Avoidance learning: a review of theoretical models and recent developments

Expectation of pain and relief: A dynamical model of the neural basis for pain-trauma co-morbidity

Posttraumatic Stress Disorder (PTSD) is highly co-morbid with chronic pain conditions. When present, PTSD significantly worsens chronic pain outcomes. Likewise, pain contributes to a more severe PTSD as evidenced by greater disability, more frequent use of harmful opioid analgesics and increased pain severity. The biomechanism behind this comorbidity is incompletely understood, however recent work strongly supports the widely-accepted role of expectation, in the entanglement of chronic pain and trauma symptoms. This work has shown that those with trauma have a maladaptive brain response while expecting stress and pain, whereas those with chronic pain may have a notable impairment in brain response while expecting pain relief. This dynamical expectation model of the interaction between neural systems underlying expectation of pain onset (traumatic stress) and pain offset (chronic pain) is biologically viable and may provide a biomechanistic insight into pain-trauma comorbidity. These predictive mechanisms work through interoceptive pathways in the brain critically the insula cortex. Here we highlight how the neural expectation-related mechanisms augment the existing models of pain and trauma to better understand the dynamics of pain and trauma comorbidity. These ideas will point to targeted complementary clinical approaches, based on mechanistically separable neural biophenotypes for the entanglement of chronic pain and trauma symptoms.

Extinction and beyond: an expanded framework for exposure and response prevention for obsessive-compulsive disorder

Exposure therapy is a first-line, empirically validated treatment for anxiety, obsessive-compulsive, and trauma-related disorders. Extinction learning is the predominant theoretical framework for exposure therapy, whereby repeated disconfirmation of a feared outcome yields fear reduction over time. Although this framework has strong empirical support and substantial translational utility, extinction learning is unlikely to be the sole process underlying the therapeutic effects of exposure therapy. In our clinic, we commonly treat obsessive-compulsive disorder (OCD) patients successfully with exposure therapy even when some or all of their feared outcomes are not amenable to disconfirmation and, by extension, to extinction learning. Herein, we present a generic clinical vignette illustrating a commonly encountered feared outcome in OCD that cannot be disconfirmed through exposure (damnation resulting from blasphemous thoughts). We describe two specific non-extinction-based strategies we commonly employ in such cases, and we associate these strategies with known change mechanisms that might account for their effectiveness: (1) non-associative habituation to aversive stimuli, and (2) fear-memory elicitation and subsequent reconsolidation. We discuss the limitations inherent in the reverse-translational approach taken and its opportunities for expanding the framework of exposure therapy.

Pavlovian-to-instrumental transfer in individuals with chronic pain

Avoidance of pain has been argued to be key factor leading pain events to chronic disability. In this respect, research has focused on investigating the working mechanisms of avoidance's acquisition. Avoidance of painful stimuli has been traditionally studied using a combination of Pavlovian and Instrumental procedures. However, such approach seems to go against real-life scenarios where avoidance is commonly acquired more readily. Using a novel pain avoidance paradigm, we tested whether pain avoidance can be installed in absence of associations between a cue and pain omission, and whether such avoidance differs between pain patients and healthy controls. Participants first learned to avoid painful stimuli by pressing a grip bar. Then, they passively encountered pairings of one geometrical shape with pain and of another geometrical shape without pain. Lastly, participants encountered the geometrical shapes while being able to use the grip bar. Results showed that participants pressed the bar more vigorously when encountering the previously pain-related shape compared to the pain-unrelated shape. This effect did not seem to differ between pain patients and healthy control. Our study could inspire a new way in measuring avoidance in pain, possibly paving the way to better understanding how avoidance is installed in chronic pain.

Acute stress yields a sex-dependent facilitation of signaled active avoidance in rats

Post-traumatic stress disorder (PTSD) is a debilitating disorder characterized by excessive fear, hypervigilance, and avoidance of thoughts, situations or reminders of the trauma. Among these symptoms, relatively little is known about the etiology of pathological avoidance. Here we sought to determine whether acute stress influences avoidant behavior in adult male and female rats. We used a stress procedure (unsignaled footshock) that is known to induce long-term sensitization of fear and potentiate aversive learning. Rats were submitted to the stress procedure and, one week later, underwent two-way signaled active avoidance conditioning (SAA). In this task, rats learn to prevent an aversive outcome (shock) by performing a shuttling response when exposed to a warning signal (tone). We found that acute stress significantly enhanced SAA acquisition rate in females, but not males. Female rats exhibited significantly greater avoidance responding on the first day of training relative to controls, reaching similar levels of performance by the second day. Males that underwent the stress procedure showed similar rates of acquisition to controls but exhibited resistance to extinction. This was manifest as both elevated avoidance and intertrial responding across extinction days relative to non-stressed controls, an effect that was not observed in females. In a second experiment, acute stress sensitized footshock unconditioned responses in males, not females. However, males and females exhibited similar levels of stress-enhanced fear learning (SEFL), which was expressed as sensitized freezing to a shock-paired context. Together, these results reveal that acute stress facilitates SAA performance in both male and female rats, though the nature of this effect is different in the two sexes. We did not observe sex differences in SEFL, suggesting that the stress-induced sex difference in performance was selective for instrumental avoidance. Future work will elucidate the neurobiological mechanisms underlying the differential effect of stress on instrumental avoidance in male and female rats.

Responding to threat: Associations between neural reactivity to and behavioral avoidance of threat in pediatric anxiety

BACKGROUND

Despite broad recognition of the central role of avoidance in anxiety, a lack of specificity in its operationalization has hindered progress in understanding this clinically significant construct. The current study uses a multimodal approach to investigate how specific measures of avoidance relate to neural reactivity to threat in youth with anxiety disorders.

METHODS

Children with anxiety disorders (ages 6-12 years; n = 65 for primary analyses) completed laboratory task- and clinician-based measures of avoidance, as well as a functional magnetic resonance imaging task probing neural reactivity to threat. Primary analyses examined the ventral anterior insula (vAI), amygdala, and ventromedial prefrontal cortex (vmPFC).

RESULTS

Significant but distinct patterns of association with task- versus clinician-based measures of avoidance emerged. Clinician-rated avoidance was negatively associated with right and left vAI reactivity to threat, whereas laboratory-based avoidance was positively associated with right vAI reactivity to threat. Moreover, left vAI-right amygdala and bilateral vmPFC-right amygdala functional connectivity were negatively associated with clinician-rated avoidance but not laboratory-based avoidance.

LIMITATIONS

These results should be considered in the context of the restricted range of our treatment-seeking sample, which limits the ability to draw conclusions about these associations across children with a broader range of symptomatology. In addition, the limited racial and ethnic diversity of our sample may limit the generalizability of findings.

CONCLUSION

These findings mark an important step towards bridging neural findings and behavioral patterns using a multimodal approach. Advancing understanding of behavioral avoidance in pediatric anxiety may guide future treatment optimization by identifying individual-specific targets for treatment.

