Threat intensity widens fear generalization gradients

Suffering more in imagination than in reality? Mental imagery and fear generalization

Mental imagery may represent a weaker form of perception and, thus, mental images may be more ambiguous than visual percepts. If correct, the acquisition of fear would be less specific for imagined fears in comparison to perceptual fears, perhaps facilitating broader fear generalization. To test this idea, a two-day differential fear conditioning experiment (N = 98) was conducted. On day one, two groups of participants underwent differential fear conditioning such that a specific Gabor patch orientation (CS+) was paired with mild shocks (US) while a second Gabor patch of orthogonal orientation (CS-) was never paired with shock. Critically, one group imagined the Gabor patches and the other group was visually presented the Gabor patches. Next, both groups were presented visual Gabor patches of similar orientations (GCS) to the CS+. On day two, to assess the persistence of imagined fear, participants returned to the lab and were tested on the GCS devoid of shock. For day one, in contrast to our primary hypothesis, both self-report and skin conductance response measures did not show a significant interaction between the GCS and groups. On day two, both measures demonstrated a persistence of imagined fear, without US delivery. Taken together, rather than demonstrating an overgeneralization effect, the results from this study suggest that imagery-based fear conditioning generalizes to a similar extent as perceptually acquired fear conditioning. Further, the persistence of imagery-based fear may have unique extinction qualities in comparison to perceptual-based fear.

Medial anterior prefrontal cortex stimulation downregulates implicit reactions to threats and prevents the return of fear

Downregulating emotional overreactions toward threats is fundamental for developing treatments for anxiety and post-traumatic disorders. The prefrontal cortex (PFC) is critical for top-down modulatory processes, and despite previous studies adopting repetitive transcranial magnetic stimulation (rTMS) over this region provided encouraging results in enhancing extinction, no studies have hitherto explored the effects of stimulating the medial anterior PFC (aPFC, encompassing the Brodmann area 10) on threat memory and generalization. Here we showed that rTMS over the aPFC applied before threat memory retrieval immediately decreases implicit reactions to learned and novel stimuli in humans. These effects enduringly persisted 1 week later in the absence of rTMS. No effects were detected on explicit recognition. Critically, rTMS over the aPFC resulted in a more pronounced reduction of defensive responses compared to rTMS targeting the dorsolateral PFC. These findings reveal a previously unexplored prefrontal region, the modulation of which can efficiently and durably inhibit implicit reactions to learned threats. This represents a significant advancement toward the long-term deactivation of exaggerated responses to threats.

Dissociable contributions of the amygdala and ventral hippocampus to stress-induced changes in defensive behavior

BACKGROUND

Severe stress can produce multiple persistent changes in defensive behavior relevant to psychiatric illness. While much is known about the circuits supporting stress-induced associative fear, how stress-induced circuit plasticity supports non-associative changes in defensive behavior remains unclear.

METHODS

Mice were exposed to an acute severe stressor, and subsequently, both associative and non-associative defensive behavioral responses were assessed. A mixture of local protein synthesis inhibition, pan-neuronal chemogenetic inhibition, and projection-specific chemogenetic inhibition were utilized to isolate the roles of the basolateral amygdala (BLA) and ventral hippocampus (vHC) to the induction and expression of associative and non-associative defensive behavioral changes.

RESULTS

Stress-induced protein synthesis in the BLA was necessary for enhancements in stress sensitivity but not enhancements in anxiety-related behaviors, whereas protein synthesis in the vHC was necessary for enhancements in anxiety-related behavior but not enhancements in stress sensitivity. Like protein synthesis, neuronal activity of the BLA and vHC were found to differentially support the expression of these same defensive behaviors. Additionally, projection-specific inhibition of BLA-vHC connections failed to alter these behaviors, indicating that these defensive behaviors are regulated by distinct BLA and vHC circuits. Lastly, contributions of the BLA and vHC to stress sensitivity and anxiety-related behavior were independent of their contributions to associative fear.

CONCLUSIONS

Stress-induced plasticity in the BLA and vHC were found to support dissociable non-associative behavioral changes, with BLA supporting enhancements in stress sensitivity and vHC supporting increased anxiety-related behavior. These findings demonstrate that independent BLA and vHC circuits are critical for stress-induced defensive behaviors, and that differential targeting of BLA and vHC circuits may be needed in disease treatment.

Mental threat rehearsal increases fear generalization

BACKGROUND AND OBJECTIVES

Fear generalization to harmless stimuli characterizes anxiety-related disorders, but much remains unknown about its determinants. Based on studies showing that mental imagery of threat can increase conditioned fear responding, we tested whether it also facilitates fear generalization, and whether threat inflation moderates this effect.

METHODS

In a fear conditioning study, 120 participants first completed an acquisition phase, in which one of two pictures was followed by an aversive sound (human scream). Then, the sound was presented 11 times at an increasing (threat inflation) or constant volume (no threat inflation). Finally, a generalization stimulus was presented, and some participants were asked to imagine the last sound (threat rehearsal) and others were not (no threat rehearsal).

RESULTS

Bayesian informative hypotheses tests indicated that imagery-based threat rehearsal increased generalization of threat expectancy, and, combined with threat inflation, it also resulted in stronger generalized distress.

LIMITATIONS

due to the absence of a test phase, it is unclear whether our effects would transfer to other GSs and whether they would persist beyond the manipulation phase.

CONCLUSIONS

Mental imagery of threat may put individuals at risk for fear generalization. Future studies should examine whether modulating imagery may prevent clinical anxiety.

