Does Transcranial Direct Current Stimulation Affect Post-stressor Intrusive Memories and Rumination? An Experimental Analogue Study

Do emotionally negative events impair working memory as a result of intrusive thoughts?

Individuals exposed to highly stressful negative events show alterations in working memory (WM) function. The correlational nature of these studies makes it impossible to determine whether exposure to negative events itself decreases WM. Such events elicit intrusive thoughts which may cause interference in WM. The main objective of this study was to verify the causal impact of a recent negative event on WM, and to examine the role of intrusive thoughts. One hundred and twenty participants completed a WM task (n-Back). Then, 90 of these participants watched an emotionally negative video and 30 watched a neutral video. The emotional impact of the video was assessed, and the frequency of intrusive thoughts were measured. WM was measured a second time (n-Back) while recording EEG (P300). Contrary to our hypothesis, the negative video did not impair behavioural WM performance compared to the neutral video. However, it disrupted WM neurocognitive processes (lower P300 amplitude) under low WM load. In the high load condition, greater emotional reaction was linked to poorer accuracy and more intrusive thoughts, which in turn slowed response times. Our results suggest that the impact of negative emotions on WM depends on both individual sensitivity and cognitive load.

A systematic review and meta-analysis of experimental methods for modulating intrusive memories following lab-analogue trauma exposure in non-clinical populations

Experiencing trauma leads to intrusive memories (IMs), a hallmark symptom of post-traumatic stress disorder (PTSD), which also occurs transdiagnostically. Understanding why IMs increase or decrease is pivotal in developing interventions to support mental health. In this preregistered meta-analysis (PROSPERO: CRD42021224835), we included 134 articles (131 techniques, 606 effect sizes and 12,074 non-clinical participants) to investigate how experimental techniques alter IM frequency, intrusion-related distress and symptoms arising from lab-analogue trauma exposure. Eligible articles were identified by searching eight databases until 12 December 2023. To test potential publication biases, we employed methods including Egger's test and three-parameter selection models. We employed three-level multilevel modelling and meta-regressions to examine whether and how experimental techniques would modulate IM frequency and associated outcomes. Results showed that techniques (behavioural, pharmacological, neuromodulation) significantly reduced intrusion frequency (g = 0.16, 95% confidence interval [0.09, 0.23]). Notably, techniques aimed to reduce IMs also ameliorated intrusion-related distress and symptoms, while techniques that increased IMs exacerbated these related outcomes, thus highlighting IM's centrality in PTSD-like symptoms. Techniques tapping into mental imagery processing (for example, trauma reminder followed by playing Tetris) reduced intrusions when administered immediately after, or at a delayed time after trauma. Although our meta-analysis is limited to symptoms induced by lab-analogue trauma exposure, some lab-based results have now generalized to real-world trauma and IMs, highlighting the promising utility of lab-analogue trauma paradigms for intervention development.

Executive functions involved in thought suppression: An attempt to integrate research in two paradigms

There are two main thought suppression research paradigms: the White Bear and Think/No-Think paradigms. In Think/No-Think research, thought suppression is effective and is considered to be mediated by prepotent response inhibition. Conversely, in White Bear studies, thought suppression is counterproductive and appears to engage resistance to proactive interference. However, findings regarding the involvement of these executive functions in each task are mixed. In the current study, two thought suppression procedures were compared. Using Friedman and Miyake's inhibitory functions model (2004) it was investigated whether the differences between thought suppression tasks can be explained by involvement of different executive functions. The results showed that the suppression phases of both procedures were correlated, but the outcomes of suppression were unrelated. There was no evidence supporting the involvement of the examined executive functions in either thought suppression task. Commonalities and discrepancies of the two tasks are discussed along with their external validity.

Electrophysiological and behavioral effects of unilateral and bilateral rTMS; A randomized clinical trial on rumination and depression

BACKGROUND

Rumination is significantly frequent in major depressive disorder (MDD). However, not a lot of studies have investigated the effects of repetitive transcranial magnetic stimulation (rTMS) on rumination.