An ascending vagal sensory-central noradrenergic pathway modulates retrieval of passive avoidance memory

Background

Visceral feedback from the body is often subconscious, but plays an important role in guiding motivated behaviors. Vagal sensory neurons relay "gut feelings" to noradrenergic (NA) neurons in the caudal nucleus of the solitary tract (cNTS), which in turn project to the anterior ventrolateral bed nucleus of the stria terminalis (vlBNST) and other hypothalamic-limbic forebrain regions. Prior work supports a role for these circuits in modulating memory consolidation and extinction, but a potential role in retrieval of conditioned avoidance remains untested.

Results

To examine this, adult male rats underwent passive avoidance conditioning. We then lesioned gut-sensing vagal afferents by injecting cholecystokinin-conjugated saporin toxin (CSAP) into the vagal nodose ganglia (Experiment 1), or lesioned NA inputs to the vlBNST by injecting saporin toxin conjugated to an antibody against dopamine-beta hydroxylase (DSAP) into the vlBNST (Experiment 2). When avoidance behavior was later assessed, rats with vagal CSAP lesions or NA DSAP lesions displayed significantly increased conditioned passive avoidance.

Conclusions

These new findings support the view that a gut vagal afferent-to-cNTSNA-to-vlBNST circuit plays a role in modulating the expression/retrieval of learned passive avoidance. Overall, our data suggest a dynamic modulatory role of vagal sensory feedback to the limbic forebrain in integrating interoceptive signals with contextual cues that elicit conditioned avoidance behavior.

Eating and drinking experience in patients with idiopathic pulmonary fibrosis: a qualitative study

OBJECTIVE

To explore eating and drinking experiences of patients with idiopathic pulmonary fibrosis (IPF), the impact of any changes associated with their diagnosis and any coping mechanisms developed by patients.

SETTING

Pulmonary fibrosis support groups around the UK and the regional Interstitial Lung Diseases Clinic, Newcastle upon Tyne.

PARTICIPANTS

15 patients with IPF (9 men, 6 women), median age 71 years, range (54-92) years, were interviewed. Inclusion criteria included competent adults (over the age of 18 years) with a secure diagnosis of IPF as defined by international consensus guidelines. Patients were required to have sufficient English language competence to consent and participate in an interview. Exclusion criteria were a history of other lung diseases, a history of pre-existing swallowing problem of other causes that may be associated with dysphagia and individuals with significant communication or other memory difficulties that render them unable to participate in an interview.

DESIGN

A qualitative study based on semistructured interviews used purpose sampling conducted between February 2021 and November 2021. Interviews were conducted via video videoconferencing call platform or telephone call, transcribed and data coded and analysed using a reflexive thematic analysis.

RESULTS

Three main themes were identified, along with several subthemes, which were: (1) Eating, as such, is no longer a pleasure. This theme mainly focused on the physical and sensory changes associated with eating and drinking and their effects and the subsequent emotional and social impact of these changes; (2) It is something that happens naturally and just try and get on with it. This theme centred on the self-determined strategies employed to manage changes to eating and drinking; and (3) What is normal. This theme focused on patients seeking information to better understand the changes in their eating and drinking and the patients' beliefs about what has changed their eating and drinking.

CONCLUSIONS

To our knowledge, this is the first study to report on IPF patients' lived experience of eating and drinking changes associated with their diagnosis. Findings demonstrate that some patients have substantial struggles and challenges with eating and drinking, affecting them physically, emotionally and socially. There is a need to provide better patient information for this area and further study.

Infralimbic parvalbumin neural activity facilitates cued threat avoidance

The infralimbic cortex (IL) is essential for flexible behavioral responses to threatening environmental events. Reactive behaviors such as freezing or flight are adaptive in some contexts, but in others a strategic avoidance behavior may be more advantageous. IL has been implicated in avoidance, but the contribution of distinct IL neural subtypes with differing molecular identities and wiring patterns is poorly understood. Here, we study IL parvalbumin (PV) interneurons in mice as they engage in active avoidance behavior, a behavior in which mice must suppress freezing in order to move to safety. We find that activity in inhibitory PV neurons increases during movement to avoid the shock in this behavioral paradigm, and that PV activity during movement emerges after mice have experienced a single shock, prior to learning avoidance. PV neural activity does not change during movement toward cued rewards or during general locomotion in the open field, behavioral paradigms where freezing does not need to be suppressed to enable movement. Optogenetic suppression of PV neurons increases the duration of freezing and delays the onset of avoidance behavior, but does not affect movement toward rewards or general locomotion. These data provide evidence that IL PV neurons support strategic avoidance behavior by suppressing freezing.

High-Anxious People Generalize Costly Pain-Related Avoidance Behavior More to Novel Safe Contexts Compared to Low-Anxious People

Pain-related avoidance is adaptive when there is a bodily threat, but when it generalizes to safe movements/situations, it may become disabling. Both subclinical anxiety-a vulnerability marker for chronic pain-and chronic pain are associated with excessive fear generalization to safe stimuli/situations. Previous research focused mainly on passive fear correlates (psychophysiological arousal and self-reports) leaving avoidance behavior poorly understood. Therefore, we tested whether high-anxious individuals generalize their pain-related avoidance behavior more to novel, safe contexts than low-anxious people. In a robotic-arm-reaching task, both groups (low vs high trait anxiety) performed 1 of 3 movements to reach a target. In the threat context (black background), a painful stimulus could be partly/completely prevented by performing more effortful trajectories (longer and more force needed); in the safe context (white background), no pain occurred. Generalization of avoidance was tested in 2 novel contexts (light/dark gray backgrounds). We assessed pain expectancy, pain-related fear, startle eyeblink responses for all trajectories, and avoidance behavior (ie, maximal deviation from shortest trajectory). Results indicated that differential fear and expectancy selectively generalized to the novel context resembling the original threat context in both groups. Interestingly and in contrast with the verbal reports, high-anxious participants avoided more in the novel context resembling the original safe context, but not in the 1 resembling the threat context. No generalization emerged in the startle data. Because excessive pain-related avoidance specifically may cause withdrawal from daily life activities, these findings suggest that high-anxious individuals may be vulnerable to developing chronic pain disability. PERSPECTIVE: This paper shows that high-anxious people do not overgeneralize pain-related fear and pain expectancy learned in a threat context more to novel, safe contexts than low-anxious individuals, but that they do avoid more in those contexts. These findings suggest that high-anxious individuals may be vulnerable to developing chronic pain disability.

The spread of affective and semantic valence representations across states

In many decision problems, outcomes are not reached after a single action but rather after a series of events or states. To optimize decisions over multiple states, representations of how good or bad the outcomes are, that is, the outcomes' valence, should spread across states. One mechanism for valence spreading is a temporal, state-independent process in which a single valence representation is updated when an outcome is experienced and fades away afterwards. Each state's valence is based on its temporal proximity to the experienced outcome. An alternative, state-dependent mechanism relies on the structure of transitions between states, updating a separate valence representation for each state according to its spatial distance from the outcomes. We examined how these mechanistic accounts shape the spread of two formats of valence representation, feelings (affective valence) and knowledge (semantic valence), between states. In two pre-registered experiments (N = 585), we used a novel task in which participants move in a four-state maze, one of which contains an outcome. The participants provide self-reports of affective and semantic valence throughout the maze and after finishing it. Results show that the affective representation of negative valence is more localized in state-space than the semantic representation. We also found evidence for the relative reliance of the affective valence on a temporal, state-independent mechanism and of the semantic valence on a structured, state-dependent mechanism. Our findings provide mechanistic accounts for the differences between affective and semantic valence representations and indicate how such representations may play a role in associative learning and decision-making.

