Protection from extinction

Increased Generalization, Stronger Acquisition, or Reduced Extinction? Investigation of the Mechanisms Underlying the Acquisition-in-Multiple-Contexts Effect

Prior research has demonstrated that conducting acquisition in multiple contexts results in more responding to the point that it can even nullify the benefit of subsequent extinction in multiple contexts on reducing renewal of excitatory responding. The underlying mechanism to explain why this happens has not been systematically examined. Using self-reported expectancy of the outcome, the current study investigates three mechanisms that potentially explain why acquisition in multiple contexts results in more responding-greater generalization, stronger acquisition learning, or slower extinction learning. Participants (N = 180) received discriminative training with a conditioned stimulus (CS+) and outcome pairing and a CS- → noOutcome pairing in either one or three contexts. This was followed by either extinction treatment in a novel context or no extinction. Finally, testing occurred in the acquisition context, the extinction context, or a novel context. Stronger renewal of extinguished conditioned expectation was observed for participants who received CS+ → Outcome pairings in three contexts relative to one context. There was no effect of the number of contexts on the strength of the excitatory CS+ → Outcome association or degree of inhibitory learning that occurred during extinction. This suggests that generalization is the mechanism responsible for the adverse impact to extinction learning when acquisition is conducted in multiple contexts.

Effects of social buffering on fear extinction in adolescent rats

Across social species, the presence of another individual can reduce stress reactions to adverse stimuli, a phenomenon known as social buffering. The present study investigated whether social buffering influences the expression and extinction of learned fear in adolescence, a developmental period of diminished fear inhibition and increased social interaction. Quality of maternal care and degree of social investigation were examined as factors that may influence social buffering. In adolescence, male rats were fear conditioned and then given extinction training either in the presence of a same-age rat or alone. Animals were then tested alone for extinction retention. In two experiments, the presence of a conspecific robustly reduced conditioned fear responses during extinction training. Interestingly, a persistent social buffering effect was observed when the extinction and conditioning contexts had prominent differences in features (Experiment 1), but not when these contexts were relatively similar (Experiment 2). Neither quality of maternal care nor degree of social investigation predicted the effects of social buffering. These findings suggest that social buffering robustly dampens fear responses during adolescence when a peer is present and this suppression can persist, in some instances, even when the peer is absent.

Intermixed safety cues facilitate extinction retention in adult and adolescent mice

Extinction learning is tremendously adaptive as it allows an animal to adjust their behavior in a changing environment. Yet, extinction is not without limitations and fear often reemerges over time (i.e. spontaneous recovery). Relative to adults, adolescent rodents and humans are particularly prone to spontaneous recovery following extinction. In this study, we aimed to address whether combining methods of fear regulation (extinction and conditioned inhibition) can facilitate extinction retention. Early adolescent (29 days old, n = 81) and adult (70 days old, n = 80) mice underwent extinction with or without a safety cue present. Safety cue presentations were systematically varied to overlap with or alternate with fear cue presentations. We found that initial safety learning was faster in adolescent mice. In addition, intermixing safety cues into extinction reduced spontaneous recovery during a test two weeks later. The decrease in spontaneous recovery relative to a standard extinction protocol was greater in adolescents than adults. Together, our findings provide initial evidence that safety learning may be inherently stronger during adolescence. These results inform the parameters by which conditioned safety and extinction learning may be merged to augment the inhibition of fear. While methods to enhance fear regulation are valuable for any age, the potential to do so during adolescence is particularly striking.

A model for recovery-from-extinction effects in Pavlovian conditioning and exposure therapy

Exposure therapy is an effective intervention for anxiety-related problems. The mechanism of this intervention has been the extinction procedure in Pavlovian conditioning, and this application has provided many successful instances for the prevention of relapse. However, traditional associative theories cannot comprehensively explain many findings. In particular, it is difficult to explain the recovery-from-extinction effects, which is the reappearance of the conditioned response following extinction. In this paper, we propose an associative model that is a mathematical extension of Bouton's (1993, Psychological Bulletin, 114, 80-99) model for the extinction procedure. The core of our model is that the asymptotic strength of the inhibitory association depends on the degree of excitatory association retrieved in a context in which a conditioned stimulus (CS) is presented and that the retrieval is determined by the similarity between contexts during both reinforcement and non-reinforcement and the retrieval context. Our model provides an explanation of the recovery-from-extinction effects, and implications for exposure therapy.

The effect of information seeking behaviors in fear control

BACKGROUND AND OBJECTIVES

Individuals experiencing conditioned fear reactions often resort to avoidance and escape behaviors as attempts to decrease fear. Nevertheless, these strategies are not always available. In such cases, people seek information to mitigate aversive events. This study aimed at evaluating the effect of information seeking behaviors on self-reported fear, predictability, and physiological responses.

