Memory control in post-traumatic stress disorder: evidence from item method directed forgetting in civil war victims in Northern Uganda

The effect of chronic academic stress on intentional forgetting

This study investigated whether chronic academic stress could affect the directed forgetting (DF) process. Both the stress group (undergoing preparation for a major academic examination) and the control group performed a DF task. A forgetting cue was presented after a to-be-forgotten (TBF) word, whereas no cue appeared after a to-be-remembered (TBR) item in the study phase. An old/new recognition test was used in the test phase. The results showed that (1) the stress group showed a higher level of self-reported stress, state anxiety, negative affect, and decreased cortisol awakening response (CAR) compared with the control group, suggesting a higher level of stress for the stress group. (2) Both groups showed superior recognition performance of TBR than TBF items, suggesting a DF effect. (3) The stress group showed inferior recognition performance of TBF items and an enhanced DF effect compared with the control group. These results demonstrated that the intentional memory control process might be enhanced under chronic academic stress.

Depersonalization Disorder: Directed Forgetting as a Function of Emotionality

There exists some evidence for a link between dissociation and emotionally avoidant information processing, yet studies to date have been contradictory. Our goal was to investigate emotionally avoidant processing in Depersonalization Disorder (DDD) using a directed forgetting (DF) paradigm. Thirty-two participants with DSM-IV DDD and 40 healthy controls performed an item-method DF task using positive, negative, and neutral words. Participants were also administered the Dissociative Experiences Scale (DES) and the Childhood Trauma Questionnaire (CTQ). The DDD group demonstrated significantly lower directed forgetting for negative, but not positive or neutral, words compared to controls. In the combined sample, DES total, depersonalization/derealization, and amnesia scores significantly inversely predicted explicit cued recall for to-be-forgotten negative words (higher dissociation, lower forgetting), while the CTQ was not predictive. The findings do not support emotionally avoidant processing in this paradigm; rather, DDD may be characterized by a diminished capacity to actively control attention and direct it away from emotionally disturbing material when instructed to do so.

Different ways to forget: Electrophysiological mechanisms underlying item-method directed forgetting of angry and neutral faces

Emotional stimuli, including faces, receive preferential processing and are consequently better remembered than neutral stimuli. Therefore, they may also be more resistant to intentional forgetting. The present study investigates the behavioral and electrophysiological consequences of instructions to selectively remember or forget angry and neutral faces. In an item-method directed forgetting experiment, angry and neutral faces were randomly presented to 25 student participants (4 males). Each face was followed by an instruction to either forget or remember it and the participants’ EEG was recorded. Later, recognition memory was unexpectedly tested for all items. Behaviorally, both hit and false alarm rates were higher for angry alike than for neutral faces. Directed forgetting occurred for neutral and angry faces as reflected in a reduction of both recognition accuracy and response bias. Event-related potentials revealed a larger late positive potential (LPP, 450 – 700 ms) for angry than for neutral faces during face presentation and, in line with selective rehearsal of remember items, a larger LPP following remember than forget cues. Forget cues generally elicited a larger frontal N2 (280 – 400 ms) than remember cues, in line with the forget instruction eliciting conflict monitoring and inhibition. Selectively following angry faces, a larger cue-evoked P2 (180 – 280 ms) was observed. Notably, forget cues following angry faces elicited a larger late frontal positivity (450 - 700 ms) potentially signaling conflict resolution. Thus, whereas both angry and neutral faces are subject to directed forgetting, on a neural level, different mechanisms underlie the effect. While directed forgetting for neutral faces may be achieved primarily by selective rehearsal, directed forgetting of angry faces involves an additional late frontal positivity, likely reflecting higher cognitive demands imposed by forgetting angry faces.