Functional correlates of a novel 8-factor model of PTSD in U.S. military veterans: Results from the National Health and Resilience in Veterans Study

Emerging evidence indicates that more nuanced models of posttraumatic stress disorder (PTSD) may better capture the condition's symptom structure. Recent theoretical and empirical work suggest that an 8-factor model of PTSD with separate internally- (e.g. flashbacks) and externally- (e.g. trauma-cue related physiological reactivity) generated intrusive symptom clusters may advance understanding of PTSD and its treatment and course. However, the model's functional and clinical significance still requires evaluation. To this end, we analyzed data from the National Health and Resilience in Veterans Study, a nationally representative sample of 3847 trauma-exposed U.S. military veterans. Multivariable regressions were performed to assess the relationship between the 8 PTSD symptom clusters, assessed using the PTSD Checklist for DSM-5, and clinical and functional measures. Results revealed that externally-generated intrusions were associated with higher odds of current depression and anxiety and worse mental, cognitive, and psychosocial functioning. Anhedonia (e.g., loss of interest in enjoyable activities) symptoms were associated with all the correlates tested, while negative affect (e.g., having strong negative feelings such as fear) symptoms were associated with all measures except depression. Avoidance symptoms were associated with lower odds of current anxiety while externalizing behavior symptoms were linked to higher odds of suicidal ideation. Anxious arousal symptoms were associated with lower odds of suicidal ideation but higher odds of PTSD-related impairment/distress, while dysphoric arousal symptoms were associated with higher odds of current depression, PTSD-related impairment/distress and worse mental and cognitive functioning. Results suggest that a more nuanced 8-factor model of PTSD symptoms may help inform understanding of the clinical and functional correlates of this multi-faceted disorder.

A history of avoidance does not impact extinction learning in male rats

Pervasive avoidance is one of the central symptoms of all anxiety-related disorders. In treatment, avoidance behaviors are typically discouraged because they are assumed to maintain anxiety. Yet, it is not clear if engaging in avoidance is always detrimental. In this study, we used a platform-mediated avoidance task to investigate the influence of avoidance history on extinction learning in male rats. Our results show that having the opportunity to avoid during fear acquisition training does not significantly influence the extinction of auditory-cued fear in rats subjected to this platform-mediated avoidance procedure, which constitutes a realistic approach/avoidance conflict. This holds true irrespective of whether or not avoidance was possible during the extinction phase. This suggests that imposing a realistic cost on avoidance behavior prevents the adverse effects that avoidance has been claimed to have on extinction. However, avoidance does not appear to have clear positive effects on extinction learning nor on retention either.

Devaluation of response-produced safety signals reveals circuits for goal-directed versus habitual avoidance in dorsal striatum

Active avoidance responses (ARs) are instrumental behaviors that prevent harm. Adaptive ARs may contribute to active coping, whereas maladaptive avoidance habits are implicated in anxiety and obsessive-compulsive disorders. The AR learning mechanism has remained elusive, as successful avoidance trials produce no obvious reinforcer. We used a novel outcome-devaluation procedure in rats to show that ARs are positively reinforced by response-produced feedback (FB) cues that develop into safety signals during training. Males were sensitive to FB-devaluation after moderate training, but not overtraining, consistent with a transition from goal-directed to habitual avoidance. Using chemogenetics and FB-devaluation, we also show that goal-directed vs. habitual ARs depend on dorsomedial vs. dorsolateral striatum, suggesting a significant overlap between the mechanisms of avoidance and rewarded instrumental behavior. Females were insensitive to FB-devaluation due to a remarkable context-dependence of counterconditioning. However, degrading the AR-FB contingency suggests that both sexes rely on safety signals to perform goal-directed ARs.

Generalization and discrimination of inhibitory avoidance differentially engage anterior and posterior retrosplenial subregions

Introduction

In a variety of behavioral procedures animals will show selective fear responding in shock-associated contexts, but not in other contexts. However, several factors can lead to generalized fear behavior, where responding is no longer constrained to the conditioning context and will transfer to novel contexts.

Methods

Here, we assessed memory generalization using an inhibitory avoidance paradigm to determine if generalized avoidance behavior engages the retrosplenial cortex (RSC). Male and female Long Evans rats received inhibitory avoidance training prior to testing in the same context or a shifted context in two distinct rooms; one room that had fluorescent lighting (Light) and one that had red LED lighting (Dark).

Results

We found that animals tested in a light context maintained context-specificity; animals tested in the same context as training showed longer latencies to cross and animals tested in the shifted context showed shorter latencies to cross. However, animals tested in the dark generalized their avoidance behavior; animals tested in the same context and animals tested in the shifted context showed similarly-high latencies to cross. We next examined expression of the immediate early gene zif268 and perineuronal nets (PNNs) following testing and found that while activity in the basolateral amygdala corresponded with overall levels of avoidance behaviors, anterior RSC (aRSC) activity corresponded with learned avoidance generally, but posterior RSC (pRSC) activity seemed to correspond with generalized memory. PNN reduction in the RSC was associated with memory formation and retrieval, suggesting a role for PNNs in synaptic plasticity. Further, PNNs did not reduce in the RSC in animals who showed a generalized avoidance behavior, in line with their hypothesized role in memory consolidation.

Discussion

These findings suggest that there is differential engagement of retrosplenial subregions along the rostrocaudal axis to generalization and discrimination.

Relation among, trait anxiety, intolerance to uncertainty and early maltreatment experiences on fear discrimination learning and avoidance generalization online task

BACKGROUND AND OBJECTIVES

Early aversive experiences, which have been associated with elevated anxiety and intolerance of uncertainty (IUS), may contribute negatively to fear conditioning learning. The aim of the present study was to analyze the relation among individual differences in childhood maltreatment experiences, trait anxiety, and IUS in adulthood; and to determine how these variables could affect fear learning discrimination and avoidance generalization.

METHODS

We adapted an avoidance procedure in an online fear learning task. Two pictures of different lamp colors (CS+) were first associated with two aversive images (US), while a third color was not (CS-). Next, clicking a button during one CS + could effectively avoid the US (CS + av), but not during the other (CS + unav). Finally, avoidance generalization was tested to lamp colors that were between CS- and CS + av (safety dimension) and CS + av and CS + unav (avoidability dimension). With a sample of 67 participants, we measured ratings of relief, expectancy, and anxiety, as well as button presses and individual differences (STAI, IUS and MAES).

RESULTS

Aversive early experiences were positively related to trait anxiety and intolerance of uncertainty. The results of the task further suggested that maltreatment experience contributes to be more attentive to aversive signals, which could be implicated in leading to difficulties in discrimination learning.

LIMITATIONS

Online experiments implies some loss of control over subjects and environment that can threaten internal validity. Likewise, the commitment of participants may be low.