METHODS

Participants were randomly assigned to two groups. In group one, individuals were given the choice to perform an instrumental behavior which provided information about the occurrence of either an aversive or a neutral event (100% contingency). In group two, individuals were also allowed to perform an instrumental behavior. However, such behavior provided partial information (50% contingency).

RESULTS

Individuals in group one presented lower levels of fear compared to individuals assigned to group two.

LIMITATIONS

The generalizability of the results may be restricted to undergraduate students.

CONCLUSIONS

The results suggests that when avoidance and escape are not available, individuals seek information that provides control over fear. Clinical implications are discussed.

Laboratory models of post-traumatic stress disorder: The elusive bridge to translation

Post-traumatic stress disorder (PTSD) is a debilitating mental illness composed of a heterogeneous collection of symptom clusters. The unique nature of PTSD as arising from a precipitating traumatic event helps simplify cross-species translational research modeling the neurobehavioral effects of stress and fear. However, the neurobiological progress on these complex neural circuits informed by animal models has yet to produce novel, evidence-based clinical treatment for PTSD. Here, we provide a comprehensive overview of popular laboratory models of PTSD and provide concrete ideas for improving the validity and clinical translational value of basic research efforts in humans. We detail modifications to simplified animal paradigms to account for myriad cognitive factors affected in PTSD, which may contribute to abnormalities in regulating fear. We further describe new avenues for integrating different areas of psychological research underserved by animal models of PTSD. This includes incorporating emerging trends in the cognitive neuroscience of episodic memory, emotion regulation, social-emotional processes, and PTSD subtyping to provide a more comprehensive recapitulation of the human experience to trauma in laboratory research.

Agency rescues competition for credit assignment among predictive cues from adverse learning conditions

A fundamental assumption of learning theories is that the credit assigned to predictive cues is not simply determined by their probability of reinforcement, but by their ability to compete with other cues present during learning. This assumption has guided behavioral and neural science research for decades, and tremendous empirical and theoretical advances have been made identifying the mechanisms of cue competition. However, when learning conditions are not optimal (e.g., when training is massed), cue competition is attenuated. This failure of the learning system exposes the individual’s vulnerability to form spurious associations in the real world. Here, we uncover that cue competition in rats can be rescued when conditions are suboptimal provided that the individual has agency over the learning experience. Our findings reveal a new effect of agency over learning on credit assignment among predictive cues, and open new avenues of investigation into the underlying mechanisms.

Inhibitory causal structures in serial and simultaneous feature negative learning

We have previously reported that human participants trained with a simultaneous feature negative discrimination (intermixed A+/AB− trials) show only modest transfer of inhibitory properties of feature B to a separately trained excitor in a summation test. Their self-reported causal structure suggested that many participants learned that the effect of feature B was somewhat specific to the excitor it had been trained with (modulation), rather than learning that the feature prevented the outcome (prevention). This pattern is reminiscent of the distinction between negative occasion-setting and conditioned inhibition in the animal conditioning literature. However, in animals, occasion-setting is more commonly seen with a serial procedure, in which the feature (B) precedes the training excitor (A). Accordingly, we ran three experiments to compare serial with simultaneous training in an allergist causal judgement task. Transfer in a summation test was stronger to a previously modulated test excitor compared to a simple excitor after both simultaneous and serial training. There was a numerical trend towards a larger effect in the serial group, but it failed to reach significance and the Bayes Factor indicated support for the null. Serial training had no differential effect on the self-reported causal structure and did not significantly reduce overall transfer. After both simultaneous and serial training, transfer was strongest in participants who reported a prevention structure, replicating and extending our previous results to a previously modulated excitor. These results suggest that serial feature negative training does not promote a qualitatively different inhibitory causal structure compared to simultaneous training in humans.

BEHAVIORAL AND NEUROBIOLOGICAL MECHANISMS OF PAVLOVIAN AND INSTRUMENTAL EXTINCTION LEARNING

This article reviews the behavioral neuroscience of extinction, the phenomenon in which a behavior that has been acquired through Pavlovian or instrumental (operant) learning decreases in strength when the outcome that reinforced it is removed. Behavioral research indicates that neither Pavlovian nor operant extinction depends substantially on erasure of the original learning but instead depends on new inhibitory learning that is primarily expressed in the context in which it is learned, as exemplified by the renewal effect. Although the nature of the inhibition may differ in Pavlovian and operant extinction, in either case the decline in responding may depend on both generalization decrement and the correction of prediction error. At the neural level, Pavlovian extinction requires a tripartite neural circuit involving the amygdala, prefrontal cortex, and hippocampus. Synaptic plasticity in the amygdala is essential for extinction learning, and prefrontal cortical inhibition of amygdala neurons encoding fear memories is involved in extinction retrieval. Hippocampal-prefrontal circuits mediate fear relapse phenomena, including renewal. Instrumental extinction involves distinct ensembles in corticostriatal, striatopallidal, and striatohypothalamic circuits as well as their thalamic returns for inhibitory (extinction) and excitatory (renewal and other relapse phenomena) control over operant responding. The field has made significant progress in recent decades, although a fully integrated biobehavioral understanding still awaits.