Negative Consequences of Pressure on Marksmanship May be Offset by Early Training Exposure to Contextually Relevant Threat Training: A Systematic Review and Meta-Analysis

OBJECTIVE

The purpose of this meta-analytic review is to examine the relationship between increased psychological pressure and Use of Force (UOF) behaviours, identifying current training methodologies and effectiveness of transfer of training interventions in high threat-simulated scenarios.

BACKGROUND

Data from UOF performance within Law Enforcement indicates a low transfer of marksmanship training into real-world UOF, resulting in unnecessary damage to property, personal injury and increased risk to loss of life. This meta-analysis examines both the impact of increased pressure and current training interventions.

METHOD

A meta-analysis was conducted across a wide range of published research to answer the primary research questions.

RESULTS

Increased levels of perceived pressure demonstrated an average decrease in marksmanship accuracy of 14.8%, together with a small increase in incorrect Decision Making (DM) and faster reaction Times (RT). Experience demonstrated a mitigating effect for pressure for marksmanship with a 1.1% increase for every one year of service but no effect on DM or RT. Training interventions utilizing a variety of early contextually relevant exposures to increased pressure improved performance over traditional training on average by 10.6%.

CONCLUSION

The outcomes illustrate the negative effect of pressure on marksmanship and UOF behaviours, and that early exposure to contextually relevant pressure may increase the transfer of training to real-world performance.

APPLICATION

Occupational experience is an important component in reducing the impact of pressure on UOF performance, and transfer of training may be enhanced through training methodologies that combine early exposure to contextually relevant pressure, that may replicate the benefits of experience.

No influence of threat uncertainty on fear generalization

Fear overgeneralization and perceived uncertainty about future outcomes have been suggested as risk factors for clinical anxiety. However, little is known regarding how they influence each other. In this study, we investigated whether different levels of threat uncertainty influence fear generalization. Three groups of healthy participants underwent a differential fear conditioning protocol followed by a generalization test. All groups learned to associate one female face (conditioned stimulus, CS+) with a female scream (unconditioned stimulus, US), whereas the other face (CS-) was not associated with the scream. In order to manipulate threat uncertainty, one group (low uncertainty, n = 26) received 80%, the second group (moderate uncertainty, n = 32) received 60%, and the third group (high uncertainty, n = 30) 40% CS-US contingency. In the generalization test, all groups saw CS+ and CS- again along with four morphs resembling the CSs in steps of 20%. Subjective (expectancy, valence, and arousal ratings), psychophysiological (skin conductance response, SCR), and visuocortical (steady-state visual evoked potentials, ssVEPs) indices of fear were registered. Participants expected the US according to their reinforcement schedules and the discriminative responses to CS+/CS- increased with more uncertainty in skin conductance. However, acquisition of conditioned fear was not evident in ssVEPs. During the generalization test, we found no effect of threat uncertainty in any of the measured variables, but the strength of generalization for threat expectancy ratings was positively correlated with dispositional intolerance of uncertainty. This study suggests that mere threat uncertainty does not modulate fear generalization.

Prefrontal cortex state representations shape human credit assignment

People learn adaptively from feedback, but the rate of such learning differs drastically across individuals and contexts. Here, we examine whether this variability reflects differences in what is learned. Leveraging a neurocomputational approach that merges fMRI and an iterative reward learning task, we link the specificity of credit assignment-how well people are able to appropriately attribute outcomes to their causes-to the precision of neural codes in the prefrontal cortex (PFC). Participants credit task-relevant cues more precisely in social compared vto nonsocial contexts, a process that is mediated by high-fidelity (i.e., distinct and consistent) state representations in the PFC. Specifically, the medial PFC and orbitofrontal cortex work in concert to match the neural codes from feedback to those at choice, and the strength of these common neural codes predicts credit assignment precision. Together this work provides a window into how neural representations drive adaptive learning.

Consensus design of a calibration experiment for human fear conditioning

Fear conditioning is a widely used laboratory model to investigate learning, memory, and psychopathology across species. The quantification of learning in this paradigm is heterogeneous in humans and psychometric properties of different quantification methods can be difficult to establish. To overcome this obstacle, calibration is a standard metrological procedure in which well-defined values of a latent variable are generated in an established experimental paradigm. These intended values then serve as validity criterion to rank methods. Here, we develop a calibration protocol for human fear conditioning. Based on a literature review, series of workshops, and survey of N = 96 experts, we propose a calibration experiment and settings for 25 design variables to calibrate the measurement of fear conditioning. Design variables were chosen to be as theory-free as possible and allow wide applicability in different experimental contexts. Besides establishing a specific calibration procedure, the general calibration process we outline may serve as a blueprint for calibration efforts in other subfields of behavioral neuroscience that need measurement refinement.

Fear generalization and behavioral responses to multiple dangers

Animals often exhibit consistent-individual differences (CIDs) in boldness/fearfulness, typically studied in the context of predation risk. We focus here on fear generalization, where fear of one danger (e.g., predators) is correlated with fear of other dangers (e.g., humans, pathogens, moving vehicles, or fire). We discuss why fear generalization should be ecologically important, and why we expect fear to correlate across disparate dangers. CIDs in fear are well studied for some dangers in some taxa (e.g., human fear of pathogens), but not well studied for most dangers. Fear of some dangers has been found to correlate with general fearfulness, but some cases where we might expect correlated fears (e.g., between fear of humans, familiar predators, and exotic predators) are surprisingly understudied.

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.