METHODS

61 participants with a minimum Hamilton Depression Rating Scale (HAM-D) score of 20 were randomly assigned to sham, bilateral stimulation (BS) or unilateral stimulation (US) groups. EEG, The Ruminative Response Scale (RRS), and HAM-D were administered before and after the 20 sessions of rTMS. Phase locked values (PLV) were calculated as a measure of connectivity.

RESULTS

There was a significant decrease in HAM-D scores in both BS and US. In responders, BS and US differed significantly in RRS total scores, with greater reduction in BS. PLV significantly changed in the default mode network (DMN) in delta, theta, alpha, and beta in BS, in responders of which PLV decreased in the DMN in beta and gamma. Positive correlations between PLV and brooding in delta and theta, and negative correlations between PLV and reflection were found in theta, alpha, and beta. In US, connectivity in the DMN increased in beta, and PLV increased in theta and beta, and decreased in alpha and beta in its responders. Positive correlations between PLV and brooding in the delta and theta, as well as negative correlations between PLV and reflection in theta were observed in the DMN.

CONCLUSION

US and BS resulted in different modulations in the DMN, however, both could alleviate both rumination and depression. Reductions in the beta and alpha frequency bands in the DMN can be considered as potential EEG-based markers of response to bilateral and unilateral rTMS, respectively.

Enhancing reappraisal of negative emotional memories with transcranial direct current stimulation

Reappraisal of negative memories and experiences is central for mental health and well-being. Deficiency of reappraisal lies at the core of many psychiatric disorders and is a key target for treatment. Here we apply transcranial direct current stimulation (tDCS) to enhance reappraisal of negative emotional memories. In a randomised, sham-controlled, 2 × 2 between-subject and double-blinded study, we applied single sessions of anodal and sham tDCS over the right dorsolateral prefrontal cortex (dlPFC) of 101 healthy participants while reappraising a personal negative memory or engaging in a control task. We hypothesised that (i) reappraisal decreases negative valence, arousal and evaluations of the memory and leads to improved decision making, and (ii) tDCS leads to additional changes in these reappraisal outcomes. In line with these hypotheses, participants’ personal memories were rated as less negative and less arousing following reappraisal. Anodal tDCS during reappraisal was associated with significant short-term reductions in negative valence compared to sham stimulation. Our results indicate that tDCS may enhance some of the effects of reappraisal. If replicated, our findings suggest potential benefits elicited by tDCS stimulation that may help optimise current treatment approaches for psychiatric disorders.

Does non-invasive brain stimulation modulate emotional stress reactivity?

Excessive emotional responses to stressful events can detrimentally affect psychological functioning and mental health. Recent studies have provided evidence that non-invasive brain stimulation (NBS) targeting the prefrontal cortex (PFC) can affect the regulation of stress-related emotional responses. However, the reliability and effect sizes have not been systematically analyzed. In the present study, we reviewed and meta-analyzed the effects of repetitive transcranial magnetic (rTMS) and transcranial direct current stimulation (tDCS) over the PFC on acute emotional stress reactivity in healthy individuals. Forty sham-controlled single-session rTMS and tDCS studies were included. Separate random effects models were performed to estimate the mean effect sizes of emotional reactivity. Twelve rTMS studies together showed no evidence that rTMS over the PFC influenced emotional reactivity. Twenty-six anodal tDCS studies yielded a weak beneficial effect on stress-related emotional reactivity (Hedges’ g = −0.16, CI_95% = [−0.33, 0.00]). These findings suggest that a single session of NBS is insufficient to induce reliable, clinically significant effects but also provide preliminary evidence that specific NBS methods can affect emotional reactivity. This may motivate further research into augmenting the efficacy of NBS protocols on stress-related processes.

