Review
The role of the parahippocampal cortex in cognition

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Highlights

  • This synthesis of current research characterizes the functional roles of the PHC.

  • Contextual associative processing is proposed as the core function of this region.

  • This proposal unifies findings for the PHC, creating convergence for future research.

The parahippocampal cortex (PHC) has been associated with many cognitive processes, including visuospatial processing and episodic memory. To characterize the role of PHC in cognition, a framework is required that unifies these disparate processes. An overarching account was proposed whereby the PHC is part of a network of brain regions that processes contextual associations. Contextual associations are the principal element underlying many higher-level cognitive processes, and thus are suitable for unifying the PHC literature. Recent findings are reviewed that provide support for the contextual associations account of PHC function. In addition to reconciling a vast breadth of literature, the synthesis presented expands the implications of the proposed account and gives rise to new and general questions about context and cognition.

Section snippets

Converging towards a more inclusive view of PHC function

The parahippocampal cortex (PHC) encompasses a large portion of the medial temporal lobe. It is located at the junction between brain regions described as essential to memory formation (e.g., the hippocampus) and high-level visual processing (e.g., the fusiform cortex). A significant body of research has provided evidence of a number of different processes related to the signal elicited from the PHC by diverse classes of stimuli, tasks, and environments. Thus, efforts to define a single

PHC anatomy and connectivity

To fully understand the role of a brain region it is necessary to examine not only its functional activity but also its anatomy, because the location and connections of the region can provide valuable cues about its function. The PHC is distinct anatomically within the medial temporal lobe (MTL) and is distinguished from other MTL regions such as the perirhinal, entorhinal, and hippocampal cortices. The perirhinal and entorhinal cortices provide the rostral border for the PHC 4, 5, and the

Functional characterizations of the PHC

The PHC has been studied extensively and has been ascribed many functions. Two prominent groups of research and claims have emerged: episodic memory and visuospatial processing. Specifically, it has been reported that the PHC is involved in episodic memory relating to associative memory, source memory, and recollection 13, 14, 15, and to visuospatial processing relating to scene perception 16, 17, 18, spatial representation 19, 20, 21, and navigation 22, 23. However, beyond those two dominant

Contextual associative processing in the PHC and beyond

It has been repeatedly shown that the processing of strong, long-term, contextual associations elicits activity within the PHC, as well as the RSC (which includes regions of the retrosplenial cortex, extending into the posterior cingulate cortex, and the precuneus), the medial prefrontal cortex (MPFC), and the transverse occipital sulcus (TOS) (Figure 2) 2, 3, 59, 60, 61, 62, 63, 64, 65, 66, 67. Contexts can be formed by repeated exposure to prototypical clustering of objects (both physical and

A parsimonious account of PHC activity

How can we reconcile the fact that so many different cognitive processes activate the same general cortical area? We propose that contextual associative processing is a fundamental mechanism that can account for the various tasks and stimuli that activate the PHC. Most of the processes that elicit PHC activity can be seen as relying on associative processing at their core. For example, episodic memory accounts all rely on the association and binding of items belonging to the same episode.

Future directions in studying the PHC

Establishing the PHC as a node for processing of contextual associations offers a new roadmap of future potential insights to explain brain–behavior relations (Box 4).

  • (i)

    fMRI signals across the brain have a functional profile that does not reflect strict category boundaries. For example, researchers compared the activity elicited by faces and objects with that elicited by scenes to functionally define the PPA and contrasted scenes and objects with faces to functionally define the FFA 16, 83.

Concluding remarks

A contextual processing framework can account for many of the findings related to the PHC. Moreover, a contextual processing framework provides a parsimonious explanation for linking of the posterior parahippocampal gyrus (PHG) to anterior regions of the PHG, linking of the PHC to other medial temporal lobe structures, linking of the PHC to the greater network it is connected to (e.g., RSC and MPFC), and reconciling why both episodic memory and spatial processing engage the same region of the

Acknowledgments

Our work is supported by NSF grant BCS-0842947 and Israeli Center of Research Excellence in Cognition (ICORE) grant 51/11 to M.B., NIH grant K01MH084011 to K.K., and Office of Navy Research MURI contract N000141010934 with CNBC and the Department of Robotics at Carnegie Mellon University to E.A.

Glossary

Context
conglomerate of conditions that help to define, represent, and bring meaning to the environment. The conditions carry long-term associations built up over repeated exposure. Although this paper focuses on conditions defined by objects and configurations, conditions can also be defined in other domains such as temporal (e.g., order of events), behavioral (e.g., mindset, goal orientation), and emotional domains.
Contextual association
link between contextual items. Examples are the link

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