Zooming In and Out on One’s Life: Autobiographical Representations at Multiple Time Scales Arnaud D’Argembeau Abstract ■ The ability to decouple from the present environment and ex- this view, past and future thoughts rely on two main systems— plore other times is a central feature of the human mind. Research event simulation and autobiographical knowledge—that allow us in cognitive psychology and neuroscience has shown that the to represent experiential contents that are decoupled from sen- personal past and future is represented at multiple timescales sory input and to place these on a personal timeline scaffolded and levels of resolution, from broad lifetime periods that span from conceptual knowledge of the content and structure of our years to short-time slices of experience that span seconds. Here, life. The neural basis of this cognitive architecture is discussed, I review this evidence and propose a theoretical framework for emphasizing the possible role of the medial pFC in integrating understanding mental time travel as the capacity to flexibly nav- layers of autobiographical representations in the service of mental igate hierarchical layers of autobiographical representations. On time travel. ■ INTRODUCTION representations of one’s past and anticipated future—which Time is a central feature of mental life. All we ever directly places remembered and imagined events in a personal life experience is the present moment, and yet our minds relent- context (D’Argembeau & Mathy, 2011; Conway, 2005). lessly create other times. Consider the myriad mental trips to Here, I review this evidence and propose a theoretical frame- the past and future that we make on a daily basis: We think work for understanding mental time travel as the capacity to about what we did minutes ago, remember a conversation flexibly navigate layers of autobiographical representations at we had yesterday, reflect on a decision we made last year, multiple timescales, from broad lifetime periods that span make plans for the weekend, ponder options for our next years to short-time slices of experience that span seconds. vacation, envision opportunities for our career, and so forth. This ability to decouple from the present environment— mental time travel—is no small feat and may be central to REPRESENTATIONS OF THE PERSONAL PAST what makes us humans (Suddendorf & Corballis, 2007; A wealth of evidence indicates that the personal past is rep- Tulving, 2005). Its significance and impact on personal and resented in memory at multiple timescales and levels of collective life cannot be overstated—it drives many of our specificity or generality (Mace & Clevinger, 2013; Piolino decisions and actions (Baumeister, Vohs, & Oettingen, et al., 2010; Thomsen, 2009; Skowronski et al., 2007; 2016) and grounds our very sense of who we are (Prebble, Dijkstra & Kaup, 2005; Burt, Kemp, & Conway, 2003; Addis, & Tippett, 2013). Conway & Bekerian, 1987). Not only are we able to remem- The cognitive and neural mechanisms that support mental ber specific events, but we extract regularities from our expe- time travel are increasingly well understood (Suddendorf, riences (Barsalou, 1988), organize them in coherent themes Bulley, & Miloyan, 2018; Sheldon & Levine, 2016; D’Argembeau, and sequences (Brown & Schopflocher, 1998), and ultimately 2012; Schacter et al., 2012; Szpunar, 2010). Research has shown construct an overarching personal story that gives meaning that mental representations of past and future events are and purpose to our life (McAdams, 2001). Fundamentally, constructed from informational contents provided by epi- this diversity of memory representations can be understood sodic and semantic memory (Schacter, Benoit, & Szpunar, in terms of two main representational systems that retain 2017; Irish & Piguet, 2013). In addition, a growing number traces of prior experiences and that organize knowledge of studies suggest that mental time travel also relies on about the content and structure of our life: episodic memory higher-order autobiographical knowledge—general and autobiographical knowledge (Conway, 2001, 2005). This article is part of a Special Focus deriving from a symposium Episodic Memory at the 2019 annual meeting of Cognitive Neuroscience Society, entitled, “Mental Models of Time.” Episodic memory represents dimensions of prior experience University of Liège (e.g., perceptions, actions, thoughts, emotions) for events © 2020 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 32:11, pp. 2037–2055 https://doi.org/10.1162/jocn_a_01556 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn_a_01556 by guest on 23 September 2021 that usually span minutes or hours, allowing us to mentally contextual details) and conceptual processing, reflecting