Think twice, it’s all right: Long lasting effects of disrupted reconsolidation on brain and behavior in human long-term fear

Life-threatening, high-intensity trauma- and context-dependent anxiety in zebrafish and its modulation by epinephrine

Trauma-related psychopathology transpires in some individuals after exposure to a life-threatening event. While aberrant adrenergic processes may contribute to this, a clear understanding of how said processes influence trauma-related conditions, remain inadequate. Here, we aimed to develop and describe a novel zebrafish (Danio rerio) model of life-threatening trauma-induced anxiety that may be representative of trauma related anxiety, and to evaluate the impact of stress-paired epinephrine (EPI) exposure in the model system. Four groups of zebrafish were each exposed to different and unique stress-related paradigms, i.e., i) a sham (trauma free), ii) high-intensity trauma (triple hit; THIT), iii) high-intensity trauma in the presence of EPI exposure (EHIT), and iv) EPI exposure on its own, all applied in the presence of a color context. Novel tank anxiety was subsequently assessed at 1, 4, 7 and 14 days after the traumatic event. The present results demonstrate that 1) through day 14, THIT or EPI exposure alone induced persistent anxiety-like behavior, 2) EHIT blunted the delayed anxiety-like sequalae associated with severe trauma, 3) exposure to a trauma-paired color context prior to anxiety testing bolstered the subsequent anxiety-like behavior of THIT, but not EHIT -exposed fish, and 4) despite this, THIT- and EPI-exposed fish showed a lesser degree of contextual avoidance behavior compared to sham- or EHIT-exposed fish. These results indicate that the stressors induced long-lasting anxiety-like behavior reminiscent of post trauma anxiety, while EPI displays complex interactions with the stressor, including a buffering effect to subsequent exposure of a trauma-paired cue.

Face your fears: attenuating remote fear memories by reconsolidation-updating

Traumatic events generate some of the most enduring memories, yet little is known about how long-lasting fear memories can be attenuated. In this review, we collect the surprisingly sparse evidence on remote fear memory attenuation from both animal and human research. What is becoming apparent is twofold: although remote fear memories are more resistant to change compared with recent ones, they can nevertheless be attenuated when interventions are targeted toward the period of memory malleability instigated by memory recall, the reconsolidation window. We describe the physiological mechanisms underlying remote reconsolidation-updating approaches and highlight how they can be enhanced through interventions promoting synaptic plasticity. By capitalizing on an intrinsically relevant phase of memory, reconsolidation-updating harbors the potential to permanently alter remote fear memories.

The effectiveness of extinction training in male rats: Temporal considerations and brain mechanisms

The extinction of conditioned fear is frequently used in laboratories as a model for human exposure therapy and is crucial for studies of posttraumatic stress disorder (PTSD). However, the efficacy of specific protocols can vary greatly, and the underlying brain mechanisms are not sufficiently clarified. To address this issue, variable starting time (one or twenty-eight days after fear conditioning) and extinction protocols were used, and the efficacy and durability of fear extinction were also studied. Changes in the behavior, stress hormone levels and neuronal activation patterns of stressed rats were analyzed. Conditioned fear was rapidly and efficiently extinguished by all the protocols investigated. However, when these extinction protocols were initiated one day after fear training, conditioned fear relapsed spontaneously four weeks later. In contrast, when extinction trials were started 28 days after conditioning, no relapse occurred. Hormone measurements taken by the end of extinction trials indicated that adrenocorticotropin, but not corticosterone responses reflected behavioral extinction without any sign of relapse. The last extinction training increased the activation of the medial prefrontal cortex and decreased the activation of the central and medial amygdala when extinction began one day after fear conditioning. By contrast, the activation of the basolateral amygdala and the entire hippocampus decreased by the last training session when extinction started 28 days after fear conditioning. Our findings show that extinction training can extinguish remote fear memories more effectively than recent ones, and that the brain mechanisms underlying remote and recent fear memory extinction differ. Laboratory models should also focus on a later time point to increase their translational value.