Forgetting positive social feedback is difficult: ERP evidence in a directed forgetting paradigm

Voluntary forgetting of unwanted memories is an adaptive cognitive function. However, it remains unknown how voluntary forgetting of unwanted social feedback may influence subsequent memories and evaluations, and what the underlying neurocognitive processes are. Here, we presented participants with peer photos together with feedback indicating social acceptance or rejection, followed by "remember" or "forget" instructive cues, while electroencephalograms were recorded during the experiment. We examined the Directed Forgetting (DF) effect in a recognition memory test, and tested participants' explicit and implicit attitudes toward the peers using a social evaluation task and an affect misattribution procedure (AMP). Both the memory test and the AMP were examined immediately and 3 days after the DF task so to estimate both the instant and the long-term effects of memory control. Behaviorally, immediate memory test showed smaller DF effect for positive than negative social feedback, which suggests that forgetting positive social feedback was more difficult than forgetting negative social feedback. Regarding the ERP results, although participants showed comparable frontal N2 amplitudes (reflecting inhibitory control efforts) following the instruction of forgetting positive and negative social feedback, positive feedback elicited larger late positive potential (LPP) amplitudes than negative feedback during initial encoding phase, suggesting an encoding bias for positive self-relevant information. Intriguingly, voluntary efforts to forget negative social feedback enhanced people's explicit and implicit evaluations toward the feedback senders. These findings provide new evidence for the adaptive function of memory control, which broadens the influence of voluntary forgetting in the context of social interaction and social evaluation.

Wakefulness impairs selective consolidation of relevant trauma-associated memories resulting in more frequent intrusions

Recent studies show that sleep reduces intrusive memories after analog trauma. This effect is assumed to be caused by sleep's impact on memory consolidation. However, the underlying processes of this phenomenon have not been uncovered. Thus, the current study investigates the hypothesis that sleep reduces intrusive memories by supporting the selective consolidation of relevant memories. Seventy-five participants were exposed to traumatic picture stories before nocturnal sleep or wakefulness during daytime. Memory for relevant and irrelevant trauma-associated stimuli was assessed prior to and after the retention period. Consistent with the hypothesis, results demonstrate reduced memory loss for relevant as opposed to irrelevant trauma-associated stimuli after sleep but not after wakefulness. Moreover, an incremental retention benefit for relevant trauma-associated stimuli was negatively correlated with the number of intrusive trauma memories after wakefulness. These results suggest that lack of sleep impairs selective gating of relevant trauma-associated memories, thereby enhancing intrusion development after trauma.

What can directed forgetting tell us about clinical populations?

This paper reviews and critically assesses the implications of directed forgetting (DF) research on clinical populations. We begin by reviewing the typical methods and results of the item method and list method directed forgetting procedures and provide best practice recommendations for future studies using clinical populations. Next, we note that DF was often interpreted as being due to inhibition, and when clinical populations showed impaired directed forgetting, it was treated as evidence in inhibitory control difficulties. However, inhibition may not be the cause of DF effects, based on current understanding of these cognitive tasks. We instead suggest that item method DF is tied to attentional control, which might include inhibitory mechanisms (or might not). In contrast, list method DF is tied to two forms of memory control: control of mental context (indicated by effective forgetting of List 1), and changes in the strategies used to remember (indicated by better learning of List 2). We review the current state of the clinical DF literature, assess its strength based on our best practice recommendations, and call for more research when warranted.

Inhibitory control of threat remembering in PTSD

Intrusive traumatic recollections suggest an inability in Posttraumatic Stress Disorder (PTSD) to control and notably to inhibit memories for trauma-related information. Supported by inhibitory deficits found on experimental settings in PTSD, memory functioning and memory biases in the disorder were usually explained through inhibitory and control deficits in the processing of trauma-related information. The present study aimed to directly assess this hypothesis by investigating memory control abilities for emotional information in PTSD. For this purpose, 34 patients diagnosed with PTSD were compared to 37 non-PTSD controls on an item-cued directed forgetting paradigm for emotional words combined with a Remember/Know recognition procedure. Results revealed enhanced amounts of Remember recognitions for trauma-related words in PTSD. Moreover, we replicated findings of memory control impairments in the disorder. However, such impairments only occurred for non-trauma-related words. Accordingly, it appeared that PTSD patients presented preserved memory control abilities for trauma-related words, at the expenses of other emotional valences. Surprisingly, PTSD patients presented a preserved ability to control and notably to inhibit their memory functioning for trauma-related material. In addition to potential theoretical and clinical relevance, these results are discussed in the light of resource reallocation hypotheses and vigilant-avoidant theories of information processing in PTSD.

