Intrusive memories: A mechanistic signature for emotional memory persistence

Exploration of stress reactivity and fear conditioning on intrusive memory frequency in a conditioned-intrusion paradigm

BACKGROUND AND OBJECTIVES

The conditioned-intrusion paradigm was designed to provide insight into the relationship between fear conditioning and intrusive memory formation, which is relevant to understanding posttraumatic stress disorder symptoms and treatment. However, boundary conditions of this new paradigm have not been explored and it is currently not known whether findings from this work are valid in a clinical context.

METHODS

In the current study, we explored the relationship between stress reactivity to trauma film clips, usual exposure to violent media, renewal of fear conditioning using skin conductance as well as subjective ratings, and the effect of shock versus film clip during conditioning on the frequency of intrusive memories. An adapted fear conditioning paradigm using trauma clips as unconditional stimuli was used, and participants subsequently reported intrusive memories of the trauma clips.

RESULTS

Skin conductance responses to conditioned stimuli paired with shocks and film clips were significantly higher than conditioned stimuli paired with film clips alone. Subjective stress reactivity, previous exposure to violent media, and film valence rating were associated with the frequency of intrusive memories. No aspects of fear conditioning were associated with intrusive memories, and factor analysis suggested the fear conditioning and stress related to film clip viewing were mostly separate constructs. Similarly, content and triggers of intrusive memories were usually film-clip related rather than conditional stimulus related.

LIMITATIONS

We did not observe strong conditioning effects of the unconditional stimuli to conditional stimuli, which were shapes rather than high frequency stimuli such as faces.

CONCLUSIONS

These findings provide potential boundary conditions for this paradigm and suggest multiple ways in which the validity of the paradigm can be tested in the future.

Distress reactions and susceptibility to misinformation for an analogue trauma event

Accuracy of memory is critical in legal and clinical contexts. These contexts are often linked with high levels of emotional distress and social sources that can provide potentially distorting information about stressful events. This study investigated how distress was associated with susceptibility to misinformation about a trauma analogue event. We employed an experimental design whereby in Phase 1, participants (N = 243, aged 20-72, 122 females, 117 males, 4 gender diverse) watched a trauma film (car crash) and heard an audio summary that contained misinformation (misled items), true reminders (consistent items), and no reminders (control items) about the film. Participants rated their total distress, and symptoms of avoidance, intrusions, and hyperarousal, in response to the film. They then completed cued recall, recognition, and source memory tasks. One week later in Phase 2, participants (N = 199) completed the same measures again. Generalised linear mixed models were used. A significant misinformation effect was found, and importantly, participants with higher distress levels showed a smaller misinformation effect, owing to especially poor memory for consistent items compared to their less distressed counterparts. Distress was also associated with improved source memory for misled items. Avoidance of the film's reminders was associated with a smaller misinformation effect during immediate retrieval and a larger misinformation effect during delayed retrieval. Findings suggest that distress is associated with decreased susceptibility to misinformation in some cases, but also associated with poorer memory accuracy in general. Limitations are discussed, and the need for further research is highlighted.

Exploring the 'mood congruency' hypothesis of attention allocation - An eye-tracking study

BACKGROUND

The 'mood-congruency' hypothesis of attention allocation postulates that individuals' current emotional states affect their attention allocation, such that mood-congruent stimuli take precedence over non-congruent ones. This hypothesis has been further suggested as an underlying mechanism of biased attention allocation in depression.

METHODS

The present research explored the mood-congruency hypothesis using a novel video-based mood elicitation procedure (MEP) and an established eye-tracking attention allocation assessment task, elaborating prior research in the field. Specifically, in Study 1 (n = 91), a video-based MEP was developed and rigorously validated. In study 2 (n = 60), participants' attention allocation to sad and happy face stimuli, each presented separately alongside neutral faces, was assessed before and after the video-based MEP, with happiness induced in one group (n = 30) while inducing sadness in the other (n = 30).

RESULTS

In Study 1, the MEP yielded the intended modification of participants' current mood states (eliciting either sadness or happiness). Study 2 showed that while the MEP modified mood in the intended direction in both groups, replicating the results of Study 1, corresponding changes in attention allocation did not ensue in either group. A Bayesian analysis of pre-to-post mood elicitation changes in attention allocation supported this null finding. Moreover, results revealed an attention bias to happy faces across both groups and assessment points, suggestive of a trait-like positive bias in attention allocation among non-selected participants.

