Multimodal evidence for delayed threat extinction learning in adolescence and young adulthood

Examining threat responses through a developmental lens

Adolescence has been characterized by risk taking and fearlessness. Yet, the emergence of anxiety disorders that are associated with fear peaks during this developmental period. Moreover, adolescents show heightened sensitivity to stress relative to children and adults. To address inconsistencies between the common characterization of adolescents as fearless and the evidence of heightened anxiety and stress during this time, we build upon foundational discoveries of threat-related circuitry and behavior in adult rodents by Joseph LeDoux and colleagues. Specifically, the conservation of this circuitry across species has provided opportunities for identifying mechanisms underlying threat responses that we have extended to developing humans and rodents. We elucidate situations in which adolescents show heightened threat responses and others where they appear fearless and link them to developmental changes of threat circuitry during this period. We discuss the potential adaptiveness of these threat responses for survival of the individual and species but also the potential risks for anxiety and stress. We end by offering potential new ways in which behavioral treatments for youth with anxiety and stress-related disorders may be optimized to target the developing vs developed brain.

Fear extinction retention in children, adolescents, and adults

Past results suggest that fear extinction and the return of extinguished fear are compromised in adolescents. However, findings have been inconclusive as there is a lack of fear extinction and extinction retention studies including children, adolescents and adults. In the present study, 36 children (6-9 years), 40 adolescents (13-17 years) and 44 adults (30-40 years), underwent a two-day fear conditioning task. Habituation, acquisition, and extinction were performed on the first day and an extinction retention test > 24 h later. Skin conductance responses were recorded during all phases of fear conditioning and functional magnetic resonance imaging (fMRI) was conducted during the fear retention test. All groups acquired and extinguished fear as measured with SCR, with no group differences in SCR during extinction retention. The groups had largely similar neural fear responses during the retention test, apart from adolescents displaying stronger amygdala fear response than children, with no differences between adolescents and adults. The findings do not support an adolescent extinction dip, and there was only marginal evidence of progressive changes in fear conditioning across development. In contrast to findings in rodents, fear conditioning in humans may elicit similar physiological responses and recruit similar neural networks from childhood to adulthood.

The NExT trial: Protocol for a two-phase randomized controlled trial testing transcranial magnetic stimulation to augment exposure therapy for youth with OCD

BACKGROUND

Exposure with Response Prevention (ERP) is a first-line treatment for OCD, but even when combined with first-line medications it is insufficiently effective for approximately half of patients. Compulsivity in OCD is thought to arise from an imbalance of two distinct neural circuits associated with specific subregions of striatum. Targeted modulation of these circuits via key cortical nodes (dorsolateral prefrontal cortex [dlPFC] or presupplementary motor area [pSMA]) has the potential to improve ERP efficacy by decreasing compulsions during therapy.

METHODS

The NExT (Neuromodulation + Exposure Therapy) trial is a two-phase, multisite early-stage randomized controlled trial designed to examine whether TMS augmentation of ERP alters activity in dlPFC and/or pSMA-associated circuitry and reduces compulsions during therapy in youth with OCD age 12-21 years. Phase 1 (N = 60) will compare two different active TMS regimens with sham: A. continuous theta burst stimulation (cTBS) to pSMA vs. B. intermittent theta burst stimulation (iTBS) to dlPFC. A priori "Go/No-Go" criteria will inform a decision to proceed to Phase 2 and the choice of TMS regimen. Phase 2 (N = 60) will compare the selected TMS regimen vs. sham in a new sample.

DISCUSSION

This trial is the first to test TMS augmentation of ERP in youth with OCD. Results will inform the potential of TMS to enhance ERP efficacy and enhance knowledge about mechanisms of change.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05931913. Registered prospectively on July 5, 2023.

Intolerance of uncertainty enhances adolescent fear generalization in both perceptual-based and category-based tasks: fNIRS studies

Fear generalization undergoes marked changes during adolescence, which may relate to the high prevalence of anxiety disorders. While intolerance of uncertainty (IU) is a key factor that amplifies fear generalization, its impact and neural basis in adolescence remain unclear. Here, we investigated the effects of IU on perceptual-based (n = 72) and category-based (n = 68) fear generalization in adolescents aged 12-15 years. Specifically, Experiment 1 utilized two different size rings as conditioned stimuli, with middle-sized rings serving as the generalized stimuli; Experiment 2 employed pictures of sparrows and refrigerators as conditioned stimuli, with other animals categorically related to the sparrow as generalized stimuli. We collected self-reported threat expectancy, response times, and fear ratings in both experiments, and conducted functional near-infrared spectroscopy in Experiment 2. Results showed that high IU adolescents had higher threat expectancy in both experiments compare to low IU. Moreover, in category-based generalization, high IU adolescents had higher fear ratings, shorter response times and reduced engagement of the left dorsolateral prefrontal cortex (DLPFC). Results indicated that IU may enhance fear generalization by deficient left DLPFC recruitment. Together the present findings point to a behavioral and neural mechanism that can render adolescents vulnerable for mental disorders.

