Is Trauma Memory Special? Trauma Narrative Fragmentation in PTSD: Effects of Treatment and Response

Self-Improvising Memory: A Perspective on Memories as Agential, Dynamically Reinterpreting Cognitive Glue

Many studies on memory emphasize the material substrate and mechanisms by which data can be stored and reliably read out. Here, I focus on complementary aspects: the need for agents to dynamically reinterpret and modify memories to suit their ever-changing selves and environment. Using examples from developmental biology, evolution, and synthetic bioengineering, in addition to neuroscience, I propose that a perspective on memory as preserving salience, not fidelity, is applicable to many phenomena on scales from cells to societies. Continuous commitment to creative, adaptive confabulation, from the molecular to the behavioral levels, is the answer to the persistence paradox as it applies to individuals and whole lineages. I also speculate that a substrate-independent, processual view of life and mind suggests that memories, as patterns in the excitable medium of cognitive systems, could be seen as active agents in the sense-making process. I explore a view of life as a diverse set of embodied perspectives-nested agents who interpret each other's and their own past messages and actions as best as they can (polycomputation). This synthesis suggests unifying symmetries across scales and disciplines, which is of relevance to research programs in Diverse Intelligence and the engineering of novel embodied minds.

Integrating and fragmenting memories under stress and alcohol

Stress can powerfully influence the way we form memories, particularly the extent to which they are integrated or situated within an underlying spatiotemporal and broader knowledge architecture. These different representations in turn have significant consequences for the way we use these memories to guide later behavior. Puzzlingly, although stress has historically been argued to promote fragmentation, leading to disjoint memory representations, more recent work suggests that stress can also facilitate memory binding and integration. Understanding the circumstances under which stress fosters integration will be key to resolving this discrepancy and unpacking the mechanisms by which stress can shape later behavior. Here, we examine memory integration at multiple levels: linking together the content of an individual experience, threading associations between related but distinct events, and binding an experience into a pre-existing schema or sense of causal structure. We discuss neural and cognitive mechanisms underlying each form of integration as well as findings regarding how stress, aversive learning, and negative affect can modulate each. In this analysis, we uncover that stress can indeed promote each level of integration. We also show how memory integration may apply to understanding effects of alcohol, highlighting extant clinical and preclinical findings and opportunities for further investigation. Finally, we consider the implications of integration and fragmentation for later memory-guided behavior, and the importance of understanding which type of memory representation is potentiated in order to design appropriate interventions.

Predicting DSM-5 PTSD symptomatology 6 months to 2 years after burn: The role of early psychological risk factors

BACKGROUND

Major burn injuries may have long-term mental health consequences, such as posttraumatic stress disorder (PTSD). This study extended prior work to investigate DSM-5 PTSD symptoms at 6 months, 1 year, and 2 years post-burn as well as the contribution of two sets of early psychological risk factors to DSM-5 PTSD symptoms: Established PTSD risk factors (prior adjustment problems, past trauma, perception of life threat, peritraumatic emotions and dissociation) and theory-derived cognitive factors (negative appraisals of the trauma and its sequelae, memory disorganization, trauma-related rumination, and thought suppression).

METHOD

The current study recruited a sample of 118 adult burn patients (75.4% men, mean age 41.8, mean TBSA 18.3%) consecutively admitted to a large regional burn center in Northern Taiwan, who were assessed at 6, 12, and 24 months following their burn injury.

RESULTS

A total of 11.0%, 5.9%, and 7.6% met probable DSM-5 PTSD at 6 months, 1 year, and 2 years post-burn, respectively. The rates rose to 15.3%, 10.2%, and 11.0% using the cutoff method. After controlling for covariates, the regression model with theory-derived cognitive factors explained an additional significant 15.9%, 17.2%, and 17.7% of the variance in DSM-5 PTSD symptoms at 6 months, 1 year, and 2 years post-burn, respectively. In contrast, the regression model with established PTSD risk factors explained an additional significant 7.2%, 14.4%, and 10.5% of the variance in DSM-5 PTSD symptoms at 6 months, 1 year, and 2 years post-burn, respectively. Of all predictors, negative appraisals of intrusions was consistently and strongly predictive of DSM-5 PTSD symptomatology post-burn across time, followed by prior depression.

CONCLUSIONS

The results underscore the role of early cognitive risk factors in the development and persistence of DSM-5 PTSD symptomatology following burn injury.