CONCLUSION

Current results provide no evidence supporting the mood-congruency hypothesis, which suggests that (biased) attention allocation may be better conceptualized as a depressive trait, rather than a mood-congruent state.

The aversiveness of intrusiveness: Evidence from involuntary musical imagery

OBJECTIVE

Intrusive thoughts are characterized by a sense of intrusiveness of foreign entry into cognition. While not always consisting of negative content, intrusive thoughts are almost solely investigated in that context. Involuntary Musical Imagery (INMI) offers a promising alternative, as it is a type of involuntary cognition that can be used to evaluate intrusiveness without negative content.

METHODS

In Study 1, 200 participants completed self-report questionnaires to assess several aspects of intrusiveness: meta-awareness, control, repetitiveness, frequency, and subjective experience of INMI. In Study 2, 203 participants completed self-report questionnaires to explore the clinical characteristics (depression, stress, anxiety, and rumination) which might mediate the connection between INMI frequency and INMI negative experience.

RESULTS

Study 1 revealed, through exploratory factor analysis, that intrusiveness shares variance with the negative experience of INMI but not with INMI frequency. In Study 2, ruminative thinking was found to mediate the relationship between frequent INMI and the negative experience of INMI.

CONCLUSION

These results suggest that INMI might be used to investigate intrusiveness in the lab without the potential confound of negative emotions. In addition, the results suggest that neither the content nor the frequency of intrusive thoughts can solely explain why these thoughts are aversive to some but not others. Ruminative style might be the missing link to explain how and why these intrusive thoughts become aversive and obsessive. In other words, we suggest that the cause for intrusiveness lies not in the thought or repetitiveness, but in the thinker.

Inhibitory control as possible risk and/or resilience factor for the development of trauma related symptoms-a study of the Utøya terror attack survivors

PTSD symptomatology is known to be associated with executive dysfunction. Inhibitory control is a core component of executive functioning, and inhibitory skills are essential both for adequate functioning in everyday life and important in situations following trauma. The aim of the present study was to examine the relationship between trauma exposure, inhibitory control and PTSD symptomatology in adolescent survivors of the terror attack at Utøya, Norway on the 22nd of July, 2011. In this cross-sectional case-control study, 20 trauma exposed adolescents and 20 healthy controls matched in age and gender were compared on a neuropsychological test of cognitive inhibition (Color-Word Interference Test) and a self-report measure of inhibition ability (BRIEF-A). Our analyses revealed that the trauma exposed group differed significantly on the self-reported measure of inhibitory control compared to the control group, but there were no differences between groups on the objective measures of cognitive inhibition. Follow-up analyses with subgroups in the trauma exposed group based on PTSD symptomatology (PTSD + and PTSD-) and the control group revealed that the PTSD- group showed significantly better results than both the PTSD + and the control group on the measures of inhibitory control. Moreover, the follow-up analyses showed that the PTSD + group showed significantly poorer results from the other two groups on the measures of inhibitory control and self-reported inhibition. We conclude that impaired inhibitory control, measured both objectively and by self-reported questionnaire, is related to PTSD symptomatology. Findings suggest that inhibitory dysfunctions may be a vulnerability factor for the development of PTSD symptomatology in trauma exposed adolescents, and thus it seems that the ability to exhibit inhibitory control could be a possible resilience factor to prevent the development of PTSD symptoms.

Can RNA Affect Memory Modulation? Implications for PTSD Understanding and Treatment

Memories are a central aspect of our lives, but the mechanisms underlying their formation, consolidation, retrieval, and extinction remain poorly understood. In this review, we explore the molecular mechanisms of memory modulation and investigate the effects of RNA on these processes. Specifically, we examine the effects of time and location on gene expression alterations. We then discuss the potential for harnessing these alterations to modulate memories, particularly fear memories, to alleviate post-traumatic stress disorder (PTSD) symptoms. The current state of research suggests that transcriptional changes play a major role in memory modulation and targeting them through microRNAs may hold promise as a novel approach for treating memory-related disorders such as PTSD.

