Although interpretation biases are well documented among youth with anxiety disorders, understanding of their neural correlates is limited. In particular, there has been little study of how anxious youth neurobiologically represent changing contextual cues that may trigger anxiety. This study examined neural responses during a task in which participants viewed neutral faces paired with experimentally manipulated contextual stimuli.
Participants (16 youth with a primary anxiety disorder diagnosis and 15 age- and gender-matched controls) passively viewed neutral faces that were paired with either neutral descriptive vignettes or with vignettes that were potentially anxiety provoking (for example, those that involved performance/social evaluation).
The two groups were differentiated by their medial prefrontal cortex (mPFC) responses, such that context modulated mPFC activation in anxious youth while non-anxious youth demonstrated no such differentiation. Counter to expectations, the performance/evaluation frames were not associated with amygdala reactivity for either group.
The present investigation is among the first to identify how context modulates mPFC responding to neutral stimuli among anxious youth. It takes an important step toward understanding the neurobiological correlates underlying interpretation biases of neutral stimuli in this population.
Anxiety disorders; Adolescence; FMRI
Accumulating evidence over the past decade has highlighted an important role of the endocannabinoid (eCB) system in the regulation of stress and emotional behavior across divergent species, from rodents to humans. The general findings from this work indicate that the eCB system plays an important role in gating and buffering the stress response, dampening anxiety and regulating mood. Work in rodents has allowed researchers to determine the neural mechanisms mediating this relationship while work in human populations has demonstrated the possible importance of this system in stress-related psychiatric diseases, such as post-traumatic stress disorder, generalized anxiety and major depression. These stress-protective effects of eCB signaling appear to be primarily mediated by their actions within corticolimbic structures, particularly the amygdala and the prefrontal cortex. The aim of this review is to provide an up-to-date discussion of the current level of knowledge in this field, as well as address the current gaps in knowledge and specific areas of research that require attention.
Endocannabinoid; Anandamide; 2-AG; Stress; Anxiety; Depression; PTSD
Several mental illnesses, including anxiety, can manifest during development, with onsets in late childhood. Understanding the neurobiological underpinnings of risk for anxiety is of crucial importance for early prevention and intervention approaches. Translational neuroscience offers tools to investigate such mechanisms in human and animal models. The current review describes paradigms derived from neuroscience, such as fear conditioning and extinction and overviews studies that have used these paradigms in animals and humans across development. The review also briefly discusses developmental trajectories of the relevant neural circuits and the emergence of clinical anxiety. Future studies should focus on developmental changes in these paradigms, paying close attention to neurobiological and hormonal changes associated with childhood and adolescence.
Anxiety disorders; Development; Childhood; Adolescence; Fear conditioning; Extinction
Extinction learning is proposed to be one key mechanism of action underlying exposure-based cognitive-behavioral therapy (CBT) in specific phobia. Beyond that, cognitive reappraisal, one important strategy to regulate negative emotions, is a crucial component of CBT interventions, but has been disregarded in previous studies investigating neural change processes in specific phobia. The aim of this study was to investigate the association of individual differences in habitual/dispositional cognitive reappraisal usage and the time course of brain activation during phobic stimulation in specific phobia.
Dental phobic patients and healthy control subjects participated in a functional magnetic resonance imaging (fMRI) study whilst being confronted with phobic, disgust, fear and neutral pictures. Individual differences in cognitive reappraisal usage were assessed via a self-report questionnaire and correlated with activation decreases over the course of time.
Phobic individuals with higher dispositional cognitive reappraisal scores showed a more pronounced activation decline in the right dorsomedial prefrontal cortex (dmPFC) which might be associated with a diminution of explicit cognitive emotion regulation over the course of time. Less decrease of activation in the right ventromedial prefrontal cortex (vmPFC) and the lateral orbitofrontal cortex (lOFC) over time in subjects with higher cognitive reappraisal scores might be related to a stronger automatic regulation of emotions or even emotional relearning. Additionally, phobic subjects compared with healthy controls showed a stronger habituation of the left dmPFC over the course of symptom provocation.