Functional connectivity between the nucleus accumbens and amygdala underlies avoidance learning during adolescence: Implications for developmental psychopathology

BACKGROUND

Reward and threat processes work together to support adaptive learning during development. Adolescence is associated with increasing approach behavior (e.g., novelty-seeking, risk-taking) but often also coincides with emerging internalizing symptoms, which are characterized by heightened avoidance behavior. Peaking engagement of the nucleus accumbens (NAcc) during adolescence, often studied in reward paradigms, may also relate to threat mechanisms of adolescent psychopathology.

METHODS

47 typically developing adolescents (9.9-22.9 years) completed an aversive learning task during functional magnetic resonance imaging, wherein visual cues were paired with an aversive sound or no sound. Task blocks involved an escapable aversively reinforced stimulus (CS+r), the same stimulus without reinforcement (CS+nr), or a stimulus that was never reinforced (CS-). Parent-reported internalizing symptoms were measured using Revised Child Anxiety and Depression Scales.

RESULTS

Functional connectivity between the NAcc and amygdala differentiated the stimuli, such that connectivity increased for the CS+r (p = .023) but not for the CS+nr and CS-. Adolescents with greater internalizing symptoms demonstrated greater positive functional connectivity for the CS- (p = .041).

CONCLUSIONS

Adolescents show heightened NAcc-amygdala functional connectivity during escape from threat. Higher anxiety and depression symptoms are associated with elevated NAcc-amygdala connectivity during safety, which may reflect poor safety versus threat discrimination.

Late positive potential reveals sustained threat contingencies despite extinction in adolescents but not adults

BACKGROUND

Major theories link threat learning processes to anxiety symptoms, which typically emerge during adolescence. While this developmental stage is marked by substantial maturation of the neural circuity involved in threat learning, research directly examining adolescence-specific patterns of neural responding during threat learning is scarce. This study compared adolescents and adults in acquisition and extinction of conditioned threat responses assessed at the cognitive, psychophysiological, and neural levels, focusing on the late positive potential (LPP), an event-related potential (ERP) component indexing emotional valence.

METHOD

Sixty-five adults and 63 adolescents completed threat acquisition and extinction, 24 h apart, using the bell conditioning paradigm. Self-reported fear, skin conductance responses (SCR), and ERPs were measured.

RESULTS

Developmental differences emerged in neural and psychophysiological responses during threat acquisition, with adolescents displaying heightened LPP responses to threat and safety cues as well as heightened threat-specific SCR compared to adults. During extinction, SCR suggested comparable reduction in conditioned threat responses across groups, while LPP revealed incomplete extinction only among adolescents. Finally, age moderated the link between anxiety severity and LPP-assessed extinction, whereby greater anxiety severity was associated with reduced extinction among younger participants.

CONCLUSIONS

In line with developmental theories, adolescence is characterized by a specific age-related difficulty adapting to diminishing emotional significance of prior threats, contributing to heightened vulnerability to anxiety symptoms. Further, LPP appears to be sensitive to developmental differences in threat learning and may thus potentially serve as a useful biomarker in research on adolescents, threat learning, and anxiety.

Sensitivity and specificity in affective and social learning in adolescence

Adolescence is a period of heightened affective and social sensitivity. In this review we address how this increased sensitivity influences associative learning. Based on recent evidence from human and rodent studies, as well as advances in computational biology, we suggest that, compared to other age groups, adolescents show features of heightened Pavlovian learning but tend to perform worse than adults at instrumental learning. Because Pavlovian learning does not involve decision-making, whereas instrumental learning does, we propose that these developmental differences might be due to heightened sensitivity to rewards and threats in adolescence, coupled with a lower specificity of responding. We discuss the implications of these findings for adolescent mental health and education.

