A neuroimaging method for the study of threat in adolescents

Extinction Learning Across Development: Neurodevelopmental Changes and Implications for Pediatric Anxiety Disorders

Alterations in extinction learning relate to the development and maintenance of anxiety disorders across the lifespan. While exposure therapy, based on principles of extinction, can be highly effective for treating anxiety, many patients do not show sufficient improvement following treatment. In particular, evidence suggests that exposure therapy does not work sufficiently for up to 40% of children who receive this evidence-based treatment.Importantly, fear learning and extinction, as well as the neural circuitry supporting these processes, undergo dynamic changes across development. An improved understanding of developmental changes in extinction learning and the associated neural circuitry may help to identify targets to improve treatment response in clinically anxious children and adolescents. In this chapter, we provide a brief overview of methods used to study fear learning and extinction in developmental populations. We then review what is currently known about the developmental changes that occur in extinction learning and related neural circuitry. We end this chapter with a discussion of the implications of these neurodevelopmental changes for the characterization and treatment of pediatric anxiety disorders.

Influences of affective context on amygdala functional connectivity during cognitive control from adolescence through adulthood

Emotion processing is believed to dominate over other brain functions during adolescence, including inhibitory control. However, few studies have examined the neural underpinnings of affective states during cognitive control. Here, we characterized the brain in an affective state by cross-sectionally assessing age-related changes in amygdala background connectivity during an affective inhibitory control task. Participants completed an antisaccade (AS) fMRI task while affective auditory stimuli were presented, and a 5-minute resting state scan. Results showed that while adolescents reported similar arousal levels across emotional conditions, adults perceived negative sounds to be more “arousing” and performed better than adolescents in negative trials. Amygdala background connectivity showed age-related increases with brain regions related to attention and executive control, which were not evident during resting state. Together, results suggest that amygdala connectivity within an affective context is fairly low in mid-adolescence but much stronger in adulthood, supporting age-related improvements in inhibitory control within an affective state. These findings suggest limitations during adolescence in differentiating between the arousing effects of various emotions, potentially undermining the ability to optimally engage inhibitory control. Furthermore, the age-related fMRI findings suggest that low amygdala connectivity to brain areas involved in executive control may underlie these limited abilities during adolescence.

Using a Developmental Ecology Framework to Align Fear Neurobiology Across Species

Children's development is largely dependent on caregiving; when caregiving is disrupted, children are at increased risk for numerous poor outcomes, in particular psychopathology. Therefore, determining how caregivers regulate children's affective neurobiology is essential for understanding psychopathology etiology and prevention. Much of the research on affective functioning uses fear learning to map maturation trajectories, with both rodent and human studies contributing knowledge. Nonetheless, as no standard framework exists through which to interpret developmental effects across species, research often remains siloed, thus contributing to the current therapeutic impasse. Here, we propose a developmental ecology framework that attempts to understand fear in the ecological context of the child: their relationship with their parent. By referring to developmental goals that are shared across species (to attach to, then, ultimately, separate from the parent), this framework provides a common grounding from which fear systems and their dysfunction can be understood, thus advancing research on psychopathologies and their treatment.

The need for standards in the design of differential fear conditioning and extinction experiments in youth: A systematic review and recommendations for research on anxiety

Fear extinction studies in youth have yielded mixed results due to developmental processes and variations in design, methodology and dependent measures. This systematic review focused on studies with healthy youth between 2 and 17 years of age to identify experimental parameters of studies documenting extinction effects. Thirty-five studies met inclusion criteria and the following themes emerged (a) some studies employed parameters and task demands that are complex and require active participant involvement whereas others involved simple stimulus configurations and passive participant involvement, and (b) variation exists among dependent measures in units of measurement, timing and type of measurement. The review identified that studies using geometric shape conditioned stimuli (CS) paired with a tone unconditioned stimulus (US) (e.g., metal scraping on slate), as well as face CSs with a scream US produced the most reliable extinction effects, although the latter combination may be associated with higher drop-out than shape CSs and a tone US. The most commonly used and effective dependent measures for revealing extinction effects were skin conductance responses (SCR) and subjective ratings (SR) of CS valence, fearfulness and arousal. Fear potentiated startle (FPS) blink reflexes were also an effective but less commonly used measure. It is recommended that future studies use shape CSs and the metal scraping on slate US in studies involving children and either shape CSs and the metal scraping on slate US or face CSs paired with a scream US with adolescents. It is also recommended that US expectancy ratings and CS evaluations are assessed trial-by-trial and between-phase, and that startle-eliciting stimuli to measure startle blink reflexes are delivered on every second trial per CS so that SCR and FPS can be examined. However, further research is required to determine whether increased participant involvement due to providing trial-by-trial and between-phase ratings of the CSs and US differentially influences responding, particularly in children relative to adolescents and adults.

