Experimental extinction in Pavlovian conditioning: Behavioural and neuroscience perspectives

Microstructural differences in the cingulum and the inferior longitudinal fasciculus are associated with (extinction) learning

Cognitive functions, such as learning and memory processes, depend on effective communication between brain regions which is facilitated by white matter tracts (WMT). We investigated the microstructural properties and the contribution of WMT to extinction learning and memory in a predictive learning task. Forty-two healthy participants completed an extinction learning paradigm without a fear component. We examined differences in microstructural properties using diffusion tensor imaging to identify underlying neural connectivity and structural correlates of extinction learning and their potential implications for the renewal effect. Participants with good acquisition performance exhibited higher fractional anisotropy (FA) in WMT including the bilateral inferior longitudinal fasciculus (ILF) and the right temporal part of the cingulum (CNG). This indicates enhanced connectivity and communication between brain regions relevant to learning and memory resulting in better learning performance. Our results suggest that successful acquisition and extinction performance were linked to enhanced structural connectivity. Lower radial diffusivity (RD) in the right ILF and right temporal part of the CNG was observed for participants with good acquisition learning performance. This observation suggests that learning difficulties associated with increased RD may potentially be due to less myelinated axons in relevant WMT. Also, participants with good acquisition performance were more likely to show a renewal effect. The results point towards a potential role of structural integrity in extinction-relevant WMT for acquisition and extinction.

Extinction in multiple contexts reduces the return of extinguished responses: A multilevel meta-analysis

Extinguished responses have been shown to reappear under several circumstances, and this reappearance is considered to model behaviors such as relapse after exposure therapy. Conducting extinction in multiple contexts has been explored as a technique to decrease the recovery of extinguished responses. The present meta-analysis aimed to examine whether extinction in multiple contexts can consistently reduce the recovery of extinguished responses. After searching in several databases, experiments were included in the analysis if they presented extinction in multiple contexts, an experimental design, and an adequate statistical report. Cohen's d was obtained for each critical comparison and weighted to obtain the sample's average weighted effect size. Analyses were then performed using a multilevel meta-analytic approach. Twenty-five studies were included, with a total sample of 37 experiments or critical comparisons. The analyses showed a large effect size for the sample, moderated by the length of conditioned stimulus exposure, type of experimental subject, and type of recovery. The robust effect of extinction in multiple contexts on relapse should encourage clinicians to consider extinction in multiple contexts as a useful technique in therapy and research.

Cortisol decreases activation in extinction related brain areas resulting in an impaired recall of context-dependent extinction memory

Conditioned responding gradually stops during successful extinction learning. The renewal effect is defined as the recovery of a extinguished conditioned response when the context of extinction is different from acquisition. The stress hormone cortisol is known to have an influence on extinction memory and associative learning. Different effects of cortisol on behaviour and brain activity have been observed with respect to stress timing, duration, and intensity. However, the influence of cortisol prior to the initial encoding of stimulus-outcome associations on extinction learning, renewal and its behavioural and neurobiological correlates is still largely unknown. In our study, 60 human participants received 20 mg cortisol or placebo and then learned, extinguished, and recalled the associations between food stimuli presented in distinct contexts and different outcomes in three subsequent task phases. Learning performance during acquisition and extinction phases was equally good for both treatment groups. In the cortisol group, significantly more participants showed renewal compared to placebo. In the subgroup of participants with renewal, cortisol treated participants showed significantly better extinction learning performance compared to placebo. Participants showing renewal had in general difficulties with recalling extinction memory, but in contrast to placebo, the cortisol group exhibited a context-dependent impairment of extinction memory recall. Imaging analyses revealed that cortisol decreased activation in the hippocampus during acquisition. The cortisol group also showed reduced dorsolateral prefrontal cortex activation when extinction learning took place in a different context, but enhanced activation in inferior frontal gyrus during extinction learning without context change. During recall, cortisol decreased ventromedial prefrontal cortex activation. Taken together, our findings illustrate cortisol as a potent modulator of extinction learning and recall of extinction memory which also promotes renewal.

Fear Learning in Genital Pain: Toward a Biopsychosocial, Ecologically Valid Research and Treatment Model

Although fear learning mechanisms are implicated in the development, maintenance, exacerbation, and reduction of genital pain, systematic research on how fear of genital pain emerges, spreads, persists, and reemerges after treatment is lacking. This paper provides an overview of the literature on pain-related fear, integrates the ideas on learning and sexual arousal responding, and specifies the pathways through which compromised learning may contribute to the development and persistence of genital pain. In order to refine theories of genital pain and optimize treatments, we need to adopt a biopsychosocial framework to pain-related fear learning and uncover potential moderators that shape individual trajectories. This involves examining the role of physiological processes, subjective experiences, as well as partner and relational cues in fear acquisition, excessive generalization and impaired safety learning, extinction of fear, counterconditioning, and return of fear. Recent methodological advances in fear conditioning and sex research are promising to enable more symptom-specific and ecologically valid experimental paradigms.

Characterisation of the neural basis underlying appetitive extinction & renewal in Cacna1c rats

Recent studies have revealed impairments in Cacna1c ± heterozygous animals (a gene that encodes the Cav 1.2 L-type voltage-gated calcium channels and is implicated in risk for multiple neuropsychiatric disorders) in aversive forms of learning, such as latent inhibition, reversal learning or context discrimination. However, the role of Cav 1.2 L-type voltage-gated calcium channels in extinction of appetitive associations remains under-investigated. Here, we used an appetitive Pavlovian conditioning task and evaluated extinction learning (EL) with a change of context from that of training and test (ABA) and without such a change (AAA) in Cacna1c ± male rats versus their wild-type (WT) littermates. In addition, we used fluorescence in situ hybridization of somatic immediate early genes (IEGs) Arc and Homer1a expression to scrutinize associated changes in the medial prefrontal cortex and the amygdala. Cacna1c ± animals successfully adapt their responses by engaging in appetitive EL and renewal. However, the regional IEG expression profile changed. For the EL occurring in the same context, Cacna1c ± animals presented higher IEG expression in the infralimbic cortex and the central amygdala than controls. The prelimbic region presented a larger neural ensemble in Cacna1c ± than WT animals, co-labelled for the time window of EL in the original context and prolonged exposure to the unrewarded context. With a context change, the Cacna1c ± infralimbic region displayed higher IEG expression during renewal than controls. Taken together, our findings provide novel evidence of distinct brain activation patterns occurring in Cacna1c ± rats after appetitive extinction and renewal despite preserved behavioral responses. This article is part of the Special Issue on "L-type calcium channel mechanisms in neuropsychiatric disorders".

