Extinction during reconsolidation eliminates recovery of fear conditioned to fear-irrelevant and fear-relevant stimuli

Conflict Dynamics of Post-Retrieval Extinction: A Comparative Analysis of Unconditional and Conditional Reminders Using Skin Conductance Responses and EEG

The post-retrieval extinction paradigm, rooted in reconsolidation theory, holds promise for enhancing extinction learning and addressing anxiety and trauma-related disorders. This study investigates the impact of two reminder types, mild US-reminder (US-R) and CS-reminder (CS-R), along with a no-reminder extinction, on fear recovery prevention in a categorical fear conditioning paradigm. Scalp EEG recordings during reminder and extinction processes were conducted in a three-day design. Results show that the US-R group exhibits a distinctive extinction learning pattern, characterized by a slowed-down yet successful process and pronounced theta-alpha desynchronization (source-located in the prefrontal cortex) during CS processing, followed by enhanced synchronization (source-located in the anterior cingulate) after shock cancellation in extinction trials. These neural dynamics correlate with the subtle advantage of US-R in the Day 3 recovery test, presenting faster spontaneous recovery fading and generally lower fear reinstatement responses. Conversely, the CS reminder elicits CS-specific effects in later episodic tests. The unique neural features of the US-R group suggest a larger prediction error and subsequent effortful conflict learning processes, warranting further exploration.

Extinction of negative conditioned stimulus valence in human fear conditioning

Fear conditioning is a common experimental paradigm for modelling the development, and exposure-based treatment, of anxiety disorders. Measures of fear such as threat-expectancy, physiological arousal, and fear ratings typically extinguish, however feared stimuli may still be evaluated negatively (i.e. retain negative valence). This systematic review provides the first investigation of the relationship between fear conditioning methodology and extinction of negative stimulus valence. Principal findings were that type of CS (conditioned stimulus) and the CS-US pairing (i.e. specific combination of CS and unconditioned stimulus) predicted extinction outcome. Extinction of absolute negative CS valence was always achieved with shape CSs; often achieved with low fear-relevant animals as CSs, and less frequently achieved with faces as CSs - particularly neutral faces paired with a shock US. Modified extinction procedures typically achieved the same outcome as standard extinction procedures, except for partially-reinforced extinction, which was less effective than standard extinction, and positive imagery training, which was more effective than standard extinction. Further studies are warranted to evaluate the influence of fear conditioning methodology on extinction of absolute negative CS valence.

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.

Angry and fearful compared to happy or neutral faces as conditional stimuli in human fear conditioning: A systematic review and meta-analysis

Some previous research has shown stronger acquisition and impaired extinction of fear conditioned to angry or fearful compared to happy or neutral face conditional stimuli (CS) - a difference attributed to biological 'preparedness'. A systematic review and meta-analysis of fear conditioning studies comparing face CSs of differing expressions identified thirty studies, eighteen of which were eligible for meta-analysis. Skin conductance responses were larger to angry or fearful faces compared to happy or neutral faces during habituation, acquisition and extinction. Significant differences in differential conditioning between angry, fearful, neutral, and happy face CSs were also found, but differences were more prominent between angry and neutral faces compared to angry/fearful and happy faces. This is likely due to lower arousal elicited by neutral compared to happy faces, which may be more salient as CSs. The findings suggest there are small to moderate differences in differential conditioning when angry or fearful compared to happy or neutral faces are used as CSs. These findings have implications for fear conditioning study design and the preparedness theory.

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.

The influence of dispositional cognitive reappraisal and expressive suppression on post-retrieval and standard extinction

