A modified counterconditioning procedure prevents the renewal of conditioned fear in rats

Counterconditioning reduces contextual renewal in a novel context but not in the acquisition context

As extinction is a context-dependent form of learning, conditioned responses tend to return when the conditioned stimulus (CS) is encountered outside the extinction context, known as contextual renewal. Counterconditioning is a technique that may lead to a more persistent reduction of the conditioned response. However, the effects of aversive-to-appetitive counterconditioning on contextual renewal in rodent studies are mixed. Further, research in humans is sparse, particularly direct statistical comparisons between counterconditioning and standard extinction techniques within the same study. Using a causal associative learning framework (the allergist task) implemented online, we compared the effectiveness of counterconditioning to standard extinction in preventing the renewal of judgements on the allergic properties of different food items (CSs). In a between-subjects design, 328 participants first learned that particular food items (CSs) lead to an allergic reaction in a specific restaurant (context A). Next, one CS was extinguished (no allergic reaction) while another CS was counterconditioned (positive outcome) in restaurant B. Causal judgements of the allergic properties of food items occurred in either the response acquisition context (ABA group, N = 112), the response reduction context where extinction and counterconditioning had occurred (ABB group, N = 107), or a novel context (ABC group, N = 109). Results showed that counterconditioning, compared to extinction, diminished the renewal of causal judgements to the CS in a novel context (ABC group). Still, casual judgements returned for both counter-conditioned and extinguished CSs in the response acquisition context (ABA group). Counterconditioning and extinction were similarly effective at preventing recovery of causal judgements in the response reduction context (ABB group); however, only in context B did participants choose the counter-conditioned CS as less likely to cause an allergic reaction in comparison to the extinguished CS. These findings indicate scenarios in which counterconditioning is more effective than standard extinction at diminishing the return of threat associations, with implications for improving the generalization of safety learning.

Behavioral and neural processes in counterconditioning: Past and future directions

Counterconditioning refers both to the technique and putative process by which behavior is modified through a new association with a stimulus of an opposite valence. Similar to extinction, counterconditioning is considered a form of inhibition that interferes with the expression of the originally learned response without erasing it. But whereas interest in extinction continues to rise, counterconditioning has received far less attention. Here, we provide an in-depth review of counterconditioning research and detail whether counterconditioning is any more effective than extinction at preventing relapse of the originally learned behavior. We consider the clinical implications of counterconditioning, describe recent neurobiological and neuroimaging research in this area, and consider future avenues in need of further investigation.

The effects of aversive-to-appetitive counterconditioning on implicit and explicit fear memory

Counterconditioning (CC) is a form of retroactive interference that inhibits expression of learned behavior. But similar to extinction, CC can be a fairly weak and impermanent form of interference, and the original behavior is prone to relapse. Research on CC is limited, especially in humans, but prior studies suggest it is more effective than extinction at modifying some behaviors (e.g., preference or valence ratings) than others (e.g., physiological arousal). Here, we used a within-subjects design to compare the effects of aversive-to-appetitive CC versus standard extinction on two separate tests of long-term memory in human adults: implicit physiological arousal and explicit episodic memory. Participants underwent Pavlovian fear conditioning to two semantic categories (animals, tools) paired with an electric shock. Conditioned stimuli (i.e., category exemplars) from one category were then extinguished, while stimuli from the other category were paired with a positive outcome. Participants returned 24-h later for a test of skin conductance responses (SCR) to the conditioned exemplars, as well as a surprise recognition memory test for stimuli encoded the previous day. Results showed reduced SCRs at a test for unique stimuli from a category that had undergone CC, relative to stimuli from a category that had undergone standard extinction. Additionally, participants selectively remembered more stimuli encoded during CC than extinction. These results provide new evidence that aversive-to-appetitive CC, as compared to extinction, strengthens memory for items directly associated with a positive outcome, which may provide stronger retrieval competition against a fear memory at test to help diminish fear relapse.

Effect of a Standardized Four-Week Desensitization and Counter-Conditioning Training Program on Pre-Existing Veterinary Fear in Companion Dogs

Simple Summary

Reducing veterinary fear in dogs is important for canine health and welfare. It is commonly suggested that dog owners perform counter-conditioning and desensitization training to reduce veterinary fear levels, yet the efficacy of this training has not been evaluated. We recruited owned dogs with pre-existing fear and conducted mock veterinary appointments before and after training to assess changes in fear responses. Owners of dogs in the training group (n = 15) were instructed to perform exam-style handling and to visit the veterinary clinic on a weekly basis for four weeks, and owners of control dogs (n = 22) received no instructions. Compliance to training protocols was poor, with 44% of owners non-compliant to the training program. We found that, during the examination, trained dogs had less reduced posture than control dogs, but trained dogs showed more lip licking during clinic entrance and examination. Owners reported an observable improvement in their dog’s fear levels across the training sessions, and general fear scores lowered during the second examination for trained dogs. We suggest that, although few behavioural indicators of fear changed in the predicted direction, veterinarians should continue to recommend this training until further research is conducted.

