Fear one, fear them all: A systematic review and meta-analysis of fear generalization in pathological anxiety

Examining attentional avoidance in post-traumatic stress disorder: an exploratory 'Face in the Crowd' paradigm using eye-tracking

Background: Maladaptive patterns of attention to emotional stimuli are a clinical feature of posttraumatic stress disorder (PTSD). Using eye-tracking-based methodology, research points out the presence of sustained attention to threatening stimuli in individuals with PTSD. However, most eye-tracking studies in this field used free-viewing tasks on negative stimuli.Methods: PTSD patients (n = 38), trauma-exposed healthy controls (TEHC; n = 30), and non-trauma-exposed healthy controls (HC; n = 33) performed a Face in the Crowd (FiC) task. The FiC task was chosen to explore specific responses to emotional stimuli within a competitive visual environment, thus providing insights into visual search patterns. Both reaction time and gaze patterns (dwell time, scanpath length, first fixation duration, and latency) were recorded.Results: Individuals with a provisional PTSD diagnosis presented decreased dwell time on both positive and negative targets in comparison with HC and TEHC, as well as shorter scanpath length for all matrixes when no targets were present. No evidence of attentional bias was observed in the TEHC group based on reaction times or eye-tracking measures in response to positive, negative, or neutral cues.Discussion: We found an attentional avoidance pattern among PTSD patients, along with indexes of lowered perceptual threshold for all emotional information. This study allows raising the question of cognitive load on the emergence of differential attentional strategies presented by PTSD participants. We discuss the generalization of fear processes across different emotional stimuli and underscore the need for incorporating a variety of emotional stimuli in PTSD research.

Comparing psychiatric symptom networks between individuals in resilience and non-resilience trajectories of adaptation amid the global pandemic

OBJECTIVE

The current study compared symptom networks between individuals exhibiting resilience and non-resilience trajectories of adaptation two years after the COVID-19 outbreak.

METHOD

A population-representative sample (N = 906) reported symptoms of anxiety and depression in February-July 2020 (T1), March-August 2021 (T2), and September 2021-February 2022 (T3), as well as symptoms of post-traumatic stress disorder (PTSD) and adjustment disorder (AD) at T3. After differentiating between individuals with resilience and non-resilience trajectories using growth mixture modeling, network analyses were conducted to investigate group differences in T3 network symptoms (undirected and directed).

RESULTS

Despite non-significant group differences (M = 0.184, p = .380; S = 0.096, p = .681), distinctive qualitative characteristics were observed between networks. Difficulty relaxing was identified as the single root cause in the more diffused resilience network, with anxiety and depressive symptoms as additional starting points in the non-resilience network, which was more interconnected into clusters with clear-cut diagnostic boundaries. Sad mood demonstrated a transdiagnostic communicative role across common mental disorders.

CONCLUSION

Our results contribute to the understanding of anxiety-depression-PTSD-AD symptom networks in resilient and non-resilient individuals by highlighting the consequences of heterogeneity in adaptation capacity in the development of pandemic-related psychopathology.

The probabilistic and dynamic nature of perception in human generalization behavior

Generalization theories traditionally overlook how our mental representations dynamically change in the process of transferring learned knowledge to new contexts. We integrated perceptual and generalization theories into a computational model using data from 80 participants who underwent Pavlovian fear conditioning experiments. The model analyzed continuous measures of perception and fear generalization to understand their relationship. Our findings revealed large individual variations in perceptual processes that directly influence generalization patterns. By examining how perceptual and generalization mechanisms work together, we uncovered their combined role in producing generalization behavior. This research illuminates the probabilistic perceptual foundations underlying individual differences in generalization, emphasizing the crucial integration between perceptual and generalization processes. Understanding this relationship enhances our knowledge of generalization behavior and has potential implications for various cognitive domains including categorization, motor learning, language processing, and face recognition-all of which rely on generalization as a fundamental cognitive process.

