Human reconsolidation: a reactivation and update

New in, old out: Does learning a new language make you forget previously learned foreign languages?

Anecdotal evidence suggests that learning a new foreign language (FL) makes you forget previously learned FLs. To seek empirical evidence for this claim, we tested whether learning words in a previously unknown L3 hampers subsequent retrieval of their L2 translation equivalents. In two experiments, Dutch native speakers with knowledge of English (L2), but not Spanish (L3), first completed an English vocabulary test, based on which 46 participant-specific, known English words were chosen. Half of those were then learned in Spanish. Finally, participants' memory for all 46 English words was probed again in a picture naming task. In Experiment 1, all tests took place within one session. In Experiment 2, we separated the English pre-test from Spanish learning by a day and manipulated the timing of the English post-test (immediately after learning vs. 1 day later). By separating the post-test from Spanish learning, we asked whether consolidation of the new Spanish words would increase their interference strength. We found significant main effects of interference in naming latencies and accuracy: Participants speeded up less and were less accurate to recall words in English for which they had learned Spanish translations, compared with words for which they had not. Consolidation time did not significantly affect these interference effects. Thus, learning a new language indeed comes at the cost of subsequent retrieval ability in other FLs. Such interference effects set in immediately after learning and do not need time to emerge, even when the other FL has been known for a long time.

The Role of Serotonin in Fear Learning and Memory: A Systematic Review of Human Studies

Fear is characterized by distinct behavioral and physiological responses that are essential for the survival of the human species. Fear conditioning (FC) serves as a valuable model for studying the acquisition, extinction, and expression of fear. The serotonin (5-hydroxytryptamine, 5-HT) system is known to play a significant role in emotional and motivational aspects of human behavior, including fear learning and expression. Accumulating evidence from both animal and human studies suggests that brain regions involved in FC, such as the amygdala, hippocampus, and prefrontal cortex, possess a high density of 5-HT receptors, implicating the crucial involvement of serotonin in aversive learning. Additionally, studies exploring serotonin gene polymorphisms have indicated their potential influence on FC. Therefore, the objective of this work was to review the existing evidence linking 5-HT with fear learning and memory in humans. Through a comprehensive screening of the PubMed and Web of Science databases, 29 relevant studies were included in the final review. These studies investigated the relationship between serotonin and fear learning using drug manipulations or by studying 5-HT-related gene polymorphisms. The results suggest that elevated levels of 5-HT enhance aversive learning, indicating that the modulation of serotonin 5-HT2A receptors regulates the expression of fear responses in humans. Understanding the role of this neurochemical messenger in associative aversive learning can provide insights into psychiatric disorders such as anxiety and post-traumatic stress disorder (PTSD), among others.

Tackling childbirth-related intrusive memories with a single-session behavioural intervention involving a visuospatial task: protocol for a single-blind, waitlist-controlled randomised trial

INTRODUCTION

Approximately 12.3% of mothers experience childbirth-related post-traumatic stress symptoms (CB-PTSS). However, evidence-based interventions to treat CB-PTSS are lacking. Intrusive memories (IM), a key CB-PTSS, are distressing and can trigger other PTSS by reliving the traumatic event. Emerging evidence shows that a behavioural intervention involving a visuospatial task (BI-VT) can reduce the number of IM and PTSS, supposedly by interfering with the reconsolidation of the trauma memory. This study aims to test the efficacy of a single-session BI-VT targeting IM to reduce the number of childbirth-related (CB-)IM and PTSS, in comparison to a waitlist control group (WCG).

METHODS AND ANALYSIS

In this multicentre, single-blind, randomised controlled trial being undertaken at one regional and one university hospital in Switzerland, 60 participants will be allocated to the Immediate Intervention Group (IIG), receiving the immediate intervention on day 15, and 60 participants to the WCG receiving the delayed intervention on day 30. All participants will report their CB-IM during the 2 weeks preimmediate and postimmediate intervention in diaries. The IIG will additionally report their CB-IM over weeks 5 and 6 postimmediate intervention. Self-report questionnaires will assess CB-PTSS at 2 weeks preimmediate and postimmediate intervention in both groups, and at 6 weeks postimmediate intervention in the IIG. A feedback questionnaire will evaluate the intervention acceptability. The primary outcome will be group differences in the number of CB-IM between the 2 weeks preimmediate and postimmediate intervention. Secondary outcomes will be CB-PTSS at 2 and 6 weeks postimmediate intervention, the number of CB-IM at weeks 5 and 6 postimmediate intervention, and intervention acceptability.

ETHICS AND DISSEMINATION

Ethical approval was granted by the Human Research Ethics Committee of the Canton of Vaud (study number 202200652). Participants will provide an informed consent before study participation. Results will be presented in peer-reviewed journals and at conferences.

TRIAL REGISTRATION NUMBER

NCT05381155.

Making Leaps and Hitting Boundaries in Reconsolidation: Overcoming Boundary Conditions to Increase Clinical Translatability of Reconsolidation-based Therapies

Reconsolidation results in the restabilisation, and thus persistence, of a memory made labile by retrieval, and interfering with this process is thought to enable modification or weakening of the original trace. As such, reconsolidation-blockade has been a focus of research aiming to target the maladaptive memories underlying mental health disorders, including post-traumatic stress disorder and drug addiction. Current first-line therapies are not effective for all patients, and a substantial proportion of those for whom therapies are effective later relapse. A reconsolidation-based intervention would be invaluable as an alternative treatment for these conditions. However, the translation of reconsolidation-based therapies to the clinic presents a number of challenges, with arguably the greatest being the overcoming of the boundary conditions governing the opening of the reconsolidation window. These include factors such as the age and strength of memory, and can broadly be divided into two categories: intrinsic features of the targeted memory itself, and parameters of the reactivation procedure used. With maladaptive memory characteristics inevitably varying amongst individuals, manipulation of the other limitations imposed by procedural variables have been explored to circumvent the boundary conditions on reconsolidation. Although several apparently discrepant results remain to be reconciled and these limitations yet to be truly defined, many studies have produced successful results which encouragingly demonstrate that boundary conditions may be overcome using various proposed strategies to enable translation of a reconsolidation-based intervention to clinical use.