The results of this study show for the first time that individual differences in cognitive reappraisal usage are associated with the time course of brain activation during symptom provocation in specific phobia. Additionally, the present study gives first indications for the importance of considering individual differences in cognitive reappraisal usage in the treatment of specific phobia.
Specific phobia; Emotion regulation; Cognitive reappraisal; vmPFC; Insula; Habituation; Extinction; fMRI; CBT
Although several psychological and pharmacological treatment options are available for anxiety disorders, not all patients respond well to each option. Furthermore, given the relatively long duration of adequate treatment trials, finding a good treatment fit can take many months or longer. Thus, both clinicians and patients would benefit from the identification of objective pre-treatment measures that predict which patients will best respond to a given treatment. Recent studies have begun to use biological measures to help predict symptomatic change after treatment in anxiety disorders. In this review, we summarize studies that have used structural and functional neuroimaging measures to predict treatment response in obsessive-compulsive disorder (OCD), posttraumatic stress disorder (PTSD), generalized anxiety disorder (GAD), and social anxiety disorder (SAD). We note the limitations of the current studies and offer suggestions for future research. Although the literature is currently small, we conclude that pre-treatment neuroimaging measures do appear to predict treatment response in anxiety disorders, and future research will be needed to determine the relative predictive power of neuroimaging measures as compared to clinical and demographic measures.
Social anxiety disorder; Obsessive-compulsive disorder; Posttraumatic stress disorder; Generalized anxiety disorder; Amygdala; Medial prefrontal cortex; Anterior cingulate cortex; Orbitofrontal cortex; fMRI; PET
Social Anxiety Disorder (SAD) is a common and debilitating condition that typically manifests in adolescence. Here we describe cognitive factors engaged by brain-imaging tasks, which model the peer-based social interactions that evoke symptoms of SAD. We then present preliminary results from the Virtual School paradigm, a novel peer-based social interaction task. This paradigm is designed to investigate the neural mechanisms mediating individual differences in social response flexibility and in participants’ responses to uncertainty in social contexts. We discuss the utility of this new paradigm for research on brain function and developmental psychopathology.
fMRI; Development; Peers; Uncertainty; Social cognition; Affect; Behavioral inhibition; Response flexibility; Peer victimization; Bullying
Various neuropsychiatric conditions, including posttraumatic stress disorder (PTSD), are characterized by deficient fear extinction, but individuals differ greatly in risk for these. While there is growing evidence that fear extinction is influenced by certain procedural variables, it is unclear how these influences might vary across individuals and subpopulations. To model individual differences in fear extinction, prior studies identified a strain of inbred mouse, 129S1/SvImJ (S1), which exhibits a profound deficit in fear extinction, as compared to other inbred strains, such as C57BL/6J (B6).
Here, we assessed the effects of procedural variables on the impaired extinction phenotype of the S1 strain and, by comparison, the extinction-intact B6 strain. The variables studied were 1) the interval between conditioning and extinction, 2) the interval between cues during extinction training, 3) single-cue exposure before extinction training, and 4) extinction of a second-order conditioned cue.
Conducting extinction training soon after (‘immediately’) conditioning attenuated fear retrieval in S1 mice and impaired extinction in B6 mice. Spacing cue presentations with long inter-trial intervals during extinction training augmented fear in S1 and B6 mice. The effect of spacing was lost with one-trial fear conditioning in B6, but not S1 mice. A single exposure to a conditioned cue before extinction training did not alter extinction retrieval, either in B6 or S1 mice. Both the S1 and B6 strains exhibited robust second-order fear conditioning, in which a cue associated with footshock was sufficient to serve as a conditioned exciter to condition a fear association to a second cue. B6 mice extinguished the fear response to the second-order conditioned cue, but S1 mice failed to do so.
These data provide further evidence that fear extinction is strongly influenced by multiple procedural variables and is so in a highly strain-dependent manner. This suggests that the efficacy of extinction-based behavioral interventions, such as exposure therapy, for trauma-related anxiety disorders will be determined by the procedural parameters employed and the degree to which the patient can extinguish.