Neural responding during uncertain threat anticipation in pediatric anxiety

Excessive fear responses to uncertain threat are a key feature of anxiety disorders (ADs), though most mechanistic work considers adults. As ADs onset in childhood and confer risk for later psychopathology, we sought to identify conditions of uncertain threat that distinguish 8-17-year-old youth with AD (n = 19) from those without AD (n = 33), and assess test-retest reliability of such responses in a companion sample of healthy adults across three sites (n = 19). In an adapted uncertainty of threat paradigm, visual cues parametrically signaled threat of aversive stimuli (fear faces) in 25 % increments (0 %, 25 %, 50 %, 100 %), while participants underwent functional magnetic resonance imaging (fMRI). We compared neural response elicited by cues signaling different degrees of probability regarding the subsequent delivery of fear faces. Overall, youth displayed greater engagement of bilateral inferior parietal cortex, fusiform gyrus, and lingual gyrus during uncertain threat anticipation in general. Relative to healthy youth, AD youth exhibited greater activation in ventrolateral prefrontal cortex (vlPFC)/BA47 during uncertain threat anticipation in general. Further, AD differed from healthy youth in scaling of ventral striatum/sgACC activation with threat probability and attenuated flexibility of responding during parametric uncertain threat. Complementing these results, significant, albeit modest, cross-site test-retest reliability in these regions was observed in an independent sample of healthy adults. While preliminary due to a small sample size, these findings suggest that during uncertainty of threat, AD youth engage vlPFC regions known to be involved in fear regulation, response inhibition, and cognitive control. Findings highlight the potential of isolating neural correlates of threat anticipation to guide treatment development and translational work in youth.

Getting Better with Age? A Review of Psychophysiological Studies of Fear Extinction Learning Across Development

A critical developmental task is learning what constitutes reliable threat and safety signals in the environment. In humans, atypical fear learning processes are implicated in many mental health conditions, particularly fear and anxiety disorders, pointing to the potential for laboratory measures of fear learning to facilitate early identification of at-risk individuals. This chapter reviews studies of fear learning and extinction learning that incorporate peripheral measures of psychophysiological response and include a developmental sample. Broadly, these studies indicate substantial consistency in differential learning and extinction across development, as assessed with multiple paradigms, across physiological indices. Importantly, though, response coherence across measures (e.g., physiological, neural, and behavioral) was inconsistent across studies. There was also less consistency in results from studies that probed associations between anxiety and fear learning processes. These mixed findings highlight the need for additional examination of when and why there is variability, both across development and in relation to individual differences factors, including mental health, childhood adversity, and sex. In addition, there remains a need for studies that test for developmental change in extinction recall learning and whether stimulus type impacts learning across development. Longitudinal studies designed to address these questions could provide novel insight into the developmental trajectory of fear learning and extinction.

Neurodevelopmental mechanisms linking early experiences and mental health: Translating science to promote well-being among youth

Early experiences can have profound and lasting effects on mental health. Delineating neurodevelopmental pathways related to risk and resilience following adversity exposure is critical for promoting well-being and targeting interventions. A rapidly growing cross-species literature has facilitated advances in identifying neural and behavioral mechanisms linking early experiences with mental health, highlighting a central role of corticolimbic circuitry involved in learning and emotion regulation. Building upon knowledge of corticolimbic development related to stress and buffering factors, we describe the importance of the developmental timing and experiential elements of adversity in mental health outcomes. Finally, we discuss opportunities to translate knowledge of the developing brain and early experiences to optimize interventions for youth with psychopathology and to inform policy that promotes healthy development at the societal level. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Unique Associations between Conditioned Cognitive and Physiological Threat Responses and Facets of Anxiety Symptomatology in Youth

This study examined associations between anxiety symptomatology and cognitive and physiological threat responses during threat learning in a large sample of children and adolescents. Anxiety symptomatology severity along different dimensions (generalized anxiety, separation anxiety, social anxiety, and panic symptoms) was measured using parental and self-reports. Participants completed differential threat acquisition and extinction using an age-appropriate threat conditioning task. They then returned to the lab after 7-10 days to complete an extinction recall task that also assessed threat generalization. Results indicated that more severe overall anxiety was associated with greater cognitive and physiological threat responses during acquisition, extinction, and extinction recall. During acquisition and extinction, all anxiety dimensions manifested greater cognitive threat responses, while panic, separation anxiety, and social anxiety symptoms, but not generalized anxiety, were related to heightened physiological threat responses. In contrast, when we assessed generalization of cognitive threat responses, we found only generalized anxiety symptoms were associated with greater threat response generalization. The study provides preliminary evidence of specificity in threat responses during threat learning across youth with different anxiety symptoms.