CONCLUSIONS

Results suggest that early aversive experience and anxiety could contribute to the development of IUS, which likely contributes to the development of avoidance behavior.

The subiculum role on learning and memory tasks using rats and mice: A scoping review

This scoping review aimed to systematically identify and summarize data related to subiculum involvement in learning and memory behavioral tasks in rats and mice. Following a systematic strategy based on PICO and PRISMA guidelines, we searched five indexed databases (PubMed, Web of Science, EMBASE, Scopus, and PsycInfo) using a standardized search strategy to identify peer-reviewed articles published in English (pre-registration: osf.io/hm5ea). We identified 31 articles investigating the role of the subiculum in spatial, working, and recognition memories (n = 11), memories related to addiction models (n = 9), aversive memories (n = 7), and memories related to appetitive learning (n = 5). We highlight a dissociation in the dorsoventral axis of the subiculum with many studies exploring the ventral subiculum (n = 21) but only a few exploring the dorsal one (n = 10). We also observe the necessity of more data including mice, female animals, genetic tools, and better statistical approaches for replication purposes and research refinement. These findings provide a broad framework of the subiculum involvement in learning and memory, showing essential questions that can be explored by further studies.

Persistence of extensively trained avoidance is not elevated in anxiety disorders in an outcome devaluation paradigm

BACKGROUND

A habitual avoidance component may enforce the persistence of maladaptive avoidance behavior in anxiety disorders. Whether habitual avoidance is acquired more strongly in anxiety disorders is unclear.

METHODS

Individuals with current social anxiety disorder, panic disorder and/or agoraphobia (n = 62) and healthy individuals (n = 62) completed a devaluation paradigm with extensive avoidance training, followed by the devaluation of the aversive outcome. In the subsequent test phase, habitual response tendencies were inferred from compatibility effects. Neutral control trials were added to assess general approach learning in the absence of previous extensive avoidance training.

RESULTS

The compatibility effects indicating habitual control did not differ between patients with anxiety disorders and healthy controls. Patients showed lower overall approach accuracy, but this effect was unrelated to the compatibility effects.

CONCLUSIONS

In this study, anxiety disorders were characterized by reduced approach but not stronger habitual avoidance. These results do not indicate a direct association between anxiety disorders and the acquisition of pervasive habitual avoidance in this devaluation paradigm.

Controlling intrusive thoughts of future fears under stress

Negative outlooks of our future may foster unwanted and intrusive thoughts. To some extent, individuals have control over their ability to suppress intrusions and downregulate their frequency. Acute stress impairs intentional suppression, leading to an increased frequency of intrusions. The aim of this study was to gain insight into the mechanism underlying stress-induced impairments in intentional suppression of intrusions by investigating the combined and independent roles of the two major stress hormones, noradrenaline and cortisol. Healthy participants (N = 181) were administered propranolol (to block the noradrenergic response), metyrapone (to block the cortisol response), or a placebo before being exposed to the Maastricht Acute Stress Test. Intrusive thoughts of autobiographical future fears were then measured via the Imagine/No-Imagine task. Results demonstrated that the stress response was successfully altered because of the drug and stress manipulations. In all groups, repeated suppression of future fears reduced intrusions. Across the sample, an enhanced decrease over time was associated with greater attenuation of anxiety towards the related fears. The groups did not differ in the total frequency of intrusions. Though, trait anxiety increased the total number of intrusions. Our findings show that stress hormones did not influence the ability to suppress intrusions. However, our results do add support to previous research linking anxiety to memory control deficits. When using autobiographical content, future research should focus on the quality and characteristics of the individual memories to explain more of the variation observed in intentional memory control.

The effect of SSRIs on fear learning: a systematic review and meta-analysis

RATIONALE

Selective serotonin reuptake inhibitors (SSRIs) are considered first-line medication for anxiety-like disorders such as panic disorder, generalized anxiety disorder, and post-traumatic stress disorder. Fear learning plays an important role in the development and treatment of these disorders. Yet, the effect of SSRIs on fear learning are not well known.

OBJECTIVE

We aimed to systematically review the effect of six clinically effective SSRIs on acquisition, expression, and extinction of cued and contextual conditioned fear.

METHODS

We searched the Medline and Embase databases, which yielded 128 articles that met the inclusion criteria and reported on 9 human and 275 animal experiments.

RESULTS

Meta-analysis showed that SSRIs significantly reduced contextual fear expression and facilitated extinction learning to cue. Bayesian-regularized meta-regression further suggested that chronic treatment exerts a stronger anxiolytic effect on cued fear expression than acute treatment. Type of SSRI, species, disease-induction model, and type of anxiety test used did not seem to moderate the effect of SSRIs. The number of studies was relatively small, the level of heterogeneity was high, and publication bias has likely occurred which may have resulted in an overestimation of the overall effect sizes.

CONCLUSIONS

This review suggests that the efficacy of SSRIs may be related to their effects on contextual fear expression and extinction to cue, rather than fear acquisition. However, these effects of SSRIs may be due to a more general inhibition of fear-related emotions. Therefore, additional meta-analyses on the effects of SSRIs on unconditioned fear responses may provide further insight into the actions of SSRIs.

Associative learning in the box jellyfish Tripedalia cystophora

Associative learning, such as classical or operant conditioning, has never been unequivocally associated with animals outside bilatarians, e.g., vertebrates, arthropods, or mollusks. Learning modulates behavior and is imperative for survival in the vast majority of animals. Obstacle avoidance is one of several visually guided behaviors in the box jellyfish, Tripedalia cystophora Conant, 1897 (Cnidaria: Cubozoa), and it is intimately associated with foraging between prop roots in their mangrove habitat. The obstacle avoidance behavior (OAB) is a species-specific defense reaction (SSDR) for T. cystophora, so identifying such SSDR is essential for testing the learning capacity of a given animal. Using the OAB, we show that box jellyfish performed associative learning (operant conditioning). We found that the rhopalial nervous system is the learning center and that T. cystophora combines visual and mechanical stimuli during operant conditioning. Since T. cystophora has a dispersed central nervous system lacking a conventional centralized brain, our work challenges the notion that associative learning requires complex neuronal circuitry. Moreover, since Cnidaria is the sister group to Bilateria, it suggests the intriguing possibility that advanced neuronal processes, like operant conditioning, are a fundamental property of all nervous systems.

Understanding anxiety symptoms as aberrant defensive responding along the threat imminence continuum

Threat-anticipatory defensive responses have evolved to promote survival in a dynamic world. While inherently adaptive, aberrant expression of defensive responses to potential threat could manifest as pathological anxiety, which is prevalent, impairing, and associated with adverse outcomes. Extensive translational neuroscience research indicates that normative defensive responses are organized by threat imminence, such that distinct response patterns are observed in each phase of threat encounter and orchestrated by partially conserved neural circuitry. Anxiety symptoms, such as excessive and pervasive worry, physiological arousal, and avoidance behavior, may reflect aberrant expression of otherwise normative defensive responses, and therefore follow the same imminence-based organization. Here, empirical evidence linking aberrant expression of specific, imminence-dependent defensive responding to distinct anxiety symptoms is reviewed, and plausible contributing neural circuitry is highlighted. Drawing from translational and clinical research, the proposed framework informs our understanding of pathological anxiety by grounding anxiety symptoms in conserved psychobiological mechanisms. Potential implications for research and treatment are discussed.