Investigating the effects of sleep and sleep loss on the different stages of episodic emotional memory: A narrative review and guide to the future

For two decades, sleep has been touted as one of the primary drivers for the encoding, consolidation, retention, and retrieval of episodic emotional memory. Recently, however, sleep’s role in emotional memory processing has received renewed scrutiny as meta-analyses and reviews have indicated that sleep may only contribute a small effect that hinges on the content or context of the learning and retrieval episodes. On the one hand, the strong perception of sleep’s importance in maintaining memory for emotional events may have been exacerbated by publication bias phenomena, such as the “winner’s curse” and “file drawer problem.” On the other hand, it is plausible that there are sets of circumstances that lead to consistent and reliable effects of sleep on emotional memory; these circumstances may depend on factors such as the placement and quality of sleep relative to the emotional experience, the content and context of the emotional experience, and the probes and strategies used to assess memory at retrieval. Here, we review the literature on how sleep (and sleep loss) influences each stage of emotional episodic memory. Specifically, we have separated previous work based on the placement of sleep and sleep loss in relation to the different stages of emotional memory processing: (1) prior to encoding, (2) immediately following encoding during early consolidation, (3) during extended consolidation, separated from initial learning, (4) just prior to retrieval, and (5) post-retrieval as memories may be restructured and reconsolidated. The goals of this review are three-fold: (1) examine phases of emotional memory that sleep may influence to a greater or lesser degree, (2) explicitly identify problematic overlaps in traditional sleep–wake study designs that are preventing the ability to better disentangle the potential role of sleep in the different stages of emotional memory processing, and (3) highlight areas for future research by identifying the stages of emotional memory processing in which the effect of sleep and sleep loss remains under-investigated. Here, we begin the task of better understanding the contexts and factors that influence the relationship between sleep and emotional memory processing and aim to be a valuable resource to facilitate hypothesis generation and promote important future research.

Verbal manipulations of learning expectancy do not enhance reconsolidation

Objectives

Pharmacological studies using propranolol suggest that if reactivation signals that new information will be learned (i.e., there is an expectation for learning) reconsolidation can be enhanced. We examined if the verbal instructions to expect new learning will enhance reconsolidation of fear memories using the post-retrieval extinction paradigm.

Methods

On day one, participants (n = 48) underwent differential fear conditioning to two images (CS+ and CS-). On day two, participants were randomly assigned to one of three groups; groups one and two had their memory for the CS+ reactivated (i.e., a single presentation of the CS+) 10 minutes prior to extinction, whereas group three did not have their memory reactivated but went right to extinction (no reactivation group). One reactivation group was told that they would learn something new about the images (expectation for learning group), and the other group was told that they would not learn anything new (no expectation for learning group). On day three, return of fear was measured following reinstatement (i.e., four shocks). Fear potentiated startle (FPS) and skin conductance response (SCR) were measured throughout.

Results

There was evidence of fear acquisition for participants for SCR but not FPS. With regards to reconsolidation, SCR increased for the CS+ and CS-in all groups from the end of extinction to the beginning of re-extinction (i.e., return of fear). For FPS, post-hoc tests conducted on the sub-group of participants showing fear learning showed that FPS remained stable in the two reactivation groups, but increased to the CS+, but not the CS- in the no reactivation group.

Implications

These findings suggest that a verbal manipulation of the expectation for learning may not be salient enough to enhance reconsolidation. Results are discussed in relation to theories on differences in between SCR, as a measure of cognitive awareness, and FPS, as a measure of fear.

The promise of low-tech intervention in a high-tech era: Remodeling pathological brain circuits using behavioral reverse engineering

As an academic pursuit, neuroscience is enjoying a golden age. From a clinical perspective, our field is failing. Conventional 20th century drugs and devices are not well-matched to the heterogeneity, scale, and connectivity of neural circuits that produce aberrant mental states and behavior. Laboratory-based methods for editing neural genomes and sculpting activity patterns are exciting, but their applications for hundreds of millions of people with mental health disorders is uncertain. We argue that mechanisms for regulating adult brain plasticity and remodeling pathological activity are substantially pre-wired, and we suggest new minimally invasive strategies to harness and direct these endogenous systems. Drawing from studies across the neuroscience literature, we describe approaches that identify neural biomarkers more closely linked to upstream causes-rather than downstream consequences-of disordered behavioral states. We highlight the potential for innovation and discovery in reverse engineering approaches that refine bespoke behavioral "agonists" to drive upstream neural biomarkers in normative directions and reduce clinical symptoms for select classes of neuropsychiatric disorders.

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.

Embodiment of an Emotional State Concurs with a Stress-Induced Reconsolidation Impairment Effect on an Auditory Verbal Word-List Memory

Stress alters memory. Understanding how and when acute stress improves or impairs memory is a challenge. Stressors can affect memory depending on a combination of factors. Typically, mild stressors and stress hormones might promote consolidation of memory processing and impair memory retrieval. However, studies have shown that during reconsolidation, stressors may either enhance or impair recalled memory. We propose that a function of reconsolidation is to induce changes in the behavioral expression of memory. Here, we adapted the Rey Auditory Verbal Learning Test (RAVLT) to evaluate the effect of cold pressor stress (CPS) during the reconsolidation of this declarative memory. A decay in memory performance attributable to forgetting was found at the time of memory reactivation 5 d after training (day 6). Contrary to our initial predictions, the administration of CPS after memory reactivation impaired long-term memory expression (day 7), an effect dependent on the presence of a mismatch during Reactivation Session. No differences in recognition tests were found. To assess putative sources of the negative memory modulation effects induced during reconsolidation, current emotional state was evaluated immediately after Testing Session (day 7). An increase in arousal was revealed only when CPS was administered concurrently with memory reactivation-labilization. The possibility of integration during reconsolidation of independent associations of these emotive components in the trace is a critical factor in modulating neutral memories during reconsolidation by stressors.