Individual differences in the ability to habitually regulate emotion may impact the efficacy of fear memory extinction. The aim of this study was to assess the relationship between dispositional cognitive reappraisal and expressive suppression with post-retrieval and standard extinction. Fear memory and extinction were measured with the recovery of skin conductance responses. We also examined the relationship between a temporal feature of electrodermal responding (half-recovery time) and each of the emotion regulation strategies. University students (N = 80) underwent a three-day fear conditioning procedure using a within-subject design consisting of acquisition on day one, post-retrieval extinction and standard extinction on day two, and recovery test on day three. Individual difference data on self-reported levels of cognitive reappraisal, expressive suppression, trait anxiety, and depression were collected. We did not detect a relationship between the two emotion regulation strategies measured in this study and acquisition or extinction. We found, however, that increased dispositional use of cognitive reappraisal was associated with lower spontaneous recovery to both the post-retrieval extinction and standard extinction stimulus after controlling for age, trait anxiety, and depression. There were no associations between expressive suppression and conditioned responses. We also observed patterns of faster dissipation of arousal for reappraisal and slower for suppression to the conditioned stimulus during extinction training, which may represent the unique influence of each emotion strategy on the regulation of fear. We conclude greater daily use of cognitive reappraisal, but not expressive suppression, associates with extinction retention after receiving both standard and post-retrieval extinction.

Demarcating the boundary conditions of memory reconsolidation: An unsuccessful replication

Disrupting memory reconsolidation provides an opportunity to abruptly reduce the behavioural expression of fear memories with long-lasting effects. The success of a reconsolidation intervention is, however, not guaranteed as it strongly depends on the destabilization of the memory. Identifying the necessary conditions to trigger destabilization remains one of the critical challenges in the field. We aimed to replicate a study from our lab, showing that the occurrence of a prediction error (PE) during reactivation is necessary but not sufficient for destabilization. We tested the effectiveness of a reactivation procedure consisting of a single PE, compared to two control groups receiving no or multiple PEs. All participants received propranolol immediately after reactivation and were tested for fear retention 24 h later. In contrast to the original results, we found no evidence for a reconsolidation effect in the single PE group, but a straightforward interpretation of these results is complicated by the lack of differential fear retention in the control groups. Our results corroborate other failed reconsolidation studies and exemplify the complexity of experimentally investigating this process in humans. Thorough investigation of the interaction between learning and memory reactivation is essential to understand the inconsistencies in the literature and to improve reconsolidation interventions.

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.

Presentation of unpaired unconditional stimuli during extinction reduces renewal of conditional fear and slows re-acquisition

Past research has shown that presenting unconditional stimuli (US) during extinction training, either paired with the conditional stimulus (CS) or explicitly unpaired, can reduce spontaneous recovery and slow the re-acquisition of conditional fear. Whether contextual renewal of conditioned fear as indexed by electrodermal responses and self-report measures of anxiety and CS evaluations is also reduced after presentation of paired or unpaired USs during extinction training is currently unclear. Three groups of participants (Paired, Unpaired, Standard Extinction) completed a sequence of habituation, acquisition, extinction, renewal, and re-acquisition phases. During extinction, five CS-US pairings were presented in group Paired, whereas five US were presented alone in group Unpaired. No US were presented during standard extinction. For all groups, extinction was conducted in a context that was different from that of the other phases. Extinction of differential electrodermal responding was evident in groups Unpaired and Standard, but not in group Paired. Contextual renewal and fast re-acquisition, as indexed by differential electrodermal responding, were evident in group Standard, but not in group Unpaired and differential electrodermal responding persisted in group Paired. After extinction, self-reported anxiety was higher in groups Paired and Unpaired, but differential CS evaluations were evident in group Paired only. The current results suggest that presenting additional unpaired USs during extinction training strengthens extinction and protects against the renewal of differential electrodermal responding.

Apparent reconsolidation interference without generalized amnesia

Memories remain dynamic after consolidation, and when reactivated, they can be rendered vulnerable to various pharmacological agents that disrupt the later expression of memory (i.e., amnesia). Such drug-induced post-reactivation amnesia has traditionally been studied in AAA experimental designs, where a memory is initially created for a stimulus A (be it a singular cue or a context) and later reactivated and tested through exposure to the exact same stimulus. Using a contextual fear conditioning procedure in rats and midazolam as amnestic agent, we recently demonstrated that drug-induced amnesia can also be obtained when memories are reactivated through exposure to a generalization stimulus (GS, context B) and later tested for that same generalization stimulus (ABB design). However, this amnestic intervention leaves fear expression intact when at test animals are instead presented with the original training stimulus (ABA design) or a novel generalization stimulus (ABC design). The underlying mechanisms of post-reactivation memory malleability and of MDZ-induced amnesia for a generalization context remain largely unknown. Here, we evaluated whether, like typical CS-mediated (or AAA) post-reactivation amnesia, GS-mediated (ABB) post-reactivation amnesia displays key features of a destabilization-based phenomenon. We first show that ABB post-reactivation amnesia is critically dependent on prediction error at the time of memory reactivation and provide evidence for its temporally graded nature. In line with the known role of GluN2B-NMDA receptor activation in memory destabilization, we further demonstrate that pre-reactivation administration of ifenprodil, a selective antagonist of GluN2B-NMDA receptors, prevents MDZ-induced ABB amnesia. In sum, our data reveal that ABB MDZ-induced post-reactivation amnesia exhibits the hallmark features of a destabilization-dependent phenomenon. Implication of our findings for a reconsolidation-based account of post-reactivation amnesia are discussed.

