Deficits in episodic memory and mental time travel in patients with post-traumatic stress disorder

https://doi.org/10.1016/j.pnpbp.2017.12.014Get rights and content

Highlights

  • PTSD patients show impairments in episodic memory formation and mental time travel.

  • Impairments led to difficulties in utilizing past information to solve problems.

  • Deficits correlated with stress and depression levels.

  • Implications for current treatment options are being discussed.

Abstract

Post-traumatic stress disorder (PTSD) is characterized by impairments in mnestic functions, especially in the domain of episodic memory. These alterations might affect different aspects of episodic memory functioning. Here we tested PTSD patients and healthy controls (matched for age, sex and education) in a newly developed virtual reality episodic memory test (VR-EMT), a test for mental time travel, episodic future thinking, and prospective memory (M3xT). In a cross-validation experiment, their performance was further evaluated in the Rivermead Behavioral Memory Test (RBMT). PTSD patients demonstrated impairments in episodic memory formation and mental time travel and showed difficulties in utilizing information from episodic memory to solve problems. Diminished attention and concentration in PTSD did not account for performance deficits in these tasks but higher levels of negative arousal were found in PTSD patients. Furthermore, performance in the VR-EMT and RBMT in PTSD patients correlated negatively with self-reported measures of stress and depression. Our results suggest that deficits in episodic memory formation and mental time travel in PTSD lead to difficulties in utilizing the content of episodic memories for solving problems in the present or to plan future behavior. Clinical implications of these findings and suggestions for cognitive-behavioral treatment of PTSD are discussed.

Introduction

The episodic memory system allows us to encode specific autobiographical information of events that we have experienced in terms of “what happened,” “where it happened,” and “when it happened” (Dere et al., 2010, Pause et al., 2013, Zlomuzica et al., 2014). Episodic memories also contain perceptions, thoughts, emotions, and feelings we had during that experience. The concept of episodic memory has emerged as a central framework for examining the psychological and neurobiological processes that contribute to the development of PTSD. Current psychological treatment approaches of PTSD such as the (narrative) exposure therapy have revolved around the phenomena related to episodic memory in PTSD (Ehlers and Clark, 2000). Thus, a better understanding of aberrant episodic memory dysfunctions in the context of PTSD is important for both, the etiology and therapeutic management of this highly devastating disorder.

The idea that intrusions and flashbacks that are associated with PTSD might be a consequence of an undamped activation of a pathological episodic memory for the trauma experience has received considerable empirical support (Brewin, 2014, Isaac et al., 2006, Moradi et al., 2008). Similar to other emotionally relevant episodic memories, trauma-related memories are highly vivid and can be activated by either trauma-related stimuli or “spontaneously” due to retrieval-cue generalization leading to the patient's experience of re-living the traumatic episode (Brewin, 2015, Tulving, 2001, Tulving, 2002).

Although there is ample literature available that indicates episodic memory dysfunction in PTSD patients (Brewin, 2014, Dere et al., 2010, Isaac et al., 2006, Moradi et al., 2008) these findings are predominantly based on studies using tasks which do not necessarily capture the whole complexity of the episodic memory concept (Brewin et al., 2007, Isaac et al., 2006, Pause et al., 2010, Pause et al., 2013, Zlomuzica et al., 2014).

Apart from the remembrance of past experiences, the episodic memory concept involves the ability to perform mental time travel (MTT), to execute episodic future thinking and to establish prospective memories (Blix and Brennen, 2011, Breeden et al., 2016, Brown et al., 2014, Suddendorf, 2013, Suddendorf and Corballis, 1997). MTT is defined as the ability to recollect past events from episodic memory (MTT into the past) and to anticipate or imagine events in the future (MTT into the future). From a biological perspective, MTT seems to have evolved to serve a) the optimization of decision-making processes, b) efficient problem solving, c) the preparation for future needs, and d) the formation of intentions to perform actions at a specific time point in the future (Breeden et al., 2016). It is evident that patients with impaired MTT function would encounter problems in their social and professional functioning. Indeed, there is evidence that PTSD patients show difficulties in planning and structuring everyday activities (Mehnert et al., 2010, Scrignaro et al., 2011) and exhibit compromised social problem-solving abilities (Reich et al., 2015). However, it is unclear whether these difficulties can be attributed to impairments in MTT. Furthermore, very little work has been conducted to examine the integrity and functional significance of MTT, episodic future thinking and prospective memory in the context of PTSD (but see Kleim et al., 2014). Finally, the successful retrieval and use of specific personal experiences as a clue to solve anticipated future problems represents a central element of cognitive-behavioral treatment approaches for PTSD (Zlomuzica et al., 2014).

