different in that layer I of area 35 tends to be thicker than that of area 36, the cells in area 35 are organised radially, the presence of large, heart-shaped pyramidal cells in layer V of area 35 and finally layers II and III are distinctly separated in area 36 and not in area 35 (Krieg, 1946b;Burwell and Amaral, 1998a,b;Burwell, 2001).…”

“…It is bordered rostrally by the posterior agranular insular cortex (bordering with areas 35 and 36) and the visceral area (area 36 only), caudally by the postrhinal cortex, dorsally by the ventral temporal association cortex and ventrally by the lateral entorhinal cortex ( Fig. 1a; Burwell et al, 1995;Burwell, 2001;Paxinos and Watson, 2005).…”

“…The two areas can also be distinguished based on their connections with the entorhinal cortex, the perirhinal cortex projects mainly to the lateral entorhinal cortex and the postrhinal cortex projects mainly to the medial entorhinal cortex (Naber et al, 1997). Despite these differences, there is a debate in the literature as to whether to count the postrhinal cortex as a separate area to the perirhinal cortex (Deacon et al, 1983;Burwell et al, 1995) or whether to The perirhinal cortex is found along the rhinal sulcus (dotted line) and is comprised of cortical areas 35 (dark grey) and 36 (light grey). Area 36 occupies the dorsal bank of rhinal sulcus whereas area 35 occupies the ventral bank.…”

“…Neighbouring the perirhinal cortex are the posterior agranular insular cortex, the visceral area, the postrhinal cortex, the ventral temporal association cortex and the lateral entorhinal cortex. Diagram summarised from Burwell et al (1995), Burwell (2001), and Paxinos and Watson (2005). (b) Subdivisions of the perirhinal and postrhinal cortices in the rat brain.…”