Thought suppression inhibits the generalization of fear extinction

A challenge for translating fear extinction research into clinical treatments for stress and anxiety disorders is that extinction learning tends not to generalize beyond the treatment context. This may be because the hippocampus limits the expression of extinction memories. Consequently, downregulating the hippocampus may help to promote the generalization of extinction learning. One nonpharmacological strategy to downregulate hippocampal activity in humans is motivated forgetting, in which a participant deliberately attempts to suppress the encoding and/or retrieval of episodic memories. Here, we evaluated whether this strategy could facilitate extinction generalization by augmenting extinction training with thought suppression. Participants were threat conditioned using two conditioned stimulus (CS) categories paired with an electrical shock. Subsequently, during extinction training, one CS category was accompanied by thought suppression. Participants were tested for extinction generalization 24h later with conceptual variations of the extinguished stimuli. Contrary to our prediction, we found that extinction training paired with thought suppression resulted in enhanced shock expectancy (i.e., worse generalization) relative to standard extinction. We conclude that thought suppression during memory encoding likely acts as an inhibitory cue that blocks the acquisition of extinction memories, and therefore may not be a viable tactic to promote extinction generalization in the treatment of anxiety disorders.

Adaptive behaviour under conflict: Deconstructing extinction, reversal, and active avoidance learning

In complex environments, organisms must respond adaptively to situations despite conflicting information. Under natural (i.e. non-laboratory) circumstances, it is rare that cues or responses are consistently paired with a single outcome. Inconsistent pairings are more common, as are situations where cues and responses are associated with multiple outcomes. Such inconsistency creates conflict, and a response that is adaptive in one scenario may not be adaptive in another. Learning to adjust responses accordingly is important for species to survive and prosper. Here we review the behavioural and brain mechanisms of responding under conflict by focusing on three popular behavioural procedures: extinction, reversal learning, and active avoidance. Extinction involves adapting from reinforcement to non-reinforcement, reversal learning involves swapping the reinforcement of cues or responses, and active avoidance involves performing a response to avoid an aversive outcome, which may conflict with other defensive strategies. We note that each of these phenomena relies on somewhat overlapping neural circuits, suggesting that such circuits may be critical for the general ability to respond appropriately under conflict.

Different methods of fear reduction are supported by distinct cortical substrates

Understanding how learned fear can be reduced is at the heart of treatments for anxiety disorders. Tremendous progress has been made in this regard through extinction training in which the aversive outcome is omitted. However, current progress almost entirely rests on this single paradigm, resulting in a very specialized knowledgebase at the behavioural and neural level of analysis. Here, we used a dual-paradigm approach to show that different methods that lead to reduction in learned fear in rats are dissociated in the cortex. We report that the infralimbic cortex has a very specific role in fear reduction that depends on the omission of aversive events but not on overexpectation. The orbitofrontal cortex, a structure generally overlooked in fear, is critical for downregulating fear when novel predictions about upcoming aversive events are generated, such as when fear is inflated or overexpected, but less so when an expected aversive event is omitted.

Reduced renewal of conditioned suppression following lesions of the dorsal hippocampus in male rats

Extinguished responding will renew when the conditioned stimulus occurs outside the extinction context. Although studies of conditioned freezing have consistently demonstrated a role for the hippocampus in renewal, several studies have demonstrated intact renewal of conditioned suppression despite damage to the hippocampus (Frohardt, Guarraci, & Bouton, 2000; Todd, Jiang, DeAngeli, & Bucci, 2017; Wilson, Brooks, & Bouton, 1995). Because these prior studies have examined renewal when testing occurred in the original conditioning context ("Context A"), the present conditioned suppression experiments examined the role of the hippocampus when testing occurred in a context not associated with prior conditioning ("Context C"). In Experiments 1 and 2, conditioning occurred in Context A, and extinction in Context B. Renewal of conditioned suppression was observed when the extinguished conditioned stimulus (CS) was tested in Context C. However, renewal was attenuated in rats with lesions of the dorsal hippocampus (DH). Summation testing failed to detect conditioned inhibition in the extinction context, suggesting instead that the context acquired negative occasion-setting properties. Attenuated renewal was not due to an inability of DH lesioned rats to discriminate contexts (Experiment 3). These experiments thus demonstrate a role for the DH in renewal of conditioned suppression when testing occurs in a neutral context. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

The study of active avoidance: A platform for discussion

Traditional active avoidance tasks have advanced the field of aversive learning and memory for decades and are useful for studying simple avoidance responses in isolation; however, these tasks have limited clinical relevance because they do not model several key features of clinical avoidance. In contrast, platform-mediated avoidance (PMA) more closely resembles clinical avoidance because the response i) is associated with an unambiguous safe location, ii) is not associated with an artificial termination of the warning signal, and iii) is associated with a decision-based appetitive cost. Recent findings on the neuronal circuits of PMA have confirmed that amygdala-striatal circuits are essential for avoidance. In PMA, however, the prelimbic cortex facilitates the avoidance response early during the warning signal, perhaps through disinhibition of the striatum. Future studies on avoidance should account for additional factors such as sex differences and social interactions that will advance our understanding of maladaptive avoidance contributing to neuropsychiatric disorders.

