Recent advances in the brain imaging of social anxiety disorder

Brain circuitry underlying the ABC model of anxiety

Anxiety Disorders are prevalent and often chronic, recurrent conditions that reduce quality of life. The first-line treatments, such as serotonin reuptake inhibitors and cognitive behavioral therapy, leave a significant proportion of patients symptomatic. As psychiatry moves toward targeted circuit-based treatments, there is a need for a theory that unites the phenomenology of anxiety with its underlying neural circuits. The Alarm, Belief, Coping (ABC) theory of anxiety describes how the neural circuits associated with anxiety interact with each other and domains of the anxiety symptoms, both temporally and spatially. The latest advancements in neuroimaging techniques offer the ability to assess these circuits in vivo. Using Neurosynth, a large open-access meta-analytic imaging database, the association between terms related to specific neural circuits was explored within the ABC theory framework. Alarm-related terms were associated with the amygdala, anterior cingulum, insula, and bed nucleus of stria terminalis. Belief-related terms were associated with medial prefrontal cortex, precuneus, bilateral temporal poles, and hippocampus. Coping-related terms were associated with the ventrolateral and dorsolateral prefrontal cortices, basal ganglia, and anterior cingulate. Neural connections underlying the functional neuroanatomy of the ABC model were observed. Additionally, there was considerable interaction and overlap between circuits associated with the symptom domains. Further neuroimaging research is needed to explore the dynamic interaction between the functional domains of the ABC theory. This will pave the way for probing the neuroanatomical underpinnings of anxiety disorders and provide an evidence-based foundation for the development of targeted treatments, such as neuromodulation.

Network analysis reveals disrupted functional brain circuitry in drug-naive social anxiety disorder

Social anxiety disorder (SAD) is a common and disabling condition characterized by excessive fear and avoidance of public scrutiny. Psychoradiology studies have suggested that the emotional and behavior deficits in SAD are associated with abnormalities in regional brain function and functional connectivity. However, little is known about whether intrinsic functional brain networks in patients with SAD are topologically disrupted. Here, we collected resting-state fMRI data from 33 drug-naive patients with SAD and 32 healthy controls (HC), constructed functional networks with 34 predefined regions based on previous meta-analytic research with task-based fMRI in SAD, and performed network-based statistic and graph-theory analyses. The network-based statistic analysis revealed a single connected abnormal circuitry including the frontolimbic circuit (termed the "fear circuit", including the dorsolateral prefrontal cortex, ventral medial prefrontal cortex and insula) and posterior cingulate/occipital areas supporting perceptual processing. In this single altered network, patients with SAD had higher functional connectivity than HC. At the global level, graph-theory analysis revealed that the patients exhibited a lower normalized characteristic path length than HC, which suggests a disorder-related shift of network topology toward randomized configurations. SAD-related deficits in nodal degree, efficiency and participation coefficient were detected in the parahippocampal gyrus, posterior cingulate cortex, dorsolateral prefrontal cortex, insula and the calcarine sulcus. Aspects of abnormal connectivity were associated with anxiety symptoms. These findings highlight the aberrant topological organization of functional brain network organization in SAD, which provides insights into the neural mechanisms underlying excessive fear and avoidance of social interactions in patients with debilitating social anxiety.

The left middle temporal gyrus in the middle of an impaired social-affective communication network in social anxiety disorder

BACKGROUND

Previous studies on patients diagnosed with social anxiety disorder (SAD) reported changed patterns of the resting-state functional connectivity network (rs-FCN) between the prefrontal cortices and other prefrontal, amygdalar or striatal regions. Using a graph theory approach, this study explored the modularity-based community profile and patterns of inter-/intra-modular communication for the rs-FCN in SAD.

METHODS

In total, for 28 SAD patients and 27 healthy controls (HC), functional magnetic resonance imaging (fMRI) data were acquired in resting-state and subjected to a graph theory analysis.

RESULTS

The within-module degree z-score for a hub region [out of a total of 10 hub regions ranked using the participation coefficient] named left middle temporal gyrus was impaired in SAD compared to HC, proportional to the severity of clinician-scored and patient-reported functional impairment in SAD.