Weak evidence for increased motivated forgetting of trauma-related words in dissociated or traumatised individuals in a directed forgetting experiment

Motivated forgetting is the idea that people can block out, or forget, upsetting or traumatic memories, because there is a motivation to do so. Some researchers have cited directed forgetting studies using trauma-related words as evidence for the theory of motivated forgetting of trauma. In the current article subjects used the list method directed forgetting paradigm with both trauma-related words and positive words. After one list of words was presented subjects were directed to forget the words previously learned, and they then received another list of words. Each list was a mix of positive and trauma-related words, and the lists were counterbalanced. Later, subjects recalled as many of the words as they could, including the ones they were told to forget. Based on the theory that motivated forgetting would lead to recall deficits of trauma-related material, we created eight hypotheses. High dissociators, trauma-exposed, sexual trauma-exposed, and high dissociators with trauma-exposure participants were hypothesised to show enhanced forgetting of trauma words. Results indicated only one of eight hypotheses was supported: those higher on dissociation and trauma recalled fewer trauma words in the to-be-forgotten condition, compared to those low on dissociation and trauma. These results provide weak support for differential motivated forgetting.

Dissociation between working memory performance and proactive interference control in post-traumatic stress disorder

Deficits in working memory (WM) and cognitive control processes have been reported in post-traumatic stress disorder (PTSD), in addition to clinical symptoms such as hypervigilance, re-experiencing, and avoidance of trauma reminders. Given the uncontrollable nature of intrusive memories, an important question is whether PTSD is associated with altered control of interference in WM. Some studies also suggest that episodic memory shows a material-specific dissociation in PTSD, with greater impairments in verbal memory and relative sparing of nonverbal memory. It is unclear whether this dissociation applies to WM, as no studies have used identical task parameters across material. Here we tested 29 combat Veterans with PTSD and 29 age-matched control Veterans on a recent probes WM task with words and visual patterns in separate blocks. Participants studied four-item sets, followed by a probe stimulus that had been presented in the previous set (recent probe) or not (nonrecent probe). Participants with PTSD made more errors than controls, and this decrement was similar for verbal and visual stimuli. Proactive interference from items recently presented, but no longer relevant, was not significantly different in the PTSD group and showed no relationship to re-experiencing symptom severity. These results demonstrate that PTSD is not reliably associated with increased intrusions of irrelevant representations into WM when non-emotional stimuli are used. Future studies that use trauma-related material may provide insight into the flashbacks and intrusive thoughts that plague those with PTSD.

Are Hallucinations Due to an Imbalance Between Excitatory and Inhibitory Influences on the Brain?

This review from the International Consortium on Hallucinations Research intends to question the pertinence of the excitatory-to-inhibitory (E/I) imbalance hypothesis as a model for hallucinations. A large number of studies suggest that subtle impairments of the E/I balance are involved in neurological and psychiatric conditions, such as schizophrenia. Emerging evidence also points to a role of the E/I balance in maintaining stable perceptual representations, suggesting it may be a plausible model for hallucinations. In support, hallucinations have been linked to inhibitory deficits as shown with impairment of gamma-aminobutyric acid transmission, N-methyl-d-aspartate receptor plasticity, reductions in gamma-frequency oscillations, hyperactivity in sensory cortices, and cognitive inhibition deficits. However, the mechanisms by which E/I dysfunctions at the cellular level might relate to clinical symptoms and cognitive deficits remain unclear. Given recent data advances in the field of clinical neuroscience, it is now possible to conduct a synthesis of available data specifically related to hallucinations. These findings are integrated with the latest computational frameworks of hallucinations, and recommendations for future research are provided.

Memory control ability modulates intrusive memories after analogue trauma

BACKGROUND

Most people suffer from intrusive memories in the aftermath of trauma. For survivors' well-being, it is key that these intrusions are controlled. Memory control can be exerted through retrieval suppression. Poor retrieval suppression, however, should be associated with persistent distressing intrusions and posttraumatic stress disorder (PTSD). This study tested the hypothesis that individual differences in retrieval suppression predict intrusive memories after trauma. Retrieval suppression was examined with the think/no-think task (TNT) using behavioral and event related potential (ERP) measures.

