The postrhinal cortex is not necessary for landmark control in rat head direction cells

Abstract

The rodent postrhinal cortex (POR), homologous to primate areas TH/TF and the human ‘parahippocampal place area’, has been implicated in processing visual landmark and contextual information about the environment. Head direction (HD) cells are neurons that encode allocentric head direction, independent of the animal’s location or behavior, and are influenced by manipulations of visual landmarks. The present study determined whether the POR plays a role in processing environmental information within the HD circuit. Experiment 1 tested the role of the POR in processing visual landmark cues in the HD system during manipulation of a visual cue. HD cells from POR lesioned animals had similar firing properties, shifted their preferred firing direction following rotation of a salient visual cue, and in darkness had preferred firing directions that drifted at the same rate as controls. Experiment 2 tested the POR’s involvement in contextual fear conditioning, where the animal learns to associate a shock with both a tone and a context in which the shock was given. In agreement with previous studies, POR lesioned animals were able to learn the tone-shock pairing, but displayed less freezing relative to controls when reintroduced into the environment previously paired with a shock. Therefore, HD cells from POR lesioned animals, with demonstrated impairments in contextual fear conditioning, were able to use a visual landmark to control their preferred direction. Thus, despite its importance in processing visual landmark information in primates, the POR in rats does not appear to play a pivotal role in controlling visual landmark information in the HD system.

The anatomy and function of the postrhinal cortex.

“…Animals with sham lesions were able to differentiate between the two contexts by the third day of training, as shown by decreased freezing in the nonshock paired context, whereas animals with POR lesions tended to freeze more in both contexts, showing an inability to distinguish the two contexts. A similar conclusion can be drawn from subsequent studies showing that animals with POR lesions froze less across all contexts following successful fear conditioning training, with the result being a tendency for animals with POR lesions to overgeneralize rather than differentiate between contexts (Burwell et al, 2004; Peck & Taube, 2017). A series of lesion experiments also demonstrated the importance of the POR in contextual scene representation (Eacott & Gaffan, 2005; Gaffan et al, 2004; Norman & Eacott, 2005).…”

Convergent Projections from Perirhinal and Postrhinal Cortices Suggest a Multisensory Nature of Lateral, but Not Medial, Entorhinal Cortex

“…In line with predictions from path-integration models (Burak and Fiete, 2006;McNaughton et al, 2006;Bush and Burgess, 2014), MEC grid cells intrinsically contain this HD signal (Bonnevie et al, 2013), which is fundamental, because disruption of the HD input leads to loss of their grid cell phenotype (Winter et al, 2015). The other exclusive MEC input structure, RSC that selectively targets layer V (Czajkowski et al, 2013), has also been portrayed as providing visuospatial information to the PHR-HF system (Julian et al, 2018), because it contains HD cells and is involved in their relationships to available landmarks in the environment, similar to what has been reported for PrS and PaS (Peck and Taube, 2017).…”

Landmark-modulated directional coding in postrhinal cortex

“…Our results also agree with lesion studies implicating the POR in orienting ( 42 ) and visual discrimination ( 43 , 44 ) behavior and may relate to cue-related firing found throughout the hippocampal formation ( 10 , 45 – 48 ). However, the POR is unlikely to be a major source of visual landmark information for earlier stages of the HD circuit (e.g., in the ATN) ( 49 ), which could be conveyed by the postsubiculum ( 50 , 51 ).…”