Concurrent excitors limit the extinction of conditioned fear in humans

Exposure Therapy and Its Mechanisms

Exposure therapy is the gold-standard treatment approach for pathological anxiety. This therapeutic approach builds on principles of extinction training from traditional fear conditioning and extinction protocols. In this chapter, we discuss principles of exposure therapy in the clinic and the laboratory experimental results that guide our decisions in the therapy. We discuss emotional processing theory and inhibitory learning principles, with a focus on expectation violation. We conclude with future research directions needed to improve exposure therapy outcomes among patients with anxiety-related disorders.

Merging Our Understanding of Anxiety and Exposure: Using Inhibitory Learning to Target Anxiety Sensitivity in Exposure Therapy

Exposure-based therapies are the gold standard treatment for anxiety disorders, and recent advancements in basic and clinical research point to the need to update the implementation of exposure. Recent research has highlighted the importance of transdiagnostic factors such as anxiety sensitivity (AS), or fear of anxiety-related sensations. Elevated AS is common among all anxiety disorders and contains three dimensions, or expectancies, that can be used to guide treatment. Recently, treatments directly targeting AS have shown potential in reducing symptoms of anxiety. In addition, inhibitory learning theory (ILT) provides an alternative explanation of exposure processes based on basic learning research. ILT extends the current framework by accounting for renewal of fear, which is important given the substantial number of individuals who experience a return of symptoms following treatment. The current paper will provide an overview of ILT and discuss several ILT techniques that can be used to target AS. These two converging bodies of research hold strong potential for optimizing treatment for anxiety.

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

BACKGROUND

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

DESIGN

Randomized controlled trial, factorial design.

METHODS

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

RESULTS

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

CONCLUSIONS

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

CLINICAL TRIAL REGISTRATION

(clinicaltrials.gov)NCT02160470.

The clinical applications and practical relevance of human conditioning paradigms for posttraumatic stress disorder

The classical conditioning paradigm of fear learning has spawned a number of experimental variations for the explanation of posttraumatic stress disorder (PTSD) etiology. These paradigms include extinction learning and recall, fear inhibition, fear generalization, and conditioned avoidance. As such, each of these paradigms have significant applications for understanding the development, maintenance, treatment, and relapse of the fear-related features of PTSD. In the present review, we describe each of these conditioning-based paradigms with reference to the clinical applications, and supported by case examples from patients with severe PTSD symptoms. We also review the neurobiological models of conditioning and extinction in animals, psychiatrically healthy humans, and PTSD patients, and discuss the current balance of evidence suggesting a number of biological, behavioral, and cognitive mechanisms/moderators of the conditioning and extinction process in experimental and clinical contexts.

Endogenous salivary α-amylase does not interact with skin conductance response during fear extinction in posttraumatic stress disorder

Posttraumatic Stress Disorder (PTSD) is associated with elevated noradrenergic signaling, which has an impact on emotional learning and memory. Fear extinction is thought to underlie the processes of exposure therapy, however the relationship between noradrenaline and extinction in PTSD is unclear. Participants with PTSD (n = 21), trauma-exposure without PTSD (TC; n = 36), and non-trauma-exposed controls (NTC; n = 27) completed a fear conditioning and extinction paradigm, and conditioned fear was indexed by skin conductance response (SCR). Salivary α-amylase (sAA) collected at baseline and immediately post-fear acquisition was used as an index of noradrenaline, and we examined whether sAA in response to fear acquisition was a moderator between fear extinction and PTSD symptoms. While there was a significant increase in sAA from baseline to post-fear acquisition, this was not modulated by group. Compared to TC and NTC, the PTSD group displayed a slower decline in SCRs during early extinction, which generalized across stimulus type, and was not moderated by sAA. These findings suggest that the relationship between fear extinction and PTSD symptoms does not change as a function of sAA levels; however previous research suggests other processes of fear learning may be associated with noradrenergic activity in PTSD.

Negative appraisals and fear extinction are independently related to PTSD symptoms

BACKGROUND

Considerable research has revealed impaired fear extinction to be a significant predictor of PTSD. Fear extinction is also considered the primary mechanism of exposure therapy, and a critical factor in PTSD recovery. The cognitive theory of PTSD proposes that symptoms persist due to excessive negative appraisals about the trauma and its sequelae. Research has not yet examined the relationship between fear extinction and negative appraisals in PTSD.

METHODS

A cross-sectional sample of participants with PTSD (n =21), and trauma-exposed controls (n =33) underwent a standardized differential fear conditioning and extinction paradigm, with skin conductance response (SCR) amplitude serving as the index of conditioned responses. The Posttraumatic Cognitions Inventory (PTCI) was used to index catastrophic negative appraisals.