Test–retest reliability of human threat conditioning and generalization across a 1‐to‐2‐week interval

Given the increasing use of threat conditioning and generalization for clinical-translational research efforts, establishing test-retest reliability of these paradigms is necessary. Specifically, it is an empirical question whether the same participant evinces a similar generalization gradient of conditioned responses across two sessions with the identical contingencies and stimuli. Here, 46 human volunteers participated in an identical auditory threat acquisition and generalization protocol at two sessions separated by 1-to-2 weeks. Skin conductance responses (SCR) and trial-by-trial shock risk ratings served as primary measures. We used linear mixed effects modeling to test differential threat responses and generalization gradients, and Generalizability (G) theory coefficients as our primary formal assessment of test-retest reliability of intraindividual stability and change across time. Results showed largely invariant differential conditioning and generalization gradients across time. G coefficients indicated fair reliability for acquisition and generalization SCR. In contrast, risk rating reliabilities were mixed, and reliability was particularly low for acquisition risk ratings. Our findings generally support reliability of the threat conditioning and generalization paradigm for shorter test-retest intervals and highlight their utility for assessments of behavioral interventions in mental health research, but challenges remain and further work is needed. Threat conditioning and generalization tasks are increasingly used for translational efforts to improve behavioral interventions, and thus test-retest reliability for these tasks needs to be established. Our results support the test-retest reliability of threat conditioning and generalization over a relatively short (1-to-2 week) interval, but this depends on the measure used (physiological vs. self-report). Overall, these tasks could be appropriate for repeated testing over the course of a short-duration intervention study, but more research is needed, particularly in regard to longer-duration studies.

Generalization of threats attributed to large carnivores in areas of high human-wildlife conflict

Fear-induced generalization of threats to noninimical stimuli is a behavioral tendency of humans to minimize exposure to potential threats. In human-carnivore conflict zones, people often generalize their fear of predation by obligate carnivores to nonobligate carnivores despite differences in species' predation rates. We investigated the effect of a perceived threat of large obligate carnivores to livestock on tolerance and perception of striped hyena (Hyaena hyaena) in an area of high human-carnivore conflict. We surveyed 197 households through asemistructured questionnaire to determine people's perception and tolerance of striped hyenas in Sathyamangalam and Mudumalai Tiger Reserves after identification of the current distribution range of hyena determined through camera trap and sign surveys. Through the random forest algorithm, we modeled the level of tolerance of striped hyena as a function of loss of livestock to predation and from disease, the perceived threat of predation by hyena, and other socioeconomic attributes. Animal husbandry was a major source of income but was severely affected by livestock loss due to predation and disease. Sixty-nine percent of people were uncertain about predatory behavior of hyena; out of that, 23% reported a negative conservation attitude. Only 6 instances of hyena depredation on livestock and 2 on dogs were reported. Our model confirmed that economic instability associated with increased loss to predation and disease, livestock dependency, and a decrease in family annual income negatively affected people's tolerance of hyena. Perceptual uncertainty related to predatory behavior of hyena also negatively affected people's tolerance. In our study area, economic instability and perceptual uncertainty led to generalization of fear of large carnivores to a nonobligate predator. Such generalization may affect the attitude of people toward many other species. Understanding the role of economic instability and perceptual uncertainty should facilitate conservation of species, such as the hyena, that are vulnerable to false generalization.

Estradiol during (analogue-)trauma: Risk- or protective factor for intrusive re-experiencing?

Intrusions, a key symptom of posttraumatic stress disorder (PTSD), can occur in the form of images but also as pain sensations. Similar to audiovisual intrusions, the frequency and persistence of pain intrusions varies greatly between individuals. In the current study, we examined whether peritraumatic circulating 17β-estradiol (E2) levels are a biologic factor associated with subsequent audiovisual (i.e., film) and pain intrusion development, and whether peritraumatic stress levels modulate this relationship. Forty-one free-cycling women participated in an ecologically informed trauma-pain-conditioning (TPC) paradigm, using trauma-films and pain as unconditioned stimuli. Independent variables were salivary peritraumatic E2 levels and stress indexed by salivary cortisol and self-reported state-anxiety during TPC. Outcomes were film- and pain-intrusions occurring during daily-life in the week following TPC and a Memory-Triggering-Task in response to conditioned stimuli 24 h after TPC. In the week after analogue-trauma, higher peritraumatic E2 levels were associated with a greater probability of experiencing film-intrusions in the beginning of the week, which switched to a lower probability toward the end of the week. This time-dependent relationship between E2 and film-intrusions only held for higher state-anxious women. In contrast, results indicated a consistent inverse relationship between peritraumatic E2 levels and pain-intrusions during daily-life and Memory-Triggering-Task. Together, these data suggest that higher peritraumatic E2 levels could be associated with lower long-term visual trauma intrusions, as well as lower pain-intrusions, and thereby possibly constitute a protective biologic factor for PTSD and potentially also for chronic pain.

Sleep Deprivation During Memory Consolidation, but Not Before Memory Retrieval, Widens Threat Generalization to New Stimuli

Past aversive experiences shape our ability to deal with future dangers, through the encoding of implicit and explicit memory traces and through the ability to generalize defensive reactions to new stimuli resembling learned threats. Numerous evidence demonstrate that sleep is important for the consolidation of memories related to threatening events. However, there is a lack of studies examining the effects of sleep deprivation on the retrieval of consolidated threat memories, and previous studies on the role of sleep in threat generalization have produced mixed results. To address these issues, here we adopted a differential threat conditioning and a delayed (second half of the night) sleep deprivation during the first or the seventh night after learning. We found no effects of sleep deprivation on either implicit or explicit threat memories, regardless of its occurrence timing. Conversely, implicit but not explicit responses to novel cues similar to a learned threat displayed a widened generalization pattern, but only if sleep deprivation took place during the first night after conditioning and not if it occurred during the seventh night after conditioning. Therefore, we propose that sleeping after exposure to danger may support optimal implicit discrimination processes to evaluate new signals in the future and that even a brief period of sleeplessness may widen threat generalization to new stimuli, which is a hallmark of several threat-related disorders.