Generalization of exposure therapy: Systematic review and recommendations for future research

Limited generalization of exposure therapy effects from treatment-related to treatment-unrelated contexts and/or stimuli is a potential factor contributing to relapse after successful exposure treatment. Investigating the processes underlying exposure therapy generalization (ETG) and developing strategies to promote ETG has become a significant research area. This systematic review provides an overview of the current state of ETG research, outlining its operationalization and the methodological diversity used to detect changes in ETG. We also summarize and discuss findings from studies aimed at enhancing ETG through pharmacological and behavioral interventions. A total of 34 studies were identified, investigating ETG across therapy-related and unrelated contexts and fear stimuli. These studies primarily used physical and/or social context/stimuli manipulations to investigate ETG. Multiple response systems (subjective, psychophysiological, behavioral) were used as indices of diminished ETG, but most studies found increased subjective fear in treatment-unrelated contexts/stimuli compared to treatment-related ones. We conclude that clear definitions and criteria for assessing ETG are urgently needed. Behavioral interventions, such as multiple context exposure or sleep after exposure, seem effective in promoting ETG across different contexts/stimuli. In contrast, findings from pharmacological approaches are less encouraging, but more research is needed. We identify research gaps that require further investigation to better understand the mechanisms governing and promoting ETG. Experimental paradigms offer a clear advantage for this purpose and for screening novel strategies to maximize ETG.

Why are threatening experiences remembered so well? Insights into memory strengthening from protocols of gradual aversive learning

Aversive experiences often result in strong and persistent memory traces, which can sometimes lead to conditions such as Post-Traumatic Stress Disorder or phobias. Aversive stimulation tests are key tools in psychology and neuroscience for studying learning and memory. These tests typically use electric shocks as the unconditioned stimulus, allowing for precise control over the aversive content of the learning event. This feature has led to extensive research applying these tests with varying shock intensities to examine differences in learning, behavior, and memory formation between low- and high-aversive experiences. This line of research is particularly valuable for understanding the neurobiology underlying memory strengthening, but, to our knowledge, no review has yet compiled and organized the findings from this specific methodology. In this comprehensive review, we focus primarily on animal studies that have employed the same aversive test (i.e. Fear Conditioning, Passive Avoidance, Active Avoidance or Operant boxes) at different intensities. We will first outline and briefly describe the main aversive learning paradigms used in this field. Next, we will examine the relationship between aversiveness and memory strength. Finally, we will explore the neurobiological insights these studies have revealed over the years. Our aim is to gain a better understanding of how the nervous system gradually strengthens memory, while also addressing the remaining gaps and challenges in this area of research.

Reduced discrimination between signals of danger and safety but not overgeneralization is linked to exposure to childhood adversity in healthy adults

Childhood adversity is a strong predictor of developing psychopathological conditions. Multiple theories on the mechanisms underlying this association have been suggested which, however, differ in the operationalization of 'exposure.' Altered (threat) learning mechanisms represent central mechanisms by which environmental inputs shape emotional and cognitive processes and ultimately behavior. 1402 healthy participants underwent a fear conditioning paradigm (acquisition training, generalization), while acquiring skin conductance responses (SCRs) and ratings (arousal, valence, and contingency). Childhood adversity was operationalized as (1) dichotomization, and following (2) the specificity model, (3) the cumulative risk model, and (4) the dimensional model. Individuals exposed to childhood adversity showed blunted physiological reactivity in SCRs, but not ratings, and reduced CS+/CS- discrimination during both phases, mainly driven by attenuated CS+ responding. The latter was evident across different operationalizations of 'exposure' following the different theories. None of the theories tested showed clear explanatory superiority. Notably, a remarkably different pattern of increased responding to the CS- is reported in the literature for anxiety patients, suggesting that individuals exposed to childhood adversity may represent a specific sub-sample. We highlight that theories linking childhood adversity to (vulnerability to) psychopathology need refinement.

Memory Under Stress: From Adaptation to Disorder

Stressful events are ubiquitous in everyday life. Exposure to these stressors initiates the temporally orchestrated release of a multitude of hormones, peptides, and neurotransmitters that target brain areas that have been critically implicated in learning and memory. This review summarizes recent insights on the profound impact of stress on 4 fundamental processes of memory: memory formation, memory contextualization, memory retrieval, and memory flexibility. Stress mediators instigate dynamic alterations in these processes, thereby facilitating efficient responding under stress and the creation of a decontextualized memory representation that can effectively aid coping with novel future threats. While they are generally adaptive, the same stress-related changes may contribute to the rigid behaviors, uncontrollable intrusions, and generalized fear responding seen in anxiety disorders and posttraumatic stress disorder. Drawing on recent discoveries in cognitive neuroscience and psychiatry, this review discusses how stress-induced alterations in memory processes can simultaneously foster adaptation to stressors and fuel psychopathology. The transition from adaptive to maladaptive changes in the impact of stress on memory hinges on the nuanced interplay of stressor characteristics and individual predispositions. Thus, taking individual differences in the cognitive response to stressors into account is essential for any successful treatment of stress-related mental disorders.

