Remembering and imagining alternative versions of the personal past

Highlights

• Episodic counterfactual simulation involves constructing alternative versions of the past.

• Shifting visual perspective in memory retrieval requires similar constructive processes.

• Alternative perspectives and versions of the past recruit similar frontoparietal regions.

• Remembering becomes more like imagination when shifting visual perspective.

Abstract

Although autobiographical memory and episodic simulations recruit similar core brain regions, episodic simulations engage additional neural recruitment in the frontoparietal control network due to greater demands on constructive processes. However, previous functional neuroimaging studies showing differences in remembering and episodic simulation have focused on veridical retrieval of past experiences, and thus have not fully considered how retrieving the past in different ways from how it was originally experienced may also place similar demands on constructive processes. Here we examined how alternative versions of the past are constructed when adopting different egocentric perspectives during autobiographical memory retrieval compared to simulating hypothetical events from the personal past that could have occurred, or episodic counterfactual thinking. Participants were asked to generate titles for specific autobiographical memories from the last five years, and then, during functional magnetic resonance (fMRI) scanning, were asked to repeatedly retrieve autobiographical memories or imagine counterfactual events cued by the titles. We used an fMRI adaptation paradigm in order to isolate neural regions that were sensitive to adopting alternative egocentric perspectives and counterfactual simulations of the personal past. The fMRI results revealed that voxels within left posterior inferior parietal and ventrolateral frontal cortices were sensitive to novel visual perspectives and counterfactual simulations. Our findings suggest that the neural regions supporting remembering become more similar to those underlying episodic simulation when we adopt alternative egocentric perspectives of the veridical past.

Introduction

Remembering the personal past, or autobiographical memory (AM), is closely related to our ability to imagine hypothetical episodes that might occur in the future (i.e., episodic simulation; Schacter et al., 2008; Szpunar et al., 2014a) or how events could have turned out differently in the past (i.e., episodic counterfactual simulation; De Brigard et al., 2013). According to the constructive episodic simulation hypothesis (Schacter and Addis, 2007, 2009) both remembering and imagining are supported by a constructive episodic memory system that involves access to stored episodic details and the ability to flexibly recombine details from past episodes when memories are reconstructed or when imagining a hypothetical event. Supporting this hypothesis, AM retrieval and episodic simulation recruit a similar pattern of brain regions referred to as a core network, which includes medial temporal lobe, medial prefrontal cortex (PFC), posterior cingulate, retrosplenial cortex, and lateral temporal and parietal cortices (Addis et al., 2007, Benoit and Schacter, 2015, Buckner and Carroll, 2007, Spreng et al., 2008, Szpunar et al., 2015, Szpunar et al., 2014b). Episodic simulation, however, typically involves stronger neural recruitment in some of these core network areas, as well as additional recruitment of other brain regions attributed to greater constructive demands in recombining details when imagining a novel event (Benoit and Schacter, 2015, Schacter and Addis, 2009, Schacter et al., 2012). We and others (Hardt et al., 2010, Howe and Derbish, 2010, Newman and Lindsay, 2009, Schacter, 2012, Schacter and Addis, 2007; Schacter et al., 2011) have argued that the adaptive nature of memory, which enables the ability to simulate novel events, also makes it vulnerable to modification (e.g., Carpenter and Schacter, 2017; Schacter et al., 2017, St Jacques et al., 2013; St. Jacques and Schacter, 2013). Yet, to our knowledge, previous functional neuroimaging studies have not fully considered how reshaping the veridical past may also place similar demands on constructive processes as episodic simulation of hypothetical events. Here, we used an fMRI adaptation paradigm (Barron et al., 2016, Grill-Spector et al., 2006, Larsson et al., 2016, Szpunar et al., 2014a, Szpunar et al., 2014b) to isolate neural regions sensitive to the creation of alternative versions of the past during AM retrieval when adopting novel visual perspectives and episodic counterfactual simulations.