Can you learn to starve yourself? Inducing food avoidance in the laboratory

The restriction of energy intake is a central and persistent symptom of anorexia nervosa. Recent models of the disorder suggest that food restrictions are learned avoidance behaviours, which are acquired and maintained by classical and operant conditioning. The present study aims to test this learning model of food restriction. It investigates whether introducing negative consequences for the intake of tasty high-calorie food and introducing positive consequences for its avoidance can create food avoidance, increase fear of food, and decrease eating desires in healthy individuals. 104 women were randomly assigned to an experimental or control condition and completed an appetitive conditioning and avoidance learning task. While the experimental condition received money after avoiding the tasty high-calorie food item and heard an aversive sound after not avoiding food intake, the control condition never received these consequences. In the extinction phase, reward and punishment discontinued for both conditions. We measured avoidance frequency, mouse movements, fear, eating desires and stimulus liking. Participants in the experimental condition avoided the food more often than controls and showed increased fear, reduced eating desires and less liking for cues associated with food intake. These results support the notion that food avoidance behaviours, reduced eating desires and fear of food can be learned via classical and operant conditioning. Conditioning paradigms might be a useful tool to study the development and maintenance of food restriction in anorexia nervosa.

Incidental temporal binding in rats: A novel behavioral task

We designed a behavioral task called One-Trial Trace Escape Reaction (OTTER), in which rats incidentally associate two temporally discontinuous stimuli: a neutral acoustic cue (CS) with an aversive stimulus (US) which occurs two seconds later (CS-2s-US sequence). Rats are first habituated to two similar environmental contexts (A and B), each consisting of an interconnected dark and light chamber. Next, rats experience the CS-2s-US sequence in the dark chamber of one of the contexts (either A or B); the US is terminated immediately after a rat escapes into the light chamber. The CS-2s-US sequence is presented only once to ensure the incidental acquisition of the association. The recall is tested 24 h later when rats are presented with only the CS in the alternate context (B or A), and their behavioral response is observed. Our results show that 59% of the rats responded to the CS by escaping to the light chamber, although they experienced only one CS-2s-US pairing. The OTTER task offers a flexible high throughput tool to study memory acquired incidentally after a single experience. Incidental one-trial acquisition of association between temporally discontinuous events may be one of the essential components of episodic memory formation.

Anxiety as a disorder of uncertainty: implications for understanding maladaptive anxiety, anxious avoidance, and exposure therapy

In cognitive-behavioral conceptualizations of anxiety, exaggerated threat expectancies underlie maladaptive anxiety. This view has led to successful treatments, notably exposure therapy, but is not consistent with the empirical literature on learning and choice alterations in anxiety. Empirically, anxiety is better described as a disorder of uncertainty learning. How disruptions in uncertainty lead to impairing avoidance and are treated with exposure-based methods, however, is unclear. Here, we integrate concepts from neurocomputational learning models with clinical literature on exposure therapy to propose a new framework for understanding maladaptive uncertainty functioning in anxiety. Specifically, we propose that anxiety disorders are fundamentally disorders of uncertainty learning and that successful treatments, particularly exposure therapy, work by remediating maladaptive avoidance from dysfunctional explore/exploit decisions in uncertain, potentially aversive situations. This framework reconciles several inconsistencies in the literature and provides a path forward to better understand and treat anxiety.

Changes in brain rhythms and connectivity tracking fear acquisition and reversal

Fear conditioning is used to investigate the neural bases of threat and anxiety, and to understand their flexible modifications when the environment changes. This study aims to examine the temporal evolution of brain rhythms using electroencephalographic signals recorded in healthy volunteers during a protocol of Pavlovian fear conditioning and reversal. Power changes and Granger connectivity in theta, alpha, and gamma bands are investigated from neuroelectrical activity reconstructed on the cortex. Results show a significant increase in theta power in the left (contralateral to electrical shock) portion of the midcingulate cortex during fear acquisition, and a significant decrease in alpha power in a broad network over the left posterior-frontal and parietal cortex. These changes occur since the initial trials for theta power, but require more trials (3/4) to develop for alpha, and are also present during reversal, despite being less pronounced. In both bands, relevant changes in connectivity are mainly evident in the last block of reversal, just when power differences attenuate. No significant changes in the gamma band were detected. We conclude that the increased theta rhythm in the cingulate cortex subserves fear acquisition and is transmitted to other cortical regions via increased functional connectivity allowing a fast theta synchronization, whereas the decrease in alpha power can represent a partial activation of motor and somatosensory areas contralateral to the shock side in the presence of a dangerous stimulus. In addition, connectivity changes at the end of reversal may reflect long-term alterations in synapses necessary to reverse the previously acquired contingencies.

Inhibitory Learning during Exposure Treatment in Anorexia Nervosa: A Practical Guide

Exposure therapy is known to be an effective intervention in the treatment of anxiety-related disorders. In eating disorders, such as anorexia nervosa, anxiety and avoidance are identified as maintenance factors. Therefore, they may constitute an important treatment target, suitable for the use of exposure therapy. Remarkably, exposure techniques to target fears and avoidance behaviors are not commonly used in the treatment of anorexia nervosa. We present a practical guide for the implementation of exposure therapy in the treatment of anorexia nervosa. We outline how exposure therapy is supposed to work according to the inhibitory learning model and how the exposure intervention can be designed for individuals with anorexia nervosa. Practical examples are provided through the case presentation of a patient with anorexia nervosa who completed 31 exposure sessions that focused on her fears of food, eating, weight, weight gain, their feared social consequences and the associated safety behaviors.

The effect of experimentally induced positive affect on the generalization of pain-related avoidance and relief

Avoiding pain-associated activities can prevent tissue damage. However, when avoidance spreads excessively (or overgeneralizes) to safe activities, it may culminate into chronic pain disability. Gaining insight into ways to reduce overgeneralization is therefore crucial. An important factor to consider in this is relief, as it reinforces avoidance behavior and therefore may be pivotal in making avoidance persist. The current study investigated whether experimentally induced positive affect can reduce generalization of pain-related avoidance and relief. We used a conditioning task in which participants (N = 50) learned that certain stimuli were followed by pain, while another was not. Subsequently, they learned an avoidance response that effectively omitted pain with one stimulus, but was ineffective with another. Next, one group of participants performed an exercise to induce positive affect, while another group performed a control exercise. During the critical generalization test, novel stimuli that were perceptually similar to the original stimuli were presented. Results showed that both avoidance and relief generalized to novel stimuli, thus replicating previous work. However, increasing positive affect did not reduce generalization of avoidance, nor relief.