Stimulus Generalization in Mice during Pavlovian Eyeblink Conditioning

Here, we investigate stimulus generalization in a cerebellar learning paradigm, called eyeblink conditioning. Mice were conditioned to close their eyes in response to a 10-kHz tone by repeatedly pairing this tone with an air puff to the eye 250 ms after tone onset. After 10 consecutive days of training, when mice showed reliable conditioned eyelid responses to the 10-kHz tone, we started to expose them to tones with other frequencies, ranging from 2 to 20 kHz. We found that mice had a strong generalization gradient, whereby the probability and amplitude of conditioned eyelid responses gradually decreases depending on the dissimilarity with the 10-kHz tone. Tones with frequencies closest to 10 kHz evoked the most and largest conditioned eyelid responses and each step away from the 10-kHz tone resulted in fewer and smaller conditioned responses (CRs). In addition, we found that tones with lower frequencies resulted in CRs that peaked earlier after tone onset compared with those to tones with higher frequencies. Together, our data show prominent generalization patterns in cerebellar learning. Since the known function of cerebellum is rapidly expanding from pure motor control to domains that include cognition, reward-learning, fear-learning, social function, and even addiction, our data imply generalization controlled by cerebellum in all these domains.

Developing a feasible and sensitive judgement bias task in dairy cows

Judgement bias tasks (JBTs) are used to assess the influence of farm practices on livestock affective states. The tasks must be adjusted to the species and age group of focus. In cattle, most JBTs were designed for calves instead of adult cows. This study aimed to develop a JBT suitable for adult dairy cows, combining feasibility, validity, sensitivity and repeatability. Three JBTs were developed in which cows were trained to reach or avoid reaching a feeder, the location of which signalled a reward or punisher. The tasks differed in terms of punisher—cows being allocated either to “no-reward”, an air puff or an electric shock. Cows were then exposed twice to three ambiguous positions of the feeder, on two separate occasions. Speed of learning and proportions of correct responses to the conditioned locations were used to assess the feasibility of the task. Adjusted latencies to reach the ambiguous feeder positions were used to examine whether response patterns matched the linear and monotonic graded pattern expected in a valid and sensitive JBT at baseline. Latencies to reach the feeders in the two repeated testing sessions were compared to assess ambiguity loss over tasks’ repetitions. The validity of using spatial JBTs for dairy cows was demonstrated. While the effect on JBT feasibility was nuanced, the punisher did influence JBT sensitivity. None of the JBTs’ repeatability could be supported. We conclude that using an air puf as punisher led to the most sensitive, yet non-repeatable, JBT for dairy cows.

Neurobiology: Novel peptide pathways impact threat discrimination

Discriminating dangerous predictive stimuli from non-threatening stimuli is vital for maintaining optimal behavioral strategies. A new study finds that novel stress-related peptide pathways to the dopaminergic midbrain play a fundamental role in threat generalization.

Neural signature of delayed fear generalization under stress

Although the generalization of fear to stimuli resembling a threatening stimulus is an adaptive mechanism, fear overgeneralization is maladaptive and thought to play a key role in anxiety-related disorders. Since there is typically a delay between an initial fear experience and a situation in which fear (over)generalization may occur, we assessed delayed fear generalization and its neural signature. Moreover, as stress is known to affect fear learning, we further tested whether acute stress modulates fear generalization. Therefore, we conducted a two-day fear generalization study, with initial fear acquisition on Day 1 and a fear generalization test after a 24-hr delay in the MRI scanner. Prior to fear generalization testing, participants were exposed to a stressor or a control manipulation. Our behavioral data showed the expected generalization of fear. At a neural level, fear generalization was accompanied by increased fear-signaling for stimuli that resembled the conditioned stimulus in the bilateral insula and frontal operculum, whereas activity declined in frontal, hippocampal, and temporal regions, including the ventromedial prefrontal cortex, as stimuli became more similar to the conditioned stimulus. Importantly, stress did not modulate fear generalization, neither on a behavioral nor on a neural level. Interestingly, in an explorative comparison to two other studies that used the same paradigm but tested generalization immediately after acquisition, we observed increased fear generalization in the delayed relative to the immediate generalization test. In sum, our results suggest that stress leaves fear generalization and its neural signature unaffected but that a temporal delay might increase the extent to which fear responses are generalized to stimuli resembling the threatening stimulus.

Generalization gradients for fear and disgust in human associative learning

Previous research indicates that excessive fear is a critical feature in anxiety disorders; however, recent studies suggest that disgust may also contribute to the etiology and maintenance of some anxiety disorders. It remains unclear if differences exist between these two threat-related emotions in conditioning and generalization. Evaluating different patterns of fear and disgust learning would facilitate a deeper understanding of how anxiety disorders develop. In this study, 32 college students completed threat conditioning tasks, including conditioned stimuli paired with frightening or disgusting images. Fear and disgust were divided into two randomly ordered blocks to examine differences by recording subjective US expectancy ratings and eye movements in the conditioning and generalization process. During conditioning, differing US expectancy ratings (fear vs. disgust) were found only on CS-, which may demonstrated that fear is associated with inferior discrimination learning. During the generalization test, participants exhibited greater US expectancy ratings to fear-related GS1 (generalized stimulus) and GS2 relative to disgust GS1 and GS2. Fear led to longer reaction times than disgust in both phases, and the pupil size and fixation duration for fear stimuli were larger than for disgust stimuli, suggesting that disgust generalization has a steeper gradient than fear generalization. These findings provide preliminary evidence for differences between fear- and disgust-related stimuli in conditioning and generalization, and suggest insights into treatment for anxiety and other fear- or disgust-related disorders.