Atypical Amygdala Response to Fear Conditioning in Autism Spectrum Disorder

BACKGROUND

Anxiety is the most common comorbid psychiatric concern in individuals diagnosed with autism spectrum disorder (ASD) and can cause significant functional impairment. Fear conditioning tasks offer a useful neurodevelopmental model for anxiety, yet there are no published neuroimaging studies of fear conditioning using ASD samples.

METHODS

Twenty adults diagnosed with ASD and 19 healthy adult control subjects completed a standard fear conditioning and extinction paradigm while undergoing functional magnetic resonance imaging scanning. A burst of air on the base of the neck was the unconditioned stimulus. Participants returned 1 day later for scanning during an extinction recall phase. A priori regions of interest were analyzed with a familywise error correction rate < 0.05.

RESULTS

All regions of interest demonstrated significantly greater response to threat than safe conditions during initial fear acquisition. Compared with age-matched control subjects, the ASD group showed a significantly decreased differential response to threat versus safe cues in right amygdala during the initial fear acquisition phase and decreased response in left amygdala during the first run of extinction recall on the second day of scanning.

CONCLUSIONS

Symptoms of severe anxiety in ASD may arise from atypical neural mechanisms especially related to the differentiation of threat versus safe cues. An inability to effectively identify safety contexts may underlie chronically increased levels of anxiety in many individuals diagnosed with ASD.

Fear and Reward Circuit Alterations in Pediatric CRPS

In chronic pain, a number of brain regions involved in emotion (e.g., amygdala, hippocampus, nucleus accumbens, insula, anterior cingulate, and prefrontal cortex) show significant functional and morphometric changes. One phenotypic manifestation of these changes is pain-related fear (PRF). PRF is associated with profoundly altered behavioral adaptations to chronic pain. For example, patients with a neuropathic pain condition known as complex regional pain syndrome (CRPS) often avoid use of and may even neglect the affected body area(s), thus maintaining and likely enhancing PRF. These changes form part of an overall maladaptation to chronic pain. To examine fear-related brain circuit alterations in humans, 20 pediatric patients with CRPS and 20 sex- and age-matched healthy controls underwent functional magnetic resonance imaging (fMRI) in response to a well-established fearful faces paradigm. Despite no significant differences on self-reported emotional valence and arousal between the two groups, CRPS patients displayed a diminished response to fearful faces in regions associated with emotional processing compared to healthy controls. Additionally, increased PRF levels were associated with decreased activity in a number of brain regions including the right amygdala, insula, putamen, and caudate. Blunted activation in patients suggests that (a) individuals with chronic pain may have deficits in cognitive-affective brain circuits that may represent an underlying vulnerability or consequence to the chronic pain state; and (b) fear of pain may contribute and/or maintain these brain alterations. Our results shed new light on altered affective circuits in patients with chronic pain and identify PRF as a potentially important treatment target.

Perceived threat in childhood: a review of research and implications for children living in violent households

The current study is a review of existing literature on perceived threat across childhood (0-19 years). There is strong evidence from this body of research that threat detection emerges in infancy and is present throughout childhood, with meaningful links to child adjustment. The wide range of methodologies employed to assess threat include biological measures (event-related potential and functional magnetic resonance imaging), observational data (gaze duration and response time), and a range of ways of gathering cognitive data (threat appraisal). Across methodologies, a uniform finding is that children who have higher threat attenuation are at increased risk for the development of anxiety disorders. It also seems that children's attention to threatening stimuli may vary across development, with heightened attention in infancy and early childhood. These findings have meaningful extensions for children who are living in violent families. Since many children living in violent homes are exposed to the threat of violence beginning in infancy, these children may be at heightened risk as compared to their nonexposed peers for the development of maladaptive patterns of threat detection and response. There is some evidence that this long-standing pattern of vigilance toward threat in key developmental periods may in part explain the increased risk of the development of anxiety disorders and posttraumatic stress disorder following exposure to violence.

The importance of early experiences for neuro-affective development

This chapter considers the functional utility of the prolonged period of immaturity in human brain development. Development of the amygdala and its connections with the prefrontal cortex is used as an example system for discussing the special role of sensitive periods in shaping neural functional architecture. The argument is made that neural immaturity during childhood may be important and confer a longer period of neuroplasticity, which can increase learning from the environment.