Neural patterns differentiate traumatic from sad autobiographical memories in PTSD

For people with post-traumatic stress disorder (PTSD), recall of traumatic memories often displays as intrusions that differ profoundly from processing of 'regular' negative memories. These mnemonic features fueled theories speculating a unique cognitive state linked with traumatic memories. Yet, to date, little empirical evidence supports this view. Here we examined neural activity of patients with PTSD who were listening to narratives depicting their own memories. An intersubject representational similarity analysis of cross-subject semantic content and neural patterns revealed a differentiation in hippocampal representation by narrative type: semantically similar, sad autobiographical memories elicited similar neural representations across participants. By contrast, within the same individuals, semantically similar trauma memories were not represented similarly. Furthermore, we were able to decode memory type from hippocampal multivoxel patterns. Finally, individual symptom severity modulated semantic representation of the traumatic narratives in the posterior cingulate cortex. Taken together, these findings suggest that traumatic memories are an alternative cognitive entity that deviates from memory per se.

Changes in cognitive processes and coping strategies precede changes in symptoms during cognitive therapy for posttraumatic stress disorder

Theories of posttraumatic stress disorder (PTSD) highlight the role of cognitive and behavioral factors in its development, maintenance, and treatment. This study investigated the relationship between changes in factors specified in Ehlers and Clark's (2000) model of PTSD and PTSD symptom change in 217 patients with PTSD who were treated with cognitive therapy for PTSD (CT-PTSD) in routine clinical care. Bivariate latent change score models (LCSM) of session-by-session changes in self-report measures showed that changes in PTSD symptoms were preceded by changes in negative appraisals, flashback characteristics of unwanted memories, safety behaviours, and unhelpful responses to intrusions, but not vice versa. For changes in trauma memory disorganization and PTSD symptoms we found a bidirectional association. This study provides evidence that cognitive and behavioral processes proposed in theoretical models of PTSD play a key role in driving symptom improvement during CT-PTSD.

The Return of Repression? Evidence From Cognitive Psychology

The controversy over alleged repressed and recovered memories of childhood sexual abuse (CSA) was among the most contentious ever to embroil psychology and psychiatry. Adapting paradigms from cognitive psychology, my research group tested hypotheses pertinent to repressed memory and false memory interpretations of recovered memories. We tested adults who: (1) report recovering memories of CSA after not having thought about their abuse for years; (2) report never having forgotten their CSA; (3) believe they harbor "repressed" memories of CSA; and (4) deny having been sexually abused. We tested hypotheses about mechanisms that might figure in the inability to recall memories of one's abuse and those that might render one susceptible to developing false memories of abuse. The purpose of this article is to summarize this work. Finally, I draw on the work of Lionel Penrose to speculate about why the popularity of the concept of repressed memories of trauma-or its synonym, dissociative amnesia for trauma-may be rising today.

The dilemma of trauma-focused therapy: effects of imagery rescripting on voluntary memory

Trauma-focused imagery-based interventions are suspected to alter or even distort declarative voluntary memory of a traumatic event, especially if they involve the active modification of imagery, e.g., as used in imagery rescripting (ImRs). However, systematic research is lacking so far. To investigate whether ImRs modifies voluntary memory of a standardized autobiographical aversive event (Trier Social Stress Test) (Session 1), healthy participants (N = 100) were randomly assigned to either an intervention condition receiving one session of ImRs or to a no-intervention control condition (NIC) (Session 2). Voluntary memory was examined using a free recall (Sessions 2 and 3) and a cued recall (Sessions 3 and 4). Although voluntary memory tended to deteriorate over time, contrary to expectations, this effect was not associated with ImRs. Remarkably, the number of correct details in free recall even improved in ImRs but not in NIC. This challenges the view that ImRs alters voluntary memory.