The impact of prior and ongoing threat on the false alarm threshold for facial discrimination

BACKGROUND AND OBJECTIVES

Perceptual adaptations that facilitate rapid responses to threats can also lead to false alarms, or the failure to discriminate safe stimuli from signals of threat. We examined the impact of varying degrees of threat on false alarms in the perceptual discrimination of faces along the dimension of emotion (Experiment 1) or identity (Experiment 2).

METHODS

Participants first trained to discriminate between a target and nontarget face. Next, we tested their ability to identify the target in randomized presentations of the target, the nontarget, and nine novel stimuli morphed in 10% increments of similarity from the target to the nontarget. The task was completed under one of three randomized conditions: 1) Ongoing-Threat paired the target with an aversive outcome in both phases; 2) Prior-Threat paired the target with an aversive outcome in the training phase only; and 3) No-Threat paired the target with a neutral outcome in the training phase only.

RESULTS

In Experiment 1 (N = 90), Ongoing-Threat lowered the false alarm threshold for facial discrimination based on anger intensity compared to Prior-Threat and No-Threat. In Experiment 2 (N = 90), Ongoing-Threat and Prior-Threat each lowered the false alarm threshold for identity-based discrimination compared to No-Threat.

LIMITATIONS

The experiment did not measure generalization of threat responses.

CONCLUSION

Associating a facial expression or identity with threat leads to faster but less accurate discrimination of faces with similar features, particularly under conditions of ongoing threat. These experiments provide an avenue for examining the parameters that impact false alarms, which play a key role in anxiety disorders.

Acute stress leaves fear generalization in healthy individuals intact

Because threatening situations often occur in a similar manner, the generalization of fear to similar situations is adaptive and can avoid harm to the organism. However, the overgeneralization of fear to harmless stimuli is maladaptive and assumed to contribute to anxiety disorders. Thus, elucidating factors that may modulate fear (over)generalization is important. Based on the known effects of acute stress on learning, which are at least partly due to noradrenergic arousal, we investigated whether stress may promote fear overgeneralization and whether we could counteract this effect by reducing noradrenergic arousal. In a placebo-controlled, double-blind, between-subjects design, 120 healthy participants underwent a fear-conditioning procedure on Day 1. Approximately 24 hours later, participants received orally either a placebo or the beta-adrenergic receptor antagonist propranolol and were exposed to a stress or control manipulation before they completed a test of fear generalization. Skin conductance responses as well as explicit rating data showed a successful acquisition of conditioned fear on Day 1 and a pronounced fear generalization 24 hours later. Although physiological data confirmed the successful stress manipulation and reduction of noradrenergic arousal, the extent of fear generalization remained unaffected by stress and propranolol. The absence of a stress effect on fear generalization was confirmed by a second study and a Bayesian analysis across both data sets. Our findings suggest that acute stress leaves fear generalization processes intact, at least in a sample of healthy, young individuals.

Rule-based generalization of threat without similarity

Threat generalization to novel instances is central to adaptive behavior. Most previous work has investigated threat generalization based on the perceptual similarity between past and novel stimuli. Few studies have explored generalization based on abstract, non-perceptual relations despite their importance for cognitive flexibility. In order to measure such rule-based generalization of threat without perceptual similarity, we developed a novel paradigm that prevents perceptual features from gaining predictive value. Our results demonstrate that participants responded according to the correct abstract rule and used it to successfully generalize their anticipatory behavioral threat responses (expectancy ratings, sudomotor nerve activity, and heart rate responses). Our results further show that participants flexibly adapted their responses to an unsignaled mid-session contingency reversal. We interpret our results in the context of other rule-based generalization tasks and argue that variations of our paradigm make possible a wide range of investigations into the conceptual aspects of threat generalization.

Precise memory for pure tones is predicted by measures of learning-induced sensory system neurophysiological plasticity at cortical and subcortical levels

Despite identical learning experiences, individuals differ in the memory formed of those experiences. Molecular mechanisms that control the neurophysiological bases of long-term memory formation might control how precisely the memory formed reflects the actually perceived experience. Memory formed with sensory specificity determines its utility for selectively cueing subsequent behavior, even in novel situations. Here, a rodent model of auditory learning capitalized on individual differences in learning-induced auditory neuroplasticity to identify and characterize neural substrates for sound-specific (vs. general) memory of the training signal's acoustic frequency. Animals that behaviorally revealed a naturally induced signal-"specific" memory exhibited long-lasting signal-specific neurophysiological plasticity in auditory cortical and subcortical evoked responses. Animals with "general" memories did not exhibit learning-induced changes in these same measures. Manipulating a histone deacetylase during memory consolidation biased animals to have more signal-specific memory. Individual differences validated this brain-behavior relationship in both natural and manipulated memory formation, such that the degree of change in sensory cortical and subcortical neurophysiological responses could be used to predict the behavioral precision of memory.