Learning About Reward Identities and Time

We discuss three empirical findings that we think any theory attempting to integrate interval timing with associative learning concepts will need to address. These empirical phenomena all come from studies that combine peak timing procedures with reinforcer devaluation or conditional discrimination tasks commonly employed, respectively, in interval timing or associative learning research traditions. The three phenomena we discuss include: (1) the observation that disruptions in reward identity encoding have little to no impact on the encoding of reward time in the a peak procedure (Delamater., 1998), (2) the findings that organisms tend to average their time estimates when presented with a stimulus compound consisting of separately learned stimuli indicating short or long reward times but that such temporal averaging, itself, is sensitive to post-conditioning selective reward devaluation, and (3) that rats can learn a temporal patterning task in which two stimuli presented independently indicate one time to reward availability while their compound indicates another. We review our prior results and present new findings illustrating these three phenomena and we discuss the special challenges they pose for cascade theories of timing, for multiple-oscillator models, and for any approach that attempts to integrate interval timing and associative models. We close by illustrating some ways in which multi-layer connectionist network models might begin to address some of our key findings. We believe this will require an approach that includes separate mechanisms that code for reward identity and time, but that does so in a way that permits for integration between the two systems.

Basal forebrain cholinergic signaling in the basolateral amygdala promotes strength and durability of fear memories

The basolateral amygdala (BLA) complex receives dense cholinergic projections from the nucleus basalis of Meynert (NBM) and the horizontal limb of the diagonal band of Broca (HDB). The present experiments examined whether these projections regulate the formation, extinction, and renewal of fear memories. This was achieved by employing a Pavlovian fear conditioning protocol and optogenetics in transgenic rats. Silencing NBM projections during fear conditioning weakened the fear memory produced by that conditioning and abolished its renewal after extinction. By contrast, silencing HDB projections during fear conditioning had no effect. Silencing NBM or HDB projections during extinction enhanced the loss of fear produced by extinction, but only HDB silencing prevented renewal. Next, we found that systemic blockade of nicotinic acetylcholine receptors during fear conditioning mimicked the effects produced by silencing NBM projections during fear conditioning. However, this blockade had no effect when given during extinction. These findings indicate that basal forebrain cholinergic signaling in the BLA plays a critical role in fear regulation by promoting strength and durability of fear memories. We concluded that cholinergic compounds may improve treatments for post-traumatic stress disorder by durably stripping fear memories from their fear-eliciting capacity.

Theta coupling within the medial prefrontal cortex regulates fear extinction and renewal

Fear learning, and its extinction, are fundamental learning processes that allow for a response adaptation to aversive events and threats in the environment. Thus, it is critical to understand the neural mechanism that underpins fear learning and its relapse following extinction. The neural dynamics within the subregions of the medial prefrontal cortex, including the prelimbic cortex (PL) and the infralimbic (IL) cortex, and functional connectivity between them during fear extinction and its relapse, are not well understood. Using in-vivo electrophysiological recordings in awake behaving rats, we identified increased theta activity in the PL during fear learning and in the IL following extinction. Importantly, the PL-IL theta coupling is significantly enhanced throughout fear learning and extinction, but not in fear relapse. Together, our results provide evidence for the importance of synchronized PL-IL activity to regulate context-dependent retrieval of a fear extinction memory.

Recovery-from-extinction effects in an anuran amphibian: renewal effect, but no reinstatement

Recovery-from-extinction effects in which a conditioned response returns after extinction have been shown in mammals, birds and fish. Thus, these effects appear to be conserved among vertebrates; however, they have yet to be investigated in amphibians. Using prey catching conditioning in the fire-bellied toad (Bombina orientalis), we tested if renewal and reinstatement occurred after extinction when subjects were respectively re-exposed to the context or reinforcer used during conditioning. For renewal, a different context was used during extinction and thus renewal tests assessed if external contextual cues associated during conditioning stimulated prey catching performance. For reinstatement, the reinforcer withheld during extinction was simply delivered again prior to a test assessing if internal cues associated with recent prey consumption stimulated prey catching performance. Conditioning followed a fixed ratio 5 schedule of reinforcement, where five attempts to capture a cricket stimulus displayed on a computer screen were reinforced by delivery of a single live cricket. Performance was measured as the time to reach five prey catching attempts. A significant improvement in prey catching performance during conditioning followed by deterioration with extinction was seen in the experiments. Upon return to the context used for conditioning after extinction, toads showed a renewal effect whereby they displayed faster performance during testing compared to the end of extinction. Conversely, toads showed no reinstatement effect because pre-feeding of a cricket did not influence performance during the test that followed extinction. Reinstatement could have been lost in amphibian phylogeny due to secondary simplification of the nervous system.

Another look at the extinction of conditioned flavor preferences: Amount of training and tests for spontaneous recovery

A conditioned flavor preference develops when hungry or thirsty rats experience a neutral flavor mixed in solution with a nutrient. In two sets of studies, we previously demonstrated that this learned preference is highly sensitive to flavor nonreinforcement (i.e., exposure to the flavor without the nutrient) either prior to (latent inhibition), during (partial reinforcement), or following (extinction) flavor-nutrient pairings. In each of these studies we employed a nutrient devaluation procedure to assess the integrity of specific flavor-nutrient associations following extinction, but more recently Gonzalez, Morillas, and Hall (Journal of Experimental Psychology: Animal Learning & Cognition, 42, 380-390, 2016) observed that sensitivity to extinction in thirsty rats in this preparation may depend upon use of a post-conditioning nutrient devaluation procedure. To assess the generality of our earlier results, but without including a post-conditioning nutrient devaluation phase, we assessed in three experiments the role of the number of flavor-nutrient pairings given prior to extinction and the possibility of spontaneous recovery following a 3-week delay. We observed that extinction consistently weakened the flavor preference in thirsty rats (in spite of the absence of a nutrient devaluation procedure) and also found no evidence for spontaneous recovery. These results establish that our prior findings that conditioned flavor preferences are weakened by extinction are quite robust in thirsty rats and that these extinction effects may be fairly permanent.