Fear extinction learning and retention during adolescence in rats and mice: A systematic review

Despite exposure-based treatments being recommended for anxiety disorders, these treatments are ineffective for over half of all adolescents who receive them. The limited efficacy of exposure during adolescence may be driven by a deficit in extinction. Although indications of diminished extinction learning during adolescence were first reported over 10 years ago, these findings have yet to be reviewed and compared. This review (k = 34) found a stark inter-species difference in extinction performance: studies of adolescent mice reported deficits in extinction learning and retention of both cued and context fear. In contrast, studies of adolescent rats only reported poor extinction retention specific to cued fear. Adolescent mice and rats appeared to have only one behavioral outcome in common, being poor extinction retention of cued fear. These findings suggest that different behavioral phenotypes are present across rodent species in adolescence and highlight that preclinical work in rats and mice is not interchangeable. Further investigation of these differences offers the opportunity to better understand the etiology, maintenance, and treatment of fear-based disorders.

Early Adversity and Development: Parsing Heterogeneity and Identifying Pathways of Risk and Resilience

Adversity early in life is common and is a major risk factor for the onset of psychopathology. Delineating the neurodevelopmental pathways by which early adversity affects mental health is critical for early risk identification and targeted treatment approaches. A rapidly growing cross-species literature has facilitated advances in identifying the mechanisms linking adversity with psychopathology, specific dimensions of adversity and timing-related factors that differentially relate to outcomes, and protective factors that buffer against the effects of adversity. Yet, vast complexity and heterogeneity in early environments and neurodevelopmental trajectories contribute to the challenges of understanding risk and resilience in the context of early adversity. In this overview, the author highlights progress in four major areas-mechanisms, heterogeneity, developmental timing, and protective factors; synthesizes key challenges; and provides recommendations for future research that can facilitate progress in the field. Translation across species and ongoing refinement of conceptual models have strong potential to inform prevention and intervention strategies that can reduce the immense burden of psychopathology associated with early adversity.

High vagal tone and rapid extinction learning as potential transdiagnostic protective factors following childhood violence exposure

Childhood exposure to violence is strongly associated with psychopathology. High resting respiratory sinus arrhythmia (RSA) is associated with lower levels of psychopathology in children exposed to violence. High RSA may help to protect against psychopathology by facilitating fear extinction learning, allowing more flexible autonomic responses to learned threat and safety cues. In this study, 165 youth (79 female, aged 9-17; 86 exposed to violence) completed assessments of violence exposure, RSA, and psychopathology, and a fear extinction learning task; 134 participants returned and completed psychopathology assessments 2 years later. Resting RSA moderated the longitudinal association of violence exposure with post-traumatic stress disorder (PTSD) symptoms and externalizing psychopathology, such that the association was weaker among youths with higher RSA. Higher skin conductance responses (SCR) during extinction learning to the threat cue (CS+) was associated with higher internalizing symptoms at follow-up and greater SCR to the safety cue (CS-) was associated with higher PTSD, internalizing, and externalizing symptoms, as well as the p-factor, controlling for baseline symptoms. Findings suggest that higher RSA may protect against emergence of psychopathology among children exposed to violence. Moreover, difficulty extinguishing learned threat responses and elevated autonomic responses to safety cues may be associated with risk for future psychopathology.

Adolescent anxiety disorders and the developing brain: comparing neuroimaging findings in adolescents and adults

Adolescence is the peak period for the incidence of anxiety disorders. Recent findings have revealed the immaturity of neural networks underlying emotional regulation in this population. Brain vulnerability to anxiety in adolescence is related to the unsynchronised development of anxiety-relevant brain functional systems. However, our current knowledge on brain deficits in adolescent anxiety is mainly borrowed from studies on adults. Understanding adolescent-specific brain deficits is essential for developing biomarkers and brain-based therapies targeting adolescent anxiety. This article reviews and compares recent neuroimaging literature on anxiety-related brain structural and functional deficits between adolescent and adult populations, and proposes a model highlighting the differences between adolescence and adulthood in anxiety-related brain networks. This model emphasises that in adolescence the emotional control system tends to be hypoactivated, the fear conditioning system is immature, and the reward and stress response systems are hypersensitive. Furthermore, the striatum’s functional links to the amygdala and the prefrontal cortex are strengthened, while the link between the prefrontal cortex and the amygdala is weakened in adolescence. This model helps to explain why adolescents are vulnerable to anxiety disorders and provides insights into potential brain-based approaches to intervene in adolescent anxiety disorders.

