Observing the suppression of individual aversive memories from conscious awareness.

When reminded of an unpleasant experience, people often try to exclude the unwanted memory from awareness, a process known as retrieval suppression. Here we used multivariate decoding (MVPA) and representational similarity analyses on EEG data to track how suppression unfolds in time and to reveal its impact on item-specific cortical patterns. We presented reminders to aversive scenes and asked people to either suppress or to retrieve the scene. During suppression, mid-frontal theta power within the first 500 ms distinguished suppression from passive viewing of the reminder, indicating that suppression rapidly recruited control. During retrieval, we could discern EEG cortical patterns relating to individual memories-initially, based on theta-driven visual perception of the reminders (0 to 500 ms) and later, based on alpha-driven reinstatement of the aversive scene (500 to 3000 ms). Critically, suppressing retrieval weakened (during 360 to 600 ms) and eventually abolished item-specific cortical patterns, a robust effect that persisted until the reminder disappeared (780 to 3000 ms). Representational similarity analyses provided converging evidence that retrieval suppression weakened the representation of target scenes during the 500 to 3000 ms reinstatement window. Together, rapid top-down control during retrieval suppression abolished cortical patterns of individual memories, and precipitated later forgetting. These findings reveal a precise chronometry on the voluntary suppression of individual memories.

Memory control immediately improves unpleasant emotions associated with autobiographical memories of past immoral actions.

The ability to stop unwanted memories from coming to mind is theorised to be essential for maintaining good mental health. People can employ intentional strategies to prevent conscious intrusions of negative memories, and repeated attempts to stop retrieval both reduces the frequency of intrusions and improves subsequent emotions elicited by those memories. However, it is still unknown whether memory control can improve negative emotions immediately, at the time control is attempted. It is also not clear which strategy is most beneficial for emotion regulation; clearing the mind of any thoughts of negative memories via direct suppression, or substituting memory recall with alternative thoughts. Here, we provide novel evidence that memory control immediately regulates negative emotions associated with autobiographical memories of morally wrong actions. Repeated control significantly improved negative emotions over time, regardless of the strategy used to implement control. Thought substitution involving either positive diversionary thinking or counterfactual thinking both induced positive feelings, whereas direct suppression neutralised emotions, regardless of whether memories were positive or negative. These empirical findings have implications for clinical practice as they indicate that memory control strategies could be effective emotion regulation methods for real-world intrusive memories.

Everything you ever wanted to know about the Think/No-Think task, but forgot to ask.

The Think/No-Think (TNT) task has just celebrated 20 years since its inception, and its use has been growing as a tool to investigate the mechanisms underlying memory control and its neural underpinnings. Here, we present a theoretical and practical guide for designing, implementing, and running TNT studies. For this purpose, we provide a step-by-step description of the structure of the TNT task, methodological choices that can be made, parameters that can be chosen, instruments available, aspects to be aware of, systematic information about how to run a study and analyze the data. Importantly, we provide a TNT training package (as Supplementary Material), that is, a series of multimedia materials (e.g., tutorial videos, informative HTML pages, MATLAB code to run experiments, questionnaires, scoring sheets, etc.) to complement this method paper and facilitate a deeper understanding of the TNT task, its rationale, and how to set it up in practice. Given the recent discussion about the replication crisis in the behavioral sciences, we hope that this contribution will increase standardization, reliability, and replicability across laboratories.

Amnesia in healthy people via hippocampal inhibition: A new forgetting mechanism.

Structural damage to the hippocampus gives rise to a severe memory deficit for personal experiences known as organic amnesia. Remarkably, such structural damage may not be the only way of creating amnesia; windows of amnesia can also arise when people deliberately disengage from memory via a process known as retrieval suppression. In this review, we discuss how retrieval suppression induces systemic inhibition of the hippocampus, creating "amnesic shadow" intervals in people's memory for their personal experiences. When new memories are encoded or older memories are reactivated during this amnesic shadow, these memories are disrupted, and such disruption even arises when older memories are subliminally cued. Evidence suggests that the systemic inhibition of the hippocampus during retrieval suppression that gives rise to the amnesic shadow may be mediated by engagement of hippocampal GABAergic inhibitory interneurons. Similar amnesic shadow effects are observed during working memory tasks like the n-back, which also induce notable hippocampal downregulation. We discuss our recent proposal that cognitive operations that require the disengagement of memory retrieval, such as retrieval suppression, are capable of mnemonic process inhibition (the inhibition of mnemonic processes such as encoding, consolidation, and retrieval and not simply individual memories). We suggest that people engage mnemonic process inhibition whenever they shift attention from internal processes to demanding perceptual-motor tasks that may otherwise be disrupted by distraction from our inner world. This hitherto unstudied model of inhibition is a missing step in understanding what happens when attentional shifts occur between internally and externally oriented processes to facilitate goal-directed behaviour. This process constitutes an important novel mechanism underlying the forgetting of life events.