General Pavlovian-instrumental transfer tests reveal selective inhibition of the response type - whether Pavlovian or instrumental - performed during extinction

The present experiments examined whether extinction of a stimulus predicting food affects the ability of that stimulus to energize instrumental performance to obtain food. We first used a general Pavlovian instrumental transfer (PIT) paradigm in which rats were first given Pavlovian conditioning with a stimulus predicting one type of food outcome and were then trained to lever press for a different food outcome. We found that the Pavlovian stimulus enhanced performance of the lever press response and that this enhancement was preserved after extinction of that stimulus (Experiment 1) even when the context was manipulated to favor the expression of extinction (Experiment 2). Next, we assessed whether extinction influenced the excitatory effect of a stimulus when it was trained as a discriminative stimulus. Extinction of this stimulus alone had no effect on its ability to control instrumental performance; however, when extinguished with its associated lever press response, discriminative control was lost (Experiments 3 and 4). Finally, after instrumental and Pavlovian training, we extinguished a Pavlovian stimulus predicting one food outcome with a lever press response that delivered a different outcome. In a general PIT test, we found this extinction abolished the ability of the Pavlovian stimulus to elevate responding on a lever trained with a different outcome, revealing for the first time that extinction can abolish the general PIT effect. We conclude that extinction can produce an inhibitory association between the stimulus and the general response type, whether Pavlovian or instrumental, performed during the extinction training.

The lesser evil: Pavlovian-instrumental transfer & aversive motivation

While our understanding of appetitive motivation includes accounts of rich cognitive phenomena, such as choice, sensory-specificity and outcome valuation, the same is not true in aversive processes. A highly sophisticated picture has emerged of Pavlovian fear conditioning and extinction, but progress in aversive motivation has been somewhat limited to these fundamental behaviors. Many differences between appetitive and aversive stimuli permit different kinds of analyses; a widely used procedure in appetitive studies that can expand the scope of aversive motivation is Pavlovian-instrumental transfer (PIT). Recently, this motivational transfer effect has been used to examine issues pertaining to sensory-specificity and the nature of defensive control in avoidance learning. Given enduring controversies and unresolved criticisms surrounding avoidance research, PIT offers a valuable, well-controlled procedure with which to similarly probe this form of motivation. Furthermore, while avoidance itself can be criticized as artificial, PIT can be an effective model for how skills learned through avoidance can be practically applied to encounters with threatening or fearful stimuli and stress. Despite sensory-related challenges presented by the limited aversive unconditioned stimuli typically used in research, transfer testing can nevertheless provide valuable information on the psychological nature of this historically controversial phenomenon.

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

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

How predictive learning influences choice: Evidence for a GPCR-based memory process necessary for Pavlovian-instrumental transfer

Predictive learning endows stimuli with the capacity to signal both the sensory-specific and general motivational properties of their associated rewards or outcomes. These two signals can be distinguished behaviorally by their influence on the selection and performance of instrumental actions, respectively. This review focuses on how sensory-specific predictive learning guides choice between actions that earn otherwise equally desirable outcomes. We describe evidence that outcome-specific predictive learning is encoded in the basolateral amygdala and drives the accumulation of delta-opioid receptors on the surface of cholinergic interneurons located in the nucleus accumbens shell. This accumulation constitutes a novel form of cellular memory, not for outcome-specific predictive learning per se but for the selection of, and choice between, future instrumental actions. We describe recent evidence regarding the cascade of events necessary for the formation and expression of this cellular memory and point to open questions for future research into this process. Beyond these mechanistic considerations, the discovery of this new form of memory is consistent with recent evidence suggesting that intracellular rather than synaptic changes can mediate learning-related plasticity to modify brain circuitry to prepare for future significant events.

The Role of the Rodent Lateral Orbitofrontal Cortex in Simple Pavlovian Cue-Outcome Learning Depends on Training Experience

The orbitofrontal cortex (OFC) is a critical structure in the flexible control of value-based behaviors. OFC dysfunction is typically only detected when task or environmental contingencies change, against a backdrop of apparently intact initial acquisition and behavior. While intact acquisition following OFC lesions in simple Pavlovian cue-outcome conditioning is often predicted by models of OFC function, this predicted null effect has not been thoroughly investigated. Here, we test the effects of lesions and temporary muscimol inactivation of the rodent lateral OFC on the acquisition of a simple single cue-outcome relationship. Surprisingly, pretraining lesions significantly enhanced acquisition after overtraining, whereas post-training lesions and inactivation significantly impaired acquisition. This impaired acquisition to the cue reflects a disruption of behavioral control and not learning since the cue could also act as an effective blocking stimulus in an associative blocking procedure. These findings suggest that even simple cue-outcome representations acquired in the absence of OFC function are impoverished. Therefore, while OFC function is often associated with flexible behavioral control in complex environments, it is also involved in very simple Pavlovian acquisition where complex cue-outcome relationships are irrelevant to task performance.

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.

Molecular Mechanisms of Reconsolidation-Dependent Memory Updating

Memory is not a stable record of experience, but instead is an ongoing process that allows existing memories to be modified with new information through a reconsolidation-dependent updating process. For a previously stable memory to be updated, the memory must first become labile through a process called destabilization. Destabilization is a protein degradation-dependent process that occurs when new information is presented. Following destabilization, a memory becomes stable again through a protein synthesis-dependent process called restabilization. Much work remains to fully characterize the mechanisms that underlie both destabilization and subsequent restabilization, however. In this article, we briefly review the discovery of reconsolidation as a potential mechanism for memory updating. We then discuss the behavioral paradigms that have been used to identify the molecular mechanisms of reconsolidation-dependent memory updating. Finally, we outline what is known about the molecular mechanisms that support the memory updating process. Understanding the molecular mechanisms underlying reconsolidation-dependent memory updating is an important step toward leveraging this process in a therapeutic setting to modify maladaptive memories and to improve memory when it fails.