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

BACKGROUND

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

METHODS

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

RESULTS

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

LIMITATIONS

The design limits the causal interpretation of observed improvements.

CONCLUSION

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

Finding positive meaning in memories of negative events adaptively updates memory

Finding positive meaning in past negative memories is associated with enhanced mental health. Yet it remains unclear whether it leads to updates in the memory representation itself. Since memory can be labile after retrieval, this leaves the potential for modification whenever its reactivated. Across four experiments, we show that positively reinterpreting negative memories adaptively updates them, leading to the re-emergence of positivity at future retrieval. Focusing on the positive aspects after negative recall leads to enhanced positive emotion and changes in memory content during recollection one week later, remaining even after two months. Consistent with a reactivation-induced reconsolidation account, memory updating occurs only after a reminder and twenty four hours, but not a one hour delay. Multi-session fMRI showed adaptive updates are reflected in greater hippocampal and ventral striatal pattern dissimilarity across retrievals. This research highlights the mechanisms by which updating of maladaptive memories occurs through a positive emotion-focused strategy.

Cognitive effects of rapid-acting treatments for resistant depression: Just adverse, or contributing to clinical efficacy?

Major Depressive Disorder is a major public health problem and has a high rate of treatment resistance. Fear conditioning has been proposed as a potential mechanism sustaining negative affect in mood disorders. With the aim of exploring cognitive effects of rapid-acting antidepressant treatments as a potential mechanism of action that can be targeted by neuromodulation, we performed a narrative review of the extant literature on effects of electroconvulsive therapy, ketamine or esketamine, and sleep deprivation on emotional/fear memory retrieval-reconsolidation. We explore interference with reconsolidation as a potential common pathway that explains in part the efficacy of rapid-acting antidepressant treatments with disparate mechanisms of action. We propose the testable hypothesis that fear learning circuits can be specifically targeted by neuromodulation to attempt rapid amelioration of depressive symptoms (especially repetitive negative thinking) while limiting unspecific, untoward cognitive side effects.

Memories are not written in stone: Re-writing fear memories by means of non-invasive brain stimulation and optogenetic manipulations

The acquisition of fear associative memory requires brain processes of coordinated neural activity within the amygdala, prefrontal cortex (PFC), hippocampus, thalamus and brainstem. After fear consolidation, a suppression of fear memory in the absence of danger is crucial to permit adaptive coping behavior. Acquisition and maintenance of fear extinction critically depend on amygdala-PFC projections. The robust correspondence between the brain networks encompassed cortical and subcortical hubs involved into fear processing in humans and in other species underscores the potential utility of comparing the modulation of brain circuitry in humans and animals, as a crucial step to inform the comprehension of fear mechanisms and the development of treatments for fear-related disorders. The present review is aimed at providing a comprehensive description of the literature on recent clinical and experimental researches regarding the noninvasive brain stimulation and optogenetics. These innovative manipulations applied over specific hubs of fear matrix during fear acquisition, consolidation, reconsolidation and extinction allow an accurate characterization of specific brain circuits and their peculiar interaction within the specific fear processing.

What can we teach Lymnaea and what can Lymnaea teach us?

This review describes the advantages of adopting a molluscan complementary model, the freshwater snail Lymnaea stagnalis, to study the neural basis of learning and memory in appetitive and avoidance classical conditioning; as well as operant conditioning of its aerial respiratory and escape behaviour. We firstly explored ‘what we can teach Lymnaea’ by discussing a variety of sensitive, solid, easily reproducible and simple behavioural tests that have been used to uncover the memory abilities of this model system. Answering this question will allow us to open new frontiers in neuroscience and behavioural research to enhance our understanding of how the nervous system mediates learning and memory. In fact, from a translational perspective, Lymnaea and its nervous system can help to understand the neural transformation pathways from behavioural output to sensory coding in more complex systems like the mammalian brain. Moving on to the second question: ‘what can Lymnaea teach us?’, it is now known that Lymnaea shares important associative learning characteristics with vertebrates, including stimulus generalization, generalization of extinction and discriminative learning, opening the possibility to use snails as animal models for neuroscience translational research.

Neural Computations of Threat

A host of learning, memory, and decision-making processes form the individual's response to threat and may be disrupted in anxiety and post-trauma psychopathology. Here we review the neural computations of threat, from the first encounter with a dangerous situation, through learning, storing, and updating cues that predict it, to making decisions about the optimal course of action. The overview highlights the interconnected nature of these processes and their reliance on shared neural and computational mechanisms. We propose an integrative approach to the study of threat-related processes, in which specific computations are studied across the various stages of threat experience rather than in isolation. This approach can generate new insights about the evolution, diagnosis, and treatment of threat-related psychopathology.

A study on episodic memory reconsolidation that tells us more about consolidation

Awake quiescence immediately after encoding is conducive to episodic memory consolidation. Retrieval can render episodic memories labile again, but reconsolidation can modify and restrengthen them. It remained unknown whether awake quiescence after retrieval supports episodic memory reconsolidation. We sought to examine this question via an object-location memory paradigm. We failed to probe the effect of quiescence on reconsolidation, but we did observe an unforeseen “delayed” effect of quiescence on consolidation. Our findings reveal that the beneficial effect of quiescence on episodic memory consolidation is not restricted to immediately following encoding but can be achieved at a delayed stage and even following a period of task engagement.

Easy to Make, Hard to Revise: Updating Spontaneous Trait Inferences in the Presence of Trait-Inconsistent Information

Previous research has shown that perceivers spontaneously form trait inferences from others' behaviors received at a single point in time. The present work examined the persistence of spontaneous trait inferences (STIs) in the presence of trait-inconsistent information about others. We hypothesized that STIs should be resistant to change over time and in the presence of new trait-inconsistent information due to perceivers forming and storing multiple STIs independently in memory. Consistently, Experiments 1a and 1b showed that initial STIs were not affected by new trait-inconsistent information. Experiments 2 and 3 revealed that STIs were persistent over 48 hours. Two experiments also tested memory reconsolidation as a possible mechanism of updating first impressions. While STIs were not substantially affected, spontaneous goal inferences (SGIs) were elevated among those with a better explicit memory of behaviors after learning trait-inconsistent information following a memory reactivation procedure. Implications of these findings on impression formation and updating processes are discussed.