relive specific happenings—a lunch with colleagues, a trip the influence of event schema during remembering and to the library, a conversation with a friend, and so forth the reinstatement of conceptual processes that were en- (Conway, 2009; Tulving, 2002). The various features that gaged while experiencing past events (Renoult, Irish, constitute an experience are processed in distributed brain Moscovitch, & Rugg, 2019; Strikwerda-Brown, Mothakunnel, regions, and the evidence suggests that the medial temporal Hodges, Piguet, & Irish, 2019; Irish & Piguet, 2013; Binder lobe (in particular, the hippocampus) is involved in the inte- & Desai, 2011; Greenberg & Verfaellie, 2010). gration of memory details to support the conscious represen- The fact that episodic memories are not literal reproduc- tation of past events (Reagh & Ranganath, 2018; Horner & tions of the past is notably highlighted in recent studies Doeller, 2017; Moscovitch, Cabeza, Winocur, & Nadel, 2016; showing that the unfolding of events is temporally com- Rugg & Vilberg, 2013; Davachi, 2006; Schacter, Norman, & pressed when remembering: Events are mentally replayed Koutstaal, 1998). Of particular interest here are studies that at a faster rate than the actual event duration (Jeunehomme shed light on the temporal structure of episodic memories, &D’Argembeau, 2019; Michelmann, Staresina, Bowman, & revealing how the unfolding of events is represented. Hanslmayr, 2019; Faber & Gennari, 2015). To investigate Memories for real-life events are typically composed of how this compression mechanism operates, Jeunehomme a succession of moments or slices of prior experience that et al. (2018) capitalized on wearable camera technology are organized in chronological order (Jeunehomme, Folville, to compare the temporal structure of episodic memories Stawarczyk, Van der Linden, & D’Argembeau, 2018; Radvansky, with the actual content and duration of past events. It was Copeland, & Zwaan, 2005; Anderson & Conway, 1993). found that memories often included temporal discontinu- Cognitive and neural evidence indicates that these memory ities in the representation of the unfolding of events: Some units are formed as a result of the segmentation of experi- portions of events were not represented during mental ence into discrete events and subevents (for reviews, see replay (see also Jeunehomme & D’Argembeau, 2019). A Clewett, DuBrow, & Davachi, 2019; Brunec, Moscovitch, & recent study that tracked memory replay of video clips using Barense, 2018; Radvansky & Zacks, 2017). Dynamic changes magnetoencephalography provided further evidence for in various dimensions of ongoing experience (e.g., loca- this time-compressed replay mechanism: Some video frag- tions, characters, objects, and goals) determine the percep- ments were replayed at the same speed as perception, tion of event boundaries (Zacks, Speer, Swallow, Braver, & whereas other fragments were skipped, such that mental Reynolds, 2007), which structure the integration and sepa- replay was overall faster than perception (Michelmann ration of information into meaningful memory components et al., 2019). The global rate of episodic memory compres- (Clewett et al., 2019; Radvansky & Zacks, 2017). A recent sion is not constant but varies across events and depends in fMRI study provided compelling evidence that event seg- part on the grain size of event segmentation (Jeunehomme mentation processes occur at multiple timescales through- &D’Argembeau, 2020). out the cortical hierarchy, beginning with short segments Overall, the evidence suggests that episodic memory re- in primary sensory regions and building into event models tains moments or slices of prior experience in chronological in the posteromedial cortex and angular gyrus, with the sequences that represent the unfolding of events. The tem- latter corresponding to a larger extent to the segments poral structure of memories depends on cortico-hippocampal identified by human observers (Baldassano et al., 2017). mechanisms that segment and store events in discrete chunks Event boundaries in higher-level areas triggered the hip- of experience. The resulting memories are not literal records pocampus to encode the current situation model into epi- of experience and often include temporal discontinuities, sodic memory, which was later reinstated during memory such that the unfolding of events is represented in a time- retrieval (see also Ben-Yakov & Henson, 2018). These and compressed form. related findings suggest that episodic memories are struc- tured by the interplay of the hippocampus and cortical regions that segment ongoing experience into meaningful Autobiographical Knowledge units; remembering then involves the reinstatement of a specific event