Metaplastic contribution of neuropeptide Y receptors to spatial memory acquisition

Neuropeptide Y (NPY) is highly abundant in the brain and is released as a co-transmitter with plasticity-related neurotransmitters such as glutamate, GABA and noradrenaline. Functionally, its release is associated with appetite, anxiety, and stress regulation. NPY acting on Y2 receptors (Y₂R), facilitates fear extinction, suggesting a role in associative memory. Here, we explored to what extent NPY action at Y₂R contributes to hippocampus-dependent spatial memory and found that dorsal intrahippocampal receptor antagonism improved spatial reference memory acquired in a water maze in rats, without affecting anxiety levels, or spontaneous motor activity. Water maze training resulted in an increase of Y₂R, but not Y₁R expression in the hippocampus. By contrast, in the prefrontal cortex there was a decrease in Y₂R, and an increase of Y₁R expression. Our results indicate that neuropeptide Y₂R are significantly involved in hippocampus-dependent spatial memory and that receptor expression is dynamically regulated by this learning experience. Effects are consistent with a metaplastic contribution of NPY receptors to cumulative spatial learning.

Testing the judgment-related account for the extinction of evaluative conditioning

Evaluative conditioning (EC) effects refer to changes in the liking of a neutral (conditioned) stimulus (CS) due to pairing with an affective (unconditioned) stimulus (US). Some research found that EC effects are resistant to presentations of the CS without the US, whereas other studies found evidence for extinction effects. A recent study found extinction of EC only when participants rated the CS before and after the CS-only presentations, but not when CS evaluation was measured once or indirectly with the evaluative priming task. In two experiments (total N = 2,181), we found no evidence that indirectly measured evaluation is sensitive to extinction, using an indirect evaluation measure with high sensitivity - the Implicit Association Test. However, unlike previous research, we found that evaluation of any stimuli (and not only the CS) before the CS-only presentations decreases self-reported EC effects. Our results are compatible with the conclusion that the extinction of EC is limited to evaluation measured directly. We discuss the theoretical implications of these results, and conclude that the specific conditions (and mechanisms) that change the direct evaluative response are yet to be clarified.

Contextual reinstatement promotes extinction generalization in healthy adults but not PTSD

For episodic memories, reinstating the mental context of a past experience improves retrieval of memories formed during that experience. Does context reinstatement serve a similar role for implicit, associative memories such as fear and extinction? Here, we used a fear extinction paradigm to investigate whether the retrieval of extinction (safety) memories is associated with reactivation of the mental context from extinction memory formation. In a two-day Pavlovian conditioning, extinction, and renewal protocol, we collected functional MRI data while healthy adults and adults with PTSD symptoms learned that conditioned stimuli (CSs) signaled threat through association with an electrical shock. Following acquisition, conceptually related exemplars from the CS category no longer signaled threat (i.e., extinction). Critically, during extinction only, task-irrelevant stimuli were presented between each CS trial to serve as "context tags" for subsequent identification of the possible reinstatement of this extinction context during a test of fear renewal the next day. We found that healthy adults exhibited extinction context reinstatement, as measured via multivariate pattern analysis of fMRI data, in the medial temporal lobe that related to behavioral performance, such that greater reinstatement predicted CSs being rated as safe instead of threatening. Moreover, context reinstatement positively correlated with univariate activity in the ventromedial prefrontal cortex and hippocampus, regions which are thought to be important for extinction learning. These relationships were not observed in the PTSD symptom group. These findings provide new evidence of a contextual reinstatement mechanism that helps resolve competition between the retrieval of opposing associative memories of threat and safety in the healthy adult brain that is dysregulated in PTSD.

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).

Evidence for Persistence of Sexual Evaluative Learning Effects

INTRODUCTION

Several studies demonstrated that genital arousal and enhanced positive affect toward neutral stimuli due to sexual conditioning did not extinguish during a brief extinction phase, but other studies showed contrasting results. Possible resistance to extinction of conditioned human sexual response has, however, not been studied using extensive extinction trials.

AIM

To study resistance to extinction of conditioned sexual response in men and women.

METHODS

Healthy sexually functional men (N = 34) and women (N = 32) participated in a differential conditioning experiment, with neutral pictures as conditioned stimuli (CSs) and genital vibrostimulation as unconditioned stimulus. Only one CS (the CS+) was followed by the unconditioned stimulus during the acquisition phase.

MAIN OUTCOME MEASURE

Penile circumference and vaginal pulse amplitude were assessed, and ratings of affective value and subjective sexual arousal were obtained. In addition, a stimulus response compatibility task was included to assess automatic approach and avoidance tendencies.

RESULTS

Men and women rated the CS+ as more positive than the CS- during all 24 extinction trials and demonstrated a slight tendency to approach the CS+ directly after the extinction procedure. Participants rated the CS+ as more sexually arousing than the CS- during 20 extinction trials. No evidence was found for conditioned genital sexual response.

CLINICAL IMPLICATIONS

Learned sexual evaluations may be difficult to modify through an extinction procedure; therefore, unwanted but persistent subjective sexual evaluations may be better targeted by interventions such as the deployment of emotion regulation strategies.

STRENGTH & LIMITATIONS

Extensive extinction trials were used; however, only relatively short-term effects within one experimental session were studied and there was no (unpaired) control condition.

CONCLUSION

The results provide evidence that conditioned sexual likes are relatively persistent, also at the behavioral level. Both S, Brom M, Laan E, et al. Evidence for Persistence of Sexual Evaluative Learning Effects. J Sex Med 2020;17:505-517.