As noted above, episodic simulation typically involves greater neural recruitment than AM retrieval. For example, some studies have shown greater recruitment of the hippocampus when imagining future events (Schacter and Addis, 2009, Schacter et al., 2017), and stronger coupling with the frontoparietal control network when planning plausible future events (Gerlach et al., 2014b, Spreng et al., 2010). Although episodic simulations of the future and the past have been shown to recruit similar core network regions (e.g., Addis et al., 2009), there are some reported differences. For example, episodic counterfactual thinking preferentially engages posterior dorsal medial PFC (Van Hoeck et al., 2012). Further, De Brigard et al. (2013) found that probable or likely episodic counterfactual simulations, in contrast to unlikely episodic counterfactual simulations, recruited a more similar pattern of neural activity to that associated with AM retrieval. A recent meta-analysis by Benoit and Schacter (2015) revealed that episodic simulations, including counterfactual thinking, involved greater engagement of core network areas than AM retrieval within the left inferior parietal cortex, dorsolateral PFC and hippocampus, as well as additional recruitment of precuneus and other brain regions overlapping with the frontoparietal control network. Such differences in the neural regions between episodic simulation and AM retrieval are thought to reflect additional constructive demands involved in recombining disparate episodic details to form novel coherent scenarios (for discussion see Schacter and Addis, 2009; Schacter et al., 2017, 2015). Importantly, however, previous research comparing episodic simulation and memory retrieval has focused on AM conditions that placed minimal demands on constructive processes. For example, participants are typically instructed to recall memories in accurate detail and/or in similar ways to which they were originally experienced. It is well known that AMs can be reconstructed in multiple ways (Hirst and Echterhoff, 2012, Marsh, 2007, Pasupathi, 2001). Yet it is not well understood how the different ways we can retrieve memories influence the neural mechanisms typically associated with additional recombination demands during episodic simulation.

One of the most prominent ways we reconstruct AMs is by retrieving them from multiple egocentric or self-centered visual perspectives. Although we typically experience the world from our own eyes, when we retrieve AMs we can flexibly shift our first person viewpoint from inside to outside the body, seeing ourselves in the memory (Nigro and Neisser, 1983, Rice and Rubin, 2009). Retrieving AMs from visual perspectives that were never experienced is thought to reflect reconstructive processes that can reshape memories (Butler et al., 2016, McDermott et al., 2016, Robinson and Swanson, 1993). Supporting this idea, adopting a particular visual perspective influences the content and phenomenological properties of AM retrieval (Berntsen and Rubin, 2006, McIsaac and Eich, 2002, Robinson and Swanson, 1993) and recruits different neural processes (Eich et al., 2009, n et al., 2014, Grol et al., 2017). We recently provided evidence concerning the neural mechanisms that contribute to changes in memories online and during subsequent memory retrieval when retrieving AMs from novel visual perspectives (St. Jacques et al., 2017). In this functional magnetic resonance imaging (fMRI) study, participants were asked to retrieve AMs during scanning while repeatedly adopting an identical own eyes perspective or shifting to a novel observer perspective. We found that adopting a novel observer perspective reduced subjective ratings of emotional intensity online, and also biased the natural visual perspective memories were subsequently retrieved from. Neural recruitment in the precuneus, bilateral inferior parietal cortex, and lateral PFC supported the ability to adopt a novel versus an identical visual perspective during AM retrieval. However, only the precuneus supported online and subsequent changes in AMs attributable to constructing memories from a novel visual perspective.

In the current fMRI study, we examined whether increasing constructive demands on the veridical past by requiring participants to retrieve personal memories from novel visual perspectives would evoke neural activity in regions associated with constructive processing and that are typically more active for episodic simulation than remembering. Participants generated the titles of AMs in a pre-scanning session. One week later, they repeatedly retrieved or created an episodic counterfactual event while adopting an own eyes or observer visual perspective. We used an fMRI adaptation approach to isolate neural regions that were sensitive to adopting a novel visual perspective during AM retrieval compared to adopting a novel episodic counterfactual simulation. We predicted that the precuneus, inferior parietal cortex and lateral PFC would be sensitive to construction of alternative versions of the past for both AM retrieval and episodic simulation.