A dynamical model of C. elegans thermal preference reveals independent excitatory and inhibitory learning pathways

Caenorhabditis elegans is capable of learning and remembering behaviorally relevant cues such as smells, tastes, and temperature. This is an example of associative learning, a process in which behavior is modified by making associations between various stimuli. Since the mathematical theory of conditioning does not account for some of its salient aspects, such as spontaneous recovery of extinguished associations, accurate modeling of behavior of real animals during conditioning has turned out difficult. Here, we do this in the context of the dynamics of the thermal preference of C. elegans. We quantify C. elegans thermotaxis in response to various conditioning temperatures, starvation durations, and genetic perturbations using a high-resolution microfluidic droplet assay. We model these data comprehensively, within a biologically interpretable, multi-modal framework. We find that the strength of the thermal preference is composed of two independent, genetically separable contributions and requires a model with at least four dynamical variables. One pathway positively associates the experienced temperature independently of food and the other negatively associates with the temperature when food is absent. The multidimensional structure of the association strength provides an explanation for the apparent classical temperature-food association of C. elegans thermal preference and a number of longstanding questions in animal learning, including spontaneous recovery, asymmetric response to appetitive vs. aversive cues, latent inhibition, and generalization among similar cues.

Dietary Protection against Cognitive Impairment, Neuroinflammation and Oxidative Stress in Alzheimer's Disease Animal Models of Lipopolysaccharide-Induced Inflammation

Alzheimer's disease (AD) is a rapidly growing epidemic with a heavy social and economic burden. Evidence suggests that systemic inflammation, dysregulation of the immune response and the resulting neuroinflammation and neurodegeneration play a significant role in AD pathogenesis. Currently, given that there is no fully convincing cure for AD, the interest in lifestyle factors (such as diet), which potentially delay onset and reduce the severity of symptoms, is increasing. This review is aimed at summarizing the effects of dietary supplementation on cognitive decline, neuroinflammation and oxidative stress in AD-like animal models with a focus on neuroinflammation induced by lipopolysaccharide (LPS) injection, which mimics systemic inflammation in animals. The compounds reviewed include curcumin, krill oil, chicoric acid, plasmalogens, lycopene, tryptophan-related dipeptides, hesperetin and selenium peptides. Despite the heterogeneity of these compounds, there is a strong consensus on their counteracting action on LPS-induced cognitive deficits and neuroinflammatory responses in rodents by modulating cell-signaling processes, such as the NF-κB pathway. Overall, dietary interventions could represent an important resource to oppose AD due to their influence in neuroprotection and immune regulation.

Impaired action-safety learning and excessive relief during avoidance in patients with anxiety disorders

Anxiety-related disorders are characterized by high levels of avoidance, but experimental research into avoidance learning in patients is scarce. To fill this gap, we compared healthy controls (HC, n = 47) with patients with obsessive-compulsive disorder (OCD, n = 33), panic disorder with agoraphobia (PDA, n = 40), and post-traumatic stress disorder (PTSD, n = 66) in a computer-based avoidance learning task, in order to examine (1) differences in rates of avoidance responses, (2) differences in action-safety learning during avoidance, and (3) differences in subjective relief following successful avoidance. The task comprised aversive negative pictures (unconditional stimulus, US) that followed pictures of two colored lamps (conditional stimuli, CS+), but not a third colored lamp (safety stimulus, CS-), and could be avoided by pressing a button during one CS+ (CS+ avoidable) but not the other (CS+ unavoidable). Participants rated their US-expectancy and level of relief on a trial-by-trial basis. Compared to the HC group, patient groups displayed higher levels of avoidance to the safety stimulus, and higher levels of US-expectancy and relief following the safety and avoidable danger stimulus. We propose that patients with anxiety disorders have low confidence in the safety consequences of avoidance actions, which induces increased relief during US omissions that reinforce the avoidance action.

Fear avoidance and return to work after mild traumatic brain injury

OBJECTIVES

Fear avoidance is associated with symptom persistence after mild traumatic brain injury (mTBI). In this study, we investigated whether fear avoidance was associated with other outcomes such as return to work-related activity (RTW).

MATERIALS AND METHODS

We analyzed associations between fear avoidance and RTW 6-9 months after mTBI, in two merged prospective mTBI cohorts. Adult participants aged 16 or over (n=175), presenting to outpatient services in New Zealand within 3 months of their injury, who were engaged in work-related activity at the time of injury, were included. Participants completed the Fear Avoidance Behavior after Traumatic Brain Injury (FAB-TBI) questionnaire at enrollment and 6 months later. Associations between FAB-TBI scores and RTW outcome were analyzed using multivariate approaches.

RESULTS

Overall, 53% of participants had RTW by 6-9 months after mTBI. While early fear avoidance was weakly associated with RTW, persistent high fear avoidance between study assessments or increasing avoidance with time were associated with greater odds of still being off work 6-9 months after injury.

CONCLUSIONS

Pervasive and increasing avoidance of symptom triggers after mTBI were associated with lower rates of RTW 6-9 months after mTBI. Further research is needed to better understand transition points along the recovery trajectory where fear avoidance behaviors fade or increase after mTBI.

Understanding clinical fear and anxiety through the lens of human fear conditioning

Fear is an adaptive emotion that mobilizes defensive resources upon confrontation with danger. However, fear becomes maladaptive and can give rise to the development of clinical anxiety when it exceeds the degree of threat, generalizes broadly across stimuli and contexts, persists after the danger is gone or promotes excessive avoidance behaviour. Pavlovian fear conditioning has been the prime research instrument that has led to substantial progress in understanding the multi-faceted psychological and neurobiological mechanisms of fear in past decades. In this Perspective, we suggest that fruitful use of Pavlovian fear conditioning as a laboratory model of clinical anxiety requires moving beyond the study of fear acquisition to associated fear conditioning phenomena: fear extinction, generalization of conditioned fear and fearful avoidance. Understanding individual differences in each of these phenomena, not only in isolation but also in how they interact, will further strengthen the external validity of the fear conditioning model as a tool with which to study maladaptive fear as it manifests in clinical anxiety.

Gender Impacts the Relationship between Mood Disorder Symptoms and Effortful Avoidance Performance

We must often decide how much effort to exert or withhold to avoid undesirable outcomes or obtain rewards. In depression and anxiety, levels of avoidance can be excessive and reward-seeking may be reduced. Yet outstanding questions remain about the links between motivated action/inhibition and anxiety and depression levels, and whether they differ between men and women. Here, we examined the relationship between anxiety and depression scores, and performance on effortful active and inhibitory avoidance (Study 1) and reward seeking (Study 2) in humans. Undergraduates and paid online workers ([Formula: see text] = 545, [Formula: see text] = 310; [Formula: see text] = 368, [Formula: see text] = 450, [Formula: see text] = 22.58, [Formula: see text] = 17-62) were assessed on the Beck Depression Inventory II (BDI) and the Beck Anxiety Inventory (BAI) and performed an instructed online avoidance or reward-seeking task. Participants had to make multiple presses on active trials and withhold presses on inhibitory trials to avoid an unpleasant sound (Study 1) or obtain points toward a monetary reward (Study 2). Overall, men deployed more effort than women in both avoidance and reward-seeking, and anxiety scores were negatively associated with active reward-seeking performance based on sensitivity scores. Gender interacted with anxiety scores and inhibitory avoidance performance, such that women with higher anxiety showed worse avoidance performance. Our results illuminate effects of gender in the relationship between anxiety and depression levels and the motivation to actively and effortfully respond to obtain positive and avoid negative outcomes.