Sign-tracking behavior is difficult to extinguish and resistant to multiple cognitive enhancers

The attribution of incentive-motivational value to drug-related cues underlies relapse and craving in drug addiction. One method of addiction treatment, cue-exposure therapy, utilizes repeated presentations of drug-related cues in the absence of drug (i.e., extinction learning); however, its efficacy has been limited due to an incomplete understanding of extinction and relapse processes after cues have been imbued with incentive-motivational value. To investigate this, we used a Pavlovian conditioned approach procedure to screen for rats that attribute incentive-motivational value to reward-related cues (sign-trackers; STs) or those that do not (goal-trackers; GTs). In Experiment 1, rats underwent Pavlovian extinction followed by reinstatement and spontaneous recovery tests. For comparison, a separate group of rats underwent PCA training followed by operant conditioning, extinction, and tests of reinstatement and spontaneous recovery. In Experiment 2, three cognitive enhancers (sodium butyrate, D-cycloserine, and fibroblast growth factor 2) were administered following extinction training to facilitate extinction learning. STs but not GTs displayed enduring resistance to Pavlovian, but not operant, extinction and were more susceptible to spontaneous recovery. In addition, none of the cognitive enhancers tested affected extinction learning. These results expand our understanding of extinction learning by demonstrating that there is individual variation in extinction and relapse processes and highlight potential difficulties in applying extinction-based therapies to drug addiction treatment in the clinic.

Loss of Hierarchical Control by Occasion Setters Following Lesions of the Prelimbic and Infralimbic Medial Prefrontal Cortex in Rats

Recent work suggests complementary roles of the prelimbic and infralimbic regions of the rat medial prefrontal cortex in cognitive control processes, with the prelimbic cortex implicated in top-down modulation of associations and the infralimbic cortex playing a role in the inhibition of inappropriate responses. Following selective lesions made to prelimbic or infralimbic regions (or control sham-surgery) rats received simultaneous training on Pavlovian feature negative (A+, XA-) and feature positive (B-, YB+) discriminations designed to lead to hierarchical occasion-setting control by the features (X, Y) over their respective targets (A, B). Evidence for hierarchical control was assessed in a transfer test in which features and targets were swapped (YA, XB). All groups were able to learn the feature negative and feature positive discriminations. Whilst sham-lesioned animals showed no transfer of control by features to novel targets (a hallmark of hierarchical control), rats with lesions of prelimbic or infralimbic regions showed evidence of transfer from the positive feature (Y) to the negative target (A), and from the negative feature (X) to the positive target (B; although this only achieved significance in infralimbic-lesioned animals). These data indicate that damage to either of these regions disrupts hierarchical occasion-setting control, extending our knowledge of their role in cognitive control to encompass flexible behaviours dictated by discrete cues.

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.

Response production during extinction training is not sufficient for extinction of evaluative conditioning

Two high-powered experiments examined the role of evaluative response production in the extinction of evaluative conditioning (EC) by positioning EC in the procedural and conceptual framework of classical conditioning (CC). According to Rescorla's response inhibition hypothesis, more frequent responding during extinction training results in larger extinction during testing. Experiment 1 used three extinction conditions following response acquisition in an EC procedure: evaluative responses were measured only after extinction; after acquisition and after extinction; or were continuously measured after acquisition, during extinction and after extinction. Based on Rescorla's response inhibition hypothesis, we predicted that extinction of EC would be the highest in the third condition. Experiment 2 was aimed at further facilitating extinction of EC by encouraging participants to experience that their evaluation may change over the course of the experiment. To this end, half of the participants completed pre- and post-acquisition ratings prior to practicing continuous response expression in the extinction phase. Contrary to our predictions, no extinction of EC was observed in either of these experiments. We conclude that Rescorla's inhibition response hypothesis may not apply to EC and discuss the theoretical implications of this finding.

Context-dependent extinction of threat memories: influences of healthy aging

Although a substantial progress has been made in recent years on understanding the processes mediating extinction of learned threat, little is known about the context-dependent extinction of threat memories in elderly individuals. We used a 2-day differential threat conditioning and extinction procedure to determine whether young and older adults differed in the contextual recall of conditioned responses after extinction. On Day 1, conditioned stimuli were paired with an aversive electric shock in a 'danger' context and then extinguished in a different 'safe' context. On Day 2, the extinguished stimulus was presented to assess extinction recall (safe context), and threat renewal (danger context). Physiological and verbal report measures of threat conditioning were collected throughout the experiment. Skin conductance response (SCR data revealed no significant differences between age groups during acquisition and extinction of threat conditioning on Day 1. On Day 2, however, older adults showed impaired recall of extinction memory, with increased SCR to the extinguished stimulus in the 'safe' context, and reduced ability to process context properly. In addition, there were no age group differences in fear ratings and contingency awareness, thus revealing that aging selectively impairs extinction memories as indexed by autonomic responses. These results reveal that aging affects the capacity to use context to modulate learned responses to threat, possibly due to changes in brain structures that enable context-dependent behaviour and are preferentially vulnerable during aging.

Cocaine preexposure enhances sexual conditioning and increases resistance to extinction in male Japanese quail

The incentive-sensitization theory posits that drug addiction results from altered learning and motivational processes that stem from drug-induced changes in the brain's reward circuitry. Although it is generally accepted that problematic drug use results from these neuroadaptations, less research has focused on how these neural changes affect the incentive-motivational properties of naturally rewarding stimuli such as sex. The present set of experiments was conducted to investigate (1) dose-dependent effects of preexposure to chronic cocaine on sexual conditioning and (2) how prior cocaine exposure affects the extinction of sexually conditioned behavior in male Japanese quail. In Experiment 1, male quail were exposed to saline or to cocaine (5, 10, or 20 mg/kg ip) for 10 days, and their locomotor activity was measured. After a washout period, ten sexual-conditioning trials were conducted in which a light (CS) was presented prior to the presentation of a female quail (US) and approach to the light was measured. The results showed that cocaine dose-dependently enhanced sexually conditioned approach behavior and copulation. Experiment 2 was procedurally similar to Experiment 1, except that the quail received either saline or 10 mg/kg cocaine (ip) and 24 extinction trials were conducted. During extinction, no female was presented after the CS. The results showed that preexposure to cocaine delayed extinction. Therefore, cocaine may dose-dependently increase the strength of sexual conditioning, and this may subsequently increase resistance to extinction. These findings and their possible mechanisms are explored.