Integrating behavioral and neurophysiological insights: High trait anxiety enhances observational fear learning

Observational fear learning delineates the process by which individuals learn about potential threats through observing others' reactions. Prior research indicates that individuals with high trait anxiety (HTA) manifest pronounced fear responses in direct fear learning scenarios. However, the specific influence of trait anxiety on observational fear learning remains insufficiently explored. This study aimed to fill this gap by examining 64 university students, divided equally between those with HTA and low trait anxiety (LTA), selected from an initial pool of 483 participants. Participants were subjected to observational fear learning tasks, and their behavioral responses, physiological reactions, and brain activations were recorded. Results demonstrated that HTA participants exhibited differentiated skin conductance responses to threat and safety stimuli during the observational fear acquisition phase, notwithstanding prior assurances against shock delivery. Furthermore, during the direct test phase, HTA participants reported significantly elevated fear and shock expectancy ratings for both types of stimuli, in contrast to their LTA counterparts. Neuroimaging data, derived via functional near-infrared spectroscopy (fNIRS) revealed heightened medial prefrontal cortex activation in HTA participants when directly facing threats. This study systematically explores the influence of high trait anxiety on observational fear learning, uncovering that HTA individuals exhibit excessive fear responses. These findings highlight the critical role of trait anxiety as a significant risk factor in the development of anxiety disorders.

Fear and safety learning in anxiety- and stress-related disorders: An updated meta-analysis

Fear learning processes are believed to play a crucial role in the development and maintenance of anxiety and stress-related disorders. To integrate results across different studies, we conducted a systematic meta-analysis following PRISMA guidelines to examine differences in fear conditioning during fear acquisition, extinction, and extinction recall between individuals with anxiety-related or stress-related disorders and healthy participants. This analysis updates the work of Duits et al. (2015) while also refining distinctions between physiological and behavioral outcomes and examining extinction recall. Our meta-analysis encompasses 77 studies published from 1986 to 2022, involving 2052 patients with anxiety disorders, obsessive-compulsive disorder, or post-traumatic stress disorder, and 3258 healthy controls. The results indicate significant differences in fear acquisition, extinction, and recall between the two groups. Specifically, during acquisition patients exhibited heightened physiological and behavioral responses to the CS- and reported increased affect ratings for the CS+ . During extinction and extinction recall, patients continue to show heightened threat expectancy and negative affect ratings towards the CS- and increased affect ratings towards the CS+ . No differences were found in CS+ /CS- differentiation between groups. These findings imply that individuals with anxiety and stress-related disorders may exhibit amplified responses to safety cues and stronger reactions to threat cues during fear conditioning, lasting through extinction and extinction recall. These changes may lead to increased sensitivity in detecting fear and slower extinction process, resulting in more enduring anxiety responses. We discuss these results in the context of existing literature on fear and safety learning and consider potential underlying mechanisms.

Generalized expectancy of threat in threatening compared to safe contexts

Fear of threatening contexts often generalizes to similar safe contexts, but few studies have investigated how contextual information influences cue generalization. In this study, we explored whether fear responses to cues would generalize more broadly in a threatening compared to a safe context. Forty-seven participants underwent a differential cue-in-context conditioning protocol followed by a generalization test, while we recorded psychophysiological and subjective responses. Two faces appeared on a computer screen in two contexts. One face (CS+) in the threat context (CTX+) was followed by a female scream 80% of the time, while another face (CS-) was not reinforced. No faces were reinforced in the safe context (CTX-). In the generalization test, the CSs and four morphs varying in similarity with the CS+ were presented in both contexts. During acquisition, conditioned responses to the cues were registered for all measures and the differential responding between CS+ and CS- was higher in CTX+ for US-expectancy ratings and skin conductance responses, but the affective ratings and steady-state visual evoked potentials were not context-sensitive. During test, adaptive generalized responses were evident for all measures. Despite increased US-expectancy ratings in CTX+, participants exhibited similar cue generalization in both contexts, suggesting that threatening contexts do not influence cue generalization.