Food Restriction in Anorexia Nervosa in the Light of Modern Learning Theory: A Narrative Review

Improvements in the clinical management of anorexia nervosa (AN) are urgently needed. To do so, the search for innovative approaches continues at laboratory and clinical levels to translate new findings into more effective treatments. In this sense, modern learning theory provides a unifying framework that connects concepts, methodologies and data from preclinical and clinical research to inspire novel interventions in the field of psychopathology in general, and of disordered eating in particular. Indeed, learning is thought to be a crucial factor in the development/regulation of normal and pathological eating behaviour. Thus, the present review not only tries to provide a comprehensive overview of modern learning research in the field of AN, but also follows a transdiagnostic perspective to offer testable explanations for the origin and maintenance of pathological food rejection. This narrative review was informed by a systematic search of research papers in the electronic databases PsycInfo, Scopus and Web of Science following PRISMA methodology. By considering the number and type of associations (Pavlovian, goal-directed or habitual) and the affective nature of conditioning processes (appetitive versus aversive), this approach can explain many features of AN, including why some patients restrict food intake to the point of life-threatening starvation and others restrict calorie intake to lose weight and binge on a regular basis. Nonetheless, it is striking how little impact modern learning theory has had on the current AN research agenda and practice.

Avoidance Behavior in Patients with Chronic Dizziness: A Prospective Observational Study

Avoidance behavior in adults with chronic dizziness is common. Here, we analyzed factors that are associated with avoidance behavior in a sample of adults with chronic dizziness and/or vertigo. Therefore, 595 patients with chronic vertigo and dizziness who had been subjected to our 5-day multimodal treatment program in a tertiary care outpatient clinic for vertigo and dizziness were prospectively investigated. Both general and dizziness/vertigo-specific data were collected at baseline (n = 595) and at 6-month follow-up (n = 262). Avoidance behavior was measured using the Mobility Inventory for Agoraphobia (MI). The Hospital Anxiety and Depression Scale was used to estimate anxiety (HADS-A) and depression (HADS-D). At baseline, higher MI (higher level of avoidance) was associated with female gender, higher HADS-D, higher HADS-A, and of a higher age. HADS-D provoked the strongest effect on public places, while gender had the strongest effect on open spaces. The majority (79%) reported improvement of MI and 21% reported that MI had worsened or remained stable at follow-up. In the Generalized Estimating Equations, female gender, higher HADS-A, higher HADS-D, and of a higher age predicted higher MI at follow-up. In particular, older female persons with depressive and anxiety symptoms have a high risk for avoidance behavior related to dizziness.

No joy - why bother? Higher anhedonia relates to reduced pleasure from and motivation for threat avoidance

Anhedonia impairs various components of the pleasure cycle, including wanting, liking, and the learning of pleasure-related associations. While successfully controlling threats might be inherently pleasurable, it remains unclear whether anhedonia affects this form of pleasure as well. With aversive pictures as threats, we conducted an online study ( N = 200) to investigate the role of anhedonia during active avoidance learning process. Participants first learned cue-threat associations for different cues (threat vs. safety cues). In a subsequent avoidance learning phase, these cues signaled either avoidable, unavoidable, or no threat; participants could perform avoidance responses to prevent the upcoming threats during those cue presentations. Subjective relief pleasantness was measured after each threat omission. We found that higher trait anticipatory and consummatory anhedonia were both associated with lower relief pleasantness. Higher trait anticipatory anhedonia was also associated with fewer avoidance attempts. Since reduced threat-controlling behavior is reminiscent of a learned-helplessness state, the current results contribute to a better understanding of the connections between anhedonia and learned helplessness that have mostly been studied separately in the context of mood disturbance.

Mechanisms of Action in Exposure Therapy

PURPOSE OF REVIEW

Exposure therapy is an effective treatment for anxiety-related disorders, but many individuals do not achieve full symptom relief, and return of fear is a common occurrence. Understanding how exposure therapy works enables further development of strategies to improve its effectiveness.

RECENT FINDINGS

Recent studies have examined mechanisms of exposure-based interventions across multiple levels of analysis, from cognitive and behavioral changes that occur during treatment to the neurobiological mechanisms underlying fear extinction. Belief change and reductions in safety behaviors and avoidance mediate symptom improvements during exposure therapy, suggesting plausible cognitive and behavioral mechanisms. On the neural level, increased activation of prefrontal regions during extinction learning is a likely mechanism of exposure. Improved understanding of the biological mechanisms of exposure have led to exciting developments in clinical research, including pharmacological augmentation, though clinical translation of basic research has produced mixed results. Though still in development, such translational research is a promising future direction for exposure-based interventions.

An experimental test of the effects of acute sleep deprivation on affect and avoidance

BACKGROUND AND OBJECTIVES

Avoidance and sleep have been identified as mechanisms involved in the development and maintenance of many mental health disorders. However, there has been little research into the relation between sleep and avoidance.

METHODS

To address this, a randomized controlled experiment using behavioral and self-report measures of affect and avoidance was conducted. Compared to a control group, we hypothesized that sleep-deprived individuals would demonstrate increased negative, and decreased positive, affectivity, more avoidance behavior toward a negatively valenced stimulus, as well as increased self-reported avoidance. Fifty-two healthy individuals ages 18-30 years old were randomly assigned to a full night of sleep deprivation or normal sleep. They completed a baseline and post-manipulation behavioral avoidance task (BAT) using a disgusting stimulus and self-reports of avoidance and state affect.

RESULTS

Repeated measures ANOVAs demonstrated negative affectivity and self-reported avoidance increased, and positive affectivity decreased, from pre-to post-manipulation in the sleep loss condition as expected. However, there were no effects of sleep deprivation on avoidance behaviors.

LIMITATIONS

This study emphasized internal validity over generalizability. Additionally, the at-home sleep deprivation limited researcher control over the overnight activities of participants.

CONCLUSIONS

Results replicate prior work on the affective consequences of sleep deprivation and highlight a discrepancy between the effect of sleep deprivation on behavioral avoidance toward a specific stimulus compared to self-reported cognitive and social avoidance behaviors.

The ABC of academic procrastination: Functional analysis of a detrimental habit

Academic procrastination – habitually delaying work with academic tasks to the extent that the delays become detrimental to performance, wellbeing, and health – represents a substantial personal, systemic, and societal problem. Still, efforts to prevent and reduce it are surprisingly scarce and often offered as treatment regimens rather than preventive efforts. Based on the principles of functional analysis and a broad examination of factors that are important for academic procrastinatory behaviors, this paper aims to describe a strategy for analyzing individual controlling conditions for procrastination and give parallel advice on how to change those controlling conditions. Both are ideographic, allowing for individual and dynamic analyses of factors responsible for instigating and maintaining procrastination, as well as tailor-made remedies that address controlling conditions in preventive and curative efforts to reduce procrastination. Although functional analysis integrates well with important research findings in the procrastination field, this approach suggests new criteria for identifying procrastinatory behaviors and an alternative model for analyzing their control conditions. We conclude that a functional approach may supplement procrastination research and efforts to prevent and alleviate this detrimental habit.