Extinction and Latent Inhibition Involve a Similar Form of Inhibitory Learning that is Stored in and Retrieved from the Infralimbic Cortex

Extinction and latent inhibition each refer to a reduction in conditioned responding: the former occurs when pairings of a conditioned stimulus (CS) and an unconditioned stimulus (US) are followed by repeated presentations of the CS alone; the latter occurs when CS alone presentations precede its pairings with the US. The present experiments used fear conditioning to test the hypothesis that both phenomena involve a similar form of inhibitory learning that recruits common neuronal substrates. We found that the initial inhibitory memory established by extinction is reactivated in the infralimbic (IL) cortex during additional extinction. Remarkably, this reactivation also occurs when the initial inhibitory memory had been established by latent inhibition. In both cases, the inhibitory memory was strengthened by pharmacological stimulation of the IL. Moreover, NMDA receptor blockade in the IL disrupted the weakening in conditioned responding produced by either latent inhibition or extinction. These findings, therefore, indicate that latent inhibition and extinction produce a similar inhibitory memory that is retrieved from the IL. They also demonstrate that the IL plays a wide role in fear regulation by promoting the retrieval of inhibitory memories generated by CS alone presentations either before or after this CS has been rendered dangerous.

Role Played by the Passage of Time in Reversal Learning

Reversal learning is thought to involve an extinction-like process that inhibits the expression of the initial learning. However, behavioral evidence for this inhibition remains difficult to interpret as various procedures have been employed to study reversal learning. Here, we used a discrimination task in rats to examine whether the inhibition produced by reversal learning is as sensitive to the passage of time as the inhibition produced by extinction. Experiment 1 showed that when tested immediately after reversal training, rats were able to use the reversed contingencies to solve the discrimination task in an outcome-specific manner. This ability to use outcome-specific information was lost when a delay was inserted between reversal training and test. However, interpretation of these data was made difficult by a potential floor effect. This concern was addressed in Experiment 2 in which it was confirmed that the passage of time impaired the ability of the rats to use the reversed contingencies in an outcome-specific manner to solve the task. Further, it revealed that the delay between initial learning and test was not responsible for this impairment. Additional work demonstrated that solving the discrimination task was unaffected by Pavlovian extinction but that the discriminative stimuli were able to block conditioning to a novel stimulus, suggesting that Pavlovian processes were likely to contribute to solving the discrimination. We therefore concluded that the expression of reversal and extinction learning do share the same sensitivity to the effect of time. However, this sensitivity was most obvious when we assessed outcome-specific information following reversal learning. This suggests that the processes involved in reversal learning are somehow distinct from those underlying extinction learning, as the latter has usually been found to leave outcome-specific information relatively intact. Thus, the present study reveals that a better understanding of the mechanisms supporting reversal training requires assessing the impact that this training exerts on the content of learning rather than performance per se.

The infralimbic cortex encodes inhibition irrespective of motivational significance

Evidence indicates that the infralimbic cortex (IL) encodes and retrieves the inhibitory memory produced by fear extinction. Recently, we have shown that the IL is also involved in the inhibitory memory generated by stimulus pre-exposure that causes latent inhibition. These results are surprising because a stimulus undergoing fear extinction carries aversive motivational value, whereas a pre-exposed stimulus is neutral. The present experiments tested the hypothesis that the IL encodes inhibition irrespective of the motivational information about the stimulus. Using rats, we first confirmed that IL activity during stimulus pre-exposure is required for latent inhibition. Then, we found that pharmacological stimulation of the IL facilitated aversive extinction to a stimulus that had been trained and extinguished as an appetitive stimulus. This facilitation was stimulus specific and required appetitive extinction. The same facilitation was found when appetitive extinction was replaced with random presentations of the stimulus and an appetitive outcome. Together, these findings indicate that non-reinforced stimulus presentations establish an inhibitory memory that is reactivated and strengthened in the IL during subsequent aversive extinction. This is consistent with the view that the IL encodes inhibition irrespective of motivational value, suggesting that this brain region plays a general role in inhibitory learning.

Role of orexin-1 receptors in the dorsal hippocampus (CA1 region) in expression and extinction of the morphine-induced conditioned place preference in the rats

Orexinergic system is involved in reward processing and drug addiction. Objectives here, we investigated the effect of intra-hippocampal CA1 administration of orexin-1 receptor (OX1r) antagonist on the expression, and extinction of morphine-induced place preference in rats. Conditioned place preference (CPP) was induced by subcutaneous injection of morphine (5 mg/kg) during a 3-day conditioning phase. Two experimental plots were designed; SB334867 as a selective OX1r antagonist was dissolved in 12% DMSO, prepared in solutions with different concentrations (3, 30, and 300 nM), and microinjected into the CA1 and some neighboring regions (0.5 μl/side), bilaterally. CPP score and locomotor activity were recorded during the CPP test. Results demonstrated that intra-CA1 administration of the OX1r antagonist attenuates the expression of morphine-induced CPP. Furthermore, higher concentrations of SB334867 facilitated the extinction period of morphine-induced CPP and reduced its latency. Nevertheless, solely administration of DMSO did not have any influence on the CPP scores and locomotion in both phases. Our findings suggest that OX1rs in the CA1 region of the hippocampus are involved in the expression of morphine CPP. Moreover, blockade of OX1rs could facilitate extinction and may extinguish the ability of drug-related cues. It seems that the antagonist might be considered as a propitious therapeutic agent in suppressing drug-seeking behaviors.

Prior exposure to nutritive and artificial sweeteners differentially alters the magnitude and persistence of sucrose-conditioned flavor preferences in BALB/c and C57BL/6 inbred mouse strains

Murine genetic variance affects sucrose's ability to condition flavor preferences (CFP) relative to saccharin. Whereas BALB/c mice display robust sucrose- and fructose-CFP, C57BL/6 mice only display sucrose-CFP. Prior exposure to sucrose or saccharin solutions alters subsequent food choice responsiveness. The present study examined whether pre-exposure for one month to 10% sucrose or 0.2% saccharin altered subsequent sucrose-CFP in male and female BALB/c and C57BL/6 mice. Two weeks later, food-restricted mice were exposed to 10 CFP training trials with uniquely flavored 16% sucrose and 0.2% saccharin solutions. Two-bottle choice tests of the flavors mixed in saccharin followed for 4 weeks. Male mice weighed more than females across all conditions, and male BALB/c, but not C57BL mice consumed more 85 sucrose than females. No other notable sex differences were observed. BALB/c mice consumed more sucrose during pre-exposure and one-bottle training than C57BL/6 mice. Although the magnitudes of sucrose-CFP were comparable in two-bottle choice tests in water-exposed BALB/c and C57BL/6 mice, sucrose- and saccharin-exposed BALB/c mice displayed significantly greater sucrose-CFP preferences relative to C57BL/6 counterparts. These data indicate murine genetic variance in the effects of prior exposure to nutritive or non-nutritive sweeteners upon the magnitude of adult sugar-CFP.