Mitochondrial Impairment: A Common Motif in Neuropsychiatric Presentation? The Link to the Tryptophan-Kynurenine Metabolic System

Nearly half a century has passed since the discovery of cytoplasmic inheritance of human chloramphenicol resistance. The inheritance was then revealed to take place maternally by mitochondrial DNA (mtDNA). Later, a number of mutations in mtDNA were identified as a cause of severe inheritable metabolic diseases with neurological manifestation, and the impairment of mitochondrial functions has been probed in the pathogenesis of a wide range of illnesses including neurodegenerative diseases. Recently, a growing number of preclinical studies have revealed that animal behaviors are influenced by the impairment of mitochondrial functions and possibly by the loss of mitochondrial stress resilience. Indeed, as high as 54% of patients with one of the most common primary mitochondrial diseases, mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome, present psychiatric symptoms including cognitive impairment, mood disorder, anxiety, and psychosis. Mitochondria are multifunctional organelles which produce cellular energy and play a major role in other cellular functions including homeostasis, cellular signaling, and gene expression, among others. Mitochondrial functions are observed to be compromised and to become less resilient under continuous stress. Meanwhile, stress and inflammation have been linked to the activation of the tryptophan (Trp)-kynurenine (KYN) metabolic system, which observably contributes to the development of pathological conditions including neurological and psychiatric disorders. This review discusses the functions of mitochondria and the Trp-KYN system, the interaction of the Trp-KYN system with mitochondria, and the current understanding of the involvement of mitochondria and the Trp-KYN system in preclinical and clinical studies of major neurological and psychiatric diseases.

Randomized Trial on the Effects of a Group EMDR Intervention on Narrative Complexity and Specificity of Autobiographical Memories: A Path Analytic and Supervised Machine-Learning Study

Narratives of autobiographical memories may be impaired by adverse childhood experiences, generating narrative fragmentation and increased levels of perceived distress. Eye movement desensitization and reprocessing (EMDR) proved to be an effective treatment to overcome traumatic experiences and to promote coherent autobiographical narratives. However, the specific mechanisms by which EMDR promotes narrative coherence remains largely unknown. We conducted a randomized controlled pilot trial (ClinicalTrials.gov Identifier NCT05319002) in a non-clinical sample of 27 children recruited in a primary school. Participants were randomly assigned to the experimental and control groups. The experimental group underwent a three-week group EMDR intervention. Subjective unit of distress (SUD), validity of cognition (VoC), classification of autobiographical memories, narrative complexity and specificity were assessed before and after the group EMDR intervention. The group EMDR intervention was able to improve SUD and VoC scales, narrative complexity and specificity, and promoted the classification of autobiographical memories as relational. The path analysis showed that SUD was able to predict VoC and narrative specificity, which, in turn, was able to predict both narrative complexity and the classification of autobiographical memories as relational. Machine-learning analysis showed that random tree classifier outperformed all other models by achieving a 93.33% accuracy. Clinical implications are discussed.

Imaginal exposure processing during Concurrent Treatment of PTSD and Substance Use Disorders using Prolonged Exposure (COPE) therapy: Examination of linguistic markers of cohesiveness

Concurrent Treatment of PTSD and Substance Use Disorders Using Prolonged Exposure (COPE) is an integrated, evidence-based treatment that results in significant reductions in posttraumatic stress disorder (PTSD) and substance use disorder (SUD) severity. Emotional processing theory suggests that successful prolonged exposure-based treatments should result in more cohesive trauma narratives due to better integration and organization of trauma memory into cognitive conceptualizations of fear. Therefore, we hypothesized that language used by patients would become more cohesive over time and increased language cohesion would be related to larger reductions in PTSD and SUD outcomes. Broadly, language cohesion refers to several linguistic devices that help establish and cohere meaning throughout spoken and written discourse (e.g., increased use of transition words like "and," "then," and "but"). This was the first known study to examine changes in language related to both PTSD and SUD severity during COPE treatment. The sample included 28 military veterans with current comorbid PTSD/SUD enrolled in a larger COPE study. A text analysis program, Coh-Metrix, was used to analyze language cohesiveness. No language cohesion variables significantly changed over time. Narrativity levels significantly moderated change in PTSD outcomes, R β 2 $R_\beta ^2\;$ = 0.11. Adversative connectives significantly moderated change in SUD outcomes, R β 2 $R_\beta ^2\;$ = 0.26. The findings illuminate potential processes underlying successful COPE treatment. Less use of language conveying a narrative and more use of contrast-indicative words (e.g., but, whereas) was associated with larger reductions in PTSD and SUD outcomes during treatment. These results contribute to the extant literature on associations between trauma exposure, language, and emotional processing.