Differential Phosphorylation of the Glucocorticoid Receptor in Hippocampal Subregions Induced by Contextual Fear Conditioning Training

Aversive events induce the release of glucocorticoid stress hormones that facilitate long-term memory consolidation, an effect that depends on the activation of glucocorticoid receptors (GRs). GRs are distributed widely in the hippocampus. The dorsal region of the hippocampus has been related to cognitive functions and the ventral region to stress and emotion. GR acts as a transcription factor which after hormone binding becomes phosphorylated, affecting its cellular distribution and transcriptional activity. Two functionally well-described GR phosphorylation sites are serine 232 (pSer232), which enhances gene expression, and serine 246 (pSer246), having the opposite effect. Since gene expression is one of the plastic mechanisms needed for memory consolidation, we investigated if an aversive learning task would induce GR phosphorylation in the dorsal (DH) and the ventral (VH) hippocampus. We trained rats in contextual fear conditioning (CFC) using different foot-shock intensities (0.0, 0.5, or 1.5 mA). One subgroup of animals trained with each intensity was sacrificed 15 min after training and blood was collected to quantify corticosterone (CORT) levels in serum. Another subgroup was sacrificed 1 h after training and brains were collected to evaluate the immunoreactivity (IR) to GR, pSer232 and pSer246 by SDS-PAGE/Western blot in DH and VH, and by immunohistochemistry in dorsal and ventral CA1, CA2, CA3, and dentate gyrus (DG) hippocampal regions. The conditioned freezing response increased in animals trained with 0.5 and 1.5 mA during training and extinction sessions. The degree of retention and CORT levels were directly related to the intensity of the foot-shock. Although total GR-IR remained unaffected after conditioning, we observed a significant increase of pSer246-IR in the dorsal region of CA1 and in both dorsal and ventral DG. The only region in which pSer232-IR was significantly elevated was ventral CA3. Our results indicate that fear conditioning training is related to GR phosphorylation in specific subregions of the hippocampus, suggesting that its transcriptional activity for gene expression is favored in ventral CA3, whereas its repressor activity for gene-silencing is increased in dorsal CA1 and in both dorsal and ventral DG.

Patients with dorsolateral prefrontal cortex lesions are capable of discriminatory threat learning but appear impaired in cognitive regulation of subjective fear

Humans are able to cognitively regulate emotions by changing their thoughts. Neuroimaging studies show correlations between dorsolateral prefrontal cortex (dlPFC) activity and cognitive regulation of emotions. Here our objective was to investigate whether dlPFC damage is associated with impaired cognitive regulation of emotion. We therefore tested the ability of patients with dlPFC lesions (N = 6) and matched control participants (N = 19) to utilize a laboratory version of cognitive regulation training (CRT) to regulate subjective fear and autonomic threat responses following Pavlovian threat conditioning. We found that patients with dlPFC lesions were able to acquire conditioned threat but seemed impaired in their ability to utilize CRT to cognitively regulate subjective fear to a threatening stimulus. Despite inclusion of a limited number of lesion patients, our results suggest that the dlPFC is important for the cognitive regulation of subjective fear.

Making translation work: Harmonizing cross-species methodology in the behavioural neuroscience of Pavlovian fear conditioning

Translational neuroscience bridges insights from specific mechanisms in rodents to complex functions in humans and is key to advance our general understanding of central nervous function. A prime example of translational research is the study of cross-species mechanisms that underlie responding to learned threats, by employing Pavlovian fear conditioning protocols in rodents and humans. Hitherto, evidence for (and critique of) these cross-species comparisons in fear conditioning research was based on theoretical viewpoints. Here, we provide a perspective to substantiate these theoretical concepts with empirical considerations of cross-species methodology. This meta-research perspective is expected to foster cross-species comparability and reproducibility to ultimately facilitate successful transfer of results from basic science into clinical applications.

Time-dependent effects of psychosocial stress on the contextualization of neutral memories

Memories about stressful experiences need to be both specific and generalizable to adequately guide future behavior. Memory strength is influenced by emotional significance, and contextualization (i.e., encoding experiences with their contextual details) enables selective context-dependent retrieval and protects against overgeneralization. The current randomized-controlled study investigated how the early and late phase of the endogenous stress response affects the contextualization of neutral and negative information. One hundred healthy male participants were randomly divided into three experimental groups that performed encoding either 1) without stress (control), 2) immediately after acute stress (early) or 3) two hours after acute stress (late). Stress was induced via the Trier Social Stress Test and salivary alpha-amylase and cortisol levels were measured throughout the experiment. In the Memory Contextualization Task, neutral and angry faces (items) were depicted against unique context pictures during encoding. During testing 24 h later, context-dependent recognition memory of the items was assessed by presenting these in either congruent or incongruent contexts (relative to encoding). Multilevel analyses revealed that neutral information was more contextualized when encoding took place two hours after psychosocial stress, than immediately after the stressor. Results suggest that the late effects in the unique, time-dependent sequence of a healthy endogenous stress response, could complement reduced contextualization immediately after stress. The contextualization of negative information was not influenced by psychosocial stress, as opposed to earlier reported effects of exogenous hydrocortisone administration. An imbalance between the early and late effects of the endogenous stress response could increase vulnerability for stress-related psychopathology.

Implicit and explicit systems differently predict possible dangers

One strategy to address new potential dangers is to generate defensive responses to stimuli that remind learned threats, a phenomenon called fear generalization. During a threatening experience, the brain encodes implicit and explicit memory traces. Nevertheless, there is a lack of studies comparing implicit and explicit response patterns to novel stimuli. Here, by adopting a discriminative threat conditioning paradigm and a two-alternative forced-choice recognition task, we found that the implicit reactions were selectively elicited by the learned threat and not by a novel similar but perceptually discriminable stimulus. Conversely, subjects explicitly misidentified the same novel stimulus as the learned threat. This generalization response was not due to stress-related interference with learning, but related to the embedded threatening value. Therefore, we suggest a dissociation between implicit and explicit threat recognition profiles and propose that the generalization of explicit responses stems from a flexible cognitive mechanism dedicated to the prediction of danger.

