Functional neuroanatomy of the parahippocampal region in the rat: The perirhinal and postrhinal cortices

Abstract

The parahippocampal region in the rodent brain includes the perirhinal, postrhinal, and entorhinal cortices, the presubiculum, and the parasubiculum. In recent years, the perirhinal and postrhinal cortices have been a focus in memory research because they supply highly processed, polymodal sensory information to the hippocampus, both directly and via the entorhinal cortex. Available evidence indicates that these cortices receive different complements of cortical information, which are then forwarded to the hippocampus via parallel pathways. Here we have summarized the cortical, subcortical, and hippocampal connections of the perirhinal and postrhinal cortices in order to provide further insight into the nature of the information that is processed by these regions prior to arriving in the hippocampus. As has been previously described, the cortical afferents of the rodent postrhinal cortex are dominated by structures known to be involved in the processing of visual and spatial information, whereas the cortical afferents of the perirhinal cortex result in remarkable convergence of polymodal sensory information. The two regions are also differentiated by their cortical efferents. The perirhinal cortex projects more strongly to piriform, frontal, and insular regions, whereas the postrhinal cortex projects preferentially to visual and visuospatial regions. The subcortical connections of the two regions provide further evidence that they have different functions. For example, the perirhinal cortex has strong reciprocal connections with the amygdala, which suggest involvement in processing affective stimuli. Subcortical input to the postrhinal cortex is dominated by projections from dorsal thalamic structures, particularly the lateral posterior nucleus. Although the perirhinal and postrhinal cortices are considered to contribute to the episodic memory system, many questions remain about their particular roles. A detailed description of the anatomical connections of the perirhinal and postrhinal cortices will permit the generation of new, anatomically guided, hypotheses about their role in episodic memory and other cognitive processes.

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

“…Approximately half of all subcortical afferents to area 36 originate in the amygdala, terminating in the rostral region of area 36 (Furtak et al, 2007b). Furtak et al (2007b) also report that area 35 receives approximately half of its subcortical inputs from the amygdala, terminating in the caudal region of area 35. The accessory basal, basal and lateral nuclei project heavily to area 35 and form a weaker projection to area 36 (McDonald and Jackson, 1987;Pikkarainen and Pitkä nen, 2001).…”

“…The projections from area 36 project more heavily to the amygdala than those of area 35 (Shi and Cassell, 1999). Projections from the middle rostral-caudal region of area 36 terminate in the various nuclei of the amygdala (Furtak et al, 2007b). Furtak et al (2007b) report that the return projection to the amygdala from area 35 originates in the rostral region of area 35 and mainly targets the basomedial nucleus.…”

“…From the amygdala, the perirhinal cortex receives projections from the nucleus of the lateral olfactory tract, accessory basal nucleus, basal nucleus and lateral nucleus Price, 1974, 1977;McDonald and Jackson, 1987;Pikkarainen and Pitkä nen, 2001;Furtak et al, 2007b) with area 35 receiving the heaviest projections from the amygdala compared to area 36 and the accessory basal and lateral nuclei being the most prominent origins of these projections (Pitkä nen et al, 2000). Approximately half of all subcortical afferents to area 36 originate in the amygdala, terminating in the rostral region of area 36 (Furtak et al, 2007b). Furtak et al (2007b) also report that area 35 receives approximately half of its subcortical inputs from the amygdala, terminating in the caudal region of area 35.…”

“…Projections from the middle rostral-caudal region of area 36 terminate in the various nuclei of the amygdala (Furtak et al, 2007b). Furtak et al (2007b) report that the return projection to the amygdala from area 35 originates in the rostral region of area 35 and mainly targets the basomedial nucleus. Shi and Cassell (1999) report no direct connections to the central and medial amygdaloid nuclei.…”

“…Here the perirhinal cortex plays more of an associative role compared to its role in recognition memory (Kholodar-Smith et al, 2008b). Based on the anatomical projections described in Sections 3.2 and 3.3, it is not surprising that the perirhinal cortex is required for such associational learning as it forms a significant reciprocal connections with the amygdala Price, 1974, 1977;Ottersen, 1982;McDonald and Jackson, 1987;Pitkä nen et al, 2000;Pikkarainen and Pitkä nen, 2001;Furtak et al, 2007b), thalamus (Cornwall and Phillipson, 1988;Wouterlood et al, 1990;Shibata, 1993;McIntyre et al, 1996;Van Groen et al, 1999;Vertes et al, 2006), medial prefrontal cortex (Deacon et al, 1983;Sesack et al, 1989;Burwell and Amaral, 1998b;Delatour and Witter, 2002;Heidbreder and Groenewegen, 2003;Jones and Witter, 2007;Agster and Burwell, 2009) and hippocampus (Swanson and Cowan, 1977;Deacon et al, 1983;Kosel et al, 1983;Van Groen and Wyss, 1990;McIntyre et al, 1996;Naber et al, 1999;Shi and Cassell, 1999;Witter et al, 1999;Kloosterman et al, 2003b); regions of the brain which have been strongly linked with fear conditioning (Milad et al, 2006;Rosen and Donley, 2006).…”