Narrating life in the military: Links between veterans' narrative processing of service experiences and their posttraumatic stress symptoms and well-being

Military veterans frequently experience traumatic, highly stressful events; thus, it is especially important for them to find positive ways of making meaning from these experiences. The present study used the methods of narrative personality psychology to investigate the associations between veterans' narrative processing of highly stressful and significant events from their military service and postdischarge functioning, including posttraumatic stress symptoms (PTSS). United States military veterans (N = 154; M age = 64.28 years, 86.4% men, 57.8% deployed) completed an online survey in which they wrote narratives about one "highly stressful" and one "key scene" military service memory and completed questionnaires to assess PTSS, symptoms of depression and anxiety, functional impairment, and well-being. Narratives were coded for personal growth from the experience, themes of agency and interpersonal communion, affective tone, and coherence. In the highly stressful narratives, small-to-moderate negative associations emerged between both growth and agency and PTSS, depression and anxiety, and functional impairment; growth was also modestly positively associated with well-being. In contrast, affective tone and communion were each only associated modestly with one outcome, and coherence with none, and narrative processing of the key scene narrative was not linked with any mental health outcomes. These findings suggest that (1) the theory and methods of narrative identity research are relevant for studying trauma narratives, and (2) veterans who narrate themselves as growing from and exerting control over their most stressful service experiences may achieve better mental health and day-to-day functioning.

Recounting coup as the recirculation of Indigenous vitality: A narrative alternative to historical trauma

Contemporary American Indians suffer from disproportionately high degrees of psychiatric distress. Mental health researchers and professionals, as well as American Indian community members, have consistently associated these disproportionate rates of distress with Indigenous historical experiences of European and Euro-American colonization. This emphasis on the impact of colonization and associated historical consciousness within tribal communities has occasioned increasingly widespread professional consideration of historical trauma among Indigenous peoples. In contrast to personal experiences of a traumatic nature, the discourse of Indigenous historical trauma (IHT) weds the concepts of "historical oppression" and "psychological trauma" to explain community-wide risk for adverse mental health outcomes originating from the depredations of past colonial subjugation through intergenerational transmission of vulnerability and risk. Long before the emergence of accounts of IHT, however, many American Indian communities prized a markedly different form of narrative: the coup tale. By way of illustration, I explore various historical functions of this speech genre by focusing on Aaniiih-Gros Ventre war narratives, including their role in conveying vitality or life. By virtue of their recognition and celebration of agency, mastery, and vitality, Aaniiih war stories functioned as the discursive antithesis of IHT. Through comparative consideration of the coup tale and the trauma narrative, I propose an alternative framework for cultivating Indigenous community "survivance" rather than vulnerability based on these divergent discursive practices.

Immune Influencers in Action: Metabolites and Enzymes of the Tryptophan-Kynurenine Metabolic Pathway

The tryptophan (TRP)-kynurenine (KYN) metabolic pathway is a main player of TRP metabolism through which more than 95% of TRP is catabolized. The pathway is activated by acute and chronic immune responses leading to a wide range of illnesses including cancer, immune diseases, neurodegenerative diseases and psychiatric disorders. The presence of positive feedback loops facilitates amplifying the immune responses vice versa. The TRP-KYN pathway synthesizes multifarious metabolites including oxidants, antioxidants, neurotoxins, neuroprotectants and immunomodulators. The immunomodulators are known to facilitate the immune system towards a tolerogenic state, resulting in chronic low-grade inflammation (LGI) that is commonly present in obesity, poor nutrition, exposer to chemicals or allergens, prodromal stage of various illnesses and chronic diseases. KYN, kynurenic acid, xanthurenic acid and cinnabarinic acid are aryl hydrocarbon receptor ligands that serve as immunomodulators. Furthermore, TRP-KYN pathway enzymes are known to be activated by the stress hormone cortisol and inflammatory cytokines, and genotypic variants were observed to contribute to inflammation and thus various diseases. The tryptophan 2,3-dioxygenase, the indoleamine 2,3-dioxygenases and the kynurenine-3-monooxygenase are main enzymes in the pathway. This review article discusses the TRP-KYN pathway with special emphasis on its interaction with the immune system and the tolerogenic shift towards chronic LGI and overviews the major symptoms, pro- and anti-inflammatory cytokines and toxic and protective KYNs to explore the linkage between chronic LGI, KYNs, and major psychiatric disorders, including depressive disorder, bipolar disorder, substance use disorder, post-traumatic stress disorder, schizophrenia and autism spectrum disorder.