Protocols for instrumental memory reconsolidation in rodents: A methodological review

BACKGROUND

Memory reconsolidation enables the update of a previously consolidated memory trace after its reactivation. Although Pavlovian memory reconsolidation has been widely demonstrated, instrumental memory reconsolidation is still debated. Early studies suggested that instrumental memories did not undergo reconsolidation and therefore could not be disrupted, whereas other authors suggested that these memories are just more resistant to destabilization and reconsolidation in comparison to Pavlovian memories.

AIM AND RESULTS

The present paper reviews the behavioral protocols used to investigate appetitive instrumental memory reconsolidation in rodents and describes in detail the specific methods used for memory retrieval, with a critical analysis of the different experimental parameters.

CONCLUSIONS

The modalities under which the reconsolidation of appetitive (sucrose or drugs of abuse) instrumental memories occurs have been explored and partially elucidated. Further investigations are recommended on the boundary conditions that constrain instrumental memory reactivation.

Pavlovian Conditioning of Immunological and Neuroendocrine Functions

The phenomenon of behaviorally conditioned immunological and neuroendocrine functions has been investigated for the past 100 yr. The observation that associative learning processes can modify peripheral immune functions was first reported and investigated by Ivan Petrovic Pavlov and his co-workers. Their work later fell into oblivion, also because so little was known about the immune system’s function and even less about the underlying mechanisms of how learning, a central nervous system activity, could affect peripheral immune responses. With the employment of a taste-avoidance paradigm in rats, this phenomenon was rediscovered 45 yr ago as one of the most fascinating examples of the reciprocal functional interaction between behavior, the brain, and peripheral immune functions, and it established psychoneuroimmunology as a new research field. Relying on growing knowledge about efferent and afferent communication pathways between the brain, neuroendocrine system, primary and secondary immune organs, and immunocompetent cells, experimental animal studies demonstrate that cellular and humoral immune and neuroendocrine functions can be modulated via associative learning protocols. These (from the classical perspective) learned immune responses are clinically relevant, since they affect the development and progression of immune-related diseases and, more importantly, are also inducible in humans. The increased knowledge about the neuropsychological machinery steering learning and memory processes together with recent insight into the mechanisms mediating placebo responses provide fascinating perspectives to exploit these learned immune and neuroendocrine responses as supportive therapies, the aim being to reduce the amount of medication required, diminishing unwanted drug side effects while maximizing the therapeutic effect for the patient’s benefit.

Reconsolidation or interference? Aging effects and the reactivation of novel and familiar episodic memories

We examined aging effects in reconsolidation and interference in episodic memory by reactivating memories for well-learned items in young and healthy older adults while controlling memory strength and the degree semantic processes contributed to memory. In Experiment 1, young and old adults learned pairs of real words and images to a strict criterion. After 24-hours, half of the images were reactivated and new words were paired with the images and learned to criterion. Following a 1-week delay, recognition and source monitoring were measured for both sets of pairings. Experiment 2 was a replication of Experiment 1, but using previously unknown novel words and unusual images. As predicted, older adults needed more trials to learn both the A-B and A-C pairings. Older adults required more trials to learn the new associations for reactivated than the not reactivated pairs, although there was no main effect of reactivation and no Age x Reactivation interaction for measures of recognition one-week later. These results are inconsistent with previous findings concerning age differences in reactivation effects in episodic memory. Instead, they suggest that once memory strength and input from semantic memory are better controlled, young and old adults perform similarly on tests of long-term recognition memory.

Lymnaea stagnalis as model for translational neuroscience research: From pond to bench

The purpose of this review is to illustrate how a reductionistic, but sophisticated, approach based on the use of a simple model system such as the pond snail Lymnaea stagnalis (L. stagnalis), might be useful to address fundamental questions in learning and memory. L. stagnalis, as a model, provides an interesting platform to investigate the dialog between the synapse and the nucleus and vice versa during memory and learning. More importantly, the "molecular actors" of the memory dialogue are well-conserved both across phylogenetic groups and learning paradigms, involving single- or multi-trials, aversion or reward, operant or classical conditioning. At the same time, this model could help to study how, where and when the memory dialog is impaired in stressful conditions and during aging and neurodegeneration in humans and thus offers new insights and targets in order to develop innovative therapies and technology for the treatment of a range of neurological and neurodegenerative disorders.

Effects of transcranial direct current stimulation over the posterior parietal cortex on episodic memory reconsolidation

Consolidated memories may return to labile/unstable states after their reactivation, thus requiring a restabilization process that is known as reconsolidation. During this time-limited reconsolidation window, reactivated existing memories can be strengthened, weakened or updated with new information. Previous studies have shown that non-invasive stimulation of the lateral prefrontal cortex after memory reactivation strengthened existing verbal episodic memories through reconsolidation, an effect documented by enhanced delayed memory recall (24 h post-reactivation). However, it remains unknown whether the left posterior parietal cortex (PPC), a region involved during reactivation of existing episodic memories, contributes to reconsolidation. To address this question, in this double-blind experiment healthy participants (n = 27) received transcranial direct current stimulation (tDCS) with the anode over the left PPC after reactivation of previously learned verbal episodic memories. Memory recall was tested 24 h later. To rule out unspecific effects of memory reactivation or tDCS alone, we included two control groups: one that receives tDCS with the anode over the left PPC without reactivation (n = 27) and another one that receives tDCS with the anode over a control site (primary visual cortex) after reactivation (n = 27). We hypothesized that tDCS with the anode over the left PPC after memory reactivation would enhance delayed recall through reconsolidation relative to the two control groups. No significant between groups differences in the mean number of words recalled on day 3 occurred, suggesting no beneficial effect of tDCS over the left PPC. Alternative explanations were discussed, including efficacy of tDCS, different stimulation parameters, electrode montage, and stimulation site within the PPC.

