The Parahippocampal Cortex Mediates Spatial and Nonspatial Associations

Abstract

The parahippocampal cortex (PHC) has been implicated in the processing of place-related information. It has also been implicated in episodic memory, even for items that are not related to unique places. How could the same cortical region mediate such seemingly different cognitive processes? Both processes rely on contextual associations, and we therefore propose that the PHC should be viewed not as exclusively dedicated for analyzing place-related information, or as solely processing episodic memories, but instead as more generally playing a central role in contextual associative processing. To test this proposal, we created a novel learning paradigm to form new associations among meaningless visual patterns. These new associations were created to emulate either spatial or nonspatial contexts. Both spatial and nonspatial associations activated the PHC more than noncontextual items. Moreover, items from spatial contexts activated the posterior part of the PHC, whereas items from nonspatial contexts activated the anterior PHC. Therefore, we show that the PHC plays a role of processing contextual associations in general, and that these associations are not restricted to spatial information. By modifying the existing view of the PHC function accordingly, the seemingly contradicting processes that activate it can be reconciled under one overarching framework.

The proactive brain: memory for predictions

“…The major aspects of this default network overlap remarkably with the same regions that we have found as directly related to contextual associative activation (figure 3; Bar & Aminoff 2003;Aminoff et al 2007;Bar et al 2007). This overlap between the default network and the network subserving associative processing of contextually related information is taken as the cortical manifestation that associative predictions are crucial, ongoing, elements of natural thought.…”

“…On one extreme, associations are automatic, simple and unique, similar to a basic Hebbian association where associated concepts are co-activated when the representation of one of them is activated. Such associations have been the primary focus of research, and have largely been shown to be mediated by the MTL (Petrides 1985;Schacter 1987;Miyashita 1993;Shallice et al 1994;Eichenbaum & Bunsey 1995;Suzuki & Eichenbaum 2000;Stark & Squire 2001;Sperling & Chua 2003;Ranganath et al 2004;Aminoff et al 2007). Other associations are more deliberative, and their selective co-activation depends on the specific context in which they are embedded (Bar 2004).…”

Regional activation of the human medial temporal lobe during intentional encoding of objects and positions

“…Recent studies suggest a role for the parahippocampal cortex region in more complex spatial processing, such as scenes (Buffalo et al, 2006;Henderson et al, in press;Epstein et al, 2007) and other contextual stimuli (Aminoff et al, 2007). Thus, although the current spatial task may be regarded as depending on a spatial processing system per se, it may not have involved sufficiently complex visual stimuli to engage the posterior MTL region.…”

Towards a functional organization of the medial temporal lobe memory system: Role of the parahippocampal and medial entorhinal cortical areas

“…This finding subsequently was extended to reveal that the parahippocampal cortex is also activated during viewing of famous faces, wherein the contextual associations are not typically place-specific but rather associated with rich pictorial and abstract contextual information (Bar et al, 2008). In addition, the distinction between spatial and nonspatial contextual activation was clarified in a study that compared activations to simple visual patterns where the contextual associations were explicitly trained (Aminoff et al, 2007). Under the spatial context condition, three patterns were repeatedly presented together in the same spatial configuration on a computer screen.…”