Reconsolidation and Fear Extinction: An Update

Fear memories can be updated behaviorally by delivering extinction trials during the reconsolidation window, which results in a persistent attenuation of fear memories (Monfils et al., Science 324:951-955, 2009). This safe and non-invasive paradigm, termed retrieval-extinction (or post-retrieval extinction), has also been found to be successful at preventing the return of fear in healthy fear conditioned humans (Schiller et al., Nature 463:49-53, 2010), and in the time since its discovery, there has been an explosion of research on the use of retrieval-extinction in fear memories in humans and other animals, some of which have found a long-term reduction in conditioned responding, and some who have not. These discrepant findings have raised concerns as to whether retrieval-extinction really results in updating of the original fear memory, or if it simply enhances extinction. We will first review the progress made on elucidating the cellular mechanisms underlying the fear attenuating effects of retrieval-extinction and how they differ from traditional extinction. Special attention will be paid to the molecular events necessary for retrieval-extinction to successfully occur and how these reconsolidated memories are represented in the brain. Next, we will examine the parameters that determine whether or not a memory will be updated via extinction during the reconsolidation window (also known as boundary conditions). These boundary conditions will also be discussed as possible explanations for discrepant findings of the retrieval-extinction effect. Then we will examine the factors that can determine whether an individual's fears will successfully be attenuated by retrieval-extinction. These individual differences include genetics, age, and psychopathology. Finally, we will discuss recent attempts to bring the retrieval-extinction paradigm from the bench to the bedside for the behavioral treatment of anxiety and trauma disorders.

A novel stress-based intervention reduces cigarette use in non-treatment seeking smokers

Tobacco use is the leading cause of preventable mortality worldwide. Since current smoking cessation aids show only modest efficacy, new interventions are needed. Given the evidence that stress is a potent trigger for smoking, the present randomized clinical trial tested whether stress could augment the effects of a memory updating (retrieval-extinction) intervention. Non-treatment seeking smokers (n = 76) were assigned to one of four conditions composed of either a stressful or non-stressful psychosocial challenge followed by either smoking or neutral cues. Ten minutes after this manipulation, all underwent a 60-minute extinction procedure during which they viewed smoking-related videos and images and manipulated smoking paraphernalia. Compared to participants who were not exposed to the laboratory stressor, the stressor-exposed groups exhibited greater psychophysiological responses during their intervention and greater decreases in cigarette use at two- and six-weeks follow-up independent of smoking cue exposure. Together, these findings suggest that the ability of stress to activate cigarette seeking processes can be exploited to decrease cigarette use. With replication, the stress-based intervention could become a novel strategy for decreasing cigarette use in non-treatment seeking smokers.Clinicaltrials.gov identifier: NCT04843969.

Guided reactivation of personal phobic memories prior to exposure exercises prevents the renewal of fear responses in subjects with claustrophobic fears

BACKGROUND AND OBJECTIVES

Basic research suggest behavioral strategies for interferencing the reconsolidation of fear memories to be a promising approach in reducing clinical fears. However, first clinical studies revealed mixed results highlighting the need to identify boundary conditions. We experimentally tested the specific hypothesis that post-retrieval threat exposure prevents context renewal usually observed in protocols without fear memory reactivation.

METHODS

In a preliminary investigation forty-three individuals with claustrophobic fears reactivated the individual phobic memory or not during a guided emotional imagery task and then performed standardized threat exposure to provide new information for updating the original memory. During retests seven and 28 days later, the context was different from that during treatment in half of the subjects.

RESULTS

In those who were guided, the fear memory was successfully reactivated as indexed by increased skin conductance level (SCL) during the imagery of personal scenes relative to neutral scenes. During retests the subjects of the memory non-activation group showed a return of reported fear after context change that, however, was not observed after post-retrieval exposure. In line, autonomic arousal (SCL) decreased over time in the memory reactivation group only if the context changed during retest.

LIMITATIONS

Limited sample size and the inclusion of an analog sample reduce the generalizability of the results.

CONCLUSIONS

The reactivation of fear memory prior to treatment through guided imagery of past personal phobic situations prevented contextual renewal of phobic fears which was observed in those subjects without reactivation of memory.