Fear generalization in individuals with subclinical symptoms of panic disorder

Panic disorder (PD) is a debilitating mental health condition, characterized by a preoccupation with the occurrence of panic attacks. Previous research has found that PD patients display increased fear generalization, which entails inflated fear responses to ambiguous stimuli (e.g., intermediate size circles) following fear conditioning wherein a neutral stimulus (e.g., large circle) gets paired with an aversive stimulus (e.g., electric shocks), whereas another neutral stimulus (e.g., small circle) is not paired with this aversive stimulus. The overgeneralization of fear to ambiguous stimuli may be a causal mechanism in the development of panic symptoms. However, this finding requires replication, particularly among subclinical groups to establish temporal priority of fear overgeneralization prior to the development of PD symptoms. This study examines whether fear generalization levels differ between individuals with high and low levels of some PD symptoms. Participants (N = 110) underwent fear conditioning and generalization, measuring physiological and self-report fear responses. Successful fear acquisition and generalization were observed. However, fear generalization did not significantly differ between groups with high and low PD symptomatology. These findings suggest that generalization observed in clinical populations might result from psychopathology rather than causing it. Using both clinical and subclinical samples in experimental psychopathology research is therefore important.

Global precedence effect in fear generalization and the role of trait anxiety and intolerance of uncertainty

Fear overgeneralization is widely considered to be a core feature of pathological anxiety, and the excessive spread of fear can be a great burden on patients. Although perceptual processing is a basic process of human cognition, the impact of visual perception recognition on fear generalization has not yet been fully explored. In this study, 69 subjects were recruited to explore the effects of the hierarchical features of stimuli on fear generalization and examine the roles of trait anxiety (TA) and intolerance of uncertainty (IU) in this process. The results reveal that compared with the local features, the subjects showed stronger fear responses to global features of the stimuli, and the weakest fear response was to the reversed features. Furthermore, the results preliminarily suggest that in generalization dominated by global features, TA intensifies the fear response; while in generalization dominated by local features, along with TA, IU makes a unique contribution to increasing the magnitude of fear generalization. These results confirm new potential pathways for fear generalization, specifically the configurational hierarchical features of stimuli. This is explained through object recognition and cognitive bias, implying that cognitive processes and personality traits have interacting effects on fear generalization.

The representational instability in the generalization of fear learning

Perception and perceptual memory play crucial roles in fear generalization, yet their dynamic interaction remains understudied. This research (N = 80) explored their relationship through a classical differential conditioning experiment. Results revealed that while fear context perception fluctuates over time with a drift effect, perceptual memory remains stable, creating a disjunction between the two systems. Surprisingly, this disjunction does not significantly impact fear generalization behavior. Although most participants demonstrated generalization aligned with perceptual rather than physical stimulus distances, incorporating perceptual memory data into perceptual distance calculations did not enhance model performance. This suggests a potential shift in the mapping of the perceptual memory component of fear context, occurring alongside perceptual dynamics. Overall, this work provides evidence for understanding fear generalization behavior through different stimulus representational processes. Such mechanistic investigations can enhance our understanding of how individuals behave when facing threats and potentially aid in developing mechanism-specific diagnoses and treatments.

Leveraging ultra-high field (7T) MRI in psychiatric research

Non-invasive brain imaging has played a critical role in establishing our understanding of the neural properties that contribute to the emergence of psychiatric disorders. However, characterizing core neurobiological mechanisms of psychiatric symptomatology requires greater structural, functional, and neurochemical specificity than is typically obtainable with standard field strength MRI acquisitions (e.g., 3T). Ultra-high field (UHF) imaging at 7 Tesla (7T) provides the opportunity to identify neurobiological systems that confer risk, determine etiology, and characterize disease progression and treatment outcomes of major mental illnesses. Increases in scanner availability, regulatory approval, and sequence availability have made the application of UHF to clinical cohorts more feasible than ever before, yet the application of UHF approaches to the study of mental health remains nascent. In this technical review, we describe core neuroimaging methodologies which benefit from UHF acquisition, including high resolution structural and functional imaging, single (1H) and multi-nuclear (e.g., 31P) MR spectroscopy, and quantitative MR techniques for assessing brain tissue iron and myelin. We discuss advantages provided by 7T MRI, including higher signal- and contrast-to-noise ratio, enhanced spatial resolution, increased test-retest reliability, and molecular and neurochemical specificity, and how these have begun to uncover mechanisms of psychiatric disorders. Finally, we consider current limitations of UHF in its application to clinical cohorts, and point to ongoing work that aims to overcome technical hurdles through the continued development of UHF hardware, software, and protocols.