Reduced hippocampal-cortical connectivity during memory suppression predicts the ability to forget unwanted memories.

The ability to suppress unwelcome memories is important for productivity and well-being. Successful memory suppression is associated with hippocampal deactivations and a concomitant disruption of this region's functionality. Much of the previous neuroimaging literature exploring such suppression-related hippocampal modulations has focused on the region's negative coupling with the prefrontal cortex. Task-based changes in functional connectivity between the hippocampus and other brain regions still need further exploration. In the present study, we utilize psychophysiological interactions and seed connectome-based predictive modeling to investigate the relationship between the hippocampus and the rest of the brain as 134 participants attempted to suppress unwanted memories during the Think/No-Think task. The results show that during retrieval suppression, the right hippocampus exhibited decreased functional connectivity with visual cortical areas (lingual and cuneus gyrus), left nucleus accumbens and the brain-stem that predicted superior forgetting of unwanted memories on later memory tests. Validation tests verified that prediction performance was not an artifact of head motion or prediction method and that the negative features remained consistent across different brain parcellations. These findings suggest that systemic memory suppression involves more than the modulation of hippocampal activity-it alters functional connectivity patterns between the hippocampus and visual cortex, leading to successful forgetting.

Subliminal backdoors to forgetting emotional memories.

Weakening negative memories often requires first remembering those events. To bypass this distressing process, Zhu et al. elicited forgetting by subliminally reactivating negative memories near in time to retrieval suppression of unrelated memories. Casting an amnesic shadow over harmful, reactivated memories thereby brings new therapeutic possibilities, and questions, to light.

EEG evidence that morally relevant autobiographical memories can be suppressed.

Remembering unpleasant events can trigger negative feelings. Fortunately, research indicates that unwanted retrieval can be suppressed to prevent memories from intruding into awareness, improving our mental state. The current scientific understanding of retrieval suppression, however, is based mostly on simpler memories, such as associations between words or pictures, which may not reflect how people control unpleasant memory intrusions in everyday life. Here, we investigated the neural and behavioural dynamics of suppressing personal and emotional autobiographical memories using a modified version of the Think/No-Think task. We asked participants to suppress memories of their own past immoral actions, which were hypothesised to be both highly intrusive and motivating to suppress. We report novel evidence from behavioural, ERP, and EEG oscillation measures that autobiographical memory retrieval can be suppressed and suggest that autobiographical suppression recruits similar neurocognitive mechanisms as suppression of simple laboratory associations. Suppression did fail sometimes, and EEG oscillations indicated that such memory intrusions occurred from lapses in sustained control. Importantly, however, participants improved at limiting intrusions with repeated practice. Furthermore, both behavioural and EEG evidence indicated that intentional suppression may be more difficult for memories of our morally wrong actions than memories of our morally right actions. The findings elucidate the neurocognitive correlates of autobiographical retrieval suppression and have implications for theories of morally motivated memory control.

Retrieval suppression induced forgetting on 1-week-old consolidated episodic memories.

Retrieval suppression has been established to cause forgetting on a wide range of memory types, but mostly in newly formed memories. Over time, the consolidation process stabilizes memory and changes the memory locus in the brain, which may affect the effectiveness of retrieval suppression. In two experiments, we examined whether retrieval suppression can induce forgetting on consolidated episodic memories and explored its potential reliance on explicit memory reactivation or spontaneous memory intrusions to destabilize the consolidated memory. We found that, compared with associative interference, another well-established forgetting approach, retrieval suppression consistently induced forgetting on 1-week-old memories. This suppression-induced forgetting was uncovered stably via an independent retrieval cue, suggesting its effect being on the target memory itself. However, we did not find evidence of modulation on the suppression-induced forgetting by either explicit reactivation or spontaneous intrusions. Together, our results extend the suppression-induced forgetting to episodic memories that have been consolidated for 1 week and suggest that retrieval suppression could destabilize consolidated memories.

