Elsevier

Neuropsychologia

Volume 47, Issue 11, September 2009, Pages 2222-2238
Neuropsychologia

Constructive episodic simulation of the future and the past: Distinct subsystems of a core brain network mediate imagining and remembering

https://doi.org/10.1016/j.neuropsychologia.2008.10.026Get rights and content

Abstract

Recent neuroimaging studies demonstrate that remembering the past and imagining the future rely on the same core brain network. However, findings of common core network activity during remembering and imagining events and increased activity during future event simulation could reflect the recasting of past events as future events. We experimentally recombined event details from participants’ own past experiences, thus preventing the recasting of past events as imagined events. Moreover, we instructed participants to imagine both future and past events in order to disambiguate whether future-event-specific activity found in previous studies is related specifically to prospection or a general demand of imagining episodic events. Using spatiotemporal partial-least-squares (PLS), a conjunction contrast confirmed that even when subjects are required to recombine details into imagined events (and prevented from recasting events), significant neural overlap between remembering and imagining events is evident throughout the core network. However, the PLS analysis identified two subsystems within the core network. One extensive subsystem was preferentially associated with imagining both future and past events. This finding suggests that regions previously associated with future events, such as anterior hippocampus, medial prefrontal cortex and inferior frontal gyrus, support processes general to imagining events rather than specific to prospection. This PLS analysis also identified a subsystem, including hippocampus, parahippocampal gyrus and extensive regions of posterior visual cortex that was preferentially engaged when remembering past events rich in contextual and visuospatial detail.

Section snippets

Participants

Healthy, right-handed young adults with no prior history of neurological or psychiatric impairment were recruited for participation in this study. For any undergraduate students recruited, only those in their second or third year of their 4-year program were permitted to enroll, ensuring that both the last and next 5 years (the temporal interval within which events would be imagined) included both college and non-college years. For the same reason, any college graduates recruited were required

Behavioral results

Only successfully completed trials were included in the analyses. For autobiographical events, this included trials on which participants: (1) successfully imagined or retrieved a specific event as instructed and (2) described the event during the post-scan interview, resulting in the loss of an average of 3.19% (sd = 6.41%) and 1.94% (sd = 4.42%) of trials, respectively. Additionally, trials for which the reaction time was missing or excessively fast (i.e., before the trial onset of 2 s used in the

Common activation of the core network during imagining and remembering

The present study was designed to address a number of issues arising from recent neuroimaging studies on remembering the past and imagining the future. One issue concerns the underlying basis for the common activation of the core network during past and future event tasks. In our constructive episodic simulation hypothesis (Schacter and Addis, 2007a, Schacter and Addis, 2007b), we proposed that such common activation reflects the reliance of both past and future events on episodic memory: when

Acknowledgements

We thank Joe Paxton and Jill Clark for assistance with data collection and Regina Musicaro for assistance with data analysis, and Randy McIntosh for contributing his PLS expertise. We also thank reviewers for their helpful comments. This research was supported by National Institute of Mental Health (NIMH) grant MH060941, awarded to D.L.S. We are especially thankful to Endel Tulving for inspiring our interest in the issues addressed in this article, beginning with his testing of future thinking

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