Amygdala activation during emotional face processing in adolescents with affective disorders: the role of underlying depression and anxiety symptoms

Depressive and anxiety disorders are often first diagnosed during adolescence and it is known that they persist into adulthood. Previous studies often tried to dissociate depressive and anxiety disorders, but high comorbidity makes this difficult and maybe even impossible. The goal of this study was to use neuroimaging to test what the unique contribution is of depression and anxiety symptomatology on emotional processing and amygdala activation, and to compare the results with a healthy control group. We included 25 adolescents with depressive and/or anxiety disorders and 26 healthy adolescents. Participants performed an emotional face processing task while in the MRI scanner. We were particularly interested in the relation between depression/anxiety symptomatology and patterns of amygdala activation. There were no significant differences in activation patterns between the control group and the clinical group on whole brain level and ROI level. However, we found that dimensional scores on an anxiety but not a depression subscale significantly predicted brain activation in the right amygdala when processing fearful, happy and neutral faces. These results suggest that anxiety symptoms are a better predictor for differentiating activation patterns in the amygdala than depression symptoms. Although the current study includes a relatively large sample of treatment naïve adolescents with depression/anxiety disorders, results might be influenced by differences between studies in recruitment strategies or methodology. Future research should include larger samples with a more equal distribution of adolescents with a clinical diagnosis of depression and/or anxiety. To conclude, this study shows that abnormal amygdala responses to emotional faces in depression and anxiety seems to be more dependent on anxiety symptoms than on depression symptoms, and thereby highlights the need for more research to better characterize clinical groups in future studies.

Predicting the accuracy of facial affect recognition: the interaction of child maltreatment and intellectual functioning

Previous research demonstrates that both child maltreatment and intellectual performance contribute uniquely to the accurate identification of facial affect by children and adolescents. The purpose of this study was to extend this research by examining whether child maltreatment affects the accuracy of facial recognition differently at varying levels of intellectual functioning. A sample of maltreated (n=50) and nonmaltreated (n=56) adolescent females, 14 to 19 years of age, was recruited to participate in this study. Participants completed demographic and study-related questionnaires and interviews to control for potential psychological and psychiatric confounds such as symptoms of posttraumatic stress disorder, negative affect, and difficulties in emotion regulation. Participants also completed an experimental paradigm that recorded responses to facial affect displays starting in a neutral expression and changing into a full expression of one of six emotions: happiness, sadness, anger, disgust, fear, or surprise. Hierarchical multiple regression assessed the incremental advantage of evaluating the interaction between child maltreatment and intellectual functioning. Results indicated that the interaction term accounted for a significant amount of additional variance in the accurate identification of facial affect after controlling for relevant covariates and main effects. Specifically, maltreated females with lower levels of intellectual functioning were least accurate in identifying facial affect displays, whereas those with higher levels of intellectual functioning performed as well as nonmaltreated females. These results suggest that maltreatment and intellectual functioning interact to predict the recognition of facial affect, with potential long-term consequences for the interpersonal functioning of maltreated females.

Translational developmental studies of stress on brain and behavior: implications for adolescent mental health and illness?

Adolescence is the transition from childhood to adulthood, with onset marked by puberty and the offset by relative independence from parents. Across species, it is a time of incredible change that carries increased risks and rewards. The ability of the individual to respond adequately to the mental, physical and emotional stresses of life during this time is a function of both their early environment and their present state. In this article, we focus on the effects that acute threat and chronic stress have on the brain and behavior in humans and rodents. First, we highlight developmental changes in frontolimbic function as healthy individuals transition into and out of adolescence. Second, we examine genetic factors that may enhance susceptibility to stress in one individual over another using translation from genetic mouse models to human neuroimaging. Third, we examine how the timing and nature of stress varies in its impact on brain and behavior. These findings are discussed in the context of implications for adolescent mental health and illness.

Treating the developing brain: implications from human imaging and mouse genetics

A fundamental issue in psychiatric medicine is the lack of empirical evidence indicating when, during development, a treatment will be most effective for a patient. We review behavioral and brain changes that occur across development, focusing on the period of adolescence, when there is a peak in diagnosis of many psychiatric disorders. We use anxiety disorders as an example because of their high prevalence in youth (affecting as many as 1 in 10). Basic forms of fear learning, which are at the core of anxiety disorders and are the targets of behavioral therapeutics, are examined as a function of age. We also discuss how fear learning has been genetically modulated in mice and humans. Based on these findings, we provide future directions for determining the efficacy of innovative therapies and preventive strategies for anxiety disorders as a function of age and potential genetic effects inferred from mice and humans.