Aberrant resting-state functional connectivity of major depressive disorder with higher risk of suicide.

Aim: Suicide prevention for depressive patients is an important clinical issue in psychiatry. However, not all depressive patients plan or attempt suicide. In this study, we investigated the differences of functional brain networks between a high-risk group and a low-risk group for suicide by comparing resting-state functional connectivity (rsFC). Methods: The subjects were 29 patients with major depressive disorder, nine of whom had attempted suicide. The suicidal ideation of all subjects was assessed with the Columbia-Suicide Severity Rating Scale, then the subjects were divided into two groups based on the most severe suicidal ideation (MSI) in their lifetime. We compared rsFC between the two groups. Results: Of the 29 subjects, 16 were in the severe MSI group. We found that the severe MSI group members had significantly smaller rsFC in two networks: one comprised the right dorsolateral prefrontal cortex and the default-mode network, and the other comprised the left rostrolateral prefrontal cortex and the striatum, amygdala, and hippocampus. These regions are reported to be associated with rumination, retrieval suppression, and delay discounting (DD). Conclusion: Our results suggest that functional networks related to rumination, retrieval suppression, and DD might be impaired in depressive patients with severe suicidal ideation. It might be beneficial for psychiatrists to assess these characteristics in terms of suicide prevention for depressive patients.

Influence of negative mood on restrained eaters' memory suppression of food cues: An event-related potentials study.

Negative mood has been found to be a critical trigger for overeating in restrained eaters. The ability to suppress thinking of palatable food cues is crucial to control hedonic eating; nevertheless, little research has been conducted to explore inhibitory control in cognitive processes among restrained eaters. To address this gap, this study primed restrained eaters with negative (n = 23) or neutral emotions (n = 24) and applied a Think/No-think paradigm to explore their retrieval facilitation/suppression ability for food cues, while recording Electroencephalogram (EEG) data. Results indicated that the recall rate of the No-think condition (retrieval suppressing task) was higher than the Think condition (retrieval task). Negative affect did not influence the recall rate, but it did evoke smaller N2 amplitudes, larger P2 and P3 amplitudes, as well as late positive component (LPC) amplitudes. Among these components, P2 evoked by the No-think and Think conditions was larger than the perceptual control condition. Our findings suggested that in negative moods, restrained eaters need to allocate more attentional resources to suppress food cues. The findings further demonstrated that the influence of negative moods appeared at an early stage of cognitive processing and caused a resource depletion in memory suppression. This research provides a neurophysiological basis for understanding emotional influences on the process of restrained eaters' inhibition control for external food cues.

Wanting to eat matters: Negative affect and emotional eating were associated with impaired memory suppression of food cues.

OBJECTIVE: Previous studies have linked emotional eating with negative affect and decreased inhibitory control. However, studies on inhibitory control have generally focused on motor inhibition. How to stop higher-level cognitive processes, such as food-related memory retrieval or voluntary thoughts, received few direct investigation in field of food intake or food-related decision making. The current study, adopting Anderson and Green's Think/No-Think paradigm, aimed to investigate the relationship between emotional eating, negative affect and food-related memory suppression. METHOD: Sixty-one young females participated in the current study, during which they finished food specific Think/No-Think task. Their positive and negative affect and eating style were measured using Positive Affect and Negative Affect Schedule and Dutch Eating Behavior Question. The reward value of the food item used in the Think/No-Think task was measured using liking and wanting ratings. RESULTS: As hypothesized, negative affect and emotional eating were associated with decreased memory suppression of palatable food cues. Further analysis showed that higher emotional eating was associated with greater wanting only among the food items which were previously suppressed however remembered later. DISCUSSION: The current study presents the first evidence that negative affect and emotional eating were associated with impaired memory suppression of palatable food cues, and it provided insight into the interaction between reward valuation for the food cues and hippocampal memory mechanisms during retrieval suppression.