Mouse; Gene; Behavior; Fear; Second order conditioning; PTSD; Prefrontal cortex; Amygdala; Anxiety; Rodent; Exposure-based therapy
Depression is characterised partly by blunted reactions to reward. However, tasks probing this deficiency have not distinguished insensitivity to reward from insensitivity to the prediction errors for reward that determine learning and are putatively reported by the phasic activity of dopamine neurons. We attempted to disentangle these factors with respect to anhedonia in the context of stress, Major Depressive Disorder (MDD), Bipolar Disorder (BPD) and a dopaminergic challenge.
Six behavioural datasets involving 392 experimental sessions were subjected to a model-based, Bayesian meta-analysis. Participants across all six studies performed a probabilistic reward task that used an asymmetric reinforcement schedule to assess reward learning. Healthy controls were tested under baseline conditions, stress or after receiving the dopamine D2 agonist pramipexole. In addition, participants with current or past MDD or BPD were evaluated. Reinforcement learning models isolated the contributions of variation in reward sensitivity and learning rate.
MDD and anhedonia reduced reward sensitivity more than they affected the learning rate, while a low dose of the dopamine D2 agonist pramipexole showed the opposite pattern. Stress led to a pattern consistent with a mixed effect on reward sensitivity and learning rate.
Reward-related learning reflected at least two partially separable contributions. The first related to phasic prediction error signalling, and was preferentially modulated by a low dose of the dopamine agonist pramipexole. The second related directly to reward sensitivity, and was preferentially reduced in MDD and anhedonia. Stress altered both components. Collectively, these findings highlight the contribution of model-based reinforcement learning meta-analysis for dissecting anhedonic behavior.
Anhedonia; Major depressive disorder; Depression; Reinforcement learning; Reward learning; Prediction error; Computational; Meta-analysis; Reward sensitivity; Learning rate
The goal of this review is to examine the clinical studies on d-cycloserine, a partial glutamatergic N-methyl-D-aspartate agonist, as an augmentation strategy for exposure procedures during cognitive behavioral therapy for anxiety disorders. Although cognitive behavioral therapy and anxiolytic medications are more effective than placebo for treating anxiety disorders, there is still considerable room for further improvement. Traditional combination strategies typically yield disappointing results. However, recent studies based on translational research have shown promise to augment the neural circuitry underlying fear extinction with pharmacological means. We discuss the current state of the literature, including inconsistencies of findings and issues concerning the drug mechanism, dosing, and dose timing. D-cycloserine is a promising combination strategy for cognitive behavioral therapy of anxiety disorders by augmenting extinction learning. However, there is also evidence to suggest that d-cycloserine can facilitate reconsolidation of fear memory when exposure procedures are unsuccessful.
Anxiety disorder; Cognitive behavioral therapy; Glutamate; D-cycloserine; NMDA; Psychotherapy; Pharmacotherapy
Previous research suggests that individuals with posttraumatic stress disorder (PTSD) preferentially attend to trauma-related emotional stimuli and have difficulty completing unrelated concurrent tasks. Compared to trauma-exposed control groups, individuals with PTSD also exhibit lower rostral anterior cingulate cortex (rACC) activation during tasks involving interference from trauma-related stimuli. However, it is not clear whether relatively diminished rACC activation in PTSD also occurs during interference tasks involving trauma-unrelated emotional stimuli. The present study employed functional magnetic resonance imaging (fMRI) and an interference task that involves emotional facial expressions and elicits rACC activation in healthy participants.
While performing a trauma-unrelated emotional interference task, participants with PTSD (n=17) showed less rACC activation than trauma-exposed non-PTSD (TENP; n=18) participants. In the PTSD group, rACC activation was negatively correlated with the severity of re-experiencing symptoms. The two groups did not significantly differ on behavioral measures (i.e., response times and error rates).