Prospective associations between intelligence, working memory capacity, and intrusive memories of a traumatic film: Potential mediating effects of rumination and memory disorganization

BACKGROUND AND OBJECTIVES

Field research indicates that lower intelligence may predispose trauma-exposed individuals towards the development of re-experiencing symptoms. However, this assumption requires further testing in controlled prospective studies. In the current analog study, we tested whether lower fluid intelligence and lower working memory capacity (WMC) independently contribute to intrusion development. Moreover, we investigated potential mediating effects of trauma memory characteristics and trait rumination.

METHODS

118 healthy participants completed tests measuring fluid intelligence and WMC. Two days later, they were exposed to a film clip depicting traumatic events (i.e., so-called trauma film). After exposure to the film, intrusions were assessed using a diary and an intrusion triggering task.

RESULTS

Our analyses revealed a negative correlation between fluid intelligence and intrusions during the intrusion triggering task. WMC did not correlate with any intrusion measure. Moreover, planned analyses did not yield any mediation effects.

LIMITATIONS

We used the trauma film paradigm to examine analog posttraumatic stress symptoms. This approach limits the generalizability of our findings with regard to symptom development following real-life traumatic events.

CONCLUSIONS

Our results show for the first time that higher fluid intelligence is associated with fewer intrusions of a trauma film. This association was evident for laboratory but not for ambulatory intrusions. By demonstrating this association using a prospective experimental design, our study importantly corroborates previous field research.

The effects of left DLPFC tDCS on emotion regulation, biased attention, and emotional reactivity to negative content

The potentiation of neural activity in lateral prefrontal regions via transcranial direct current stimulation (tDCS) can reduce patterns of biased attention for threat and may facilitate intentional emotion regulation. The current study sought to determine whether left dorsolateral prefrontal cortex tDCS, in combination with intentional down-regulation of emotional responses would reduce negative appraisals of aversive content during emotional regulation (assessed during online tDCS), reduce patterns of biased attention and attention bias variability (assessed offline), and attenuate spontaneous (uninstructed) emotional reactivity to negative content (assessed offline) above tDCS or intentional down-regulation of emotions in isolation. Healthy participants (n = 116) were allocated to one of four experimental conditions involving either active or sham tDCS, combined with an either a down-regulate or maintain emotion regulation task. Attention bias/bias variability was assessed with an attentional probe task, and emotional reactivity was assessed in a negative video viewing task. tDCS did not affect the appraisals of negative stimuli during emotion regulation, and there were no effects on attention bias/bias variability. However, tDCS did attenuate emotional reactivity. Those receiving active stimulation showed smaller elevations in negative mood in response to viewing aversive video content compared with sham. The present findings are consistent with the potential of left frontal tDCS to attenuate negative emotional reactions to aversive content but provide no support for tDCS enhancement of emotion regulation, nor its impact on attention bias or attention bias variability.

Investigating the effect of proactive interference control training on intrusive memories

Intrusive re-experiencing is a hallmark symptom of Posttraumatic Stress Disorder (PTSD). According to prominent models of intrusive phenomena, intrusive memories may result from impairments in the efficiency of working memory capacity (WMC), more specifically proactive interference control. Yet, experimental research is scarce. Therefore, the present study aimed to investigate experimentally the role of proactive interference control in intrusive memories. We randomly assigned 57 healthy participants to either receive a high interference control training or a low interference control training. Participants were then exposed to highly distressing film clips. WMC was assessed before and after the training. Intrusion symptoms were assessed directly post-training and after one week using an Intrusion Provocation Task (IPT), a one-week intrusions diary, and the retrospective intrusion subscale of the Impact of Event Sale - Revised (IES-R). Results indicated that both groups reported improvements in WMC and fewer intrusions on the second IPT post-training, with no differences between groups. Similarly, no group differences on intrusions were found at one-week follow-up (i.e., intrusion diary and IES-R). To conclude, these data are not consistent with the hypothesis that WMC plays a role in intrusive re-experiencing. Implications for future research are discussed.