In order to examine these phenomena we developed a specific test for the utilization of episodic memories for solving problems, in the present and future, respectively. We used a VR environment to measure the ability to generate integrated memory for “what happened, where, and when” (Binder et al., 2015, Kinugawa et al., 2013, Pause et al., 2010, Pause et al., 2013, Zlomuzica et al., 2015). We tested PTSD patients and healthy controls in this VR-based episodic memory task as well as a newly developed clinical test for MTT, episodic future thinking, and prospective memory. The virtual reality episodic memory test (What-Where-When WWW Task) is based on the rationale of the episodic-like memory task we developed for rodents (e.g. Dere et al., 2005a, Dere et al., 2005b, Kart-Teke et al., 2006; Zlomuzica et al., 2007; reviewed in Binder et al., 2015), and was adapted to humans for computer-based testing (Kinugawa et al., 2013, Pause et al., 2010, Weber et al., 2014) and VR-based assessment (Zlomuzica et al., 2015). Interestingly, VR-based techniques have been increasingly used in the treatment of PTSD (Botella et al., 2015). Hence, investigating to which extent patients with PTSD and healthy subjects differ in their ability to perceive and process complex information in VR and disambiguate different contexts is of valuable interest.

In an attempt to overcome some of the previous methodological weaknesses when assessing mnestic functions in PTSD (see Isaac et al., 2006), age, education and sex-matched healthy participants were used as controls. A complementary neuropsychological examination of attention and everyday memory capacity (Moradi et al., 1999) was also conducted.

Section snippets

Participants

Twenty-one participants who fulfilled DSM-IV criteria for PTSD (4 males, 17 females) and 21 healthy controls (4 males, 17 females) without a psychiatric diagnosis participated in this study. The presence of an Axis-I diagnosis was determined for all participants by means of the Diagnostic Interview for Mental Disorders-short version (Mini-DIPS, Margraf, 1994). PTSD patients were recruited via board advertisements in two specialist treatment centers. Exclusion criteria for PTSD patients were: a)

Sample characteristics

As shown in Table 1, groups were matched in terms of age, gender distribution or level of education. As expected, PTSD patients experienced significantly more trauma events (MPTSD = 3.9 [SD = 2.1], Mcontrols = 0.7 [SD = 0.9], F(1,40) = 41.41; p < 0.001) and reported more repeated traumas than healthy controls (N = 16 in the PTSD group versus N = 2 in the control sample). The PTSD group also showed higher scores of intrusion, avoidance and arousal symptoms obtained with the IES (ps < 0.001) and PDS questionnaire (

Discussion

In the present study, we used a novel VR-based approach to investigate episodic memory formation and MTT in patients with PTSD. Compared to healthy controls, PTSD patients exhibited deficits in remembering item and temporal information both in the episodic memory formation and MTT tests. Consequently, PTSD patients showed impairments in their capability to employ information from episodic memory to solve current or future problems. This is in line with a recent report (using autobiographical

Conclusions

In sum, our findings suggest that PTSD patients are impaired in the capacity to establish and utilize episodic memories. Furthermore, the PTSD patients showed deficits in MTT, which might account for impaired social and professional functioning. We suggest that cognitive behavior therapy in PTSD should include interventions that train attention and working memory and refine the ability to utilize episodic memories to solve problems. Another important outcome of cognitive behavior therapy in

Acknowledgements

This work was supported by grant ZL 59/2-1 and ZL 59/2-2 of the Deutsche Forschungsgemeinschaft (DFG) to AZ and JM. MAdSS was supported by Heisenberg Fellowship SO 1032/5-1, and IN-SENS #607616. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors declare no conflict of interest.

References (78)

  • D. Hassabis et al.

    Deconstructing episodic memory with construction

    Trends Cogn. Sci.

    (2007)
  • J.P. Hayes et al.

    Reduced hippocampal and amygdala activity predicts memory distortions for trauma reminders in combat-related PTSD

    J. Psychiatr. Res.

    (2011)
  • C.L. Isaac et al.

    Is posttraumatic stress disorder associated with specific deficits in episodic memory?

    Clin. Psychol. Rev.

    (2006)
  • A. Karl et al.