Evidence of structure and persistence in motivational attraction to serial Pavlovian cues

Sign-tracking is a form of autoshaping where animals develop conditioned responding directed toward stimuli predictive of an outcome even though the outcome is not contingent on the animal's behavior. Sign-tracking behaviors are thought to arise out of the attribution of incentive salience (i.e., motivational value) to reward-predictive cues. It is not known how incentive salience would be attributed to serially occurring cues, despite cues often occurring in a sequence in the real world as reward approaches. The experiments presented here demonstrate that reward-proximal cue responding is not altered by the presence of a distal reward cue (Experiment 1), and similarly that reward-distal cue responding which animals favor, is not altered by the presence of a reward-proximal cue (Experiment 2). Extinction of reward-proximal cues after training of the serial sequence leads to a generalized reduction in lever responding (Experiment 3). Together, we show that both Pavlovian serial lever cues acquire motivational value. These experiments also provide support to the notion that sign-tracking responses are insensitive to changes in outcome value, and that responding to serial cues creates a distinct context for outcome value.

Infralimbic dopamine D2 receptors mediate glucocorticoid-induced facilitation of auditory fear memory extinction in rats

The infralimbic (IL) cortex of the medial prefrontal cortex plays an important role in the extinction of fear memory. Also, it has been showed that both brain glucocorticoid and dopamine receptors are involved in many processes such as fear extinction that drive learning and memory; however, the interaction of these receptors in the IL cortex remains unclear. We examined a putative interaction between the effects of glucocorticoid and dopamine receptors stimulation in the IL cortex on fear memory extinction in an auditory fear conditioning paradigm in male rats. Corticosterone (the endogenous glucocorticoid receptor ligand), or RU38486 (the synthetic glucocorticoid receptor antagonist) microinfusion into the IL cortex 10 min before test 1 attenuated auditory fear expression at tests 1-3, suggesting as an enhancement of fear extinction. The effect of corticosterone, but not RU38486 was counteracted by the dopamine D2 receptor antagonist sulpiride pre-treatment administered into the IL (at a dose that failed to alter freezing behavior on its own). In contrast, intra-IL infusion of the dopamine D1 receptor antagonist SCH23390 pre-treatment failed to alter freezing behavior. These findings provide evidence for the involvement of the IL cortex D2 receptors in CORT-induced facilitation of fear memory extinction.

Hippocampal calpain is required for the consolidation and reconsolidation but not extinction of contextual fear memory

Memory consolidation, reconsolidation, and extinction have been shown to share similar molecular signatures, including new gene expression. Calpain is a Ca2+-dependent protease that exerts its effects through the proteolytic cleavage of target proteins. Neuron-specific conditional deletions of calpain 1 and 2 impair long-term potentiation in the hippocampus and spatial learning. Moreover, recent studies have suggested distinct roles of calpain 1 and 2 in synaptic plasticity. However, the role of hippocampal calpain in memory processes, especially memory consolidation, reconsolidation, and extinction, is still unclear. In the current study, we demonstrated the critical roles of hippocampal calpain in the consolidation, reconsolidation, and extinction of contextual fear memory in mice. We examined the effects of pharmacological inhibition of calpain in the hippocampus on these memory processes, using the N-Acetyl-Leu-Leu-norleucinal (ALLN; calpain 1 and 2 inhibitor). Microinfusion of ALLN into the dorsal hippocampus impaired long-term memory (24 h memory) without affecting short-term memory (2 h memory). Similarly, this pharmacological blockade of calpain in the dorsal hippocampus also disrupted reactivated memory but did not affect memory extinction. Importantly, the systemic administration of ALLN inhibited the induction of c-fos in the hippocampus, which is observed when memory is consolidated. Our observations showed that hippocampal calpain is required for the consolidation and reconsolidation of contextual fear memory. Further, the results suggested that calpain contributes to the regulation of new gene expression that is necessary for these memory processes as a regulator of Ca2+-signal transduction pathway.

A comparison of positive vicarious learning and verbal information for reducing vicariously learned fear

Research with children has demonstrated that both positive vicarious learning (modelling) and positive verbal information can reduce children's acquired fear responses for a particular stimulus. However, this fear reduction appears to be more effective when the intervention pathway matches the initial fear learning pathway. That is, positive verbal information is a more effective intervention than positive modelling when fear is originally acquired via negative verbal information. Research has yet to explore whether fear reduction pathways are also important for fears acquired via vicarious learning. To test this, an experiment compared the effectiveness of positive verbal information and positive vicarious learning interventions for reducing vicariously acquired fears in children (7-9 years). Both vicarious and informational fear reduction interventions were found to be equally effective at reducing vicariously acquired fears, suggesting that acquisition and intervention pathways do not need to match for successful fear reduction. This has significant implications for parents and those working with children because it suggests that providing children with positive information or positive vicarious learning immediately after a negative modelling event may prevent more serious fears developing.

Reducing Fear During Childhood to Prevent Anxiety Disorders Later: Insights From Developmental Psychobiology

Anxiety disorders are neurodevelopmental with the median age of onset 10 to 11 years, but developmental processes underlying fear and anxiety are rarely investigated. In the last decade, however, developmental rodent studies have increased our understanding of how to treat and prevent the persistence of anxiety. Behavioral findings from rodent studies match the observations in anxious children, and the neural and molecular findings help explain why anxiety disorders are indeed neurodevelopmental. Extinction processes that are involved in cognitive-behavioral therapy appear particularly effective in children compared with older populations. Policy should mandate school psychologists and government subsidies for therapy sessions to increase children’s mental-health-service utilization. Funding bodies also should challenge anxiety studies exclusively targeting adults to include younger people to investigate why anxiety disorders are developmental disorders and focus more on preventing their persistence later in life.