Pharmacological interventions during the process of reconsolidation of aversive memories: A systematic review

Reconsolidation is the return of a memory to a transient state of lability, following memory consolidation, that can occur when memories are evoked. During the process of reconsolidation, memories may be modified by different means, including the administration of drugs, during a period called the "reconsolidation window”. This process has been widely studied in animals, but human studies are limited and include several methodological pitfalls. Our objective was to conducte a systematic review of the literature that utilizes pharmacological interventions during the process of reconsolidation of aversive memories in humans, with a critical analysis of the methodologies used. Searches were made in the electronic databases PubMed, Scopus, Web of Science and SciELO using the following search terms: (memory) AND (consolidation OR reconsolidation) AND (pharmacological manipulation OR pharmacological intervention). We found 294 references and ten (3.4%) were included in the review, based on preestablished eligibility criteria. All studies were randomized, double-blind clinical trials. The most commonly studied drug was propranolol. Two studies used a protocol involving autobiographical aversive memories, while in the remaining aversive memories were produced in the laboratory. The timing of pharmacological interventions is a controversial issue in the field, as drug activity must occur within the reconsolidation window. The small number of studies and some methodological difficulties of this type of research highlights the need for studies that individually evaluate some of the issues discussed, particularly the timing of pharmacological interventions and the duration of reconsolidation windows.

Spatial distancing reduces emotional arousal to reactivated memories

Memories are able to update and adapt with new information about the world after they are reactivated. However, it is unknown whether the labile period following reactivation makes episodic memories more amenable to emotion regulation, an application that holds great clinical promise. Here, we investigated the efficacy of cognitive reappraisal to down regulate negative affect in response to reactivated memories. Healthy young adults (N = 119) rated the emotionality of negative pictures. After a partial reactivation of each picture 2 days later, participants voluntarily engaged in a spatial distancing regulation tactic by imagining the reactivated object extremely far away from them. Compared with no-regulation and no-reactivation controls, self-reported arousal for regulated pictures dropped significantly 2 days after the manipulation, despite no significant difference in memory accuracy or valence. These results open up a new line of work that capitalizes on reactivation-based lability to selectively alter enduring arousal responses to emotional memories.

Cortisol suppression after memory reactivation impairs later memory performance

Experiencing stressful or traumatic events can result in disabling clinical symptoms of maladaptive emotional memory retrieval, which are only partly addressed by the currently proposed treatments. Cortisol modulation has been shown to affect emotional memory retrieval and potentially reconsolidation, offering an opportunity for developing more efficient treatments for disorders with an emotional memory component. Here, we investigated if cortisol suppression after reactivation of emotional memories weakens later memory thereof. Forty healthy young men were tested in a randomized, placebo controlled, double-blind, and between-subject design, assigned either to a cortisol suppression (metyrapone) group or a placebo group. Participants of both groups, were presented with two emotional stories at an encoding session (Day 1). One of the two stories was later reactivated and followed by metyrapone vs. placebo administration (Day 3). Memory for both stories was tested at a recognition memory session (Day 7). In the group undergoing cortisol suppression after memory reactivation memory performance was weaker compared to the placebo group, tested four days after reactivation. This study shows that cortisol suppression can weaken memory for past events, possibly by altering reconsolidation processes and thus exerting long-lasting weakening effects on the original memory.

Optogenetic Stimulation of the Basolateral Amygdala Increased Theta-Modulated Gamma Oscillations in the Hippocampus

The amygdala can modulate declarative memory. For example, previous research in rats and humans showed that brief electrical stimulation to the basolateral complex of the amygdala (BLA) prioritized specific objects to be consolidated into long term memory in the absence of emotional stimuli and without awareness of stimulation. The capacity of the BLA to influence memory depends on its substantial projections to many other brain regions, including the hippocampus. Nevertheless, how activation of the BLA influences ongoing neuronal activity in other regions is poorly understood. The current study used optogenetic stimulation of putative glutamatergic neurons in the BLA of freely exploring rats to determine whether brief activation of the BLA could increase in the hippocampus gamma oscillations for which the amplitude was modulated by the phase of theta oscillations, an oscillatory state previously reported to correlate with good memory. BLA neurons were stimulated in 1-s bouts with pulse frequencies that included the theta range (8 Hz), the gamma range (50 Hz), or a combination of both ranges (eight 50-Hz bursts). Local field potentials were recorded in the BLA and in the pyramidal layer of CA1 in the intermediate hippocampus. A key question was whether BLA stimulation at either theta or gamma frequencies could combine with ongoing hippocampal oscillations to result in theta-modulated gamma or whether BLA stimulation that included both theta and gamma frequencies would be necessary to increase theta–gamma comodulation in the hippocampus. All stimulation conditions elicited robust responses in BLA and CA1, but theta-modulated gamma oscillations increased in CA1 only when BLA stimulation included both theta and gamma frequencies. Longer bouts (5-s) of BLA stimulation resulted in hippocampal activity that evolved away from the initial oscillatory states and toward those characterized more by prominent low-frequency oscillations. The current results indicated that one mechanism by which the amygdala might influence declarative memory is by eliciting neuronal oscillatory states in the hippocampus that benefit memory.

A review of boundary conditions and variables involved in the prevention of return of fear after post-retrieval extinction

Experimental evidence suggests that the return of fear may be prevented by post-retrieval extinction (PRE), a procedure consisting of extinction training after the presentation of a retrieval cue. However, attempts to replicate these findings have yielded mixed results, with some studies showing diminished fear responses after PRE, whereas others show no effect on the return of fear following this procedure. The discrepancies across studies have been interpreted as evidence that there might be conditions under which PRE is not effective (boundary conditions), but these variables have yet to be fully described. We aimed to provide an overview of PRE in humans. We briefly present the theory and research that originated post-retrieval procedures with a focus on the experimental setup used in human studies. We continue with a compilation of possible experimental boundary conditions along with some questions for future research.