Potentiated perceptual neural responses to learned threat during Pavlovian fear acquisition and extinction in adolescents

Adolescents' experience of heightened anxiety and increased vulnerability to develop anxiety disorders is believed to partly result from blunted fear extinction processes. However, whether this anxiety is mediated by adolescent-specific differences in perceptual responses to learned threat is not known. To investigate this, we used EEG to examine reinforcement-dependent changes in early visual event-related potentials in adolescents (N = 28, 13-14 years) and adults (N = 23, 25-26 years old) during a differential Pavlovian fear conditioning task, with one conditioned stimulus (CS+) paired with an aversive sound (unconditioned stimulus [US]) on 50% of trials, and another (CS-) never paired with the US. An immediate extinction phase followed, where both CSs were presented alone. We found age-dependent dissociations between explicit and implicit measures of fear learning. Specifically, both adolescents and adults demonstrated successful fear conditioning and extinction according to their explicit awareness of changes in CS contingencies and their evaluative CS ratings, and their differential skin conductance responses. However, for the first time we show age differences at the neural level in perceptual areas. Only adolescents showed greater visual P1 and N1 responses to the CS+ compared to the CS- during acquisition, a dissociation that for the N1 was maintained during extinction. We suggest that the adolescent perceptual hyper-responsivity to learned threat and blunted extinction reported here could be an adaptive mechanism to protect adolescents from harm. However, this hyper-responsivity may also confer greater vulnerability to experience pathological levels of anxiety at this developmental stage.

Comparing neural correlates of conditioned inhibition between children with and without anxiety disorders - A preliminary study

Cognitive-behavioral therapy (CBT), a first-line treatment for pediatric anxiety disorders, is based on principles of threat learning and extinction. However, CBT does not work sufficiently for up to 40% of clinically anxious youth. The neural and behavioral correlates of conditioned inhibition might provide promising targets for attempts to improve CBT response. During conditioned inhibition, threat and safety cues appear together, forming a safety compound. Here, we test whether this safety compound elicits a reduced fear response compared to pairing the threat cue with a novel cue (novel compound). The current pilot study compares behavioral, physiological, and neural correlates of conditioned inhibition between children with (n = 17, Mage = 13.09, SDage = 3.05) and without (n = 18, Mage = 14.49, SDage = 2.38) anxiety disorders. Behavioral and physiological measures did not differ between children with and without anxiety disorders during fear acquisition. During testing, children with anxiety disorders showed overall higher skin conductance response and expected to hear the aversive sound following the novel compound more often than children without anxiety disorders. Children with anxiety disorders showed more activity in the right ventromedial prefrontal cortex (vmPFC) to the safety versus novel compound. Children without anxiety disorders showed the opposite pattern - more right vmPFC activity to the novel versus safety compound (F(1,31) = 5.40, p = 0.03). No group differences manifested within the amygdala, dorsal anterior cingulate cortex, or hippocampus. These pilot findings suggest a feasible approach for examining conditioned inhibition in pediatric anxiety disorders. If replicated in larger samples, findings may implicate perturbed conditioned inhibition in pediatric anxiety disorders and provide targets for CBT.

Learning About Safety: Conditioned Inhibition as a Novel Approach to Fear Reduction Targeting the Developing Brain

Adolescence is a peak time for the onset of psychiatric disorders, with anxiety disorders being the most common and affecting as many as 30% of youths. A core feature of anxiety disorders is difficulty regulating fear, with evidence suggesting deficits in extinction learning and corresponding alterations in frontolimbic circuitry. Despite marked changes in this neural circuitry and extinction learning throughout development, interventions for anxious youths are largely based on principles of extinction learning studied in adulthood. Safety signal learning, based on conditioned inhibition of fear in the presence of a cue that indicates safety, has been shown to effectively reduce anxiety-like behavior in animal models and attenuate fear responses in healthy adults. Cross-species evidence suggests that safety signal learning involves connections between the ventral hippocampus and the prelimbic cortex in rodents or the dorsal anterior cingulate cortex in humans. Particularly because this pathway follows a different developmental trajectory than fronto-amygdala circuitry involved in traditional extinction learning, safety cues may provide a novel approach to reducing fear in youths. In this review, the authors leverage a translational framework to bring together findings from studies in animal models and humans and to bridge the gap between research on basic neuroscience and clinical treatment. The authors consider the potential application of safety signal learning for optimizing interventions for anxious youths by targeting the biological state of the developing brain. Based on the existing cross-species literature on safety signal learning, they propose that the judicious use of safety cues may be an effective and neurodevelopmentally optimized approach to enhancing treatment outcomes for youths with anxiety disorders.