Active suppression prevents the return of threat memory in humans

Unbidden distressing memories inflict serious damage on mental health. Extant research highlights the importance of associative learning in modulating aversive memory. We report that conscious active suppression eliminates learned fear responses independent of memory triggers and is related to individual difference in thought control ability; in contrast, thought diversion only reduces cue-specific fear response. These results suggest potential avenues for treatment of persistent maladaptive memories by engaging declarative mnemonic control mechanisms.

Ye Wang et al. show that conscious thought active suppression eliminates learned fear responses whereas thought diversion only reduces cue-specific fear response. This study suggests that declarative control mechanisms may be utilized to treat persistent maladaptive memories.

Retrieval-extinction as a reconsolidation-based treatment for emotional disorders:Evidence from an extinction retention test shortly after intervention

The retrieval-extinction paradigm, a non-invasive memory intervention that is methodologically similar to exposure therapy, has significant clinical application prospects for targeting memory reconsolidation. However, it is difficult to distinguish whether the effect of preventing the return of fear by retrieval-extinction depends upon the reconsolidation-based mechanism or extinction-based mechanism. This study tested extinction retention shortly after intervention to determine whether retrieval-extinction is a reconsolidation-based approach or extinction-based approach as well as exploring the effect of sleep. In our experiment, the effects on fear conditional memory of standard extinction, retrieval-extinction, and extinction-retrieval were compared using the fear test at 3 h, 12 h without a night's sleep, and 12 h with a night's sleep after the intervention. The results showed that standard extinction and extinction-retrieval procedures reduce fear 3 h after intervention, while retrieval-extinction procedure reduces fear 12 h with a night's sleep after the intervention. The results suggest that standard extinction and extinction-retrieval create an extinction memory trace that competes with original memory trace, only retrieval-extinction update the original memory trace through memory reconsolidation. These findings provide solid evidence for the reconsolidation mechanism of the retrieval-extinction paradigm and highlight the effect of sleep on memory reconsolidation.

Failures of memory and the fate of forgotten memories

This review is intended primarily to provide cognitive benchmarks and perhaps a new mindset for behavioral neuroscientists who study memory. Forgetting, defined here broadly as all types of decreases in acquired responding to stimulus-specific eliciting cues, is commonly attributed to one or more of the following families of mechanisms: (1) (4) associative interference by information similar to, but different from the target information, (2) spontaneous decay of memory with increasing retention intervals, (3) displacement from short-term memory by irrelevant information, and (4) inadequate retrieval cues at test. I briefly review each of these families and discuss data suggesting that many apparent instances of spontaneous forgetting and displacement from short-term memory can be viewed as variants of inadequate retrieval cues and associative interference. The potential for recovery of target information from each of these families of forgetting without further relevant training is then reviewed, with a conclusion that most forgetting is due to retrieval failure as opposed to irreversible erasure of memory. The more general point is made that there are logical problems with ever talking about attenuating or erasing a memory as a consequence of conventional forgetting or disrupted consolidation/reconsolidation. Consideration is then given to the frequently overlooked but highly beneficial consequences of most forgetting. Lastly, the major variables that moderate forgetting are summarized, including (a) the similarities of the target information including training context to the explicit retrieval cues and context present at test, (b) the similarities of potentially interfering acquired information to the retrieval cues and context present at test, and (c) the retention interval for the target information relative to that for the potentially interfering information. Appropriate manipulation of these variables can reduce forgetting, and increase forgetting when desired.