Theta-Burst Stimulation Combined With Virtual-Reality Reconsolidation Intervention for Methamphetamine Use Disorder: Study Protocol for a Randomized-Controlled Trial

Background

Craving associated with drug-related memory is one of the key factors that induce the relapse of methamphetamine (MA). Disruption or modulation of the reconsolidation of drug-related memory may serve as an option for clinical treatment of MA addiction. This protocol proposes to use virtual reality (VR) to retrieve drug-associated memory and then use transcranial magnetic stimulation (TMS) at the neural circuit that encodes the reward value of drug cues to provide a non-invasive intervention during reconsolidation. We aim to evaluate the effectiveness of TMS treatment after VR retrieval on the reduction of cue reactivity and craving of MA.

Methods

This is a randomized, double-blind, sham-controlled, parallel group trial, targeting participants with MA use disorder aged from 18 to 45 years old. Forty-five eligible volunteers in Shanxi Drug Rehabilitation Center will be recruited and be randomly allocated into three parallel groups, receiving either 1) MA-related cues retrieval in VR combined with active TMS (MA VR scene + TBS) or 2) sham TMS (MA VR scene + sham TBS), or 3) neutral cues retrieval in VR combined with active TMS (neutral VR scene + TBS). Two sessions of post-VR-retrieval TBS will be scheduled on two separate days within 1 week. The primary outcome will detect the memory-related activity by the electroencephalography (EEG) reactivity to drug cues in VR scenes. Secondary outcomes are the self-reported MA craving in VR scene, the physiological parameter (cue-induced heart rate) and the scores of psychological questionnaires including anxiety, depression, and mood. All primary and secondary outcomes will be assessed at baseline, 1-week, and 1-month post-intervention. Assessments will be compared between the groups of 1) MA VR scene + TBS, 2) MA VR scene + sham TBS and 3) neutral VR scene + TBS.

Discussion

This will be the first study to examine whether the TMS modulation after VR retrieval can reduce self-reported craving and drug-related cue reactivity. It will promote the understanding of the neural circuit mechanism of the reconsolidation-based intervention and provide an effective treatment for MA use disorder patients.

Clinical Trial Registration

[Chinese Clinical Trial Registry], identifier [ChiCTR1900026902]. Registered on 26 October 2019.

The evidence for and against reactivation-induced memory updating in humans and nonhuman animals

Systematic investigation of reactivation-induced memory updating began in the 1960s, and a wave of research in this area followed the seminal articulation of "reconsolidation" theory in the early 2000s. Myriad studies indicate that memory reactivation can cause previously consolidated memories to become labile and sensitive to weakening, strengthening, or other forms of modification. However, from its nascent period to the present, the field has been beset by inconsistencies in researchers' abilities to replicate seemingly established effects. Here we review these many studies, synthesizing the human and nonhuman animal literature, and suggest that these failures-to-replicate reflect a highly complex and delicately balanced memory modification system, the substrates of which must be finely tuned to enable adaptive memory updating while limiting maladaptive, inaccurate modifications. A systematic approach to the entire body of evidence, integrating positive and null findings, will yield a comprehensive understanding of the complex and dynamic nature of long-term memory storage and the potential for harnessing modification processes to treat mental disorders driven by pervasive maladaptive memories.

Can contingency rehearsal during the interval between a retrieval cue and extinction training change the effects of post-retrieval extinction?

Return of fear may be prevented by post-retrieval extinction (PRE), a procedure consisting of presenting a stimulus that was present during conditioning (retrieval cue) prior to extinction training. However, recent evidence suggests that there might be circumstances under which PRE is not effective to prevent the return of fear (boundary conditions), but some of these conditions remain unknown. We explored if rehearsing the CS, US or CS-US contingency during the interval between the retrieval cue and extinction training might change the effects of PRE. One day after differential fear conditioning, healthy human participants (n = 83) underwent either standard extinction (control condition, n = 31) or two different PRE procedures, one in which participants rehearsed the CS-US contingency during the interval between the retrieval cue and extinction (rehearsal condition, n = 25), or another in which they underwent a verbal fluency task directing their attention away from the experimental contingencies during this interval (nonrehearsal condition, n = 27). Return of fear in a reinstatement test was observed in both control and rehearsal conditions, whereas in the nonrehearsal condition there was a generalized increase in response to the CS+ and CS-. Differential response in the rehearsal condition had values slightly smaller than the control group with no significant differences from both control and nonrehearsal conditions. These results suggest that the overt behavior of participants during the interval between a retrieval cue and extinction training might change the effects of PRE in healthy human participants, but further manipulations of these variables are needed to confirm these findings.