Threat learning promotes generalization of episodic memory

The ability to generalize from and distinguish between aversive memories and novel experiences is critical to survival. Previous research has revealed mechanisms underlying generalization of threat-conditioned defensive responses, but little is known about generalization of episodic memory for threatening events. Here we tested if aversive learning influences generalization of episodic memory for threatening events in human adults. Subjects underwent Pavlovian threat-conditioning in which objects from one category were paired with a shock and objects from a different category were unpaired. The next day, subjects underwent a recognition memory test that included old, highly similar, and entirely novel items from the shock-paired and shock-unpaired object categories. Results showed that items highly similar to those from the object category previously paired with shock were mistaken for old items more often than items from the shock-unpaired category. This finding indicates that threat learning promotes generalization of episodic memory, and is consistent with the idea that threat generalization is an active process that may be adaptive for avoiding a myriad of potential threats following an emotional experience. Enhanced generalization of aversive episodic memories may be maladaptive, however, when old threat memories are inappropriately reactivated in harmless situations, exemplified in a number of stress- and anxiety-related disorders. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Aversive learning strengthens episodic memory in both adolescents and adults

Adolescence is often filled with positive and negative emotional experiences that may change how individuals remember and respond to stimuli in their environment. In adults, aversive events can both enhance memory for associated stimuli as well as generalize to enhance memory for unreinforced but conceptually related stimuli. The present study tested whether learned aversive associations similarly lead to better memory and generalization across a category of stimuli in adolescents. Participants completed an olfactory Pavlovian category conditioning task in which trial-unique exemplars from one of two categories were partially reinforced with an aversive odor. Participants then returned 24 h later to complete a recognition memory test. We found better corrected recognition memory for the reinforced versus the unreinforced category of stimuli in both adults and adolescents. Further analysis revealed that enhanced recognition memory was driven specifically by better memory for the reinforced exemplars. Autonomic arousal during learning was also related to subsequent memory. These findings build on previous work in adolescent and adult humans and rodents showing comparable acquisition of aversive Pavlovian conditioned responses across age groups and demonstrate that memory for stimuli with an acquired aversive association is enhanced in both adults and adolescents.

Emotional enhancement of memory for neutral information: The complex interplay between arousal, attention, and anticipation

It can be challenging to explain why certain mundane details circumstantial to an emotional event are nonetheless remembered long after the experience. Here, we examined how attention selectively shapes memory for neutral objects that happen to coincide with either an unexpected or anticipated emotional event. Pictures of neutral objects were presented for 2 s and terminated with either a high-intensity shock, a low-intensity shock, or no shock. Recognition memory was tested 24 -hs later in a surprise test. Results showed no effect of shock intensity on memory for attended objects when shocks were unpredictable (Experiment 1). Similarly, there was no effect of shock intensity for attended objects when shock delivery was signaled before the object appeared (Experiment 2). There was a reduction in memory for unattended objects paired with an anticipated high-intensity shock (Experiment 3). Finally, subjects recognized slightly more attended objects paired with a high-intensity shock if shock intensity was signaled one second after the object was encoded (Experiment 4). We conclude that simply pairing objects with high-intensity shocks is insufficient to drive episodic memory enhancements for neutral information. But anticipation of an impending source of arousal can induce bidirectional effects: attending to an impending emotional event interferes with encoding of neutral information, but encoding an object just prior to anticipation of an emotional event can sometimes benefit memory. Overall, these results highlight a complex interplay between arousal, attention, and anticipation on emotion-induced memory for neutral information.

Modulation of fear generalization by the zona incerta

Fear expressed toward threat-associated stimuli is an adaptive behavioral response. In contrast, the generalization of fear responses toward nonthreatening cues is a maladaptive and debilitating dimension of trauma- and anxiety-related disorders. Expressing fear to appropriate stimuli and suppressing fear generalization require integration of relevant sensory information and motor output. While thalamic and subthalamic brain regions play important roles in sensorimotor integration, very little is known about the contribution of these regions to the phenomenon of fear generalization. In this study, we sought to determine whether fear generalization could be modulated by the zona incerta (ZI), a subthalamic brain region that influences sensory discrimination, defensive responses, and retrieval of fear memories. To do so, we combined differential intensity-based auditory fear conditioning protocols in mice with C-FOS immunohistochemistry and designer receptors exclusively activated by designer drugs (DREADDs)-based manipulation of neuronal activity in the ZI. C-FOS immunohistochemistry revealed an inverse relationship between ZI activation and fear generalization: The ZI was less active in animals that generalized fear. In agreement with this relationship, chemogenetic inhibition of the ZI resulted in fear generalization, while chemogenetic activation of the ZI suppressed fear generalization. Furthermore, targeted stimulation of GABAergic cells in the ZI reduced fear generalization. To conclude, our data suggest that stimulation of the ZI could be used to treat fear generalization in the context of trauma- and anxiety-related disorders.

The ontogeny of memory persistence and specificity

Interest in the ontogeny of memory blossomed in the twentieth century following the initial observations that memories from infancy and early childhood are rapidly forgotten. The intense exploration of infantile amnesia in subsequent years has led to a thorough characterization of its psychological determinants, although the neurobiology of memory persistence has long remained elusive. By contrast, other phenomena in the ontogeny of memory like infantile generalization have received relatively less attention. Despite strong evidence for reduced memory specificity during ontogeny, infantile generalization is poorly understood from psychological and neurobiological perspectives. In this review, we examine the ontogeny of memory persistence and specificity in humans and nonhuman animals at the levels of behavior and the brain. To this end, we first describe the behavioral phenotypes associated with each phenomenon. Looking into the brain, we then discuss neurobiological mechanisms in the hippocampus that contribute to the ontogeny of memory. Hippocampal neurogenesis and critical period mechanisms have recently been discovered to underlie amnesia during early development, and at the same time, we speculate that similar processes may contribute to the early bias towards memory generalization.