Sex differences in physiological reactivity to acute psychosocial stress in adolescence

Females begin to demonstrate greater negative affective responses to stress than males in adolescence. This may reflect the concurrent emergence of underlying differences in physiological response systems, including corticolimbic circuitries, the hypothalamic-pituitary-adrenal axis (HPAA), and the autonomic nervous system (ANS). This review examines when sex differences in physiological reactivity to acute psychosocial stress emerge and the directionality of these differences over development. Indeed, the literature indicates that sex differences emerge during adolescence and persist into adulthood for all three physiological response systems. However, the directionality of the differences varies by system. The emerging corticolimbic reactivity literature suggests greater female reactivity, particularly in limbic regions densely innervated by gonadal hormone receptors. In contrast, males generally show higher levels of HPAA and ANS reactivity. We argue that the contrasting directionality of corticolimbic and peripheral physiological responses may reflect specific effects of gonadal hormones on distinct systems and also sex differences in evolved behavioral responses that demand different levels of peripheral physiological activation. Studies that examine both subjective reports of negative affect and physiological responses indicate that beginning in adolescence, females respond to acute stressors with more intense negative affect than males despite their comparatively lower peripheral physiological responses. This dissociation is not clearly explained by sex differences in the strength of the relationship between physiological and subjective responses. We suggest that females' greater subjective responsivity may instead arise from a greater activity in brain regions that translate stress responses to subjective awareness in adolescence. Future research directions include investigations of the role of pubertal hormones in physiological reactivity across all systems, examining the relationship of corticolimbic reactivity and negative affect, and sex differences in emotion regulation processes.

Human amygdala development in the absence of species-expected caregiving

In altricial species, like the human, caregiver presence is necessary for typical emotional development. Children who have been raised in institutional care early in life experience caregiver deprivation and are at significantly elevated risk for emotional difficulties. The current manuscript examines the non-human and human literatures on amygdala development following caregiver deprivation and presents an argument that in the absence of the species-expected caregiver presence, human amygdala development exhibits rapid development and perhaps premature engagement that results in some of the emotional phenotypes observed following early institutional care.

Development of anxiety: the role of threat appraisal and fear learning

Anxious individuals exhibit threat biases at multiple levels of information processing. From a developmental perspective, abnormal safety learning in childhood may establish threat-related appraisal biases early, which may contribute to chronic disorders in adulthood. This review illustrates how the interface among attention, threat appraisal, and fear learning can generate novel insights for outcome prediction. This review summarizes data on amygdala function, as it relates to learning and attention, highlights the importance of examining threat appraisal, and introduces a novel imaging paradigm to investigate the neural correlates of threat appraisal and threat-sensitivity during extinction recall. This novel paradigm can be used to investigate key questions relevant to prognosis and treatment. Depression and Anxiety, 2011.© 2010 Wiley-Liss, Inc.

Transitional and translational studies of risk for anxiety

Adolescence reflects a period of increased rates of anxiety, depression, and suicide. Yet most teens emerge from this period with a healthy, positive outcome. In this article, we identify biological factors that may increase risk for some individuals during this developmental period by: (1) examining changes in neural circuitry underlying core phenotypic features of anxiety as healthy individuals transition into and out of adolescence; (2) examining genetic factors that may enhance the risk for psychopathology in one individual over another using translation from mouse models to human neuroimaging and behavior; and (3) examining the effects of early experiences on core phenotypic features of anxiety using human neuroimaging and behavioral approaches. Each of these approaches alone provides only limited information on genetic and environmental influences on complex human behavior across development. Together, they reflect an emerging field of translational developmental neuroscience in forming important bridges between animal models of neurodevelopmental and neuropsychiatric disorders.

A translational bridge between mouse and human models of learned safety

BACKGROUND

Learned safety is established by negatively correlating the occurrence of a neutral stimulus and a noxious stimulus, which renders the previously neutral stimulus a 'safety signal'. While the neurophysiological and molecular mechanisms have been characterized in mice, it is currently not known how the neural substrates involved compare between mice and people.