Is Reconsolidation a General Property of Memory?

Memory reconsolidation holds great hope for memory modification approaches and clinical treatments of mental disorders associated with maladaptive memories. However, it remains controversial as to whether reconsolidation is a general property of all types of memory. Especially, discrepancies have been reported in research focusing on whether declarative memory undergoes reconsolidation, and whether old memories can be reorganized after retrieval. Here, we discuss how these inconsistent results can be reconciled and what information we need to uncover for the general use of reconsolidation.

Targeting the reconsolidation of traumatic memories with a brief 2-session imaginal exposure intervention in post-traumatic stress disorder

BACKGROUND

Evidence suggests that extinction during memory reconsolidation diminishes the return of defensive responses. In order to translate these effects to the clinical setting, we tested whether retrieving a traumatic memory and delivering a brief two-sessions imaginal exposure intervention during its reconsolidation would produce stronger decreases in reactivity to these memories than standard imaginal exposure method.

METHODS

Participants with Post-Traumatic Stress Disorder (PTSD) had either their traumatic (n = 21) or a neutral (n = 21) memory retrieved 1 h before an imaginal exposure session for two consecutive days. One day before and one day after, participants were exposed to script-driven imagery of their traumatic event, during which skin conductance responses were measured and, immediately after, subjective responses were assessed by means of Visual Analogue Scales.

RESULTS

Traumatic retrieval improved the physiological, but not the subjective effects of imaginal exposure intervention on over-reactivity to traumatic memories.

CONCLUSIONS

Our results suggest that delivering extinction-based treatments over the reconsolidation of traumatic memories may enhance its effects. These results suggest that this is a promising path toward the development of new therapeutic techniques.

Augmenting exposure therapy with pre-extinction fear memory reactivation and deepened extinction: A randomized controlled trial

BACKGROUND

Pre-extinction fear memory reactivation (PE-FMR) and deepened extinction (DE) enhance long-term extinction of shock-conditioned fear, and may also enhance long-term extinction of naturally acquired fear. Preliminary data suggest that PE-FMR may additionally boost the speed of fear reduction during exposure therapy.

DESIGN

Randomized controlled trial, factorial design.

METHODS

Participants with elevated fears of either spiders or snakes were randomized to (1) exposure therapy alone (n = 41), (2) exposure therapy + PE-FMR (n = 42), (3) exposure therapy + DE (n = 41), or (4) exposure therapy + PE-FMR + DE (n = 42). Participants were assessed at baseline, post-treatment, and one-week follow-up on subjective and behavioral indices of phobia. Because treatment length was tailored to speed of fear reduction, survival analyses were used to examine the speed of fear reduction during treatment.

RESULTS

DE did not improve clinical outcomes at post-treatment or follow-up, whereas PE-FMR produced more rapid fear reduction and was able to achive equivalent outcomes even when the duration of exposure therapy (tailored to speed of fear reduction) was shortened by an average of 21%.

CONCLUSIONS

Data suggest that PE-FMR is a promising strategy for reducing the overall duration of exposure-based therapies.

CLINICAL TRIAL REGISTRATION

(clinicaltrials.gov)NCT02160470.

Investigating the efficacy of the reminder-extinction procedure to disrupt contextual threat memories in humans using immersive Virtual Reality

Upon reactivation, consolidated memories can enter a temporary labile state and require restabilisation, known as reconsolidation. Interventions during this reconsolidation period can disrupt the reactivated memory. However, it is unclear whether different kinds of memory that depend on distinct brain regions all undergo reconsolidation. Evidence for reconsolidation originates from studies assessing amygdala-dependent memories using cue-conditioning paradigms in rodents, which were subsequently replicated in humans. Whilst studies providing evidence for reconsolidation of hippocampus-dependent memories in rodents have predominantly used context conditioning paradigms, studies in humans have used completely different paradigms such as tests for wordlists or stories. Here our objective was to bridge this paradigm gap between rodent and human studies probing reconsolidation of hippocampus-dependent memories. We modified a recently developed immersive Virtual Reality paradigm to test in humans whether contextual threat-conditioned memories can be disrupted by a reminder-extinction procedure that putatively targets reconsolidation. In contrast to our hypothesis, we found comparable recovery of contextual conditioned threat responses, and comparable retention of subjective measures of threat memory, episodic memory and exploration behaviour between the reminder-extinction and standard extinction groups. Our result provide no evidence that a reminder before extinction can prevent the return of context conditioned threat memories in humans.