A systematic review of the relationship between emotion and susceptibility to misinformation

Inaccurate memory reports can have serious consequences within forensic and clinical settings, where emotion and misinformation are two common sources of memory distortion. Many studies have investigated how these factors are related; does emotion protect memory or leave it more vulnerable to the distorting effects of misinformation? The findings remain diffused. Thus, the present review aimed to clarify the relationship between emotion and susceptibility to misinformation. 39 eligible studies were reviewed. Results varied according to the type and dimension of emotion measured. Level of arousal may be unrelated to susceptibility to misinformation when retrieval occurs without delay; studies including delayed retrieval were limited. Stimuli valence may be associated with increased susceptibility to peripheral misinformation but unrelated to other misinformation. The following results were reported by limited studies: short-term distress and moderate levels of stress may decrease susceptibility, while anger and greater cortisol response to stress may increase susceptibility to misinformation. Source memory may also be unaffected by emotion. The results have important potential implications for forensic and clinical practice, for example by highlighting the value of enquiring witnesses' source memory. Methodological recommendations for future studies are made.

A Naturalistic Paradigm to Investigate Postencoding Neural Activation Patterns in Relation to Subsequent Voluntary and Intrusive Recall of Distressing Events

BACKGROUND

While neuroimaging has provided insights into the formation of episodic memories in relation to voluntary memory recall, less is known about neural mechanisms that cause memories to occur involuntarily, for example, as intrusive memories of trauma. Here, we investigated brain activity shortly after viewing distressing events as a function of whether memories for those events later intruded involuntarily. The postencoding period is particularly important because it is a period when clinical interventions could be applied.

METHODS

A total of 32 healthy volunteers underwent functional magnetic resonance imaging while viewing distressing film clips, interspersed with 5 minutes of awake (postencoding) rest. Voluntary memories of the films were assessed using free recall and verbal and visual recognition tests after a week, while intrusive (involuntary) memories were recorded in a diary throughout that week.

RESULTS

When analyzing functional magnetic resonance imaging responses related to watching the films, we replicated findings that those "hotspots" (salient moments within the films) that would later become intrusive memories elicited higher activation in parts of the brain's salience network. Surprisingly, while the postencoding persistence of multivoxel correlation structures associated with entire film clips predicted subsequent voluntary recall, there was no evidence that they predicted subsequent intrusions.

CONCLUSIONS

Results replicate findings regarding the formation of intrusive memories during encoding and extend findings regarding the consolidation of information in postencoding rest in relation to voluntary memory. While we provided a first step using a naturalistic paradigm, further research is needed to elucidate the role of postencoding neural processes in the development of intrusive memories.

Reducing childbirth-related intrusive memories and PTSD symptoms via a single-session behavioural intervention including a visuospatial task: A proof-of-principle study

BACKGROUND

Intrusive memories (IMs) of traumatic events are a key symptom of posttraumatic stress disorder (PTSD), and contribute to its maintenance. This translational proof-of-principle study tested whether a single-session behavioural intervention reduced the number of childbirth-related IMs (CB-IMs) and childbirth-related PTSD (CB-PTSD) symptoms, in women traumatised by childbirth. The intervention was assumed to disrupt trauma memory reconsolidation.

METHODS

In this pre-post study, 18 participants, whose traumatic childbirth had occurred between seven months and 6.9 years before, received an intervention combining childbirth-related reminder cues (including the return to maternity unit) with a visuospatial task. They recorded their daily CB-IMs in the two weeks pre-intervention (diary 1), the two weeks post-intervention (diary 2; primary outcome), and in week 5 and 6 post-intervention (diary 3). CB-PTSD symptom severity was assessed five days pre-intervention and one month post-intervention.

RESULTS

Compared to diary 1, 15/18 participants had ≥ 50% fewer CB-IMs in diary 2. The median (IQR) reduction of the number of CB-IMs was 81.89% (39.58%) in diary 2, and persisted in diary 3 (n = 17). At one month post-intervention, CB-PTSD symptom severity was reduced by ≥ 50% in 10/18 participants. Of the 8 participants with a CB-PTSD diagnosis pre-intervention, none met diagnostic criteria post-intervention. The intervention was rated as highly acceptable.

LIMITATIONS

The design limits the causal interpretation of observed improvements.

CONCLUSION

This is the first time such a single-session behavioural intervention was tested for old and real-life single-event trauma. The promising results justify a randomized controlled trial, and may be a first step toward an innovative CB-PTSD treatment.