Stable Individual Differences in Occasion Setting

Abstract. In the current investigation, we classified participants as inhibitors or non-inhibitors depending on the extent to which they showed conditioned inhibition in a context that had been used for extinction of a conditioned response. This classification enabled us to predict participant responses in a second experiment which used a different design and a different experimental task. In the second experiment a feature-negative discrimination survived reversal training of the feature to a greater extent in the non-inhibitors than in the inhibitors and this result was supported by Bayesian analyses. We propose that the fundamental distinction between inhibitors and non-inhibitors is based on a tendency to utilize first-order (direct associations) or second-order (occasion-setting) strategies when faced with ambiguous information and that this classification is a stable individual differences attribute.

Social Company Disrupts Fear Memory Renewal: Evidence From Two Rodent Studies

Renewal of fear outside treatment context is a challenge for behavioral therapies. Prior studies suggest a social buffering effect that fear response is attenuated in the presence of social company. However, few studies have examined the role of social company in reducing fear renewal. Here, we used a Pavlovian fear conditioning procedure including acquisition, extinction and test stages to examine social buffering effect on fear memory renewal in male rats. The test context was manipulated to be either different from the extinction one in ABC model, or same as that in ACC model. All conditioned subjects underwent extinction individually in Experiment 1 but with a partner in Experiment 2. In test, both experiments manipulated social company (alone vs. accompanied) and context (ABC vs. ACC). Experiment 1 showed more freezing in ABC than in ACC model during the test-alone condition, indicating a fear renewal effect which, however, was absent during the test-accompanied condition. Also, accompanied subjects showed less freezing compared to alone subjects in the ABC model. In Experiment 2, animals showed a similar freezing in ABC and ACC models despite being tested alone, implying that social company offered at extinction disrupted fear renewal. Again, we observed reduced freezing in accompanied relative to alone subjects in the test. These results suggest that social company is effective in disrupting fear renewal after leaving treatment context.

A Social Safety Net: Developing a Model of Social-Support Figures as Prepared Safety Stimuli

Although the presence of social-support figures (e.g., close friends and family members) is known to increase feelings of safety, reduce threat responses, and improve health, the route by which these effects occur is not well understood. One explanation is that social-support figures are members of a powerful category of safety signals—prepared safety stimuli. Here, we review research demonstrating that social-support figures act as prepared safety stimuli and explore the impact that these unique safety stimuli have on fear-learning processes. According to recent work, the presence of social-support figures both reduces fear acquisition and enhances fear extinction, ultimately decreasing perceptions of threat. These findings shed light on the route by which social support buffers against threat and illustrate the unique properties of prepared safety stimuli and how they might be used to improve mental and physical health outcomes.

The role of safety signals in fear extinction: An analogue study

BACKGROUND AND OBJECTIVES

Safety signals are conditioned inhibitory stimuli that indicate the absence of unconditioned stimuli. It is not clear whether the presence of safety signals is detrimental or beneficial in extinction-based interventions. The purpose of this study was to evaluate the effect of safety signals on autonomic and expectancy fear-related responses.

METHODS

Following the conditional discrimination paradigm (AX +, BX-), undergraduate students (N = 48) underwent an aversive conditioning procedure, while safety signals were experimentally created. Participants were randomly assigned to one of two conditions during extinction: presence or absence of safety signals.

RESULTS

Significant reductions of fear-related responses were found in both groups. Expectancy measures showed that the presence of safety signals did not interfere with reduction of fear related responses at follow-up.

LIMITATIONS

The analogue nature of the study affects its ecological validity. There are some methodological issues.

CONCLUSIONS

Safety signals did not interfere with extinction learning. Attention may be a mechanism associated with the maintenance of fear responses.