Trauma and Coping Strategies in Police Officers: A Quantitative-Qualitative Pilot Study

Background. Because of their work, emergency workers, such as police officers (POs), are exposed to traumatic events on a daily basis. These experiences can have consequences in terms of physical and emotional stress. Primary attachment relationships affect the development of coping strategies for dealing with stressful events (primarily hyperactivating strategies in entangled adults and hypo-activating strategies in dismissing adults). In this study, we explored how POs describe the experience of traumatic accidents, the effects they reported and their coping strategies related to their attachment style. Methods. We used a quantitative-qualitative method. Thirty-nine POs were administered the Beck Depression Inventory, the Maslach Burnout Inventory and a semi-structured interview about traumatic events and reactions. Interviews were analyzed using Interpretative Phenomenological Analysis. Results. Traumatic events at work predominantly concerned aggressions, witnessing deaths, forced hospitalizations, and domestic violence involving children. POs with a responsible role were more likely than POs to use security-based strategies. Most POs narrated overactivation and deactivation strategies, which were associated with depressive symptoms, emotional exhaustion, and depersonalization. Conclusions. These results can be useful to improve trauma-informed interventions for POs based on their different attachment styles and coping strategies.

Are memories of sexual trauma fragmented?

Alarmingly high rates of sexual assault on campus have motivated American colleges and universities to take steps to address this serious problem. Yet university administrators have often felt ill-equipped to assess allegations of sexual assault. Unsurprisingly, they have sought the expertise of psychologists who can educate administrative staff about the complexities of traumatic memory. Dr. Rebecca Campbell is among the most influential figures teaching university administrators about sexual trauma and memory. The purpose of this article is to review research pertinent to her views on fragmentation of traumatic memories, and the possible roles of tonic immobility and alcohol consumption on how survivors of sexual assault recall their experience.

Examining relations of polytraumatization typologies with positive memory count and phenomenology

Background and Objectives: Most individuals experience multiple potentially traumatizing events (PTEs); hence, it is important to consider count and types of PTEs (polytraumatization) in relation to post-trauma health. Notably, no research has examined polytraumatization typologies in relation to positive memory count and phenomenology. We examined (1) latent subgroupings of individuals based on PTE endorsements; and (2) relation of the optimal latent class solution to positive memory count and phenomenology. Design: Participants were 203 trauma-exposed adults (Mage  = 35.40; 61.10% females); we used PTEs endorsed on the Life Events Checklist for DSM-5 as indicators for analyses. Results: Latent class analyses indicated a three-class solution differing in quantity and quality of PTE types: Low Experience, Predominant Interpersonal PTEs, and Predominant Non-Interpersonal PTEs. Further, more positive memories predicted membership in the Low Experience vs. other classes; greater sensory details of a positive memory predicted membership in the Low Experience vs. the Predominant Interpersonal PTEs Classes; and greater accessibility of a positive memory predicted membership in the Predominant Interpersonal PTEs vs. the Predominant Non-Interpersonal PTEs Classes. Conclusions: Results indicated three meaningful subgroups endorsing differing levels/types of PTEs; count, sensory details, and accessibility of positive memories, pending further investigation, may differentiate these subgroups.

Do positive memory characteristics relate to reckless behaviours? an exploratory study in a treatment-seeking traumatised sample

Reckless and self-destructive behaviours (RSDBs), common among traumatised individuals, are associated with negative health consequences. Gaining a stronger understanding of factors associated with an increased likelihood of RSDBs among traumatised individuals offers potential new avenues for research and treatment. Mounting evidence indicates relations between traumatic experiences and deficits/disturbances in characteristics of positive memories; however, relations between RSDBs and positive memory characteristics has been understudied. Using hierarchical multiple regression, we examined relations between positive memory characteristics (Memory Experiences Questionnaire-Short Form; MEQ-SF) and RSDBs, controlling for PTSD and depression severity, among a sample of treatment-seeking trauma-exposed individuals (N = 77; Mage = 33.96; 57.10% female). Results indicated that MEQ-SF subscales of Accessibility, Coherence, Emotional Intensity, and Sensory Details were significantly associated with engagement in RSDBs, above and beyond PTSD and depressive severity. Those who easily accessed emotionally evocative positive memories tended to engage in elevated RSDBs; those with less coherence and fewer sensory details in their positive memories were also more likely to engage in RSDBs. Theories related to emotion dysregulation and cognitive deficits may explain these obtained relations.

