The role of the parahippocampal cortex in cognition

Abstract

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.

Keywords: associations; contextual processing; episodic memory; parahippocampal cortex; scenes; spatial processing.

Figure 1

Contextual associations can be seen as the buildings blocks for many of the cognitions attributed to the function of the PHC.

Figure 2

Context cortical network. By comparing fMRI activity elicited for objects with strong contextual associations (left group of objects) with the activity elicited for objects with weak contextual associations (right group of objects) we reveal the network of regions that process contextual associations. This includes the parahippocampal cortex (PHC), retrosplenial complex (RSC), medial prefrontal cortex (MPFC), and the transverse occipital sulcus (TOS). Data from [62].

Figure 3

Dynamic analysis of the context network. Using MEG and phase synchrony methods the spatiotemporal dynamics within the network of regions processing contextual associations were elucidated. 1. Differential activity relating to contextual processing begins between the parahippocampal cortex (PHC) and early visual regions in the occipital cortex (OCC), 150-220ms. It is suggested that during this period contextual details are extracted from the current environment. 2. Differential activity is next demonstrated between the PHC and the retrosplenial complex (RSC), 170-240ms. It is suggested that this reflects the activation of the relevant context frame. 3. Proceeding this exchange, there is synchronous activity between RSC and OCC (310-360ms), possibly representing feedback processing. 4. The last stage of the neural mechanism lies between communication between the RSC and medial prefrontal cortex (MPFC), 370-400ms, which is suggested to generating contextually related predictions. Data from [62].

Figure 4

Scenes compared with scenes. In this experiment, participants passively viewed pictures of scenes which were presented on for 1500ms. The scenes differed in the contextual associations of the foreground object: the foreground object was either strongly associated with a context (e.g., a crib with a nursery [left pictures]), or the foreground object was weakly associated with many contexts (e.g., a bag is not strongly associated with a context [right pictures]). Comparing the activity elicited when viewing the scenes in the different conditions (strong context vs. weak context) revealed differential activity within the context network, and in particular within the PHC, in similar regions as the PPA. The results from this study demonstrate how the contextual associations within a scene can modulate activity within scene selective cortex. This poses a problem for a strictly spatial layout interpretation of the function in these regions. If it was only spatial, there should not be differential activity when comparing scenes to scenes since scenes in both conditions contain spatial layout information. Data from [59].