Effects of chemogenetic excitation or inhibition of the ventrolateral periaqueductal gray on the acquisition and extinction of Pavlovian fear conditioning

The midbrain periaqueductal gray (PAG) has been implicated in the generation and transmission of a prediction error signal that instructs amygdala-based fear and extinction learning. However, the PAG also plays a key role in the expression of conditioned fear responses. The evidence for a role of the PAG in fear learning and extinction learning has been obtained almost exclusively using PAG-dependent fear responses. It is less clear whether the PAG regulates fear learning when other measures of learned fear are used. Here we combined a chemogenetic approach, permitting excitation or inhibition of neurons in the ventrolateral PAG (VLPAG), with conditioned suppression as the measure of learned fear to assess the role of VLPAG in the acquisition and extinction of fear learning. We show that chemogenetic excitation of VLPAG (with some encroachment on lateral PAG [LPAG]) impairs acquisition of fear and, conversely, chemogenetic inhibition impairs extinction of fear. These effects on fear and extinction learning were specific to the combination of DREADD expression and injection of CNO because they were observed relative to both eYFP controls injected with CNO as well as DREADD expressing controls injected with vehicle. Taken together, these results show that activity of L/VLPAG neurons regulates both the acquisition and extinction of Pavlovian fear learning.

Imagine that! Cue-evoked representations guide rat behavior during ambiguous situations

Mental imagery involves the perceptual-like experience of an event that is not physically present, or detected by the senses. Fast and Blaisdell (2011) reported that rats use the representation of an associatively retrieved event to guide behavior in ambiguous situations. Rats were reinforced for lever-pressing during 1 of 2 lights but not both lights. They were then tested with 1 light illuminated while the second light was either covered by an opaque shield (ambiguous) or uncovered and unlit (explicitly absent). Rats lever-pressed less when the second light was covered compared with unlit, suggesting that a representation of the ambiguously absent light guided their behavior. However, Dwyer and Burgess (2011) offered an alternative mechanism in which the explicit absence of a cue gains associative value during training. Covering the light at test could effectively remove these associative properties, resulting in a generalization decrement of behavior. The current experiments were designed to test contrasting predictions made by these 2 accounts. Experiment 1 empirically established that generalization decrement can occur when an element of a compound cue is presented alone at test, but this decrement is attenuated, rather than enhanced, when the absent element is covered. Experiment 2 utilized a conditioned inhibition procedure to demonstrate that rat behavior during cue ambiguity is driven by an associatively retrieved representation rather than by generalization decrement. Collectively, the results argue against a purely nonrepresentational associative account of behavior and support a role for associatively retrieved representations in rats.

Rethinking Extinction

Extinction serves as the leading theoretical framework and experimental model to describe how learned behaviors diminish through absence of anticipated reinforcement. In the past decade, extinction has moved beyond the realm of associative learning theory and behavioral experimentation in animals and has become a topic of considerable interest in the neuroscience of learning, memory, and emotion. Here, we review research and theories of extinction, both as a learning process and as a behavioral technique, and consider whether traditional understandings warrant a re-examination. We discuss the neurobiology, cognitive factors, and major computational theories, and revisit the predominant view that extinction results in new learning that interferes with expression of the original memory. Additionally, we reconsider the limitations of extinction as a technique to prevent the relapse of maladaptive behavior and discuss novel approaches, informed by contemporary theoretical advances, that augment traditional extinction methods to target and potentially alter maladaptive memories.

Benzodiazepine administration prevents the use of error-correction mechanisms during fear extinction

Three experiments examined the effect of systemic administration of the benzodiazepine midazolam on extinction and re-extinction of conditioned fear. Experiment 1 demonstrated that midazolam administration prior to extinction of a conditioned stimulus (CS) impaired that extinction when rats were subsequently tested drug free; however, extinction was spared if rats were extinguished, reconditioned, and re-extinguished under midazolam. Experiment 2 provided a replication of this effect within-subjects; rats were conditioned to two CSs (A and B), extinguished to one (A-), reconditioned to both, and then extinguished/re-extinguished to both stimuli in compound (AB-), under either vehicle or midazolam. On the drug-free test, rats given midazolam froze more to the CS that had been extinguished (B) than the one that been re-extinguished (A). The final experiment examined whether extinction under midazolam was regulated by prediction error. Rats were trained with three CSs (A, B, C) and extinguished to two (A-, C-). These stimuli then underwent additional extinction under midazolam or vehicle, with one CS now presented in compound with the non-extinguished CS (AB-, C-). Rats were then tested for fear of A relative to C. Rats given vehicle showed a deepening of extinction to A relative to C, as is predicted from error-correction models; however, rats given midazolam failed to show any such discrepancy in responding. The results are interpreted to indicate that the drug reduced prediction error during extinction by reducing fear, and rats were able to re-extinguish fear via a retrieval mechanism that is independent of prediction error.