These findings suggest that relatively diminished rACC activation in PTSD can be observed in interference tasks involving trauma-unrelated emotional stimuli, indicating a more general functional brain abnormality in this disorder. Future neuroimaging studies need not employ trauma-related stimuli in order to detect rACC abnormalities in PTSD.
fMRI; Stroop; Posttraumatic stress disorder; Anterior cingulate; Interference; Trauma
Anxiety disorders are complex diseases, which often occur in combination with major depression, alcohol use disorder, or general medical conditions. Anxiety disorders were the most common mental disorders within the EU states in 2010 with 14% prevalence. Anxiety disorders are triggered by environmental factors in genetically susceptible individuals, and therefore genetic research offers a great route to unravel molecular basis of these diseases. As anxiety is an evolutionarily conserved response, mouse models can be used to carry out genome-wide searches for specific genes in a setting that controls for the environmental factors. In this review, we discuss translational approaches that aim to bridge results from unbiased genome-wide screens using mouse models to anxiety disorders in humans. Several methods, such as quantitative trait locus mapping, gene expression profiling, and proteomics, have been used in various mouse models of anxiety to identify genes that regulate anxiety or play a role in maintaining pathological anxiety. We first discuss briefly the evolutionary background of anxiety, which justifies cross-species approaches. We then describe how several genes have been identified through genome-wide methods in mouse models and subsequently investigated in human anxiety disorder samples as candidate genes. These studies have led to the identification of completely novel biological pathways that regulate anxiety in mice and humans, and that can be further investigated as targets for therapy.
Anxiety disorders; Anxiety-like behavior; Mouse model; Cross-species approach; Genome-wide association study; Quantitative trait locus; Gene expression; Proteomics; Candidate gene
Generalized social anxiety disorder (gSAD) is associated with a heightened neural sensitivity to signals that convey threat, as evidenced by exaggerated amygdala and/or insula activation when processing face stimuli that express negative emotions. Less clear in the brain pathophysiology of gSAD are cortical top down control mechanisms that moderate reactivity in these subcortical emotion processing regions. This study evaluated amygdala, insula, and anterior cingulate cortex (ACC) activity in gSAD with a novel “Emotional Faces Shifting Attention Task” (EFSAT), an adaptation of perceptual assessment tasks well-known to elicit amygdala response. In healthy volunteers, the task has been shown to engage the amygdala when attention is directed to emotional faces and the ACC when attention is directed to shapes, away from emotional faces.
During functional MRI, 29 participants with gSAD and 27 healthy controls viewed images comprising a trio of faces (angry, fear, or happy) alongside a trio of geometric shapes (circles, rectangles, or triangles) within the same field of view. Participants were instructed to match faces or match shapes, effectively directing attention towards or away from emotional information, respectively.
Participants with gSAD exhibited greater insula, but not amygdala, activation compared to controls when attending to emotional faces. In contrast, when attention was directed away from faces, controls exhibited ACC recruitment, which was not evident in gSAD. Across participants, greater ACC activation was associated with less insula activation.
Evidence that individuals with gSAD exhibited exaggerated insula reactivity when attending to emotional faces in EFSAT is consistent with other studies suggesting that the neural basis of gSAD may involve insula hyper-reactivity. Furthermore, greater ACC response in controls than gSAD when sustained goal-directed attention is required to shift attention away from social signals, together with a negative relationship between ACC and bilateral insula activity, indicate the ACC may have served a regulatory role when the focus of attention was directed to shapes amidst emotional faces.
Social anxiety; fMRI; Emotional faces; Threat processing; Brain imaging
In March, 2012 we held the first Mideast conference on “Depression and Anxiety Spectrum disorders: from basic science to the clinic and back”, at the University of Amman, Jordan. This event brought together both clinical and basic scientists with expertise in depression and anxiety spectrum disorders. The meeting took place in a large lecture hall at the University of Jordan Medical School. The audience included faculty, residents, and students. The Dean of the Medical School opened the meeting, welcoming the guest speakers and participants.
Social anxiety disorder (SAD) is widely thought to be characterized by heightened behavioral and limbic reactivity to socio-emotional stimuli. However, although behavioral findings are clear, neural findings are surprisingly mixed.