    A meta-analysis of structural brain abnormalities in PTSD

    Neurosci. Biobehav. Rev.

    (2006)
  • E. Kart-Teke et al.

    Wistar rats show episodic-like memory for unique experiences

    Neurobiol. Learn. Mem.

    (2006)
  • Y.R. Li et al.

    Cognitive control processes underlying time-based prospective memory impairment in individuals with high depressive symptomatology

    Acta Psychol.

    (2014)
  • A. Miyake et al.

    The unity and diversity of executive functions and their contributions to complex "Frontal Lobe" tasks: a latent variable analysis

    Cogn. Psychol.

    (2000)
  • K.A. Moores et al.

    Abnormal recruitment of working memory updating networks during maintenance of trauma-neutral information in post-traumatic stress disorder

    Psychiatry Res.

    (2008)
  • A.R. Moradi et al.

    Specificity of episodic and semantic aspects of autobiographical memory in relation to symptoms of posttraumatic stress disorder (PTSD)

    Acta Psychol.

    (2008)
  • A.R. Moradi et al.

    A pilot randomized controlled trial investigating the efficacy of MEmory Specificity Training in improving symptoms of posttraumatic stress disorder

    Behav. Res. Ther.

    (2014)
  • B.M. Pause et al.

    Induction and measurement of episodic memories in healthy adults

    J. Neurosci. Methods

    (2010)
  • C.M. Reich et al.

    Social problem solving strategies and posttraumatic stress disorder in the aftermath of intimate partner violence

    J. Anxiety Disord.

    (2015)
  • D. Schoofs et al.

    Psychosocial stress induces working memory impairments in an n-back paradigm

    Psychoneuroendocrinology

    (2008)
  • T. Suddendorf

    Mental time travel: continuities and discontinuities

    Trends Cogn. Sci.

    (2013)
  • K. Wingenfeld et al.

    Cortisol has enhancing, rather than impairing effects on memory retrieval in women with PTSD

    Psychoneuroendocrinology

    (2012)
  • N.R. Arnold et al.

    Is prospective memory related to depression and anxiety? A hierarchical MPT modelling approach

    Memory

    (2015)
  • T. Bartsch et al.

    CA1 neurons in the human hippocampus are critical for autobiographical memory, mental time travel, and autonoetic consciousness

    Proc. Natl. Acad. Sci. U. S. A.

    (2011)
  • K. Beckers et al.

    Deutsche Version des Rivermead Behavioral Memory Test

    (1992)
  • I. Blix et al.

    Mental time travel after trauma: the specificity and temporal distribution of autobiographical memories and future-directed thoughts

    Memory

    (2011)
  • C. Botella et al.

    Virtual reality exposure-based therapy for the treatment of post-traumatic stress disorder: a review of its efficacy, the adequacy of the treatment protocol, and its acceptability

    Neuropsychiatr. Dis. Treat.

    (2015)
  • P. Breeden et al.

    The mental time travel continuum: on the architecture, capacity, versatility and extension of the mental bridge into the past and future

    Rev. Neurosci.

    (2016, Jun 1)
  • C.R. Brewin

    Episodic memory, perceptual memory, and their interaction: foundations for a theory of posttraumatic stress disorder

    Psychol. Bull.

    (2014)
  • C.R. Brewin

    Re-experiencing traumatic events in PTSD: new avenues in research on intrusive memories and flashbacks

    Eur. J. Psychotraumatol.

    (2015)
  • C.R. Brewin et al.

    Memory for emotionally neutral information in posttraumatic stress disorder: a meta-analytic investigation

    J. Abnorm. Psychol.

    (2007)
  • R. Brickenkamp

    Test d2. Aufmerksamkeits-Belastungs-Test

    (1994)
  • A.D. Brown et al.

    Episodic and semantic components of autobiographical memories and imagined future events in post-traumatic stress disorder

    Memory

    (2014)
  • S. Chalavi et al.

    Abnormal hippocampal morphology in dissociative identity disorder and post-traumatic stress disorder correlates with childhood trauma and dissociative symptoms

    Hum. Brain Mapp.

    (2015)
  • E. Dere et al.

    Fellow travellers: working memory and mental time travel in rodents

    Behav. Brain Res.

    (2017 Mar 19)
  • A. Ehlers et al.

    Deutschsprachige Übersetzung der Posttraumatic Diagnostic Scale von Foa (1995)

    (1996)
  • Cited by (0)

    View full text