Reconsidering unconscious persistence: Suppressing unwanted memories reduces their indirect expression in later thoughts.

When we seek to forget unwelcome memories, does the suppressed content still exert an unconscious influence on our thoughts? Although intentionally stopping retrieval of a memory reduces later episodic retention for the suppressed trace, it remains unclear the extent to which suppressed content persists in indirectly influencing mental processes. Here we tested whether inhibitory control processes underlying retrieval suppression alter the influence of a memory's underlying semantic content on later thought. To achieve this, across two experiments, we tested whether suppressing episodic retrieval of to-be-excluded memories reduced the indirect expression of the unwanted content on an apparently unrelated test of problem solving: the remote associates test (RAT). Experiment 1 found that suppressed content was less likely than unsuppressed content to emerge as solutions to RAT problems. Indeed, suppression abolished evidence of conceptual priming, even when participants reported no awareness of the relationship between the memory and the problem solving tasks. Experiment 2 replicated this effect and also found that directing participants to use explicit memory to solve RAT problems eliminated suppression effects. Experiment 2 thus rules out the possibility that suppression effects reflect contamination by covert explicit retrieval strategies. Together, our results indicate that inhibitory control processes underlying retrieval suppression not only disrupt episodic retention, but also reduce the indirect influence of suppressed semantic content during unrelated thought processes. Considered with other recent demonstrations of implicit suppression effects, these findings indicate that historical assumptions about the persisting influence of suppressed thoughts on mental health require closer empirical scrutiny and need to be reconsidered.

Successful Goal-Directed Memory Suppression is Associated With Increased Inter-Hemispheric Coordination Between Right and Left Frontoparietal Control Networks.

The neural basis of suppressing conscious access to one's own memories has recently received considerable attention, with several studies suggesting this process engages frontal-parietal cognitive control regions. However, researchers to date have not examined the way right and left hemisphere cognitive control networks coordinate with one another to accomplish this. We had 48 participants (25 female) complete a Think/No Think (T/NT) task for memories of emotionally unpleasant visual scenes while undergoing functional magnetic resonance imaging. We used generalized psychophysiologic interaction analyses to examine functional connectivity between right and left hemisphere frontal-parietal regions during memory suppression. Participants who were better at memory suppression, as assessed by greater numbers of forgotten memories in the NT than T conditions, also showed greater functional connectivity between multiple right and left hemisphere control regions. This suggests that individual differences in memory suppression ability may be partially explained by differences in task-specific inter-hemispheric coordination.

Suppressing Unwanted Memories Reduces Their Unintended Influences.

The ability to control unwanted memories is critical for maintaining cognitive function and mental health. Prior research has shown that suppressing the retrieval of unwanted memories impairs their retention, as measured using intentional (direct) memory tests. Here, we review emerging evidence revealing that retrieval suppression can also reduce the unintended influence of suppressed traces. In particular, retrieval suppression (a) gradually diminishes the tendency for memories to intrude into awareness and (b) reduces memories' unintended expressions on indirect memory tests. We present a neural account in which, during suppression, retrieval cues elicit hippocampally triggered neocortical activity that briefly reinstates features of the original event, which, in turn, are suppressed by targeted neocortical and hippocampal inhibition. This reactivation-dependent reinstatement principle could provide a broad mechanism by which suppressing retrieval of intrusive memories limits their indirect influences.

Successfully controlling intrusive memories is harder when control must be sustained.

After unpleasant events, people often experience intrusive memories that undermine their peace of mind. In response, they often suppress these unwanted memories from awareness. Such efforts may fail, however, when inhibitory control demands are high due to the need to sustain control, or when fatigue compromises inhibitory capacity. Here we examined how sustained inhibitory demand affected intrusive memories in the Think/No-Think paradigm. To isolate intrusions, participants reported, trial-by-trial, whether their preceding attempt to suppress retrieval had triggered retrieval of the memory they intended to suppress. Such counter-intentional retrievals provide a laboratory model of the sort of involuntary retrieval that may underlie intrusive memories. Using this method, we found that longer duration trials increased the probability of an intrusion. Moreover, on later No-Think trials, control over intrusions suddenly declined, with longer trial durations triggering more relapses of items that had been previously been purged. Thus, the challenges of controlling retrieval appear to cause a decline in control over time, due to a change in state, such as fatigue. These findings raise the possibility that characteristics often true of people with psychiatric disorders - such as compromised sleep, and increased demand on control - may contribute to difficulties in suppressing intrusive memories.