Using functional magnetic resonance imaging (fMRI), we examined behavioral and brain responses in a priori emotion generative regions of interest (amygdala and insula) in 67 patients with generalized SAD and in 28 healthy controls (HC) during three distinct socio-emotional tasks. We administered these socio-emotional tasks during one fMRI scanning session: 1) looming harsh faces (Faces); 2) videotaped actors delivering social criticism (Criticism); and 3) written negative self-beliefs (Beliefs).
In each task, SAD patients reported heightened negative emotion, compared to HC. There were, however, no SAD versus HC differential brain responses in the amygdala and insula. Between-group whole-brain analyses confirmed no group differences in the responses of the amygdala and insula, and indicated different brain networks activated during each of the tasks. In SAD participants, social anxiety symptom severity was associated with increased BOLD signal in the left insula during the Faces task.
The similar responses in amygdala and insula in SAD and HC participants suggest that heightened negative emotion responses reported by patients with SAD may be related to dysfunction in higher cognitive processes (e.g., distorted appraisal, attention biases, or ineffective cognitive reappraisal). In addition, the findings of this study emphasize the differential effects of socio-emotional experimental tasks.
Social anxiety; Amygdala; Insula; Emotion reactivity; fMRI; Socio-emotional tasks
Considerable variation is evident in response to psychological therapies for mood and anxiety disorders. Genetic factors alongside environmental variables and gene-environment interactions are implicated in the etiology of these disorders and it is plausible that these same factors may also be important in predicting individual differences in response to psychological treatment. In this article, we review the evidence that genetic variation influences psychological treatment outcomes with a primary focus on mood and anxiety disorders. Unlike most past work, which has considered prediction of response to pharmacotherapy, this article reviews recent work in the field of therapygenetics, namely the role of genes in predicting psychological treatment response. As this is a field in its infancy, methodological recommendations are made and opportunities for future research are identified.
Genetics; Psychological therapy; Treatment response; Gene × environment interaction; Therapygenetics
Recent studies implicate individual differences in regulatory focus as contributing to self-regulatory dysfunction, particularly not responding to positive outcomes. How such individual differences emerge, however, is unclear. We conducted a proof-of-concept study to examine the moderating effects of genetically driven variation in dopamine signaling, a key modulator of neural reward circuits, on the association between regulatory focus and reward cue responsiveness.
Healthy Caucasians (N=59) completed a measure of chronic regulatory focus and a probabilistic reward task. A common functional genetic polymorphism impacting prefrontal dopamine signaling (COMT rs4680) was evaluated.
Response bias, the participants’ propensity to modulate behavior as a function of reward, was predicted by an interaction of regulatory focus and COMT genotype. Specifically, self-perceived success at achieving promotion goals predicted total response bias, but only for individuals with the COMT genotype (Val/Val) associated with relatively increased phasic dopamine signaling and cognitive flexibility.
The combination of success in promotion goal pursuit and Val/Val genotype appears to facilitate responding to reward opportunities in the environment. This study is among the first to integrate an assessment of self-regulatory style with an examination of genetic variability that underlies responsiveness to positive outcomes in goal pursuit.
Regulatory focus; Self-regulation; Reward responsiveness; Dopamine; COMT
Posttraumatic stress disorder (PTSD) is a debilitating anxiety disorder. Surveys of the general population suggest that while 50-85% of Americans will experience a traumatic event in their lifetime, only 2-50% will develop PTSD. Why some individuals develop PTSD following trauma exposure while others remain resilient is a central question in the field of trauma research. For more than half a century, the role of genetic influences on PTSD has been considered as a potential vulnerability factor. However, despite the exponential growth of molecular genetic studies over the past decade, limited progress has been made in identifying true genetic variants for PTSD.
In an attempt to aid future genome wide association studies (GWAS), this paper presents a systematic review of 28 genetic association studies of PTSD. Inclusion criteria required that 1) all participants were exposed to Criterion A traumatic events, 2) polymorphisms of relevant genes were genotyped and assessed in relation to participants’ PTSD status, 3) quantitative methods were used, and 4) articles were published in English and in peer-reviewed journals. In the examination of these 28 studies, particular attention was given to variables related to trauma exposure (e.g. number of traumas, type of trauma).