Translation of associative learning models into extinction reminders delivered via mobile phones during cue exposure interventions for substance use

Despite experimental findings and some treatment research supporting the use of cues as a means to induce and extinguish cravings, interventions using cue exposure have not been well integrated into contemporary substance abuse treatments. A primary problem with exposure-based interventions for addiction is that after learning not to use substances in the presence of addiction cues inside the clinic (i.e., extinction), stimuli in the naturalistic setting outside the clinic may continue to elicit craving, drug use, or other maladaptive conditioned responses. For exposure-based substance use interventions to be efficacious, new approaches are needed that can prevent relapse by directly generalizing learning from the therapeutic setting into naturalistic settings associated with a high risk for relapse. Basic research suggests that extinction reminders (ERs) can be paired with the context of learning new and more adaptive conditioned responses to substance abuse cues in exposure therapies for addiction. Using mobile phones and automated dialing and data collection software, ERs can be delivered in everyday high-risk settings to inhibit conditioned responses to substance-use-related stimuli. In this review, we describe how associative learning mechanisms (e.g., conditioned inhibition) can inform how ERs are conceptualized, learned, and implemented to prevent substance use when delivered via mobile phones. This approach, exposure with portable reminders of extinction, is introduced as an adjunctive intervention that uses brief automated ERs between clinic visits when individuals are in high-risk settings for drug use.

Associative Accounts of Recovery-from-Extinction Effects

Recovery-from-extinction effects (e.g., spontaneous recovery, renewal, reinstatement, and facilitated reacquisition) have become the focus of much research in recent years. However, despite a great deal of empirical data, there are few theoretical explanations for these effects. This paucity poses a severe limitation on our understanding of these behavioral effects, impedes advances in uncovering neural mechanisms of response recovery, and reduces our potential to prevent relapse after exposure therapy. Towards correcting this oversight, this review takes prominent models of associative learning that have been used in the past and continue to be used today to explain Pavlovian conditioning and extinction, and assesses how each model can be applied to account for recovery-from-extinction effects. The models include the Rescorla-Wagner (1972) model, Mackintosh's (1975) attentional model, Pearce and Hall's (1980) attentional model, Wagner's (1981) SOP model, Pearce's (1987) configural model, McLaren and Mackintosh's (2002) elemental model, and Stout and Miller's (2007) SOCR (comparator hypothesis) model. Each model is assessed for how well it explains or does not explain the various recovery-from-extinction phenomena. We offer some suggestions for how the models might be modified to account for these effects in those instances in which they initially fail.

Extinction in multiple virtual reality contexts diminishes fear reinstatement in humans

Although conditioned fear can be effectively extinguished by unreinforced exposure to a threat cue, fear responses tend to return when the cue is encountered some time after extinction (spontaneous recovery), in a novel environment (renewal), or following presentation of an aversive stimulus (reinstatement). As extinction represents a context-dependent form of new learning, one possible strategy to circumvent the return of fear is to conduct extinction across several environments. Here, we tested the effectiveness of multiple context extinction in a two-day fear conditioning experiment using 3-D virtual reality technology to create immersive, ecologically-valid context changes. Fear-potentiated startle served as the dependent measure. All three experimental groups initially acquired fear in a single context. A multiple extinction group then underwent extinction in three contexts, while a second group underwent extinction in the acquisition context and a third group underwent extinction in a single different context. All groups returned 24h later to test for return of fear in the extinction context (spontaneous recovery) and a novel context (renewal and reinstatement/test). Extinction in multiple contexts attenuated reinstatement of fear but did not reduce spontaneous recovery. Results from fear renewal were tendential. Our findings suggest that multi-context extinction can reduce fear relapse following an aversive event--an event that often induces return of fear in real-world settings--and provides empirical support for conducting exposure-based clinical treatments across a variety of environments.

Transient inactivation of the pigeon hippocampus or the nidopallium caudolaterale during extinction learning impairs extinction retrieval in an appetitive conditioning paradigm

The majority of experiments exploring context-dependent extinction learning employ Pavlovian fear conditioning in rodents. Since mechanisms of appetitive and aversive learning are known to differ at the neuronal level, we sought to investigate extinction learning in an appetitive setting. Working with pigeons, we established a within-subject ABA renewal paradigm based on Rescorla (Q J Exp Psychol 61:1793) and combined it with pharmacological interventions during extinction. From the fear conditioning literature, it is known that both prefrontal cortex and the hippocampus are core structures for context-specific extinction learning. Accordingly, we transiently inactivated the nidopallium caudolaterale (NCL, a functional analogue of mammalian prefrontal cortex) and the hippocampus in separate experiments by intracranial infusion of the sodium-channel blocker tetrodotoxin immediately before extinction training. We find that TTX in both structures non-specifically suppresses conditioned responding, as revealed by a reduction of response rate to both the extinguished conditioned stimulus and a control stimulus which remained reinforced throughout the experiment. Furthermore, TTX during extinction training impaired later extinction retrieval assessed under drug-free conditions. This was true when responding to the extinguished stimulus was assessed in the context of extinction but not when tested in the context of acquisition, although both contexts were matched with respect to their history of conditioning. These results indicate that both NCL and hippocampus are involved in extinction learning under appetitive conditions or, more specifically, in the consolidation of extinction memory, and that their contribution to extinction is context-specific.

