Investigating the effect of constructional demand on the neural correlates of future episodic simulation

Abstract

Future simulation is an adaptive behaviour that allows for foresight and flexibility of behavioural responses and for this reason is considered to be a major evolutionary advantage of humans (Suddendorf and Corballis, 2007). Future simulation draws on a network of regions, similar to those used to retrieve episodic memories. A key component of this network is the hippocampus which is proposed to contribute a number of functions, including flexibly recombining disparate details into coherent episodic scenarios. However, inconsistencies remain in the literature regarding the exact role of the hippocampus. This study aimed to address these inconsistencies using fMRI and a novel approach to varying the constructional demand of future simulations by manipulating the disparity of the details participants are required to integrate into each simulation. This manipulation created two future simulation conditions, the first was labelled the congruent condition because it had low detail disparity, and second was labelled the incongruent condition because it had high detail disparity. In this study we used a spatiotemporal partial least squares analysis to examine whole brain patterns of activity that related to our conditions. Our first analysis comparing the future simulation conditions with a semantic control condition was consistent with existing literature. The results of the second analysis, which compared the incongruent and congruent conditions, indicate that the left posterior hippocampus is activated during the recombination of disparate details into coherent future simulations and is modulated by changes in constructional demand. The network of regions associated with episodic future simulation was found to be more active during the congruent condition than the incongruent condition. Furthermore, our behavioural findings showed that events from the congruent condition were more detailed than those from the incongruent condition. This behavioural result, in combination with the brain regions that were more active for the congruent condition than the incongruent condition, is consistent with the interpretation that participants had greater success forming a visual-spatial context and providing semantic scaffolding for the congruent than during the incongruent condition. Unexpectedly, regions of the salience and central executive networks were recruited during the early stages of event construction for the incongruent condition providing an interesting avenue for future research in this area.