Trauma-Informed Design of Supported Housing: A Scoping Review through the Lens of Neuroscience

There is growing recognition of the importance of the design of the built environment in supporting mental health. In this context, trauma-informed design has emerged as a new field of practice targeting the design of the built environment to support wellbeing and ameliorate the physical, psychological and emotional impacts of trauma and related pathologies such as Post Traumatic Stress Disorder (PTSD). With high levels of prevalence of PTSD among people escaping homelessness and domestic violence, a priority area is the identification and application of evidence-based design solutions for trauma-informed supported housing. This study sought to examine the scope of existing evidence on the relationship between trauma, housing and design and the correlation of this evidence with trauma-informed design principles, and to identify gaps and opportunities for future research. In response to the commonly articulated limitations of the evidence-base in built environment design research, we combined a scoping review of literature on trauma, housing and design with insights from neuroscience to focus and extend understanding of the opportunities of trauma-informed design. We found that while limited in scope, there is strong alignment between existing evidence and the principles of trauma-informed design. We also identify three areas of future research related to the key domains of safety and security; control; and enriched environments.

Spontaneous instrumental avoidance learning in social contexts

Adaptation to our social environment requires learning how to avoid potentially harmful situations, such as encounters with aggressive individuals. Threatening facial expressions can evoke automatic stimulus-driven reactions, but whether their aversive motivational value suffices to drive instrumental active avoidance remains unclear. When asked to freely choose between different action alternatives, participants spontaneously-without instruction or monetary reward-developed a preference for choices that maximized the probability of avoiding angry individuals (sitting away from them in a waiting room). Most participants showed clear behavioral signs of instrumental learning, even in the absence of an explicit avoidance strategy. Inter-individual variability in learning depended on participants' subjective evaluations and sensitivity to threat approach feedback. Counterfactual learning best accounted for avoidance behaviors, especially in participants who developed an explicit avoidance strategy. Our results demonstrate that implicit defensive behaviors in social contexts are likely the product of several learning processes, including instrumental learning.

Pavlovian threat learning shapes the kinematics of action

Prompt response to environmental threats is critical to survival. Previous research has revealed mechanisms underlying threat-conditioned physiological responses, but little is known about how threats shape action. Here we tested if threat learning shapes the kinematics of reaching in human adults. In two different experiments conducted on independent samples of participants, after Pavlovian threat learning, in which a stimulus anticipated the delivery of an aversive shock, whereas another did not, the peak velocity and acceleration of reaching increased for the shocked-paired stimulus, relative to the unpaired one. These kinematic changes appeared as a direct consequence of learning, emerging even in absence of an actual threat to body integrity, as no shock occurred during reaching. Additionally, they correlated with the strength of sympathetic response during threat learning, establishing a direct relationship between previous learning and subsequent changes in action. The increase in velocity and acceleration of action following threat learning may be adaptive to facilitate the implementation of defensive responses. Enhanced action invigoration may be maladaptive, however, when defensive responses are inappropriately enacted in safe contexts, as exemplified in a number of anxiety-related disorders.

The effects of stress on avoidance in rodents: An unresolved matter

In the face of a possible threat, a range of physiological (e.g., increased heart rate) and behavioral (e.g., avoidance or escape) responses are recruited. Here, we will focus on avoidance, in its persistent form one of the core symptoms of anxiety disorders and obsessive-compulsive disorder. The initial goal of fear and avoidance responses is to increase survival, but if they become persistent or overgeneralize, they can disrupt normal daily functioning, and ultimately even result in anxiety-related disorders. Relatedly, acute stress responses promote adaptation and survival, while chronic stress has been found to aggravate pathophysiology. Thus, stress might trigger the transition from adaptive to maladaptive responses, e.g., from goal-directed to persistent avoidance. Animal models are prime tools to unravel if and how stress influences avoidance. This is typically done by performing stress inductions prior to the assessment of (passive or active) avoidance behavior. Despite its clinical relevance, the current literature on this topic is fragmented, and an overall conclusion is lacking. In this Review, we first recapitulate the state of the art regarding stress and active as well as passive avoidance procedures. We then summarize the behavioral effects of acute and chronic stress on active and passive avoidance, and discuss the main neurobiological findings of the field. Finally, we highlight possible reasons for the largely contradictory findings in the literature and we propose strategies to further unravel the effect of stress on avoidance behavior. A deeper understanding of this currently unresolved matter may provide further insights in the etiology and treatment of anxiety-related disorders.

The elegant complexity of fear in non-human animals

Activation of the fear system is adaptive, and protects individuals from impending harm; yet, exacerbation of the fear system is at the source of anxiety-related disorders. Here, we briefly review the 'why' and 'how' of fear, with an emphasis on models that encapsulate the elegant complexity of rodents' behavioral responding in the face of impending harm, and its relevance to developing treatment interventions.

Gains and Losses Affect Learning Differentially at Low and High Attentional Load

Prospective gains and losses influence cognitive processing, but it is unresolved how they modulate flexible learning in changing environments. The prospect of gains might enhance flexible learning through prioritized processing of reward-predicting stimuli, but it is unclear how far this learning benefit extends when task demands increase. Similarly, experiencing losses might facilitate learning when they trigger attentional reorienting away from loss-inducing stimuli, but losses may also impair learning by increasing motivational costs or when negative outcomes are overgeneralized. To clarify these divergent views, we tested how varying magnitudes of gains and losses affect the flexible learning of feature values in environments that varied attentional load by increasing the number of interfering object features. With this task design, we found that larger prospective gains improved learning efficacy and learning speed, but only when attentional load was low. In contrast, expecting losses impaired learning efficacy, and this impairment was larger at higher attentional load. These findings functionally dissociate the contributions of gains and losses on flexible learning, suggesting they operate via separate control mechanisms. One mechanism is triggered by experiencing loss and reduces the ability to reduce distractor interference, impairs assigning credit to specific loss-inducing features, and decreases efficient exploration during learning. The second mechanism is triggered by experiencing gains, which enhances prioritizing reward-predicting stimulus features as long as the interference of distracting features is limited. Taken together, these results support a rational theory of cognitive control during learning, suggesting that experiencing losses and experiencing distractor interference impose costs for learning.

Associations Between Repetitive Negative Thinking and Habituation of Defensive Responding Within and Between Sessions

Repetitive negative thinking (RNT) is a transdiagnostic risk factor for internalizing psychopathology, and theoretical models suggest that RNT may maintain symptoms by interfering with psychophysiological habituation. The present study therefore examined associations between RNT and habituation within and between study sessions. Community members (N=86) completed a habituation task involving exposure to acoustic probes at up to five sessions spaced 7 days apart on average. Eyeblink startle response was measured using the electromyography startle magnitude. Self-reported anxiety was assessed before and after the habituation task at each session. Multilevel growth curve modeling indicated that RNT was associated with a higher "floor" (i.e., asymptote) of startle responding as evidenced by reduced within-session startle habituation at later sessions. Results suggest that RNT may disrupt startle habituation and are consistent with theoretical models proposing that RNT sustains physiological activation to support avoidance of negative emotional contrasts or perceived future threats.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42761-022-00121-w.