Study protocol TransTAM: Transdiagnostic research into emotional disorders and cognitive-behavioral therapy of the adaptive mind

BACKGROUND

Emotional disorders such as depression and anxiety disorders share substantial similarities in their etiology and treatment. In recent decades, these commonalities have been increasingly recognized in classification systems and treatment programs crossing diagnostic boundaries.

METHODS

To examine the prospective effects of different transdiagnostic markers on relevant treatment outcomes, we plan to track a minimum of N = 200 patients with emotional disorders during their routine course of cognitive behavioral therapy at two German outpatient clinics. We will collect a wide range of transdiagnostic markers, ranging from basic perceptual processes and self-report measures to complex behavioral and neurobiological indicators, before entering therapy. Symptoms and psychopathological processes will be recorded before entering therapy, between the 20th and 24th therapy session, and at the end of therapy.

DISCUSSION

Our results could help to identify transdiagnostic markers with high predictive power, but also provide deeper insights into which patient groups with which symptom clusters are less likely to benefit from therapy, and for what reasons.

TRIAL REGISTRATION

The trial was preregistered at the German Clinical Trial Register (DRKS-ID: DRKS00031206; 2023-05-09).

Far from the threatening crowd: Generalisation of conditioned threat expectancy and fear in COVID-19 lockdown

Fear and anxiety are rarely confined to specific stimuli or situations. In fear generalisation, there is a spread of fear responses elicited by physically dissimilar generalisation stimuli (GS) along a continuum between danger and safety. The current study investigated fear generalisation with a novel online task using COVID-19-relevant stimuli (i.e., busy or quiet shopping street/mall scenes) during pandemic lockdown restrictions in the United Kingdom. Participants (N = 50) first completed clinically relevant trait measures before commencing a habituation phase, where two conditioned stimuli (CSs; i.e., a busy or quiet high street/mall scene) were presented. Participants then underwent fear conditioning where one conditioned stimulus (CS+) was followed by an aversive unconditioned stimulus (US; a loud female scream accompanied by a facial photograph of a female displaying a fearful emotion) and another (CS-) was not. In a test phase, six generalisation stimuli were presented where the US was withheld, and participants provided threat expectancy and fear ratings for all stimuli. Following successful conditioning, fear generalization was observed for both threat expectancy and fear ratings. Trait worry partially predicted generalised threat expectancy and COVID-19 fear strongly predicted generalised fear. In conclusion, a generalisation gradient was evident using an online remote generalisation task with images of busy/quiet streets during the pandemic. Worry and fear of COVID-19 predicted fear generalisation.

Overgeneralization of conditioned fear in patients with social anxiety disorder

Introduction

While abnormal responses to threat, including overgeneralization to conditioned fear, have been postulated to play a critical role in pathological anxiety, the relevance of previous findings to social anxiety disorder (SAD) is unclear. We investigated conditioned and generalized fear responses in patients with SAD using socially relevant stimuli.

Methods

A total of 26 patients with SAD and 25 healthy controls participated in a fear conditioning and generalization paradigm consisting of two neutral faces as conditioned stimuli (CS+ or CS-) and an angry face with contemptuous comments as unconditioned stimuli. Eight morphed faces of two conditioned stimuli in each continuum were given to test generalization. Behavioral data and physiological responses were acquired.

Results

Successful conditioning was observed in the risk ratings for both groups, while only a marginal indication of conditioning was noted in physiological measures. During the generalization phase, patients rated the risk higher than CS- when the stimuli close to CS- contained a portion of CS+ features. Larger skin conductance responses to this stimulus were linked to higher fear of negative evaluation. In addition, patients spent a longer time evaluating safe and ambiguous stimuli than healthy controls and exhibited consistently high levels of subjective arousal.

Discussion

Taken together, our findings suggest that SAD patients may exhibit a tendency towards overgeneralization of fear responses and show distinct patterns in processing generalized threat stimuli compared to healthy controls. Even though overgeneralization was not evident in physiological measures, it is necessary to consider this behavioral characteristic in the clinical management of patients with SAD.