RESULTS

Participants with PTSD demonstrated a slower decrease in overall SCR responses during extinction and greater negative appraisals compared to the group. A moderation analysis revealed that both negative trauma-relevant appraisals and fear extinction learning were independently associated with PTSD symptoms, but there was no moderation interaction.

LIMITATIONS

The current study was limited by a modest sample size, leading to the inclusion of participants with subclinical PTSD symptoms. Further, the current study only assessed fear extinction learning; including a second day extinction recall task may show alternative effects.

CONCLUSIONS

These findings indicate that negative appraisals and fear extinction did not interact, but had independent relationships with PTSD symptoms. Here we show for the first time in an experimental framework that negative appraisals and fear extinction play separate roles in PTSD symptoms.

Don't fear 'fear conditioning': Methodological considerations for the design and analysis of studies on human fear acquisition, extinction, and return of fear

The so-called 'replicability crisis' has sparked methodological discussions in many areas of science in general, and in psychology in particular. This has led to recent endeavours to promote the transparency, rigour, and ultimately, replicability of research. Originating from this zeitgeist, the challenge to discuss critical issues on terminology, design, methods, and analysis considerations in fear conditioning research is taken up by this work, which involved representatives from fourteen of the major human fear conditioning laboratories in Europe. This compendium is intended to provide a basis for the development of a common procedural and terminology framework for the field of human fear conditioning. Whenever possible, we give general recommendations. When this is not feasible, we provide evidence-based guidance for methodological decisions on study design, outcome measures, and analyses. Importantly, this work is also intended to raise awareness and initiate discussions on crucial questions with respect to data collection, processing, statistical analyses, the impact of subtle procedural changes, and data reporting specifically tailored to the research on fear conditioning.

Compound Stimulus Presentation Does Not Deepen Extinction in Human Causal Learning

Models of associative learning have proposed that cue-outcome learning critically depends on the degree of prediction error encountered during training. Two experiments examined the role of error-driven extinction learning in a human causal learning task. Target cues underwent extinction in the presence of additional cues, which differed in the degree to which they predicted the outcome, thereby manipulating outcome expectancy and, in the absence of any change in reinforcement, prediction error. These prediction error manipulations have each been shown to modulate extinction learning in aversive conditioning studies. While both manipulations resulted in increased prediction error during training, neither enhanced extinction in the present human learning task (one manipulation resulted in less extinction at test). The results are discussed with reference to the types of associations that are regulated by prediction error, the types of error terms involved in their regulation, and how these interact with parameters involved in training.

Changes in Cue Configuration Reduce the Impact of Interfering Information in a Predictive Learning Task

Decades of research in extinction and interference show that contexts can play a critical role at disambiguating the meaning of cues that have been paired with different outcomes at different times. For instance, if a cue x is followed by outcome 1 in the first phase of an experiment and by outcome 2 in a second phase, responses to cue x tend to be consistent with outcome 2 when tested in a context similar to that of the second phase of the experiment. However, if participants are taken back to the original context of the first phase (i.e., ABA renewal) or to a completely new context (i.e., ABC or AAB renewal), their responses to x tend to be more consistent with outcome 1. Although the role of physical and temporal contexts has been well studied, other factors that can also modulate the selective retrieval of information after interference have received less attention. The present series of experiments shows how changes in cue configuration can modulate responding in a similar manner. Across five experiments using a human predictive learning task, we found that adding, removing or replacing elements from a compound cue that had undergone an interference treatment gave rise to a recovery of responding akin to that observed after context changes in AAB renewal. These results are consistent with those of previous studies exploring the effect of changes of cue configuration on interference. Taken together, these studies suggest that a change in cue configuration can have the functional properties of a context change, a finding with important implications for formal models of configural learning and for classical accounts of interference and information retrieval.

Compound stimulus extinction reduces spontaneous recovery in humans

Fear-related behaviors are prone to relapse following extinction. We tested in humans a compound extinction design ("deepened extinction") shown in animal studies to reduce post-extinction fear recovery. Adult subjects underwent fear conditioning to a visual and an auditory conditioned stimulus (CSA and CSB, respectively) separately paired with an electric shock. The target CS (CSA) was extinguished alone followed by compound presentations of the extinguished CSA and nonextinguished CSB. Recovery of conditioned skin conductance responses to CSA was reduced 24 h after compound extinction, as compared with a group who received an equal number of extinction trials to the CSA alone.

