Involvement of the Postrhinal and Perirhinal Cortices in Microscale and Macroscale Visuospatial Information Encoding

Abstract

Whereas the postrhinal cortex (POR) is a critical center for the integration of egocentric and allocentric spatial information, the perirhinal cortex (PRC) plays an important role in the encoding of objects that supports spatial learning. The POR and PRC send afferents to the hippocampus, a structure that builds complex associative memories from the spatial experience. Hippocampal encoding of item-place experience is accompanied by the nuclear expression of immediate early gene (IEGs). Subfields of the Cornus ammonius and subregions of the hippocampus exhibit differentiated and distinct encoding responses, depending on whether the spatial location and relationships of large highly visible items (macroscale encoding) or small partially concealed items (microscale encoding), is learned. But to what extent the PRC and POR support hippocampal processing of different kinds of item-place representations is unclear. Using fluorescence in situ hybridization (FISH), we examined the effect of macroscale (overt, landmark) and microscale (subtle, discrete) item-place learning on the nuclear expression of the IEG, Arc. We observed an increase in Arc mRNA in the caudal part of PRC area 35 and the caudal part of the POR after macroscale, but not microscale item-place learning. The caudal part of PRC area 36, the rostral and middle parts of PRC areas 35 and 36, as well as the middle part of the POR responded to neither type of item. These results suggest that macroscale items may contain a strong identity component that is processed by specific compartments of the PRC and POR. In contrast small, microscale items are not encoded by the POR or PRC, indicating that item dimensions may play a role in the involvement of these structures in item processing.

The Perirhinal Cortex Engages in Area and Layer-Specific Encoding of Item Dimensions

“…Effects were distinct from the control condition where animals simply remained stationary and at rest in one corner of the experimental chamber. Behavioral data were also reported in Sethumadhavan et al (2020).…”

“…Assessment of somatic Arc expression triggered by the behavioral paradigms used revealed that Arc mRNA expression differs significantly between the experimental groups (multifactorial ANOVA: F (2,245) = 17.7158, p < 0.00001, Table 3). Post hoc analysis revealed that novel object exploration enhances item learning results in an increase in Arc mRNA expression in layer II of the caudal area 35 after macroscale item learning (Sethumadhavan et al, 2020). In the present study, a different imaging technique was used and a larger proportion of nuclei was analyzed in layer II (Figure 2, Table 1).…”

“…Anatomical and functional differences along the rostrocaudal axis have also been described (Burwell and Amaral, 1998b;Otto et al, 2000;Burwell, 2001;Furtak et al, 2007;Agster and Burwell, 2009;Albasser et al, 2013;Sethumadhavan et al, 2020). Novel object exposure has been reported to trigger a change in immediate early gene (IEG) expression in caudal areas 35 and 36 (Zhu et al, 1995b;Albasser et al, 2010).…”

“…Object recognition also triggers gene encoding in these PRC areas: Burke and colleagues examined IEG expression in layer V, or neuronal activity in layer II/III and V of the areas 35 and 36 (Burke et al, 2012a , b ), and demonstrated that novel and familiar exploration of objects results in enhanced Arc mRNA expression in layer V (Burke et al, 2012a ). In our previous work, we reported that layer II of the caudal area 35, along with the postrhinal cortex (POR), engages in the encoding of information about large objects (Sethumadhavan et al, 2020 ). Given that the PRC strongly projects to the entorhinal cortex that in turn projects to the hippocampus (Burwell and Amaral, 1998b ; Agster and Burwell, 2013 ; Doan et al, 2019 ), it is not unlikely that object dimensions also result in layer-specific neuronal encoding within the PRC.…”

A Neural Model of Intrinsic and Extrinsic Hippocampal Theta Rhythms: Anatomy, Neurophysiology, and Function

“…Spatial representations in the dorsal, or Where, cortical stream for spatial representation and action go through postrhinal cortex and MEC on their way to hippocampal cortex, whereas object representations in the ventral, or What, cortical stream for perception and object recognition go through perirhinal cortex and LEC on their way to hippocampal cortex ( Hargreaves et al, 2005 ; Norman and Eacott, 2005 ; Aminoff et al, 2007 ; Kerr et al, 2007 ; Eichenbaum and Lipton, 2008 ; van Strien et al, 2009 ; LaChance et al, 2019 ; Nilssen et al, 2019 ; Sethumadhavan et al, 2020 ), where they are merged.…”