Semantic structures facilitate threat memory integration throughout the medial temporal lobe and medial prefrontal cortex

Emotional experiences can profoundly impact our conceptual model of the world, modifying how we represent and remember a host of information even indirectly associated with that experienced in the past. Yet, how a new emotional experience infiltrates and spreads across pre-existing semantic knowledge structures (e.g., categories) is unknown. We used a modified aversive sensory preconditioning paradigm in fMRI (n = 35) to investigate whether threat memories integrate with a pre-established category to alter the representation of the entire category. We observed selective but transient changes in the representation of conceptually related items in the amygdala, medial prefrontal cortex, and occipitotemporal cortex following threat conditioning to a simple cue (geometric shape) pre-associated with a different, but related, set of category exemplars. These representational changes persisted beyond 24 h in the hippocampus and perirhinal cortex. Reactivation of the semantic category during threat conditioning, combined with activation of the hippocampus or medial prefrontal cortex, was predictive of subsequent amygdala reactivity toward novel category members at test. This provides evidence for online integration of emotional experiences into semantic categories, which then promotes threat generalization. Behaviorally, threat conditioning by proxy selectively and retroactively enhanced recognition memory and increased the perceived typicality of the semantic category indirectly associated with threat. These findings detail a complex route through which new emotional learning generalizes by modifying semantic structures built up over time and stored in memory as conceptual knowledge.

Exaggerated sensitivity to threat and reduced medial prefrontal engagement during threat generalization in reactive aggressive adolescents

Aggressive adolescents tend to exhibit abnormal fear acquisition and extinction, and reactive aggressive adolescents are often more anxious. However, the relationship between fear generalization and reactive aggression (RA) remains unknown. According to Reactive-Proactive Aggression Questionnaire (RPQ) scores, 61 adolescents were divided into two groups, namely, a high RA group (N = 30) and a low aggression (LA) group (N = 31). All participants underwent three consecutive phases of the Pavlovian conditioning paradigm (i.e., habituation, acquisition, and generalization), and neural activation of the medial prefrontal cortex (mPFC) was assessed by functional near-infrared spectroscopy (fNIRS). The stimuli were ten circles with varying sizes, including two conditioned stimuli (CSs) and eight generalization stimuli (GSs). A scream at 85 dB served as the auditory unconditioned stimulus (US). The US expectancy ratings of both CSs and GSs were higher in the RA group than in the LA group. The fNIRS results showed that CSs and GSs evoked lower mPFC activation in the RA group compared to the LA group during fear generalization. These findings suggest that abnormalities in fear acquisition and generalization are prototypical dysregulations in adolescents with RA. They provide neurocognitive evidence for dysregulated fear learning in the mechanisms underlying adolescents with RA, highlighting the need to develop emotional regulation interventions for these individuals.

Unconditioned stimulus devaluation decreases the generalization of costly safety behaviors

Safety behaviors are often maladaptive in clinical anxiety as they typically persist without realistic threat and cause various impairments. In the laboratory, safety behaviors are modelled by responses to a conditioned stimulus (CS) that reduce the occurrence of an expected aversive unconditioned stimulus (US). Preliminary evidence suggests that US devaluation, a procedure that decreases US aversiveness, devalues the threat value of the CS and thus diminishes safety behaviors to the CS. This study (n = 78) aimed to extend this finding and examined whether US-devaluation can reduce the generalization of safety behaviors to various stimuli. After acquiring safety behaviors to CSs of different categories, the US predicted by one CS category was devalued. In test, participants showed a selective reduction in safety behaviors to novel stimuli of the devalued CS category, reflecting a decrease in generalization of safety behaviors. Trait anxiety was associated with persistent generalized safety behaviors to novel stimuli of the devalued category. We discuss how US devaluation may improve treatment outcome but also the challenges of clinical translation.

Automated anxiety detection using probabilistic binary pattern with ECG signals

BACKGROUND AND AIM

Anxiety disorder is common; early diagnosis is crucial for management. Anxiety can induce physiological changes in the brain and heart. We aimed to develop an efficient and accurate handcrafted feature engineering model for automated anxiety detection using ECG signals.

MATERIALS AND METHODS

We studied open-access electrocardiography (ECG) data of 19 subjects collected via wearable sensors while they were shown videos that might induce anxiety. Using the Hamilton Anxiety Rating Scale, subjects are categorized into normal, light anxiety, moderate anxiety, and severe anxiety groups. ECGs were divided into non-overlapping 4- (Case 1), 5- (Case 2), and 6-second (Case 3) segments for analysis. We proposed a self-organized dynamic pattern-based feature extraction function-probabilistic binary pattern (PBP)-in which patterns within the function were determined by the probabilities of the input signal-dependent values. This was combined with tunable q-factor wavelet transform to facilitate multileveled generation of feature vectors in both spatial and frequency domains. Neighborhood component analysis and Chi2 functions were used to select features and reduce data dimensionality. Shallow k-nearest neighbors and support vector machine classifiers were used to calculate four (=2 × 2) classifier-wise results per input signal. From the latter, novel self-organized combinational majority voting was applied to calculate an additional five voted results. The optimal final model outcome was chosen from among the nine (classifier-wise and voted) results using a greedy algorithm.