On the evolution of a functional approach to memory

In an analysis of memory systems, Sherry and Schacter (Psychological Review, 94, 439-454, 1987) emphasized the importance of functional and evolutionary considerations for characterizing mechanisms of memory. The present article considers four different yet closely related topics from more recent research in which similar considerations have played a prominent role in shaping both experiment and theory: the seven sins of memory, mechanisms underlying memory misattribution errors, the role of memory in imagining future experiences, and the relation between associative inference and memory errors. These lines of research illustrate the usefulness of attempting to integrate functional and mechanistic considerations, in line with the general approach articulated by Sherry and Schacter.

Selectively Interfering With Intrusive but Not Voluntary Memories of a Trauma Film: Accounting for the Role of Associative Memory

Intrusive memories of a traumatic event can be reduced by a subsequent interference procedure, seemingly sparing voluntary memory for that event. This selective-interference effect has potential therapeutic benefits (e.g., for emotional disorders) and legal importance (e.g., for witness testimony). However, the measurements of intrusive memory and voluntary memory typically differ in the role of associations between a cue and the emotional memory "hotspots." To test this, we asked participants to watch a traumatic film followed by either an interference procedure (reminder plus Tetris) or control procedure (reminder only). Measurement of intrusions (using a laboratory task) and voluntary memory (recognition for film stills) were crossed with the presence or absence of associative cues. The reminder-plus-Tetris group exhibited fewer intrusions despite comparable recognition memory, replicating the results of prior studies. Note that this selective interference did not appear to depend on associative cues. This involuntary versus voluntary memory dissociation for emotional material further supports separate-trace memory theories and has applied advantages.

Threat memory devaluation by a dual-task intervention: Testing return of fear and intrusive memory over 48 hours

BACKGROUND AND OBJECTIVES

In dual-tasking, individuals recall a threat-related memory while performing a demanding dual-task. This is a fruitful approach to reduce the unpleasantness and vividness of aversive memories and to reduce conditioned fear responses. Crucially, it remains unclear whether dual-tasking can also reduce conditioned fear responses and intrusive memories over time. In this pre-registered two-day fear conditioning paradigm, we examined whether a dual-task intervention reduces return of fear and the frequency of intrusive memories of an aversive film over time.

METHODS

On Day 1, 76 healthy participants underwent fear acquisition with aversive film clips. They were then randomly allocated to one of three conditions: dual-tasking, memory recall without a dual-task ('recall only'), or no task. Afterwards, they underwent an extinction phase and were asked to record intrusive film memories over 48 h. On Day 3, return of fear was assessed.

RESULTS

On Day 1, fear acquisition and extinction were successful. On Day 3, spontaneous recovery and renewal were evident, but, overall, participants reported few intrusions. The dual-task and recall only groups reported reduced unpleasantness of threat memory compared to the no task group, but they did not show reduced (return of) fear responses or fewer intrusions.

LIMITATIONS

Intrusion frequency was low in all three groups, which limits the detection of intervention effects.

CONCLUSIONS

Even though dual-tasking and recall only devalued threat memory temporarily compared to no task, these interventions did not reduce (return of) fear responses and intrusions. Future studies could focus on improving the potency of imagery-based interventions.

Neuromodulation of Visual Cortex Reduces the Intensity of Intrusive Memories

Aversive events can be reexperienced as involuntary and spontaneous mental images of the event. Given that the vividness of retrieved mental images is coupled with elevated visual activation, we tested whether neuromodulation of the visual cortex would reduce the frequency and negative emotional intensity of intrusive memories. Intrusive memories of a viewed trauma film and their accompanied emotional intensity were recorded throughout 5 days. Functional connectivity, measured with resting-state functional magnetic resonance imaging prior to film viewing, was used as predictive marker for intrusions-related negative emotional intensity. Results indicated that an interaction between the visual network and emotion processing areas predicted intrusions’ emotional intensity. To test the causal influence of early visual cortex activity on intrusions’ emotional intensity, participants’ memory of the film was reactivated by brief reminders 1 day following film viewing, followed by inhibitory 1 Hz repetitive transcranial magnetic stimulation (rTMS) over early visual cortex. Results showed that visual cortex inhibitory stimulation reduced the emotional intensity of later intrusions, while leaving intrusion frequency and explicit visual memory intact. Current findings suggest that early visual areas constitute a central node influencing the emotional intensity of intrusive memories for negative events. Potential neuroscience-driven intervention targets designed to downregulate the emotional intensity of intrusive memories are discussed.