METHODS

Twenty-four healthy participants watched a "traumatic" film after performing the TNT task. The frequency and distress of intrusions from the "traumatic" film was measured with an electronic diary. Additionally the Impact of Event Scale (IES) was assessed.

RESULTS

In line with our hypothesis, behavioral measures of retrieval suppression ability predicted reduced distress ratings for intrusions (r=-.53, p<.01). Further ERP markers of retrieval suppression (a fronto-centrally distributed N2) predicted reduced distress ratings for intrusions (r=-.45, p<.05) and reduced IES Intrusion scores (r=-.56, p<.01).

LIMITATIONS

The presented film is a relatively mild stressor as compared to a real-life trauma. Further studies are needed to explore the role of memory control processes for real-life trauma.

CONCLUSIONS

Participants with lower retrieval suppression ability exhibited less distressing intrusive memories after analogue trauma. The ERP correlate of retrieval suppression was associated with less distressing intrusive memories and reduced IES Intrusion scores, suggesting that deficient memory control is a potential risk factor for developing PTSD.

'Forget me (not)?' - Remembering Forget-Items Versus Un-Cued Items in Directed Forgetting

Humans need to be able to selectively control their memories. This capability is often investigated in directed forgetting (DF) paradigms. In item-method DF, individual items are presented and each is followed by either a forget- or remember-instruction. On a surprise test of all items, memory is then worse for to-be-forgotten items (TBF) compared to to-be-remembered items (TBR). This is thought to result mainly from selective rehearsal of TBR, although inhibitory mechanisms also appear to be recruited by this paradigm. Here, we investigate whether the mnemonic consequences of a forget instruction differ from the ones of incidental encoding, where items are presented without a specific memory instruction. Four experiments were conducted where un-cued items (UI) were interspersed and recognition performance was compared between TBR, TBF, and UI stimuli. Accuracy was encouraged via a performance-dependent monetary bonus. Experiments varied the number of items and their presentation speed and used either letter-cues or symbolic cues. Across all experiments, including perceptually fully counterbalanced variants, memory accuracy for TBF was reduced compared to TBR, but better than for UI. Moreover, participants made consistently fewer false alarms and used a very conservative response criterion when responding to TBF stimuli. Thus, the F-cue results in active processing and reduces false alarm rate, but this does not impair recognition memory beyond an un-cued baseline condition, where only incidental encoding occurs. Theoretical implications of these findings are discussed.

Shaping the learning curve: epigenetic dynamics in neural plasticity

A key characteristic of learning and neural plasticity is state-dependent acquisition dynamics reflected by the non-linear learning curve that links increase in learning with practice. Here we propose that the manner by which epigenetic states of individual cells change during learning contributes to the shape of the neural and behavioral learning curve. We base our suggestion on recent studies showing that epigenetic mechanisms such as DNA methylation, histone acetylation, and RNA-mediated gene regulation are intimately involved in the establishment and maintenance of long-term neural plasticity, reflecting specific learning-histories and influencing future learning. Our model, which is the first to suggest a dynamic molecular account of the shape of the learning curve, leads to several testable predictions regarding the link between epigenetic dynamics at the promoter, gene-network, and neural-network levels. This perspective opens up new avenues for therapeutic interventions in neurological pathologies.

Neural mechanisms of motivated forgetting

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Motivated forgetting of unwanted memories shapes what we retain of our personal past.

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Motivated forgetting is achieved in part by inhibitory control over encoding or retrieval.

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Prefrontal cortex reduces hippocampal and cortical activity to suppress memories.

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Electrophysiological activity during motivated forgetting implicates active inhibition.

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A neurobiological model of memory control can inform disordered control over memory.

Not all memories are equally welcome in awareness. People limit the time they spend thinking about unpleasant experiences, a process that begins during encoding, but that continues when cues later remind someone of the memory. Here, we review the emerging behavioural and neuroimaging evidence that suppressing awareness of an unwelcome memory, at encoding or retrieval, is achieved by inhibitory control processes mediated by the lateral prefrontal cortex. These mechanisms interact with neural structures that represent experiences in memory, disrupting traces that support retention. Thus, mechanisms engaged to regulate momentary awareness introduce lasting biases in which experiences remain accessible. We argue that theories of forgetting that neglect the motivated control of awareness omit a powerful force shaping the retention of our past.