Results indicated that most articles did not report on the GxE interaction in the context of PTSD or present data on the main effects of E despite having data available. Furthermore, some studies that did consider the GxE interaction had significant findings, underscoring the importance of examining how genotypes can modify the effect of trauma on PTSD. Additionally, results indicated that only a small number of genes continue to be studied and that there were marked differences in methodologies across studies, which subsequently limited robust conclusions.
As trauma exposure is a necessary condition for the PTSD diagnosis, this paper identifies gaps in the current literature as well as provides recommendations for how future GWAS studies can most effectively incorporate trauma exposure data in both the design and analysis phases of studies.
Posttraumatic stress disorder; Trauma; Genetics; Genome-wide association studies; Gene–environment interaction
Recent laboratory studies employing an extended sleep deprivation model have mapped sleep-related changes in behavior onto functional alterations in specific brain regions supporting emotion, suggesting possible biological mechanisms for an association between sleep difficulties and deficits in emotion regulation. However, it is not yet known if similar behavioral and neural changes are associated with the more modest variability in sleep observed in daily life.
We examined relationships between sleep and neural circuitry of emotion using the Pittsburgh Sleep Quality Index and fMRI data from a widely used emotion regulation task focusing on cognitive reappraisal of negative emotional stimuli in an unselected sample of 97 adult volunteers (48 women; mean age 42.78±7.37 years, range 30–54 years old).
Emotion regulation was associated with greater activation in clusters located in the dorsomedial prefrontal cortex (dmPFC), left dorsolateral prefrontal cortex (dlPFC), and inferior parietal cortex. Only one subscale from the Pittsburgh Sleep Quality Index, use of sleep medications, was related to BOLD responses in the dmPFC and dlPFC during cognitive reappraisal. Use of sleep medications predicted lesser BOLD responses during reappraisal, but other aspects of sleep, including sleep duration and subjective sleep quality, were not related to neural activation in this paradigm.
The relatively modest variability in sleep that is common in the general community is unlikely to cause significant disruption in neural circuits supporting reactivity or regulation by cognitive reappraisal of negative emotion. Use of sleep medication however, may influence emotion regulation circuitry, but additional studies are necessary to determine if such use plays a causal role in altering emotional responses.
Emotion; Emotion regulation; Sleep; Sleep quality; FMRI
PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD.
Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins.
There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD.
These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.
Although the neurobiological mechanisms underlying panic disorder (PD) are not yet clearly understood, increasing amount of evidence from animal and human studies suggests that the amygdala, which plays a pivotal role in neural network of fear and anxiety, has an important role in the pathogenesis of PD. This article aims to (1) review the findings of structural, chemical, and functional neuroimaging studies on PD, (2) relate the amygdala to panic attacks and PD development, (3) discuss the possible causes of amygdalar abnormalities in PD, (4) and suggest directions for future research.
Panic disorder; Panic attack; Amygdala; Neuroimaging
Research into neural mechanisms of drug abuse risk has focused on the role of dysfunction in neural circuits for reward. In contrast, few studies have examined the role of dysfunction in neural circuits of threat in mediating drug abuse risk. Although typically regarded as a risk factor for mood and anxiety disorders, threat-related amygdala reactivity may serve as a protective factor against substance use disorders, particularly in individuals with exaggerated responsiveness to reward.
We used well-established neuroimaging paradigms to probe threat-related amygdala and reward-related ventral striatum reactivity in a sample of 200 young adult students from the ongoing Duke Neurogenetics Study. Recent life stress and problem drinking were assessed using self-report. We found a significant three-way interaction between threat-related amygdala reactivity, reward-related ventral striatum reactivity, and recent stress, wherein individuals with higher reward-related ventral striatum reactivity exhibit higher levels of problem drinking in the context of stress, but only if they also have lower threat-related amygdala reactivity. This three-way interaction predicted both contemporaneous problem drinking and problem drinking reported three-months later in a subset of participants.