Unwanted reminders: The effects of emotional memory suppression on subsequent neuro-cognitive processing.

The neural basis of voluntarily suppressing conscious access to one's own memories (retrieval suppression [RS]) has recently received considerable attention. However, to date there has been limited research examining the effects of RS on subsequent processing of associated retrieval cues. In this study 47 healthy participants completed a Think/No Think task for memories of emotionally unpleasant visual scenes. While undergoing functional magnetic resonance imaging (fMRI), participants were then presented with cues associated with both suppressed ("no-think-cues") and non-suppressed ("think-cues") memories, and then asked to perform simple arithmetic problems. We observed that, compared to think-cues, no-think-cues were associated with greater left mid/anterior insula activation and with greater insula-anterior cingulate functional connectivity; left insula activation also predicted worse arithmetic performance. These results suggest that cues associated with suppressed negative memories may lead to greater activation of the brain's "salience" network, and reduced available cognitive resources for completion of an ongoing goal-directed task.

Prefrontal-hippocampal pathways underlying inhibitory control over memory.

A key function of the prefrontal cortex is to support inhibitory control over behavior. It is widely believed that this function extends to stopping cognitive processes as well. Consistent with this, mounting evidence establishes the role of the right lateral prefrontal cortex in a clear case of cognitive control: retrieval suppression. Retrieval suppression refers to the ability to intentionally stop the retrieval process that arises when a reminder to a memory appears. Functional imaging data indicate that retrieval suppression involves top-down modulation of hippocampal activity by the dorsolateral prefrontal cortex, but the anatomical pathways supporting this inhibitory modulation remain unclear. Here we bridge this gap by integrating key findings about retrieval suppression observed through functional imaging with a detailed consideration of relevant anatomical pathways observed in non-human primates. Focusing selectively on the potential role of the anterior cingulate cortex, we develop two hypotheses about the pathways mediating interactions between lateral prefrontal cortex and the medial temporal lobes during suppression, and their cellular targets: the entorhinal gating hypothesis, and thalamo-hippocampal modulation via the nucleus reuniens. We hypothesize that whereas entorhinal gating is well situated to stop retrieval proactively, thalamo-hippocampal modulation may interrupt an ongoing act of retrieval reactively. Isolating the pathways that underlie retrieval suppression holds the potential to advance our understanding of a range of psychiatric disorders characterized by persistent intrusive thoughts. More broadly, an anatomical account of retrieval suppression would provide a key model system for understanding inhibitory control over cognition.

The origins of repetitive thought in rumination: separating cognitive style from deficits in inhibitory control over memory.

BACKGROUND AND OBJECTIVES: Rumination is a major contributor to the maintenance of affective disorders and has been linked to memory control deficits. However, ruminators often report intentionally engaging in repetitive thought due to its perceived benefits. Deliberate re-processing may lead to the appearance of a memory control deficit that is better explained as a difference in cognitive style. METHODS: Ninety-six undergraduate students volunteered to take part in a direct-suppression variant of the Think/No-Think paradigm after which they completed self-report measures of rumination and the degree to which they deliberately re-processed the to-be-suppressed items. RESULTS: We demonstrate a relation between rumination and impaired suppression-induced forgetting. This relation is robust even when controlling for deliberate re-processing of the to-be-suppressed items, a behavior itself related to both rumination and suppression. Therefore, whereas conscious fixation on to-be-suppressed items reduced memory suppression, it did not fully account for the relation between rumination and memory suppression. LIMITATIONS: The current experiment employed a retrospective measure of deliberate re-processing in the context of an unscreened university sample; future research might therefore generalize our findings using an online measure of deliberate re-processing or within a clinical population. CONCLUSIONS: We provide evidence that deliberate re-processing accounts for some--but not all--of the relation between rumination and suppression-induced forgetting. The present findings, observed in a paradigm known to engage top-down inhibitory modulation of mnemonic processing, provide the most theoretically focused evidence to date for the existence of a memory control deficit in rumination.