Exploring the boundaries of post-retrieval extinction in healthy and anxious individuals

Over a dozen studies have examined the efficacy of post-retrieval extinction (PRE) in healthy adults in the fear conditioning laboratory, with a recent meta-analysis reporting an overall small-moderate effect on attenuating the return of fear compared to standard extinction. The current study was designed to extend PRE effects to a mixed sample of healthy and anxious individuals, explore potential moderators, and examine the benefit of PRE for a memory conditioned over multiple days. Healthy (n = 49) and anxious (n = 43) adults received either one day of acquisition followed by PRE, one day of acquisition followed by extinction, or three days of acquisition followed by PRE. Comparing participants who received one day of acquisition followed by PRE or extinction, no significant effect of PRE was observed on differential skin conductance response reinstatement or reactivity to the conditioned stimulus alone. Anxiety symptoms did not moderate outcomes. There was no difference in return of fear for anxious participants who received three days of acquisition followed by PRE versus one day of acquisition followed by PRE. These results further highlight the variability of findings in the PRE literature and need for further examination of individual difference factors that may moderate PRE effects.

Related to Anxiety: Arbitrarily Applicable Relational Responding and Experimental Psychopathology Research on Fear and Avoidance

Humans have an unparalleled ability to engage in arbitrarily applicable relational responding (AARR). One of the consequences of this ability to spontaneously combine and relate events from the past, present, and future may, in fact, be a propensity to suffer. For instance, maladaptive fear and avoidance of remote or derived threats may actually perpetuate anxiety. In this narrative review, we consider contemporary AARR research on fear and avoidance as it relates to anxiety. We first describe laboratory-based research on the emergent spread of fear- and avoidance-eliciting functions in humans. Next, we consider the validity of AARR research on fear and avoidance and address the therapeutic implications of the work. Finally, we outline challenges and opportunities for a greater synthesis between behavior analysis research on AARR and experimental psychopathology.

Who is studied in de novo fear conditioning paradigms? An examination of demographic and stimulus characteristics predicting fear learning

A common challenge in fear conditioning studies is that a relatively large proportion of individuals fail to acquire a differential conditioned skin conductance response (SCR). Researchers have identified demographic factors associated with poorer fear learning and explored the use of different fear conditioning paradigms across various populations. However, few studies have strategically aimed to enhance acquisition by manipulating the unconditioned stimulus (UCS). In the current manuscript, we examined whether demographic factors predicted failure to condition (n = 274) and explored whether modifications to the UCS enhanced fear learning (n = 143). Results indicated that race, but not age, education, or gender, predicted failure to condition. Stepwise logistic regression demonstrated that race was the most influential of these predictors; African Americans were less likely to acquire a conditioned SCR, compared to non-African Americans. Also, use of a compound UCS (i.e., electric shock combined with a scream noise) led to nearly double the rate of acquisition of a conditioned SCR. Hence, use of a compound UCS may provide a way to reduce the number of excluded individuals in studies of fear-conditioned SCR and thereby improve the representativeness of research samples.

Can an aversive, extinction-resistant memory trigger impairments in walking adaptability? An experimental study using adult rats

Cognitive demands can influence the adaptation of walking, a crucial skill to maintain body stability and prevent falls. Whilst previous research has shown emotional load tunes goal-directed movements, little attention has been given to this finding. This study sought to assess the effects of suffering an extinction-resistant memory on skilled walking performance in adult rats, as an indicator of walking adaptability. Thus, 36 Wistar rats were divided in a two-part experiment. In the first part (n=16), the aversive, extinction-resistance memory paradigm was established using a fear-conditioning chamber. In the second, rats (n=20) were assessed in a neutral room using the ladder rung walking test before and tree days after inducing an extinction-resistance memory. In addition, the elevated plus-maze test was used to control the influence of the anxiety-like status on gait adaptability. Our results revealed the shock group exhibited worse walking adaptability (lower skilled walking score), when compared to the sham group. Moreover, the immobility time in the ladder rung walking test was similar to the controls, suggesting that gait adaptability performance was not a consequence of the fear generalization. No anxiety-like behavior was observed in the plus maze test. Finally, correlation coefficients also showed the skilled walking performance score was positively correlated with the number of gait cycles and trial time in the ladder rung walking test and the total crossings in the plus maze. Overall, these preliminary findings provide evidence to hypothesize an aversive, extinction-resistant experience might change the emotional load, affecting the ability to adapt walking.

Context conditioning in humans using commercially available immersive Virtual Reality

Despite a wealth of knowledge on how humans and nonhuman animals learn to associate meaningful events with cues in the environment, far less is known about how humans learn to associate these events with the environment itself. Progress on understanding spatiotemporal contextual processes in humans has been slow in large measure by the methodological constraint of generating and manipulating immersive spatial environments in well-controlled laboratory settings. Fortunately, immersive Virtual Reality (iVR) technology has improved appreciably and affords a relatively straightforward methodology to investigate the role of context on learning, memory, and emotion while maintaining experimental control. Here, we review context conditioning literature in humans and describe challenges to study contextual learning in humans. We then provide details for a novel context threat (fear) conditioning paradigm in humans using a commercially available VR headset and a cross-platform game engine. This paradigm resulted in the acquisition of subjective threat, threat-conditioned defensive responses, and explicit threat memory. We make the paradigm publicly available and describe obstacles and solutions to optimize future studies of context conditioning using iVR. As computer technology advances to replicate the sensation of realistic environments, there are increasing opportunities to bridge the translational gap between rodent and human research on how context modulates cognition, which may ultimately lead to more optimal treatment strategies for anxiety- and stress-related disorders.