Destabilizing Different Strengths of Fear Memories Requires Different Degrees of Prediction Error During Retrieval

Reactivation of consolidated memories can induce a labile period, in which these reactivated memories might be susceptible to change and need reconsolidation. Prediction error (PE) has been recognized as a necessary boundary condition for memory destabilization. Moreover, memory strength is also widely accepted as an essential boundary condition to destabilize fear memory. This study investigated whether different strengths of conditioned fear memories require different degrees of PE during memory reactivation in order for the memories to become destabilized. Here, we assessed the fear-potentiated startle and skin conductance response, using the post-retrieval extinction procedure. A violation of expectancy (PE) was induced during retrieval to reactivate enhanced (unpredictable-shock) or ordinary (predictable-shock) fear memories that were established the day before. Results showed that a PE retrieval before extinction can prevent the return of predictable-shock fear memory but cannot prevent the return of unpredictable-shock fear memory, indicating that a single PE is insufficient to destabilize enhanced fear memory. Therefore, we further investigated whether increasing the degree of PE could destabilize enhanced fear memory using different retrieval strategies (multiple PE retrieval and unreinforced CS retrieval). We found that spontaneous recovery of enhanced fear memory was prevented in both retrieval strategies, but reinstatement was only prevented in the multiple PE retrieval group, suggesting that a larger amount of PE is needed to destabilize enhanced fear memory. The findings suggest that behavioral updating during destabilization requires PE, and the degree of PE needed to induce memory destabilization during memory retrieval depends on the strength of fear memory. The study indicates that memory reconsolidation inference can be used to destabilize stronger memories, and the findings shed lights on the treatment of posttraumatic stress disorders and anxiety disorders.

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.

Boundary conditions of post-retrieval extinction: A direct comparison of low and high partial reinforcement

Research has shown that a single presentation of the conditioned stimulus prior to extinction training can diminish conditioned responses. However, replication has proven difficult and appears to be limited by boundary conditions. Here we tested the boundary condition of memory strength by comparing the effect of reinforcement rate to assess its role in post-retrieval extinction. Eighty university students had undergone a three-day fear conditioning experiment in which two partial reinforcement schedules (40%, 80%) were applied. The findings indicated that both low and high partial reinforcement groups did not demonstrate recovery of conditioned responses after post-retrieval extinction. In contrast, both groups demonstrated significant recovery to standard extinction with significantly greater recovery in the 80% group relative to the 40% group. Additionally, we found that greater physiological arousal during memory retrieval significantly predicted recovery of fear at test phase. We conclude that when compared to a lower partial reinforcement schedule, a higher partial reinforcement resulted in the formation of a stronger memory as indicated by greater physiological arousal during memory reactivation and recovery of conditioned responses after standard extinction, but that it does not function as a boundary condition of post-retrieval extinction. These data are significant because it is the first study to investigate the effect of varying partial reinforcement schedules on fear recovery and add to the body of literature that continue to identify sources of failure in the application of post-retrieval extinction.

Reactivation of the Unconditioned Stimulus Inhibits the Return of Fear Independent of Cortisol