Can fear extinction be enhanced? A review of pharmacological and behavioral findings

There is considerable interest, from both a basic and clinical standpoint, in gaining a greater understanding of how pharmaceutical or behavioral manipulations alter fear extinction in animals. Not only does fear extinction in rodents model exposure therapy in humans, where the latter is a cornerstone of behavioral intervention for anxiety disorders such as post-traumatic stress disorder and specific phobias, but also understanding more about extinction provides basic information into learning and memory processes and their underlying circuitry. In this paper, we briefly review three principal approaches that have been used to modulate extinction processes in animals and humans: a purely pharmacological approach, the more widespread approach of combining pharmacology with behavior, and a purely behavioral approach. The pharmacological studies comprise modulation by: brain derived neurotrophic factor (BDNF), d-cycloserine, serotonergic and noradrenergic drugs, neuropeptides, endocannabinoids, glucocorticoids, histone deacetylase (HDAC) inhibitors, and others. These studies strongly suggest that extinction can be modulated by drugs, behavioral interventions, or their combination, although not always in a lasting manner. We suggest that pharmacotherapeutic manipulations provide considerable promise for promoting effective and lasting fear reduction in individuals with anxiety disorders. This article is part of a Special Issue entitled 'Memory enhancement'.

Generalization of human fear acquisition and extinction within a novel arbitrary stimulus category

Adaptive anxiety relies on a balance between the generalization of fear acquisition and fear extinction. Research on fear (extinction) generalization has focused mostly on perceptual similarity, thereby ignoring the importance of conceptual stimulus relations in humans. The present study used a laboratory procedure to create de novo conceptual categories of arbitrary stimuli and investigated fear and extinction generalization among these stimuli. A matching-to-sample task produced two four-member categories of abstract figures. Next, a member from one category was coupled with an aversive electrical stimulation, while a member from the other category was presented alone. As expected, conditioned fear responses generalized to the other members of the first category (skin conductance and online shock-expectancy). Subsequent extinction of the conditioned member also generalized to the other members. However, extinguishing a non-conditioned member failed to reduce fear of the conditioned member itself. We conclude that fears generalize readily across conceptually related stimuli, but that the degree of extinction generalization depends on the stimulus subjected to extinction.

Behavioral and neurobiological mechanisms of extinction in Pavlovian and instrumental learning

This article reviews research on the behavioral and neural mechanisms of extinction as it is represented in both Pavlovian and instrumental learning. In Pavlovian extinction, repeated presentation of a signal without its reinforcer weakens behavior evoked by the signal; in instrumental extinction, repeated occurrence of a voluntary action without its reinforcer weakens the strength of the action. In either case, contemporary research at both the behavioral and neural levels of analysis has been guided by a set of extinction principles that were first generated by research conducted at the behavioral level. The review discusses these principles and illustrates how they have informed the study of both Pavlovian and instrumental extinction. It shows that behavioral and neurobiological research efforts have been tightly linked and that their results are readily integrated. Pavlovian and instrumental extinction are also controlled by compatible behavioral and neural processes. Since many behavioral effects observed in extinction can be multiply determined, we suggest that the current close connection between behavioral-level and neural-level analyses will need to continue.

The potential impact of mindfulness on exposure and extinction learning in anxiety disorders

Mindfulness based approaches have shown promise in the treatment of various anxiety disorders. However, further research is needed to more precisely elucidate mechanisms of action through which mindfulness practice may enhance treatment for anxiety. Given centrality of exposure-based procedures in the treatment of anxiety, it is important to consider ways in which mindfulness may affect exposure and extinction processes. In fact, numerous findings in the basic science of extinction point to the possible ways in which mindfulness may facilitate extinction learning. The present paper aims to critically review the literature surrounding mindfulness and extinction learning in order to more fully explore the ways in which mindfulness-based treatments may positively impact exposure and extinction processes in the treatment of anxiety disorders. This will provide a unique synthesis of newer, acceptance-based behavior therapies with established principles of effective behavioral treatments.

Expanding the intertrial interval during extinction: response cessation and recovery

We examined trial spacing during extinction following a human contingency learning task. Specifically, we assessed if an expanding retrieval practice schedule (Bjork & Bjork, 1992, 2006), in which the spacing between extinction trials was progressively increased, would result in faster immediate extinction and less recovery from extinction than uniformly spaced extinction trials. We used an ABB vs. ABA renewal design and observed that, whereas the expanding group extinguished faster during extinction treatment, the expanding and constant groups showed the same level of extinction with an immediate test in the extinction context (ABB) and the two groups showed equivalent ABA renewal at test in the training context. We conclude that the faster extinction observed in the expanding groups could be misleading in clinical treatment, if the therapist used the absence of fear during extinction as the basis for terminating treatment.