METHODS

Here we attempt to adapt the original animal protocol to humans and use functional magnetic resonance imaging to examine neural responses to the conditioned stimulus in safety conditioned and fear conditioned subjects. Diffusion tensor imaging (DTI) was used in a parallel group of subjects as a first approach to delineate the underlying neural circuitry.

RESULTS

Learned safety is associated with dampened amygdala and increased dorsolateral prefrontal cortex and caudate responses and paralleled by pupillary constriction. A neural connection between the amygdala and the dorsolateral prefrontal cortex is suggested by DTI.

CONCLUSION

We present a translational bridge between mouse and human models of learned safety in which cellular and molecular insights from animal experiments are extended to the human neural circuitry. This study provides an example of how animal experiments can be used to inform and target human studies, which in turn can corroborate results obtained in experimental animals.

A review of adversity, the amygdala and the hippocampus: a consideration of developmental timing

A review of the human developmental neuroimaging literature that investigates outcomes following exposure to psychosocial adversity is presented with a focus on two subcortical structures – the hippocampus and the amygdala. Throughout this review, we discuss how a consideration of developmental timing of adverse experiences and age at measurement might provide insight into the seemingly discrepant findings across studies. We use findings from animal studies to suggest some mechanisms through which timing of experiences may result in differences across time and studies. The literature suggests that early life may be a time of heightened susceptibility to environmental stressors, but that expression of these effects will vary by age at measurement.

The role of the amygdala in bipolar disorder development

The amygdala has received great interest as a possible neurophysiological substrate of bipolar disorder (BD). This review summarizes information about the structure and function of the amygdala with attention to its role in experienced emotion and mood. We review the evidence for amygdala pathology in psychiatric conditions and discuss the role of the amygdala in BD during development. There appear to be consistent findings in the neuroimaging literature that suggest an etiological model for BD that involves abnormalities in the structure and function of the amygdala, but also depends on the failure of prefrontal cortical regions to modulate amygdala activity. In addition, evidence is accumulating to suggest that this model has flexible outcomes, depending on factors intrinsic and extrinsic to BD, and may follow several possible paths across the course of maturational development.

Fear conditioning in adolescents with anxiety disorders: results from a novel experimental paradigm

OBJECTIVE

Considerable research examines fear conditioning in adult anxiety disorders but few studies examine youths. Adult data suggest that anxiety disorders involve elevated fear but intact differential conditioning. We used a novel paradigm to assess fear conditioning in pediatric anxiety patients.

METHOD

Sixteen individuals with anxiety disorders and 38 healthy comparisons viewed two photographs of actresses displaying neutral expressions. One picture served as the conditioned stimulus (CS), paired with a fearful expression and a shrieking scream (CS+), whereas the other picture served as a CS unpaired with the aversive outcome (CS-). Conditioning was indexed by self-reported fear. Subjects participated in two visits involving conditioning and extinction trials.

RESULTS

Both groups developed greater fear of the CS+ relative to CS-. Higher fear levels collapsed across each CS characterized anxious relative to healthy subjects, but no significant interaction between group and stimulus type emerged. Fear levels at visit 1 predicted avoidance of visit 2. Fear levels to both CS types showed stability even after extinction.

CONCLUSIONS

Consistent with adult data, pediatric anxiety involves higher fear levels following conditioning but not greater differential conditioning. Extending these methods to neuroimaging studies may elucidate neural correlates of fear conditioning. Implications for exposure therapies are discussed.

Temperament and anxiety disorders

Recently, multidisciplinary research teams have come together to assess the emergence, course, and treatment of anxiety disorders in young children and adolescents. A number of researchers have suggested that early temperament traits may play a significant role in the causes and maintenance of early anxiety. This article reviews the current understanding of temperament and anxiety as separate constructs and then attempts to examine the developmental links between the two constructs. The authors examine the outstanding issues that must be addressed before the benefits of bridging these traditionally independent fields of study can be fully exploited.

Anxious responses to predictable and unpredictable aversive events

Anxiety induced by 2 types of predictable and unpredictable aversive stimuli, an unpleasant shock or a less aversive airblast to the larynx, were investigated in a between-group design. Participants anticipated predictable (signaled) or unpredictable (not signaled) aversive events, or no aversive event. Unpredictable, relative to predictable, contexts potentiated the startle reflex in the shock group but not in the airblast group. These data suggest that unpredictability can lead to a sustained level of anxiety only when the pending stimulus is sufficiently aversive. Because predictable and unpredictable danger may induce different types of aversive responses, the proposed design can serve as a useful tool for studying the neurobiology and psychopharmacology of fear and anxiety.