Decrease in amygdala activity during repeated exposure to spider images predicts avoidance behavior in spider fearful individuals

Spider phobia is characterized by exaggerated fear of situations where spiders could be present, resulting in avoidance of such situations and compromised quality of life. An important component in psychological treatment of spider phobia is exposure to phobic situations that reduces avoidance behaviors. At the neural level, amygdala responses to phobic material are elevated, but normalizes following exposure treatment. To what extent amygdala activity decreases during a session of repeated phobic stimulation, and whether activity decrease is related to subsequent avoidance is not well studied. We hypothesized reduced amygdala activity during the course of repeated exposure to spider pictures, and that the degree of reduction would predict subsequent avoidance of spider pictures. To test our hypothesis, functional magnetic resonance imaging was performed in 45 individuals with spider fear during repeated exposure to spider pictures. Results showed that repeated exposure to spider stimuli attenuated amygdala reactivity and individual differences in activity reductions predicted subsequent avoidance behavior to spider pictures in an incentive-conflict task, with larger attenuations predicting less avoidance. At 6-month follow up, initial reductions in amygdala activation still predicted avoidance. This result demonstrates that reduction in amygdala responses is related to clinically meaningful outcomes in human anxiety, and suggests that within-session reductions in amygdala responses could be an important mechanism explaining the clinical effects of exposure therapy.

Behavioral tagging underlies memory reconsolidation

Memory reconsolidation occurs when a retrieving event destabilizes transiently a consolidated memory, triggering thereby a new process of restabilization that ensures memory persistence. Although this phenomenon has received wide attention, the effect of new information cooccurring with the reconsolidation process has been less explored. Here we demonstrate that a memory-retrieving event sets a neural tag, which enables the reconsolidation of memory after binding proteins provided by the original or a different contiguous experience. We characterized the specific temporal window during which this association is effective and identified the protein kinase A (PKA) and the extracellular signal-regulated kinase 1 and 2 (ERK 1/2) pathways as the mechanisms related to the setting of the reconsolidation tag and the synthesis of proteins. Our results show, therefore, that memory reconsolidation is mediated by a "behavioral tagging" process, which is common to different memory forms. They represent a significant advance in understanding the fate of memories reconsolidated while being adjacent to other events, and provide a tool for designing noninvasive strategies to attenuate (pathological/traumatic) or improve (education-related) memories.

No persistent attenuation of fear memories in humans: A registered replication of the reactivation-extinction effect

It has been proposed that memory retrieval can destabilize consolidated memories, after which they need to be reconsolidated in order to be retained. The presentation of relevant information during memory reconsolidation could then result in the modification of a destabilized memory trace, by allowing the memory trace to be updated before being reconsolidated. In line with this idea, Schiller et al. (2010) have demonstrated that memory retrieval shortly before extinction training can prevent the later recovery of conditioned fear responding that is observed after regular extinction training. Those findings have been the subject of considerable controversy, due in part to theoretical reasons but also due to a number of failures to obtain similar results in conceptual replication attempts. Here, we report the results of a highly powered, direct, independent replication of the critical conditions of Schiller et al. (2010, Experiment 1). Due to misrepresentation of the exclusion criteria in the original Schiller et al. (2010) report, data collection was considerably delayed. When we eventually managed to attain our pre-registered sample size, we found that we could not observe any benefit of reactivation-extinction over regular extinction training in preventing recovery of conditioned fear. The results of the present study, along with the mixed findings in the literature and the misreporting in Schiller et al. (2010), give cause to question whether there is robust evidence that reactivation-extinction prevents the return of fear in humans.