Post-retrieval oxytocin facilitates next day extinction of threat memory in humans

RATIONALE

Memories can return to a labile state and become amenable to modification by pharmacological and behavioral manipulations after retrieval. This process may reduce the impact of aversive memories and provide a promising therapeutic technique for the treatment of anxiety disorders. A growing body of evidence suggests that the mammalian neuropeptide oxytocin (OT) plays a role in the regulation of emotional memories in animals. However, the effects of OT on threat memory in humans remain largely unknown.

OBJECTIVES

This study aimed to investigate the effects of OT administration following threat memory retrieval on subsequent memory expression in human participants.

METHODS

In a double-blind, randomized, placebo-controlled, between-subject design, 61 healthy human individuals completed a 3-day experiment. All the participants underwent threat conditioning on day 1. On day 2, the participants were randomized to receive an intranasal dose of OT (40 IU) or placebo after memory retrieval, or an intranasal dose of OT (40 IU) without retrieval. On day 3, the participants were tested for extinction and reinstatement.

RESULTS

On day 3, all groups showed equivalent stimulus discrimination during the early phase of extinction. However, the group that received OT following a memory reminder showed a greater decline in stimulus discrimination by the late phase of extinction relative to the two other groups.

CONCLUSIONS

The results indicate that OT did not block reconsolidation to prevent the return of threat memory but rather interacted with post-retrieval processes to facilitate next day extinction. The study provides novel preliminary evidence for the role of OT in human threat memory.

Dopaminergic D1 receptor signalling is necessary, but not sufficient for cued fear memory destabilisation

RATIONALE

Pharmacological targeting of memory reconsolidation is a promising therapeutic strategy for the treatment of fear memory-related disorders. However, the success of reconsolidation-based approaches depends upon the effective destabilisation of the fear memory by memory reactivation.

OBJECTIVES

Here, we aimed to determine the functional involvement of dopamine D1 receptors in cued fear memory destabilisation, using systemic drug administration.

RESULTS

We observed that direct D1 receptor agonism was not sufficient to stimulate tone fear memory destabilisation to facilitate reconsolidation disruption by the glucocorticoid receptor antagonist mifepristone. Instead, administration of the nootropic nefiracetam did facilitate mifepristone-induced amnesia, in a manner that was dependent upon dopamine D1 receptor activation. Finally, while the combined treatment with nefiracetam and mifepristone did not confer fear-reducing effects under conditions of extinction learning, there was some evidence that mifepristone reduces fear expression irrespective of memory reactivation parameters.

CONCLUSIONS

The use of combination pharmacological treatment to stimulate memory destabilisation and impair reconsolidation has potential therapeutic benefits, without risking a maladaptive increase of fear.

Reconsolidation of human motor memory: From boundary conditions to behavioral interventions-How far are we from clinical applications?

The memory reconsolidation hypothesis states that a previously consolidated and stable memory can return to a temporary labile state after retrieved, requiring a new stabilization process. During the labile period, the memory trace is vulnerable to modification, which provides a potential therapeutic opportunity to weaken, updated or strengthen that memory. As such, reconsolidation has been the subject of numerous studies in different domains of human memory that seek strategies to treat post-traumatic disorders and erase or modify pathological memories. A few studies have also investigated the impairment effects of behavioral interferences on motor memory. However, very little has been researched and written about the possibility of using reconsolidation to enhance motor skill learning. Here, we present a critical review of the literature and trace possible applications for human motor memory reconsolidation. We discuss the boundary conditions and the mechanisms to trigger the reconsolidation process, as well as the effects of behavioral interventions in modifying the performance of motor skills.

On the Very-Long-Term Effect of Managing One's Own Memory: The Intention to Forget Improves Recognition After a Year's Delay

While such factors as demand characteristics, encoding, and retrieval inhibition were shown to be significant in producing the directed forgetting effect, no attention was paid to whether the intention to manage one's own memory, per se, matters. In the present article, we addressed this important gap in the literature. To control the quality of encoding we ensured that both the to-be-remembered (TBR) and to-be-forgotten (TBF) items were genuinely learned before the manipulation. We used extremely long delays between the memory instructions and testing to release inhibition associated with the content of instructions. 98 participants demonstrated flawless recall of 12 Russian - made up language word pairs. They then viewed each Russian word from a pair once, with randomized instructions "Forget", "Remember", "Repeat", or a short cognitive task. Self-reports on the mnemonic strategies were collected. Free recall and recognition tests were administered three times - 45 minutes, a month and a year (N = 58) later. Despite a strong incentive to recall all word pairs, fewer TBF pairs were recalled in comparison with TBR pairs, both after 45 minutes and after one month's delay. Recognition among all conditions was equally high. A year later free recall was close to zero. In contrast, the TBR and TBF pairs were recognized equally better than pairs presented in "Repeat" and "Task" conditions. Thus, our results show that the intention to manage one's own memory enhances the accessibility of memories at a very long time delay, no matter what type of instruction is issued.

Memory integration: An alternative to the consolidation/reconsolidation hypothesis

The original concept of consolidation considers that memory requires time to be fixed. Since 2000, a comparable protein-dependent re-stabilization phase, called reconsolidation, has been assumed to take place after memory retrieval. This consolidation/reconsolidation hypothesis, has dominated the literature for more than 50 years, despite compelling evidence that is inconsistent with it. In this review, we present an historical overview and explain how, despite serious criticisms, this hypothesis has persisted for decades and become accepted as a dogma. Based on both older and more recent evidence, we next propose the concept of memory integration which involves the linkage or embedding of new material into an already existing representation. We believe integration provides a viable explanation for retrograde amnesia in place of the consolidation/reconsolidation hypothesis. Integration can further be the basis for several major cases of memory alteration such as time dependent memory enhancement, interference, counter-conditioning, updating and other instances of memory malleability. In a final section we consider the implications this new concept may have for memory processes and its translational applications.