Reconsolidation is the post-retrieval stabilization of memories, a time-limited process during which reactivated (i.e., retrieved) memories can be updated with new information, become stronger or weaker, depending on the specific treatment. We have previously shown that the stress hormone cortisol has an enhancing effect on the reconsolidation of fear memories in men. This effect was specific, i.e., limited to the conditioned stimulus (CS) that was reactivated, and did not generalize to other previously reinforced, but not reactivated CS. Based on these results, we suggested that cortisol plays a critical role in the continuous strengthening of reactivated emotional memories, contributing to their persistence and robustness. In the current study, we aimed to achieve a more generalized reconsolidation enhancement using an alternative reactivation method, i.e., by a low-intensity unconditioned stimulus (UCS) presentation instead of the more common unreinforced CS presentation. In previous studies, UCS reactivation was shown to lead to a more generalized reconsolidation effect. Therefore, we hypothesized that the combination of cortisol treatment and UCS reactivation would lead to an enhanced fear memory reconsolidation, which would generalize from previously reinforced CS to stimuli that resemble it. We tested 75 men in a 3-day fear conditioning paradigm: fear acquisition training on day 1; UCS reactivation/no reactivation and pharmacological treatment (20 mg hydrocortisone/placebo) on day 2; extinction training, reinstatement and test (of original and modified stimuli) on day 3. In contrast to our hypothesis, UCS reactivation prevented the return of fear [observed in skin conductance responses (SCR)] regardless of the pharmacological manipulation: while reinstatement to the original CS was found in the no-reactivation group, both reactivation groups (cortisol and placebo) showed no reinstatement. As the only methodological difference between our previous study and the current one was the reactivation method, we focus on UCS reactivation as the main explanation for these unexpected findings. We suggest that the robust prediction error generated by the UCS reactivation method (as opposed to CS reactivation), combined with the lower UCS intensity, has by itself weakened the emotional value of the UCS, thus preventing the return of fear to the CS that was associated with it. We call for future research to support these findings and to examine the potential of this reactivation method, or variations thereof, as a tool for therapeutic use.

A novel method to trigger the reconsolidation of fear memory

The procedure of memory reconsolidation provides an opportunity to improve some mental disorders caused by maladaptive memories, such as Posttraumatic Stress Disorder. Prediction error was considered a necessary condition for triggering memory reconsolidation. However, it is difficult to create a satisfying prediction error to successfully open memory reconsolidation in a clinical context. The purpose of this study was to explore a more practicable method to trigger memory reconsolidation. We used a successive 4-day fear-potentiated startle paradigm to compare the effect of uncertainty with prediction error during retrieval on preventing the return of fear. Bayes factor, combined with p value and effect size, was used as the main indicator of statistical inference. The results indicated that spontaneous recovery and reinstatement of fear were not observed in the uncertainty group, whereas return of fear was observed for the prediction error group. However, the direct comparison between the two groups did not yield statistically significant results, potentially reflecting a lack of statistical power. Nonetheless, these results suggest that uncertainty retrieval could be a better means to trigger memory reconsolidation than prediction error, making uncertainty a worthwhile factor to consider in future research on memory reconsolidation.

From Extinction Learning to Anxiety Treatment: Mind the Gap

Laboratory models of extinction learning in animals and humans have the potential to illuminate methods for improving clinical treatment of fear-based clinical disorders. However, such translational research often neglects important differences between threat responses in animals and fear learning in humans, particularly as it relates to the treatment of clinical disorders. Specifically, the conscious experience of fear and anxiety, along with the capacity to deliberately engage top-down cognitive processes to modulate that experience, involves distinct brain circuitry and is measured and manipulated using different methods than typically used in laboratory research. This paper will identify how translational research that investigates methods of enhancing extinction learning can more effectively model such elements of human fear learning, and how doing so will enhance the relevance of this research to the treatment of fear-based psychological disorders.

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.

Extinction after fear memory reactivation fails to eliminate renewal in rats

Retrieving fear memories just prior to extinction has been reported to effectively erase fear memories and prevent fear relapse. The current study examined whether the type of retrieval procedure influences the ability of extinction to impair fear renewal, a form of relapse in which responding to a conditional stimulus (CS) returns outside of the extinction context. Rats first underwent Pavlovian fear conditioning with an auditory CS and footshock unconditional stimulus (US); freezing behavior served as the index of conditioned fear. Twenty-four hours later, the rats underwent a retrieval-extinction procedure. Specifically, 1h prior to extinction (45 CS-alone trials; 44 for rats receiving a CS reminder), fear memory was retrieved by either a single exposure to the CS alone, the US alone, a CS paired with the US, or exposure to the conditioning context itself. Over the next few days, conditional freezing to the extinguished CS was tested in the extinction and conditioning context in that order (i.e., an ABBA design). In the extinction context, rats that received a CS+US trial before extinction exhibited higher levels of conditional freezing than animals in all other groups, which did not differ from one another. In the renewal context, all groups showed renewal, and none of the reactivation procedures reduced renewal relative to a control group that did not receive a reactivation procedure prior to extinction. These data suggest retrieval-extinction procedures may have limited efficacy in preventing fear renewal.

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.