Abstract

Many dogs show signs of fear during veterinary appointments. It is widely recommended to use desensitization and counter-conditioning training to reduce this fear. However, the efficacy of this method for reducing veterinary fear has not been examined. We assessed the effect of a standardized four-week training program on behavioural and physiological signs of fear in dogs with pre-existing veterinary fear. Owned dogs were randomly allocated to receive training (n = 15) or no training (n = 22; Control). Owners of dogs in the training group were instructed to perform exam-style handling on their dog and to visit the veterinary clinic weekly. Owners of control dogs were given no instructions. Fear responses were assessed before and after the training period by a blinded observer during clinic arrival and examination. Despite motivated owners volunteering to participate in the current study, 44% of owners were non-compliant to this training program. During examination, control dogs had higher odds (95% confidence Interval (CI)) of reduced posture compared to trained dogs (Odds ratio (OR): 3.79, CI: 1.03–16.3). Fear scores for trained dogs lowered during the second examination (p = 0.046), and 86.7% of dog owners reported a reduction in their dog’s fear levels across the training period (p = 0.007). When entering the clinic (p = 0.002) and during examination (p = 0.002), trained female dogs had a higher rate of lip licking than control females. The training program did not influence temperature, heart rate, respiratory rate, avoidance, trembling, vocalizations, or willingness and encouragement to step on the scale. Results suggest that this four-week training program was mildly effective at reducing veterinary fear in dogs. Further research is necessary to explore the efficacy of longer, more intensive, and individualized training programs.

A dopaminergic switch for fear to safety transitions

Overcoming aversive emotional memories requires neural systems that detect when fear responses are no longer appropriate so that they can be extinguished. The midbrain ventral tegmental area (VTA) dopamine system has been implicated in reward and more broadly in signaling when a better-than-expected outcome has occurred. This suggests that it may be important in guiding fear to safety transitions. We report that when an expected aversive outcome does not occur, activity in midbrain dopamine neurons is necessary to extinguish behavioral fear responses and engage molecular signaling events in extinction learning circuits. Furthermore, a specific dopamine projection to the nucleus accumbens medial shell is partially responsible for this effect. In contrast, a separate dopamine projection to the medial prefrontal cortex opposes extinction learning. This demonstrates a novel function for the canonical VTA-dopamine reward system and reveals opposing behavioral roles for different dopamine neuron projections in fear extinction learning.

Fear memories are overcome only when it is ascertained that fearful responses are not appropriate. Here the authors demonstrate that activity in dopamine neurons is necessary to extinguish fear responses and two distinct dopamine neuron projections exert opposing effects on extinction learning.

Novelty-facilitated extinction: providing a novel outcome in place of an expected threat diminishes recovery of defensive responses

BACKGROUND

Experimental extinction serves as a model for psychiatric treatments based on associative learning. However, the effects of extinction are often transient, as evidenced by postextinction return of defensive behaviors. From a therapeutic perspective, an inherent problem with extinction may be that mere omission of threat is not sufficient to reduce future threat uncertainty. The current study tested an augmented form of extinction that replaced, rather than merely omitted, expected threat outcomes with novel nonthreat outcomes, with the goal of reducing postextinction return of defensive behaviors.

METHODS

Thirty-two healthy male Sprague-Dawley rats and 47 human adults underwent threat conditioning to a conditioned stimulus paired with an electrical shock. Subjects then underwent a standard extinction protocol with shock omitted or an augmented extinction protocol wherein the shock was replaced by a surprising tone. Tests of postextinction recovery occurred 24 hours later in the absence of the tone.

RESULTS

Replacing the shock with a novel nonthreat outcome, as compared with shock omission, reduced postextinction recovery (freezing in rats and anticipatory skin conductance responses in humans) when tested 24 hours later. Self-reported intolerance of uncertainty was positively correlated with recovery following standard extinction in humans, providing new evidence that postextinction recovery is related to sensitivity to future threat uncertainty.

CONCLUSIONS

These findings provide cross-species evidence of a novel strategy to enhance extinction that may have broad implications for how to override associative learning that has become maladaptive and offer a simple technique that could be straightforwardly adapted and implemented in clinical situations.