Constraints on Enhanced Extinction Resulting from Extinction Treatment in the Presence of an Added Excitor

Three Pavlovian fear conditioning experiments with rats as subjects explored the effect of extinction in the presence of a concurrent excitor. Our aim was to explore this particular treatment, documented in previous studies to deepen extinction, with novel control groups to shed light on the processes involved in extinction. Relative to subjects extinguished on the target CS alone, Experiments 1 and 2 found across a range of parameters that any appreciable effect of facilitated extinction due to the concurrent excitor was submerged by generalization decrement going from extinction to testing. In Experiment 3 we used different durations for the target and concurrent stimuli in order to discourage configuring and an ABC renewal design to increase sensitivity, and observed diminished renewal resulting from extinction in the presence of a second excitor. Our findings suggest that there are distinct limits to the observation of extinction in the presence of an excitor and identifies some of the sources of these limitations.

Fear generalization in humans: impact of verbal instructions

Fear generalization lies at the heart of many anxiety problems, but little is known about the factors that can influence this phenomenon. The present study investigated whether verbal instructions about specific stimulus features can influence conditioned fear generalization. All participants were fear conditioned to a yellow triangle, using an electric shock. Participants had received pre-experimental instructions saying that the shapes (or colours) of the stimuli were informative for the occurrence of shock (group Shape and group Colour, respectively). Next, generalization was tested to presentations of a blue triangle (same shape) as well as a yellow square (same colour). Fear reactions were measured through skin conductance and online ratings of shock-expectancy. The results showed strongest generalization to the same shape stimulus in group Shape, versus the same colour stimulus in group Colour. Hence, the same learning experience can have opposite effects in terms of fear generalization, depending on verbally transmitted information about the relative importance of individual stimulus features.

Spacing extinction trials alleviates renewal and spontaneous recovery

Studies of extinction in classical conditioning situations can reveal techniques that maximize the effectiveness of exposure-based behavior therapies. In three experiments, we investigated the effect of varying the intertrial interval during an extinction treatment in a fear-conditioning preparation with rats as subjects. In Experiment 1, we found less fear at test (i.e., more effective extinction) when extinction trials were widely spaced, relative to intermediate or massed extinction trials. In Experiment 2, we used an ABA renewal procedure and observed that spaced trials attenuated renewal of conditioned fear relative to massed trials. In Experiment 3, we used a similar design, but instead of changing the physical context at the time of testing, we interposed a retention interval after the extinction treatment to produce a change in the temporal context. The results showed less spontaneous recovery of fear after spaced than after massed extinction trials. These results suggest that extinction is more enduring when the extinction trials are spaced rather than massed. Although the benefits of spacing trials are small when there is no contextual change from extinction to testing, a change in either physical or temporal context following massed extinction trials leads to a recovery from extinction, which is reduced when the trials are spaced.

The development of cued versus contextual conditioning in a predictable and an unpredictable human fear conditioning preparation

In this human fear conditioning study, the online development of conditioned US-expectancy to discrete cues and background contexts was measured in two groups. In the paired group (n=30), the CS was systematically followed by an aversive shock (US). In the unpaired group (n=30), CS and US were presented explicitly unpaired. Using US-expectancy ratings, we replicated the basic finding already illustrated in humans with startle modulation. In the paired group, the CS elicited more US-expectancy than the context, whereas in the unpaired group, the context elicited more US-expectancy than the CS. Interestingly, we also observed a trial-by-trial development of conditioning to the context in the unpaired group as indicated by a significant linear trend. This gradual development and the evidence for the role of US-expectancy in contextual fear add to the idea that cued and contextual fear rely on the same basic associative processes.

Contextual-specificity of short-delay extinction in humans: renewal of fear-potentiated startle in a virtual environment

A recent fear-potentiated startle study in rodents suggested that extinction was not context dependent when extinction was conducted after a short delay following acquisition, suggesting that extinction can lead to erasure of fear learning in some circumstances. The main objective of this study was to attempt to replicate these findings in humans by examining the context specificity of short-delay extinction in an ABA renewal procedure using virtual reality environments. A second objective was to examine whether renewal, if any, would be influenced by context conditioning. Subjects underwent differential aversive conditioning in virtual context A, which was immediately followed by extinction in virtual context B. Extinction was followed by tests of renewal in context A and B, with the order counterbalanced across subjects. Results showed that extinction was context dependent. Evidence for renewal was established using fear-potentiated startle as well as skin conductance and fear ratings. In addition, although contextual anxiety was greater in the acquisition context than in the extinction context during renewal, as assessed with startle, context conditioning did not influence the renewal effect. These data do not support the view that extinction conducted shortly after acquisition is context independent. Hence, they do not provide evidence that extinction can lead to erasure of a fear memory established via Pavlovian conditioning.