Psychological and neural mechanisms of experimental extinction: a selective review

The present review examines key psychological concepts in the study of experimental extinction and implications these have for an understanding of the underlying neurobiology of extinction learning. We suggest that many of the signature characteristics of extinction learning (spontaneous recovery, renewal, reinstatement, rapid reacquisition) can be accommodated by the standard associative learning theory assumption that extinction results in partial erasure of the original learning together with new inhibitory learning. Moreover, we consider recent behavioral and neural evidence that supports the partial erasure view of extinction, but also note shortcomings in our understanding of extinction circuits as these relate to the negative prediction error concept. Recent work suggests that common prediction error and stimulus-specific prediction error terms both may be required to explain neural plasticity both in acquisition and extinction learning. In addition, we suggest that many issues in the content of extinction learning have not been fully addressed in current research, but that neurobiological approaches should be especially helpful in addressing such issues. These include questions about the nature of extinction learning (excitatory CS-No US, inhibitory CS-US learning, occasion setting processes), especially as this relates to studies of the micro-circuitry of extinction, as well as its representational content (sensory, motivational, response). An additional understudied problem in extinction research is the role played by attention processes and their underlying neural networks, although some research and theory converge on the idea that extinction is accompanied by attention decrements (i.e., habituation-like processes).

Ventral tegmental dopamine dysregulation prevents appetitive memory destabilization

Through the process of reconsolidation, memories can be updated to maintain their relevance. To reconsolidate, a memory must first be destabilized in a process that we have hypothesized is initiated by a prediction error signal. Here we demonstrate that dysregulation of ventral tegmental area (VTA) signaling, which is thought to mediate prediction errors, prevented the destabilization of an appetitive goal-tracking memory in rats. We additionally show that intra-VTA infusion of either the competitive NMDA antagonist AP5 or the noncompetitive NMDA antagonist MK-801 does not selectively disrupt reconsolidation, indicating that the VTA may not be an important neural locus of reconsolidation-related neural plasticity.

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.

On the differences in degree of renewal produced by the different renewal designs

This paper addresses sources contributing to the differences in the degree of recovery from extinction observed with different renewal paradigms. In two lick suppression experiments with rats, we assessed the role of the associative status of the acquisition context in both the weakness of AAC renewal and the sometimes observed weaker renewal resulting from an ABC design relative to an ABA design. In Experiment 1, we observed that AAC renewal relative to an AAA control group was small unless Context A had undergone associative deflation (i.e., extinction of Context A). Deflation of Context A not only decreased behavioral control by the CS in the AAA condition, but increased it in the AAC condition, thereby implicating a comparator process in addition to associative summation between the CS and test context. In Experiment 2, an excitatory acquisition context was found to enhance the difference between ABC and ABA renewal. Associative deflation of the acquisition context decreased ABA renewal more than ABC renewal. Thus, the associative value of the acquisition context (A) was more positively related to the level of renewal when the target CS (X) was tested in this context than when it was tested in a neutral but equally familiar context (C), consistent with the frequently observed greater renewal in an ABA condition than an ABC condition arising from associative summation of the CS and test context. These findings demonstrate that the excitatory status of the acquisition context influences the observed degree of renewal.

Extinction with multiple excitors

Four conditioned suppression experiments with rats, using an ABC renewal design, investigated the effects of compounding the target conditioned excitor with additional, nontarget conditioned excitors during extinction. Experiment 1 showed stronger extinction, as evidenced by less renewal, when the target excitor was extinguished in compound with a second excitor, relative to when it was extinguished with associatively neutral stimuli. Critically, this deepened extinction effect was attenuated (i.e., more renewal occurred) when a third excitor was added during extinction training. This novel demonstration contradicts the predictions of associative learning models based on total error reduction, but it is explicable in terms of a counteraction effect within the framework of the extended comparator hypothesis. The attenuated deepened extinction effect was replicated in Experiments 2a and 3, which also showed that pretraining consisting of weakening the association between the two additional excitors (Experiments 2a and 2b) or weakening the association between one of the additional excitors and the unconditioned stimulus (Experiment 3) attenuated the counteraction effect, thereby resulting in a decrease in responding to the target excitor. These results suggest that more than simple total error reduction determines responding after extinction.

Mechanisms of renewal after the extinction of instrumental behavior

Four experiments with rats examined renewal of extinguished instrumental behavior when the reinforcement histories of the contexts were equated by giving complementary training and extinction of a different response (lever press and chain pull) in each context. In Experiments 1 through 3, renewal occurred when the response was tested in the acquisition context (ABA) or outside the extinction context (AAB and ABC). Further, in Experiments 1 through 3, when both responses were simultaneously available, there was a clear preference for the response that was not in its extinction context. In Experiment 4, renewal was not reduced when testing occurred in a context that had been associated with extinction of the other instrumental response. The experimental designs rule out differential context-reinforcer associations being the only contributing mechanism of renewal, and also raise questions about configural and occasion-setting accounts. The results are consistent with the idea that during extinction an inhibitory association is formed between the context and the response.