Calcium signalling in medial intercalated cell dendrites and spines

KEY POINTS

Dendritic and spine calcium imaging in combination with electrophysiology in acute slices revealed that in medial intercalated cells of the amygdala: Action potentials back-propagate into the dendritic tree, but due to the presence of voltage-dependent potassium channels, probably Kv4.2 channels, attenuate over distance. A mixed population of AMPA receptors with rectifying and linear I-V relations are present at individual spines of a single neuron. Decay kinetics and pharmacology suggest tri-heteromeric NMDA receptors at basolateral-intercalated cell synapses. NMDA receptors are the main contributors to spine calcium entry in response to synaptic stimulation. Calcium signals in response to low- and high-frequency stimulation, and in combination with spontaneous action potentials are locally restricted to the vicinity of active spines. Together, these data show that calcium signalling in these GABAergic neurons is tightly controlled and acts as a local signal.

ABSTRACT

The amygdala plays a central role in fear conditioning and extinction. The medial intercalated (mITC) neurons are GABAergic cell clusters interspaced between the basolateral (BLA) and central amygdala (CeA). These neurons are thought to play a key role in fear and extinction, controlling the output of the CeA by feed-forward inhibition. BLA to mITC cell inputs are thought to undergo synaptic plasticity, a mechanism underlying learning, which is mediated by NMDA receptor-dependent mechanisms that require changes in cytosolic calcium. Here, we studied the electrical and calcium signalling properties of mITC neurons in GAD67-eGFP mice using whole-cell patch clamp recordings and two-photon calcium imaging. We show that action potentials back-propagate (bAP) into dendrites, and evoke calcium transients in both the shaft and the dendritic spine. However, bAP-mediated calcium rises in the dendrites attenuate with distance due to shunting by voltage-gated potassium channels. Glutamatergic inputs make dual component synapses on spines. At these synapses, postsynaptic AMPA receptors can have linear or rectifying I-V relationships, indicating that some synapses express GluA2-lacking AMPA receptors. Synaptic NMDA receptors had intermediate decay kinetics, and were only partly blocked by GuN2B selective blockers, indicating these receptors are GluN1/GluN2A/GluN2B trimers. Low- or high-frequency synaptic stimulation raised spine calcium, mediated by calcium influx via NMDA receptors, was locally restricted and did not invade neighbouring spines. Our results show that in mITC neurons, postsynaptic calcium is tightly controlled, and acts as a local signal.

Extinction of specific stimulus-outcome (S-O) associations in Pavlovian learning with an extended CS procedure

Three experiments with male and female rats were conducted to examine the effects of Pavlovian extinction training on Pavlovian-to-instrumental transfer (PIT) in a task in which the unconditioned stimulus (US) was presented at an early time point within an extended conditioned stimulus (CS). Two instrumental responses were trained with different reinforcing outcomes (R1-O1, R2-O2) and then, independently, 2 stimuli were trained with those outcomes (S1-O1, S2-O2). One group then underwent an extinction treatment (S1-, S2-) and a second was merely exposed to the experimental contexts without any stimulus events. Finally, the effects of the 2 stimuli on instrumental responding were assessed in PIT tests. Across experiments we varied the number of Pavlovian training trials prior to extinction (8, 16, or 64 trials) and the length of time following extinction prior to test (i.e., 1 or 21 days, in a test for spontaneous recovery). We observed that outcome-specific PIT was reduced by extinction in all of our training conditions and that this extinction effect was durable, surviving a 3-week spontaneous recovery interval even though conditioned magazine approach spontaneously recovered over this interval. Although extinction reduced the magnitude of PIT, the temporal expression of PIT was mostly unaffected. We found these effects in both male and female rats, though in 1 study females were extinction-resistant. These data suggest that under the conditions studied here Pavlovian extinction may permanently weaken the ability of Pavlovian cues to retrieve a representation of their associated outcomes without impacting the temporal organization of responding. This suggests that different features of learning may be differentially sensitive to extinction. (PsycINFO Database Record

The computational nature of memory modification

Retrieving a memory can modify its influence on subsequent behavior. We develop a computational theory of memory modification, according to which modification of a memory trace occurs through classical associative learning, but which memory trace is eligible for modification depends on a structure learning mechanism that discovers the units of association by segmenting the stream of experience into statistically distinct clusters (latent causes). New memories are formed when the structure learning mechanism infers that a new latent cause underlies current sensory observations. By the same token, old memories are modified when old and new sensory observations are inferred to have been generated by the same latent cause. We derive this framework from probabilistic principles, and present a computational implementation. Simulations demonstrate that our model can reproduce the major experimental findings from studies of memory modification in the Pavlovian conditioning literature.

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.

Extinction Generates Outcome-Specific Conditioned Inhibition

Extinction involves altering a previously established predictive relationship between a cue and its outcome by repeatedly presenting that cue alone. Although it is widely accepted that extinction generates some form of inhibitory learning [1-4], direct evidence for this claim has been lacking, and the nature of the associative changes induced by extinction have, therefore, remained a matter of debate [5-8]. In the current experiments, we used a novel behavioral approach that we recently developed and that provides a direct measure of conditioned inhibition [9] to compare the influence of extinguished and non-extinguished cues on choice between goal-directed actions. Using this approach, we provide direct evidence that extinction generates outcome-specific conditioned inhibition. Furthermore, we demonstrate that this inhibitory learning is controlled by the infralimbic cortex (IL); inactivation of the IL using M4 DREADDs abolished outcome-specific inhibition and rendered the cue excitatory. Importantly, we found that context modulated this inhibition. Outside its extinction context, the cue was excitatory and functioned as a specific predictor of its previously associated outcome, biasing choice toward actions earning the same outcome. In its extinction context, however, the cue acted as a specific inhibitor and biased choice toward actions earning different outcomes. Context modulation of these excitatory and inhibitory memories was mediated by the dorsal hippocampus (HPC), suggesting that the HPC and IL act in concert to control the influence of conditioned inhibitors on choice. These findings demonstrate for the first time that extinction turns a cue into a net inhibitor that can influence choice via counterfactual action-outcome associations.