The effect of mindfulness training on extinction retention

Anxiety and trauma related disorders are highly prevalent, causing suffering and high costs for society. Current treatment strategies, although effective, only show moderate effect-sizes when compared to adequate control groups demonstrating a need to develop new forms of treatment or optimize existing ones. In order to achieve this, an increased understanding of what mechanisms are involved is needed. An emerging literature indicates that mindfulness training (MFT) can be used to treat fear and anxiety related disorders, but the treatment mechanisms are unclear. One hypothesis, largely based on findings from neuroimaging studies, states that MFT may improve extinction retention, but this has not been demonstrated empirically. To investigate this question healthy subjects either completed a 4-week MFT- intervention delivered through a smart-phone app (n = 14) or were assigned to a waitlist (n = 15). Subsequently, subjects participated in a two-day experimental protocol using pavlovian aversive conditioning, evaluating acquisition and extinction of threat-related responses on day 1, and extinction retention on day 2. Results showed that the MFT group displayed reduced spontaneous recovery of threat related arousal responses, as compared to the waitlist control group, on day 2. MFT did not however, have an effect on either the acquisition or extinction of conditioned responses day 1. This clarifies the positive effect of MFT on emotional functioning and could have implications for the treatment of anxiety and trauma related disorders.

Prospects for reconsolidation-focused treatments of substance use and anxiety-related disorders

Memories are often conceptualized as permanent entities; however, retrieval of memories via stimulus prompts can return them to an active state, which initiates a period of lability before the memories are reconsolidated into long-term storage. Importantly, during this period, memories can be disrupted/altered. A growing body of work has focused on translating animal and experimental science into reconsolidation-based interventions for clinical disorders maintained by maladaptive memories. Interventions targeting reward-based and fear-based memories undergirding substance use and anxiety-related disorders, respectively, have shown significant potential. There are several promising pharmacological agents and behavioral approaches that have been used to therapeutically target memory reconsolidation. Here, we discuss the current state of science with special emphasis on the clinical utility of these approaches.

Memory boundaries: opening a window inspired by reconsolidation to treat anxiety, trauma-related, and addiction disorders

Pioneering research over the past two decades has shown that memories are far more malleable than we once thought, thereby highlighting the potential for new clinical avenues for treatment of psychopathology. We first briefly review the historical foundation of memory reconsolidation-a concept that refers to hypothetical processes that occur when a memory is retrieved and restored. Then, we provide an overview of the basic research on memory reconsolidation that has been done with humans and other animals, focusing on models of fear, anxiety-related disorders, and addiction, from the perspective that they all involve disorders of memory. This basic research has fuelled early stage developments of novel treatment techniques. More specifically, we consider behavioural interventions inspired by reconsolidation updating, namely retrieval-extinction techniques. We discuss the set of principles that would be needed for memory modifications within a putative reconsolidation time window, and review research that employs reconsolidation-based strategies with clinical populations. We conclude by highlighting current pitfalls and controversies surrounding the use of reconsolidation-based approaches, but end on an optimistic note for clinical research going forward. Despite the challenges, we believe that drawing on ideas from psychological science can help open up treatment innovation.

Modulation of naturalistic maladaptive memories using behavioural and pharmacological reconsolidation-interfering strategies: a systematic review and meta-analysis of clinical and 'sub-clinical' studies

BACKGROUND

Consolidated memories can undergo enduring modification through retrieval-dependent treatments that modulate reconsolidation. This represents a potentially transformative strategy for weakening or overwriting the maladaptive memories that underlie substance use and anxiety/trauma-related disorders. However, modulation of naturalistic maladaptive memories may be limited by 'boundary conditions' imposed on the reconsolidation process by the nature of these memories.

METHODS

We conducted a systematic review and meta-analyses of behavioural and pharmacological studies examining retrieval-dependent modulation of reward- and threat-related memories in (sub) clinical substance use and anxiety/trauma, respectively.

RESULTS

Of 4938 publications assessed for eligibility, 8 studies of substance use and 10 of anxiety (phobia)- and trauma-related symptoms were included in the meta-analyses. Overall, the findings were in the predicted direction, with most studies favouring the 'retrieval + treatment' condition. However, the magnitude of effects was dependent upon the nature of treatment, with pharmacological interventions showing a medium-sized effect (g = 0.59, p = 0.03) and behavioural treatments, a relatively small effect (g = 0.32, p = 0.10) in studies of phobia/trauma. Among studies of substance use, post-retrieval behavioural interventions yielded a larger effect (g = 0.60, p < 0.001) relative to pharmacological treatments (g = - 0.03, p = 0.91), with treatment type being a statistically significant moderator (χ2(1) = 4.20, p = 0.04).