ABA and ABC renewal of conditioned magazine approach are not impaired by dorsal hippocampus inactivation or lesions

Three experiments investigated the role of the dorsal hippocampus (DH) in renewal of conditioned and then extinguished magazine approach responding in rats. Experiments 1 and 2 found no effect of muscimol inactivation of the DH during testing on ABA and ABC renewal, respectively. However, subjects from these studies were subsequently found to be impaired on a delayed non-matching-to-place task following muscimol but not saline infusions. Experiment 3 found no effects of post-training excitotoxic lesions of the DH on ABA and ABC renewal. Lesioned subjects were, however, impaired on the delayed non-matching-to-place task compared to control subjects. These findings suggest that the DH may not play a similar role in Pavlovian extinction in appetitive learning tasks as has previously been reported in aversive learning.

Asymmetrical generalization of conditioning and extinction from compound to element and element to compound

Four appetitive conditioning experiments studied generalization between compound conditional stimuli (AB) and their elements (e.g., A or B). In Experiments 1 and 2, rats received conditioning with A and AB, and then extinction with either A or AB. During subsequent testing, there was more generalization of extinction (nonresponding) from the compound (AB) to the element (A) than from the element (A) to the compound (AB). This asymmetry was consistent with earlier results involving temporal discrimination learning in which short and long temporal intervals played the roles of A and AB. In Experiment 3, rats received conditioning with either A or AB, and then testing with A and AB. Consistent with elemental models of conditioning, there was more generalization of conditioned responding from A to AB than from AB to A. Experiment 4 found that these asymmetries in the generalization of extinction (Experiments 1 and 2) and conditioning (Experiment 3) both contribute to the feature-positive effect. Overall, the parallel between the current findings and previous results with temporal discrimination learning supports an associative analysis of interval timing. Implications for elemental and configural theories of conditioning and generalization are also discussed.

Deepened extinction of cocaine cues

BACKGROUND

A method for reducing the power of drug cues could help in treating drug abuse and addiction. Extinction has been used, with mixed success, in such an effort. Research with non-drug cues has shown that simultaneously presenting (compounding) those cues during extinction can enhance the effectiveness of extinction. The present study investigated whether this procedure could be used to similarly deepen the extinction of cocaine cues.

METHODS

Rats were first trained to self-administer cocaine during tone, click, and light stimuli. Then, these stimuli were subjected to extinction in an initial phase where they were presented individually. In a second extinction phase, one of the auditory stimuli (counterbalanced) was compounded with the light. The other auditory stimulus continued to be presented alone. Rats were then given a week of rest in their homecages prior to testing for spontaneous recovery of cocaine seeking.

RESULTS

The cue that was compounded with the light during the second phase of extinction training occasioned less spontaneous recovery of cocaine seeking than the cue that was always presented individually during extinction. Increasing the number of compound cue extinction sessions did not produce a greater deepened extinction effect.

CONCLUSIONS

The present study showed that simultaneously presenting already-extinguished cocaine cues during additional extinction training enhanced extinction. This extends the deepened extinction effect from non-drug cues to drug cues and further confirms predictions of error-correction learning theory. Incorporating deepened extinction into extinction-based drug abuse treatments could help to reduce the power of drug cues.

Extinction context as a conditioned inhibitor

Two lick suppression experiments using rats were conducted to determine whether extinction of a punctate excitor in a particular context would result in that context becoming a conditioned inhibitor, as defined by passing both summation and retardation tests. The role of extinction trial spacing was investigated as a possible determinant of whether the extinction context would become inhibitory. Experiment 1 demonstrated that, although inhibition was evident using either massed or spaced extinction trials, spaced trials reduced measurable inhibition as assessed by the summation test, but trial spacing had no influence on retardation test performance. Experiment 2 confirmed Experiment 1's conclusions while controlling for the influence of latent inhibition on the retardation test. In Experiment 2, the context proved inhibitory only following massed extinction trials. These data suggest that, at least with select parameters, an extinction context can become inhibitory.

Facets of Pavlovian and operant extinction

Research on extinction is of fundamental importance in both Pavlovian and operant approaches to the experimental analysis of learning. Although these approaches are often motivated by different empirical and theoretical questions, extinction has emerged as a research area in which common themes unite the two approaches. In this review, we focus on some common considerations in the analysis of Pavlovian and operant extinction. These include methodological challenges and interpretational issues in analyzing behavior during and after extinction. We consider the different roles that theory has played in the development of research on extinction in these preparations and conclude with some attention to applications of extinction.