Mental Time Travel in Post-Traumatic Stress Disorder: Current Gaps and Future Directions

Exposure to potentially traumatic events is a common experience throughout the world. Although many people typically do not experience mental health issues following such events, a significant minority of individuals will develop a psychiatric disorder. Post-traumatic stress disorder (PTSD) is the most frequent negative mental health outcome of traumatic events (e.g., Hoge et al., 2004) and is associated with considerable functional impairment (e.g., Silverstein et al., 2018). Although recent decades have been marked by important advances in PTSD treatments, a subset of patients still does not respond to first-line pharmacotherapy or extant evidence-based psychotherapies (Lancaster et al., 2016), underscoring the need for new treatment development. Elucidation of the neurocognitive processes underlying the pathogenesis and maintenance of PTSD may represent a critical step toward developing more optimal treatments. Among the neurocognitive processes that have been shown to be altered in individuals with PTSD are autobiographical memories (AMs), a class of self-referential, long-term memories comprised of both episodic and semantic details. AMs may be retrieved deliberately (voluntarily) or unexpectedly (involuntarily). AMs are critical for wellbeing and functioning, as they are implicated in numerous clinically-relevant processes, including problem-solving; the creation of self-concept; and the formation and maintenance of social-bonds (Bluck et al., 2005)— all processes that are dysregulated in PTSD (e.g., Lord et al., 2020). Given the integral role of AM in PTSD, it is unsurprising that numerous studies have examined AM alterations related to this disorder. One such alteration that has received considerable attention is known as the overgeneral memory (OGM), a phenomenon in which individuals demonstrate difficulty recalling discreet, discontinuous autobiographical events. That is, an AM marked by reduced specificity, which may take place repeatedly or over the course of several days. OGM has been shown to be a predictor of posttraumatic symptoms (Moore and Zoellner, 2007) and an effective target for therapy. Indeed, AM specificity training has been shown to achieve PTSD symptom reduction in half the number of sessions required using standard cognitive processing therapy treatments (e.g., Maxwell, 2016). In addition to OGM, other AM alterations have been implicated in PTSD, including changes in the emotional intensity associated with the recollection of a particular type of memory (e.g., Rubin, 2010; Niziurski et al., 2017); variations in the availability and coherence of different memory types (e.g., Rubin et al., 2008); increases in intrusive, emotionally-laden memories and prospections (e.g., Berntsen and Rubin, 2015); and greater centrality of traumatic experiences to self-identity (e.g., Berntsen and Rubin, 2006). An important function of the episodic memory system is the construction of prospective memories, also known as episodic future-thinking (EFT). Through a phenomenon known as mental time travel (MTT; Tulving, 1985), we are not only able to experience ourselves in the past, but we are also able to experience ourselves in the future. Building upon MTT theory, Schacter and Addis (2007) put forth the Constructive Episodic Simulation Hypothesis, which posits that the cognitive processes of remembering the past and thinking about the future rely on similar underlying mechanisms, and both draw upon information stored in episodic memory. Episodic memory and EFT operate by binding the context of an experience to the experience itself for the construction and reconstruction of scenes (Schacter and Addis, 2007). Importantly, this theory suggests that EFT relies on the flexible recombination of information drawn from past experiences to construct novel future scenarios. While this scenario construction can be adaptive for processes such as planning and goal-attainment, clinically-relevant biases in AM may contribute to the onset and maintenance of various disorders, including PTSD (Hallford et al., 2018). MTT is thought to serve several critical functions, including decision-making (Aupperle et al., 2011), problem-solving (Suddendorf and Corballis, 1997), and goal-setting and implementation (Breeden et al., 2016). However, further research is needed to elucidate the relationship between PTSD and alterations in MTT. While the examination of the AM component of MTT is ubiquitous in PTSD research, there is a relative dearth of information on the future thinking component of this process (however, see, e.g., Blix and Brennen, 2011; Zlomuzica et al., 2017). In line with the Constructive Episodic Simulation Hypothesis, these studies show that putative AM alterations associated with PTSD are also found in the content and characteristics of future imaginings among such individuals. The relevance of EFT and the construction of a future self in relation to psychopathology converges with a growing body of research demonstrating that prospection related to the self is associated with a wide range of cognitive, affective, and behavioral processes. For instance, we tend to evaluate ourselves in the present by comparing ourselves to the future self we hope to achieve (Bak, 2015). Relatedly, neurocognitive findings consistently link PTSD with negative self-appraisals (Engelbrecht and Jobson, 2020). The goal of the current article is to highlight the importance of MTT in PTSD. Although changes in MTT may reflect a mechanism underlying several mental health disorders, both the study and the treatment of PTSD have long focused on potential changes in the characteristics and content in AM. Given this history and the long-standing debates related to the role of memory in this disorder, as well as the targeted use of AM in treatments (e.g., Brewin, 2011), this commentary will be limited to PTSD. However, alterations in AM are by no means constrained to PTSD, and certain MTT changes may reflect transdiagnostic processes (e.g., Kellogg et al., 2020). With this opinion piece, we will (1) briefly review and consider the extant literature on memory and future-thinking in PTSD; (2) elucidate gaps in PTSD MTT research; (3) discuss future directions for PTSD MTT research. It is our hope that this piece will shed light on an understudied cognitive process and underscore areas where additional research may broaden our understanding of PTSD pathogenesis and eventually inform the development of future PTSD treatments.