CONCLUSION

Modification of naturalistic maladaptive memories during reconsolidation appears to be a viable treatment strategy for substance use and phobias/trauma disorders. However, high levels of heterogeneity and methodological variation limit the strength of conclusions that can be drawn from the reviewed studies at this stage.

Exploring the boundaries of post-retrieval extinction in healthy and anxious individuals

Over a dozen studies have examined the efficacy of post-retrieval extinction (PRE) in healthy adults in the fear conditioning laboratory, with a recent meta-analysis reporting an overall small-moderate effect on attenuating the return of fear compared to standard extinction. The current study was designed to extend PRE effects to a mixed sample of healthy and anxious individuals, explore potential moderators, and examine the benefit of PRE for a memory conditioned over multiple days. Healthy (n = 49) and anxious (n = 43) adults received either one day of acquisition followed by PRE, one day of acquisition followed by extinction, or three days of acquisition followed by PRE. Comparing participants who received one day of acquisition followed by PRE or extinction, no significant effect of PRE was observed on differential skin conductance response reinstatement or reactivity to the conditioned stimulus alone. Anxiety symptoms did not moderate outcomes. There was no difference in return of fear for anxious participants who received three days of acquisition followed by PRE versus one day of acquisition followed by PRE. These results further highlight the variability of findings in the PRE literature and need for further examination of individual difference factors that may moderate PRE effects.

Is it possible to modify fear memories in humans with extinction training within a single day?

Extinction procedures have been used widely in the study of fear memories, and different positions have been adopted regarding the efficacy of such procedures and the mechanisms involved. It has been argued that extinction may interfere with the consolidation of the fear memory if the procedure is applied with the appropriate timing after acquisition. However, the opposite position is also held, that is, that the extinction does not achieve an elimination of the fear response. The aim of the present study is to test the short-term effects of immediate extinction in fear reduction when this extinction is preceded by a retrieval trial. For this, a procedure similar to that employed by Schiller et al. (Nature 463(7277): 49-53, 2010) was used, but in a single day and with white noise as an aversive unconditioned stimulus. The results indicate that a CS+ single retrieval trial before the extinction procedure after acquisition was more effective in fear reduction than standard immediate extinction.

Multiple memory systems, multiple time points: how science can inform treatment to control the expression of unwanted emotional memories

Memories that have strong emotions associated with them are particularly resilient to forgetting. This is not necessarily problematic, however some aspects of memory can be. In particular, the involuntary expression of those memories, e.g. intrusive memories after trauma, are core to certain psychological disorders. Since the beginning of this century, research using animal models shows that it is possible to change the underlying memory, for example by interfering with its consolidation or reconsolidation. While the idea of targeting maladaptive memories is promising for the treatment of stress and anxiety disorders, a direct application of the procedures used in non-human animals to humans in clinical settings is not straightforward. In translational research, more attention needs to be paid to specifying what aspect of memory (i) can be modified and (ii) should be modified. This requires a clear conceptualization of what aspect of memory is being targeted, and how different memory expressions may map onto clinical symptoms. Furthermore, memory processes are dynamic, so procedural details concerning timing are crucial when implementing a treatment and when assessing its effectiveness. To target emotional memory in its full complexity, including its malleability, science cannot rely on a single method, species or paradigm. Rather, a constructive dialogue is needed between multiple levels of research, all the way 'from mice to mental health'.This article is part of a discussion meeting issue 'Of mice and mental health: facilitating dialogue between basic and clinical neuroscientists'.

An Update on Memory Reconsolidation Updating

The reactivation of a stored memory in the brain can make the memory transiently labile. During the time it takes for the memory to restabilize (reconsolidate) the memory can either be reduced by an amnesic agent or enhanced by memory enhancers. The change in memory expression is related to changes in the brain correlates of long-term memory. Many have suggested that such retrieval-induced plasticity is ideally placed to enable memories to be updated with new information. This hypothesis has been tested experimentally, with a translational perspective, by attempts to update maladaptive memories to reduce their problematic impact. We review here progress on reconsolidation updating studies, highlighting their translational exploitation and addressing recent challenges to the reconsolidation field.