Exploring the role of context on the existing evidence for reconsolidation of episodic memory

Recent research has provided evidence for memory modifications when a post-reactivation treatment (e.g., drugs, new learning) interferes with the memory re-stabilisation (reconsolidation) process. This finding contradicts the long-standing consolidation theory and has high practical and theoretical implications. With an object-learning paradigm, it was shown that episodic memory is highly susceptible to interfering material presented after its reactivation [Hupbach, A., Gomez, R., Hardt, O., & Nadel, L. (2007). Reconsolidation of episodic memories: A subtle reminder triggers integration of new information. Learning & Memory, 14, 47-53. doi: 10.1101/lm.365707 ]. The reactivation of a learned list (List 1) before a second learned list (List 2) led to intrusion errors from List 2 when trying to recall List 1, but not vice-versa. Their work has been widely cited and their findings have been explained according to reconsolidation theory. For the first time, we systematically explored the role of retrieval context as an alternative explanation for Hupbach's results. Our results showed that the intrusion effect occurs independently of the retrieval context (Experiment 1). Additionally, even when the intrusion rate probability is increased (i.e., List 1 memory test is performed in the List 2 learning context), the groups that did not reactivate the original list did not commit intrusion errors (Experiment 2). In sum, we found that the intrusion effect critically depends on the presence of reactivation, discarding alternative interpretations of the results.

Positive emotional induction interferes with the reconsolidation of negative autobiographical memories, in women only

After reactivation, a previously consolidated memory can enter into a labile state followed by a re-stabilization process defined as reconsolidation. The aim of this study was to explore whether an existing negative autobiographical memory can be modified by using a non-invasive interference (audiovisual positive preparation) after reactivation and to determine if this effect could be dependent on the reconsolidation process. We found that the presentation of a positive inductor after a negative autobiographical memory reactivation may lead to a change in the emotional information of the original trace and that such effect can be mediated by the reconsolidation process. The modification of the memory has been shown in women only. These results suggest that a positive audiovisual induction may play a potential role in psychotherapeutic techniques for the modification of dysfunctional autobiographical memories.

The effect of bilateral eye-movements versus no eye-movements on sexual fantasies

BACKGROUND AND OBJECTIVES

Bilateral eye-movements (EMs) and visual mental imagery both require working memory resources. When performed together, they compete for these resources, which can cause various forms of mental imagery to become impaired (e.g., less vivid). This study aimed to examine whether EMs impair sexual fantasies (a form of mental imagery) in the same manner.

METHODS

Eighty undergraduates (40 males, 40 females) took part in four counterbalanced conditions: (1) EMs and an experience-based sexual fantasy; (2) EMs and an imagination-based sexual fantasy; (3) experience-based sexual fantasy only; and (4) imagination-based sexual fantasy only. In each condition, the vividness, emotionality, and arousability of the sexual fantasy were rated pre- and post-task. All three variables were predicted to decrease in the EM conditions.

RESULTS

Sexual fantasies were reported as less vivid, positive, and arousing after performing concurrent EMs relative to fantasising only, for both memory- and imagination-based sexual fantasies. There were no gender differences. Demand did not appear to account for the effects.

LIMITATIONS

Self-report measures were used rather than objective measures. Working memory taxation and capacity were not directly assessed. Also, negatively appraised sexual fantasies were not targeted and a 'no intervention' control was not included.

CONCLUSIONS

Bilateral EMs were effective at impairing the phenomenological properties of sexual mental imagery, extending the literature on EM effects. Given the potential clinical implications, future research should focus on validating and extending these results, for example, by targeting negatively appraised sexual fantasies (including problematic and offense-related) and incorporating a 'no intervention' condition.

Behavioral reconsolidation interference with episodic memory within-subjects is elusive

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We assessed behavioral reconsolidation interference in episodic memory.

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Employed within-subjects paradigm measuring direct memory strength.

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Three experiments found no effects of reminder-potentiated interference.

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Null effects were substantiated by Bayesian analyses.

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Highlights boundary conditions for behavioral reconsolidation interference effects.

In studies of behavioral reconsolidation interference, reactivation of a consolidated memory using some form of reminder is followed by the presentation of new information that can cause interference with that memory. Under these conditions, the interference not only impairs retrieval by indirect processes such as cue interference, but supposedly disrupts the original memory trace directly. Almost all studies of behavioral reconsolidation interference in episodic memory in humans have employed between-subjects paradigms, and deduced reminder effects from intrusion errors. Such studies might introduce confounds arising, for example, from differences in retrieval strategies engendered by the pre-test treatments. We therefore set out to examine whether behavioral reconsolidation interference in episodic memory might be demonstrated within-subjects and by direct memory strength rather than intrusion errors. In three separate experiments, we attempted to disrupt reconsolidation of episodic object-picture memory using a reminder + retroactive interference manipulation. We applied the manipulation over three consecutive days, using a forced-choice recognition test without intrusions from interfering learning, keeping all other study and test parameters constant. No effects of reminder-potentiated interference were observed for measures of accuracy, response times, subjective expressions of recollection, or levels of confidence, as substantiated by Bayesian analyses. These results highlight the difficulty of observing clear behavioral reconsolidation interference effects within-subjects in human episodic memory, and provide some indications of what might be boundary conditions for its demonstration.

Psychedelics and reconsolidation of traumatic and appetitive maladaptive memories: focus on cannabinoids and ketamine

RATIONALE

Clinical data with 3,4-methylenedioxymethamphetamine (MDMA) in post-traumatic stress disorder (PTSD) patients recently stimulated interest on the potential therapeutic use of psychedelics in disorders characterized by maladaptive memories, including substance use disorders (SUD). The rationale for the use of MDMA in PTSD and SUD is being extended to a broader beneficial "psychedelic effect," which is supporting further clinical investigations, in spite of the lack of mechanistic hypothesis. Considering that the retrieval of emotional memories reactivates specific brain mechanisms vulnerable to inhibition, interference, or strengthening (i.e., the reconsolidation process), it was proposed that the ability to retrieve and change these maladaptive memories might be a novel intervention for PTSD and SUD. The mechanisms underlying MDMA effects indicate memory reconsolidation modulation as a hypothetical process underlying its efficacy.