RESULTS

Our model achieved classification accuracies of over 98.5 % for all three cases. Ablation studies confirmed the incremental accuracy of PBP-based feature engineering over traditional local binary pattern feature extraction.

CONCLUSIONS

The results demonstrated the feasibility and accuracy of our PBP-based feature engineering model for anxiety classification using ECG signals.

Fear generalization predicts post-traumatic stress symptoms: A two-year follow-up study in Dutch fire fighters

INTRODUCTION

Excessive fear generalization has been associated with pathological anxiety, including posttraumatic stress disorder (PTSD). However, studies investigating the longitudinal relationship between generalization and the development of anxiety symptomatology are scarce. This study aims to test the predictive value of fear generalization for PTSD symptoms in a high-risk profession sample and to explore the relationship between generalization and neuroticism, which are both linked to PTSD.

METHOD

Longitudinal data from a multi-wave study in 529 Dutch fire-fighters were used. Fear generalization, PTSD symptoms and neuroticism were assessed at baseline. PTSD symptoms were reevaluated at six, 12, 18, and 24 months. Generalization was assessed in a differential conditioning paradigm by measuring expectancies of an aversive outcome when presented with stimuli similar to previously conditioned stimuli.

RESULTS

Higher expectancy ratings towards stimuli most similar to safety signals predicted PTSD symptoms at follow-up after controlling for baseline PTSD symptoms, whereas higher expectancy ratings towards stimuli most similar to danger signals was associated with neuroticism. Neuroticism weakened the predictive power of fear generalization when considered simultaneously.

DISCUSSION

These findings suggest that heightened fear generalization is associated with the development of anxiety and trauma-related symptoms. Targeting problematic fear generalization may be a promising intervention approach.

Contingency Reversal in Conditioned Fear Learning: The Moderated Mediation Model of Intolerance of Uncertainty and Instruction

Objective

The study aimed to examine the roles of anxiety and intolerance of uncertainty (IU) in conditioned fear learning under an uncertain context induced by the contingency reversal of the association between the conditioned stimulus and the unconditioned stimulus (CS-US).

Methods

The study sample comprised 53 participants, randomly divided into two groups: a non-instruction group and an instruction group. The experimental procedure encompassed five stages: pre-acquisition, acquisition, generalization, reversal acquisition, and reversal generalization. Our study primarily focused on analyzing a moderated mediation model.

Results

In the instructed group, we observed that the reversed fear generalization response was directly influenced by the pre-reversal fear generalization response, while also being indirectly mediated by the IU factor. However, in the non-instructed group, we did not find a significant mediating effect of IU. Moreover, we noted that the mediation of IU was contingent on the instructional information. It is noteworthy that anxiety did not exhibit a discernible role in conditioned fear within the uncertainty condition in our study.

Conclusion

The findings provide novel insights into fear-related phenomena, emphasizing the intricate interplay between individual traits and fear generalization under conditions of uncertainty. They contribute to understanding the mechanisms of emotional and cognitive interactions in uncertain conditions.

Adult Neurogenesis, Context Encoding, and Pattern Separation: A Pathway for Treating Overgeneralization

In mammals, the subgranular zone of the dentate gyrus is one of two brain regions (with the subventricular zone of the olfactory bulb) that continues to generate new neurons throughout adulthood, a phenomenon known as adult hippocampal neurogenesis (AHN) (Eriksson et al., Nat Med 4:1313-1317, 1998; García-Verdugo et al., J Neurobiol 36:234-248, 1998). The integration of these new neurons into the dentate gyrus (DG) has implications for memory encoding, with unique firing and wiring properties of immature neurons that affect how the hippocampal network encodes and stores attributes of memory. In this chapter, we will describe the process of AHN and properties of adult-born cells as they integrate into the hippocampal circuit and mature. Then, we will discuss some methodological considerations before we review evidence for the role of AHN in two major processes supporting memory that are performed by the DG. First, we will discuss encoding of contextual information for episodic memories and how this is facilitated by AHN. Second, will discuss pattern separation, a major role of the DG that reduces interference for the formation of new memories. Finally, we will review clinical and translational considerations, suggesting that stimulation of AHN may help decrease overgeneralization-a common endophenotype of mood, anxiety, trauma-related, and age-related disorders.