These findings suggest complex interactions between stress and neural responsiveness to both threat and reward mediate problem drinking. Furthermore, they highlight a novel protective role for threat-related amygdala reactivity against drug use in individuals with high neural reactivity to reward.
Amygdala; Ventral striatum; Threat; Reward; Stress; Alcohol
Family, twin and epidemiologic studies all point to an important genetic contribution to the risk to develop mood and anxiety disorders. While some progress has been made in identifying relevant pathomechanisms for these disorders, candidate based strategies have often yielded controversial findings. Hopes were thus high when genome-wide genetic association studies became available and affordable and allowed a hypothesis-free approach to study genetic risk factors for these disorders. In an unprecendented scientific collaborative effort, large international consortia formed to allow the analysis of these genome-wide association datasets across thousands of cases and controls ( and see also http://www.broadinstitute.org/mpg/ricopili/). Now that large meta-analyses of genome-wide association studies (GWAS) have been published for bipolar disorder and major depression it has become clear that main effects of common variants are difficult to identify in these disorders, suggesting that additional approaches maybe needed to understand the genetic basis of these disorders [2,3].
Bipolar disorder (BD) is a multi-factorial disorder caused by genetic and environmental influences. It has a large genetic component, with heritability estimated between 59-93%. Recent genome-wide association studies (GWAS) using large BD patient populations have identified a number of genes with strong statistical evidence for association with susceptibility for BD. Among the most significant and replicated genes is ankyrin 3 (ANK3), a large gene that encodes multiple isoforms of the ankyrin G protein. This article reviews the current evidence for genetic association of ANK3 with BD, followed by a comprehensive overview of the known biology of the ankyrin G protein, focusing on its neural functions and their potential relevance to BD. Ankyrin G is a scaffold protein that is known to have many essential functions in the brain, although the mechanism by which it contributes to BD is unknown. These functions include organizational roles for subcellular domains in neurons including the axon initial segment and nodes of Ranvier, through which ankyrin G orchestrates the localization of key ion channels and GABAergic presynaptic terminals, as well as creating a diffusion barrier that limits transport into the axon and helps define axo-dendritic polarity. Ankyrin G is postulated to have similar structural and organizational roles at synaptic terminals. Finally, ankyrin G is implicated in both neurogenesis and neuroprotection. ANK3 and other BD risk genes participate in some of the same biological pathways and neural processes that highlight several mechanisms by which they may contribute to BD pathophysiology. Biological investigation in cellular and animal model systems will be critical for elucidating the mechanism through which ANK3 confers risk of BD. This knowledge is expected to lead to a better understanding of the brain abnormalities contributing to BD symptoms, and to potentially identify new targets for treatment and intervention approaches.
Ankyrin G; Bipolar disorder; Schizophrenia; Genome-wide association study; GWAS; Axon initial segment; Nodes of Ranvier; GABA; Neurogenesis; Synapse
Anxiety disorders are characterized by specific emotions, thoughts and physiological responses. Little is known, however, about the relationship between psychological/personality indices of anxiety responses to fear stimuli.
We studied this relationship in healthy subjects by comparing scores on psychological and personality questionnaires with results of an experimental fear conditioning paradigm using a visual conditioned stimulus (CS). We measured skin conductance response (SCR) during habituation, conditioning, and extinction; subsequently testing for recall and renewal of fear 24 hours later.
We found that multiple regression models explained 45% of the variance during conditioning to the CS+, and 24% of the variance during renewal of fear to the CS+. Factors that explained conditioning included lower levels of conscientiousness, increased baseline reactivity (SCL), and response to the shock (UCR). Low levels of extraversion correlated with greater renewal. No model could be found to explain extinction learning or extinction recall to the CS+.
The lack of correlation of fear extinction with personality and neuropsychological indices suggests that extinction may be less determined by trait variables and cognitive state, and may depend more on the subject’s current emotional state. The negative correlation between fear renewal and extraversion suggests that this personality characteristic may protect against post-treatment relapse of symptoms of anxiety disorders.
Fear; Conditioning; Extinction; Anxiety; Skin conductance; Personality traits