OBJECTIVE

Mechanistic and clinical studies with other two classes of psychedelic substances, namely cannabinoids and ketamine, are providing data in support of a potential use in PTSD and SUD based on the modulation of traumatic and appetitive memory reconsolidation, respectively. Here, we review preclinical and clinical data on cannabinoids and ketamine effects on biobehavioral processes related to the reconsolidation of maladaptive memories.

RESULTS

We report the findings supporting (or not) the working hypothesis linking the potential therapeutic effect of these substances to the underlying reconsolidation process. We also proposed possible approaches for testing the use of these two classes of drugs within the current paradigm of reconsolidation memory inhibition.

CONCLUSIONS

Metaplasticity may be the process in common between cannabinoids and ketamine/ketamine-like substance effects on the mediation and potential manipulation of maladaptive memories.

Reconsolidation of Traumatic Memories for PTSD: A randomized controlled trial of 74 male veterans

Design: A randomized waitlist-controlled design (n = 74) examined the efficacy of Reconsolidation of Traumatic Memories (RTM) among male veterans with current-month flashbacks and nightmares. Volunteers were randomly assigned to immediate treatment (three 120-minute sessions of RTM), or to a 3-week waiting condition before receiving the RTM treatment. Blinded psychometricians evaluated the symptoms at intake, 2 weeks, and 6 weeks post. Wait-listed participants were re-evaluated and then treated. Sixty-five volunteers completed the treatment. Results: Of those treated, 46 (71%) lost DSM diagnosis for post-traumatic stress disorder (PTSD) by one of the following definitions: 42 persons (65%) were in complete remission (PTSD Symptom Scale Interview (PSS-I) ≤ 20 and DSM criteria not met). Four others (6%) lost the DSM diagnosis or were otherwise sub-clinical by dichotomous criteria (PSS-I < 20 and absence of flashbacks and nightmares) but non-ambiguous on the PTSD Checklist Military Version measures. Within-group RTM effect sizes (Hedges' g) for PSS-I score changes ranged from 1.45 to 2.3. The between-group comparison between the treatment group and the untreated controls was significant (p < .001) with an effect size equivalent to two standard deviations (g = 2.13; 95% CI [1.56, 2.70]). Patient satisfaction with the intervention was high. Conclusions: RTM shows promise as a brief, cost-effective intervention for PTSD characterized primarily by intrusive symptoms. Clinical or methodological significance of this article: The article provides evidence to support a fast (5 hours or fewer) robust intervention for PTSD characterized by intrusive symptoms including current-month flashbacks, nightmares, and accompanied by sympathetic arousal in response to trauma narratives. The intervention is well tolerated and has demonstrated efficacy up to one year.

Psychedelics and reconsolidation of traumatic and appetitive maladaptive memories: focus on cannabinoids and ketamine

RATIONALE

Clinical data with 3,4-methylenedioxymethamphetamine (MDMA) in post-traumatic stress disorder (PTSD) patients recently stimulated interest on the potential therapeutic use of psychedelics in disorders characterized by maladaptive memories, including substance use disorders (SUD). The rationale for the use of MDMA in PTSD and SUD is being extended to a broader beneficial "psychedelic effect," which is supporting further clinical investigations, in spite of the lack of mechanistic hypothesis. Considering that the retrieval of emotional memories reactivates specific brain mechanisms vulnerable to inhibition, interference, or strengthening (i.e., the reconsolidation process), it was proposed that the ability to retrieve and change these maladaptive memories might be a novel intervention for PTSD and SUD. The mechanisms underlying MDMA effects indicate memory reconsolidation modulation as a hypothetical process underlying its efficacy.

OBJECTIVE

Mechanistic and clinical studies with other two classes of psychedelic substances, namely cannabinoids and ketamine, are providing data in support of a potential use in PTSD and SUD based on the modulation of traumatic and appetitive memory reconsolidation, respectively. Here, we review preclinical and clinical data on cannabinoids and ketamine effects on biobehavioral processes related to the reconsolidation of maladaptive memories.

RESULTS

We report the findings supporting (or not) the working hypothesis linking the potential therapeutic effect of these substances to the underlying reconsolidation process. We also proposed possible approaches for testing the use of these two classes of drugs within the current paradigm of reconsolidation memory inhibition.

CONCLUSIONS

Metaplasticity may be the process in common between cannabinoids and ketamine/ketamine-like substance effects on the mediation and potential manipulation of maladaptive memories.

Neural correlates of appetitive extinction in humans

Appetitive extinction receives attention as an important model for the treatment of psychiatric disorders. However, in humans, its underlying neural correlates remain unknown. To close this gap, we investigated appetitive acquisition and extinction with fMRI in a 2-day monetary incentive delay paradigm. During appetitive conditioning, one stimulus (CS+) was paired with monetary reward, while another stimulus (CS−) was never rewarded. Twenty-four hours later, subjects underwent extinction, in which neither CS was reinforced. Appetitive conditioning elicited stronger skin conductance responses to the CS+ as compared with the CS−. Regarding subjective ratings, the CS+ was rated more pleasant and arousing than the CS− after conditioning. Furthermore, fMRI-results (CS+ − CS−) showed activation of the reward circuitry including amygdala, midbrain and striatal areas. During extinction, conditioned responses were successfully extinguished. In the early phase of extinction, we found a significant activation of the caudate, the hippocampus, the dorsal and ventral anterior cingulate cortex (dACC and vACC). In the late phase, we found significant activation of the nucleus accumbens (NAcc) and the amygdala. Correlational analyses with subjective ratings linked extinction success to the vACC and the NAcc, while associating the dACC with reduced extinction. The results reveal neural correlates of appetitive extinction in humans and extend assumptions from models for human extinction learning.