Directed forgetting in post-traumatic-stress-disorder: a study of refugee immigrants in Germany

People with post-traumatic stress disorder (PTSD) often suffer from memory disturbances. In particular, previous studies suggest that PTSD patients perform atypically on tests of directed forgetting, which may be mediated by an altered emotional appraisal of the presented material. Also, a special role of dissociative symptoms in traumatized individuals’ memory performance has been suggested. Here, we investigate these issues in traumatized immigrants in Germany. In an item-method directed forgetting task, pictures were presented individually, each followed by an instruction to either remember or forget it. Later, recognition memory was tested for all pictures, regardless of initial instruction. Overall, the PTSD group’s discrimination accuracy was lower than the control group’s, as PTSD participants produced fewer hits and more false alarms, but the groups did not differ in directed forgetting itself. Moreover, the more negatively participants evaluated the stimuli, the less they were able to discriminate old from new items. Participants with higher dissociation scores were particularly poor at recognizing to-be-forgotten items. Results confirm PTSD patients’ general discrimination deficits, but provide no evidence for a distinct directed forgetting pattern in PTSD. Furthermore, data indicate that, in general, more negatively perceived items are discriminated with less accuracy than more positively appraised ones. Results are discussed in the larger context of emotion and stress-related modulations of episodic memory, with particular focus on the role of dissociative symptoms.

Emotion and cognition interactions in PTSD: a review of neurocognitive and neuroimaging studies

Posttraumatic stress disorder (PTSD) is a psychiatric syndrome that develops after exposure to terrifying and life-threatening events including warfare, motor-vehicle accidents, and physical and sexual assault. The emotional experience of psychological trauma can have long-term cognitive effects. The hallmark symptoms of PTSD involve alterations to cognitive processes such as memory, attention, planning, and problem solving, underscoring the detrimental impact that negative emotionality has on cognitive functioning. As such, an important challenge for PTSD researchers and treatment providers is to understand the dynamic interplay between emotion and cognition. Contemporary cognitive models of PTSD theorize that a preponderance of information processing resources are allocated toward threat detection and interpretation of innocuous stimuli as threatening, narrowing one's attentional focus at the expense of other cognitive operations. Decades of research have shown support for these cognitive models of PTSD using a variety of tasks and methodological approaches. The primary goal of this review is to summarize the latest neurocognitive and neuroimaging research of emotion-cognition interactions in PTSD. To directly assess the influence of emotion on cognition and vice versa, the studies reviewed employed challenge tasks that included both cognitive and emotional components. The findings provide evidence for memory and attention deficits in PTSD that are often associated with changes in functional brain activity. The results are reviewed to provide future directions for research that may direct better and more effective treatments for PTSD.

Emotion and cognition interactions in PTSD: a review of neurocognitive and neuroimaging studies

Posttraumatic stress disorder (PTSD) is a psychiatric syndrome that develops after exposure to terrifying and life-threatening events including warfare, motor-vehicle accidents, and physical and sexual assault. The emotional experience of psychological trauma can have long-term cognitive effects. The hallmark symptoms of PTSD involve alterations to cognitive processes such as memory, attention, planning, and problem solving, underscoring the detrimental impact that negative emotionality has on cognitive functioning. As such, an important challenge for PTSD researchers and treatment providers is to understand the dynamic interplay between emotion and cognition. Contemporary cognitive models of PTSD theorize that a preponderance of information processing resources are allocated toward threat detection and interpretation of innocuous stimuli as threatening, narrowing one's attentional focus at the expense of other cognitive operations. Decades of research have shown support for these cognitive models of PTSD using a variety of tasks and methodological approaches. The primary goal of this review is to summarize the latest neurocognitive and neuroimaging research of emotion-cognition interactions in PTSD. To directly assess the influence of emotion on cognition and vice versa, the studies reviewed employed challenge tasks that included both cognitive and emotional components. The findings provide evidence for memory and attention deficits in PTSD that are often associated with changes in functional brain activity. The results are reviewed to provide future directions for research that may direct better and more effective treatments for PTSD.