Humans display interindividual differences in the latent mechanisms underlying fear generalization behaviour

Human generalization research aims to understand the processes underlying the transfer of prior experiences to new contexts. Generalization research predominantly relies on descriptive statistics, assumes a single generalization mechanism, interprets generalization from mono-source data, and disregards individual differences. Unfortunately, such an approach fails to disentangle various mechanisms underlying generalization behaviour and can readily result in biased conclusions regarding generalization tendencies. Therefore, we combined a computational model with multi-source data to mechanistically investigate human generalization behaviour. By simultaneously modelling learning, perceptual and generalization data at the individual level, we revealed meaningful variations in how different mechanisms contribute to generalization behaviour. The current research suggests the need for revising the theoretical and analytic foundations in the field to shift the attention away from forecasting group-level generalization behaviour and toward understanding how such phenomena emerge at the individual level. This raises the question for future research whether a mechanism-specific differential diagnosis may be beneficial for generalization-related psychiatric disorders.

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.

Pre-Learning Stress That Is Temporally Removed from Acquisition Impairs Fear Learning

Few studies have examined the time-dependent effects of stress on fear learning. Previously, we found that stress immediately before fear conditioning enhanced fear learning. Here, we aimed to extend these findings by assessing the effects of stress 30 min prior to fear conditioning on fear learning and fear generalization. Two hundred and twenty-one healthy adults underwent stress (socially evaluated cold pressor test) or a control manipulation 30 min before completing differential fear conditioning in a fear-potentiated startle paradigm. One visual stimulus (CS+), but not another (CS-), was associated with an aversive airblast to the throat (US) during acquisition. The next day, participants were tested for their fear responses to the CS+, CS-, and several generalization stimuli. Stress impaired the acquisition of fear on Day 1 but had no significant impact on fear generalization. The stress-induced impairment of fear learning was particularly evident in participants who exhibited a robust cortisol response to the stressor. These findings are consistent with the notion that stress administered 30 min before learning impairs memory formation via corticosteroid-related mechanisms and may help us understand how fear memories are altered in stress-related psychological disorders.

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.

Stimulus diversity increases category-based fear generalization and the effect of intolerance of uncertainty

Fear generalization refers to conditioned fear responses extending to related stimuli and fear overgeneralization is a key feature of pathological anxiety. Along with perception similarity, conceptual relations affect fear generalization. We investigated whether stimulus diversity-an important principle of category-based induction-influences fear generalization. Induction studies have shown that generalization from a premise involving diverse instances is stronger than that from non-diverse instances. We adopted this framework for fear learning and established two groups. The diverse group developed fear in response to diverse instances from one category, while the non-diverse group acquired fear of non-diverse instances from the same category. An effect of stimulus diversity was observed in shock-expectancy ratings, with the diverse group displaying higher fear generalization than the non-diverse group. We also tested whether intolerance of uncertainty (IU) might affect the difference in fear generalization between the two conditions. Individuals with higher IU showed reduced difference in fear generalization between two conditions, mainly driven by heightened fear generalization to novel stimulus with ambiguous threat levels in the non-diverse condition. This study helps illustrate the mechanisms behind differential category-based fear generalization and provides a potential explanation for why higher IU individuals may develop anxiety disorders following trauma.

Time is a great healer: Peak-end memory bias in anxiety - Induced by threat of shock

Recently, we demonstrated that the peak-end memory bias, which is well established in the context of pain, can also be observed in anxiety: Retrospective evaluations of a frightening experience are worse when peak anxiety is experienced at the end of an episode. Here, we set out to conceptually replicate and extend this finding with rigorous experimental control in a threat of shock paradigm. We induced two intensity levels of anxiety by presenting visual cues that indicated different strengths of electric stimuli. Each of the 59 participants went through one of two conditions that only differed in the order of moderate and high threat phases. As a manipulation check, orbicularis-EMG to auditory startle probes, electrodermal activity, and state anxiety confirmed the effects of the specific threat exposure. Critically, after some time had passed, participants for whom exposure had ended with high threat reported more anxiety for the entire episode than those for whom it ended with moderate threat. Moreover, they ranked their experience as more aversive when compared to other unpleasant everyday experiences. This study overcomes several previous limitations and speaks to the generalizability of the peak-end bias. Most notably, the findings bear implications for exposure therapy in clinical anxiety.