Changes in Traumatic Memories and Posttraumatic Cognitions Associate with PTSD Symptom Improvement in Treatment of Multiply Traumatized Children and Adolescents

Refinement, targeting, and better dissemination of trauma-focused therapies requires understanding their underlying mechanisms of change. Research on such mechanisms among multiply traumatized children and adolescents is scarce. We examined the role of improvements in problematic qualities of traumatic memories and maladaptive posttraumatic cognitions in PTSD symptom reduction, in a randomized, pragmatic trial of narrative exposure therapy vs. treatment as usual with 40 participants 9-17 years old (48% female, 75% refugee background) repeatedly exposed to war or family violence related trauma. Posttraumatic cognitions, quality of traumatic memories and PTSD symptoms were assessed by self-report before and after treatment. Improvements in both quality of traumatic memories (r _MI = .36) and posttraumatic cognitions (r _MI = .46) correlated with symptom reduction. However, improvement during treatment was only significant for quality of traumatic memories (F _MI(11,333.56) = 4.77), not for posttraumatic cognitions. We detected no difference in effects of narrative exposure therapy and treatment as usual on cognitions or memories. We tentatively suggest problematic, overly sensory and incoherent quality of traumatic memories may be a useful target in the treatment of PTSD symptoms among multiply traumatized children and adolescents. Changing maladaptive posttraumatic cognitions, though important, may be challenging among those with severe, repeated trauma.

Mechanisms of change in psychological interventions for posttraumatic stress symptoms: A systematic review with recommendations

Psychological interventions can alleviate posttraumatic stress symptoms (PTSS). However, further development of treatment approaches calls for understanding the mechanisms of change through which diverse interventions affect PTSS. We systematically searched the literature for controlled studies of mechanisms of change in psychological interventions for PTSS. We aimed to detect all empirically studied mechanisms and evaluate the level of evidence for their role in the alleviation of PTSS. We identified 34 studies, of which nine were among children. We found evidence for improvements in maladaptive posttraumatic cognitions as a general mechanism of change involved in diverse interventions, among both adults and children. We also found some preliminary evidence for increases in mindfulness as a mechanism of change in mindfulness- and spiritually-oriented interventions among adults. We found scant, mixed empirical evidence for other mechanisms of change. Notably, studies on changes in traumatic memories as a mechanism of change were lacking, despite clinical emphasis on their importance. A major limitation across reviewed studies was that most could not establish temporal order of changes in mechanisms and PTSS. Including thorough analyses of mechanisms of change beyond cognitions in all future trials and improving the reporting of findings would aid the development and implementation of even more effective interventions.

Retrieving and Modifying Traumatic Memories: Recent Research Relevant to Three Controversies

The purpose of this article is to review recent research that is relevant to three controversies concerning memory for trauma. First, we briefly review the debate about recovered memories of childhood sexual abuse, summarizing a third interpretation distinct from both the repression and false-memory accounts. Second, we address new findings related to claims that memories of trauma, especially in people with posttraumatic stress disorder, are especially fragmented and disorganized. Third, we discuss research designed to test whether eye movements in eye-movement desensitization and reprocessing therapy are effective.

An empirical review of potential mediators and mechanisms of prolonged exposure therapy

Prolonged exposure (PE) is an empirically-supported treatment for posttraumatic stress disorder (PTSD), but the precise mechanism(s) by which PE promotes symptom change are not well established. Understanding how PE works is critical to improving clinical outcomes, advancing dissemination efforts, and enhancing transdiagnostic models of psychopathology. However, mechanisms research conducted in clinical treatment settings is complex, and findings may be difficult to interpret without appropriate context. This is the first review of potential mechanisms of PE to provide such context, by rigorously evaluating empirical findings in line with essential criteria for effective research on mechanisms (or mediators). We begin by describing six putative mechanisms identified by emotional processing theory and contemporary models of fear extinction, before thoroughly reviewing empirical findings from clinical research on PE and similar PTSD treatments. We provide a detailed description of each study and mechanism test, as well as ratings of strength of evidence and quality of evaluation based on a novel rating scheme. We highlight variables with strong evidence (belief change and between-session habituation), intermediate evidence (inhibitory learning and emotional engagement), and minimal support (narrative organization and within-session habituation). After discussing limitations of the extant literature and this review, we summarize specific challenges for research on PE mechanisms and highlight directions for future study based on clinical and research implications.