LIMITATIONS

Most of participants included in this study were undergraduate students in their early-to-mid 20's.

CONCLUSIONS

This study showed the importance of functional communication from the left middle temporal gyrus with other opercular-insular-subcortical regions for better objective functioning and lesser subjective disability in SAD.

Altered executive control network resting-state connectivity in social anxiety disorder

OBJECTIVES

Research into the neural basis of social anxiety disorder (SAD) suggests alterations in prefrontal networks, which may in turn disrupt regulation of the limbic system. Better understanding of the disturbed interface between these networks may improve current pathogenic models of this disorder.

METHODS

Applying group independent component analysis (ICA) to recordings of fMRI resting-state, connectivity in the executive control network was studied in 18 patients with SAD and 15 age- and sex-matched healthy controls.

RESULTS

Results revealed a dissociation within the left executive control network, with SAD patients showing decreased connectivity of the orbitofrontal gyrus and increased connectivity of the middle frontal gyrus compared to healthy controls. In a subsequent seed-based functional connectivity analysis, patients with SAD displayed increased connectivity between the left orbitofrontal gyrus and the left amygdala.

CONCLUSIONS

Findings suggest that hypo-connectivity in the executive control network and hyper-connectivity between the orbitofrontal cortex and the amygdala may reflect a disturbance in the balance between top-down and bottom-up control processes, potentially contributing to the development of SAD.

The aetiology and maintenance of social anxiety disorder: A synthesis of complimentary theoretical models and formulation of a new integrated model

BACKGROUND

Within maintenance models of social anxiety disorder (SAD), a number of cognitive and behavioural factors that drive the persistence of SAD have been proposed. However, these maintenance models do not address how SAD develops, or the origins of the proposed maintaining factors. There are also models of the development of SAD that have been proposed independently from maintenance models. These models highlight multiple factors that contribute risk to the onset of SAD, but do not address how these aetiological factors may lead to the development of the maintaining factors associated with SAD.

METHODS

A systematic review of the literature was conducted to identify aetiological and maintenance models of SAD. We then united key factors identified in these models and formulated an integrated aetiological and maintenance (IAM) model of SAD. A systematic review of the literature was then conducted on the components of the IAM model.

RESULTS

A number of aetiological and maintaining factors were identified in models of SAD. These factors could be drawn together into the IAM model. On balance, there is empirical evidence for the association of each of the factors in the IAM model with social anxiety or SAD, providing preliminary support for the model.

LIMITATIONS

There are relationships between components of the IAM model that require empirical attention. Future research will need to continue to test the IAM model.

CONCLUSIONS

The IAM model provides a framework for future investigations into the development and persistence of SAD.

Single dose testosterone administration alleviates gaze avoidance in women with Social Anxiety Disorder

Gaze avoidance is one of the most characteristic and persistent social features in people with Social Anxiety Disorder (SAD). It signals social submissiveness and hampers adequate social interactions. Patients with SAD typically show reduced testosterone levels, a hormone that facilitates socially dominant gaze behavior. Therefore we tested as a proof of principle whether single dose testosterone administration can reduce gaze avoidance in SAD. In a double-blind, within-subject design, 18 medication-free female participants with SAD and 19 female healthy control participants received a single dose of 0.5mg testosterone and a matched placebo, at two separate days. On each day, their spontaneous gaze behavior was recorded using eye-tracking, while they looked at angry, happy, and neutral facial expressions. Testosterone enhanced the percentage of first fixations to the eye-region in participants with SAD compared to healthy controls. In addition, SAD patients' initial gaze avoidance in the placebo condition was associated with more severe social anxiety symptoms and this relation was no longer present after testosterone administration. These findings indicate that single dose testosterone administration can alleviate gaze avoidance in SAD. They support theories on the dominance enhancing effects of testosterone and extend those by showing that effects are particularly strong in individuals featured by socially submissive behavior. The finding that this core characteristic of SAD can be directly influenced by single dose testosterone administration calls for future inquiry into the clinical utility of testosterone in the treatment of SAD.

Testosterone Modulates Altered Prefrontal Control of Emotional Actions in Psychopathic Offenders(1,2,3)

Psychopathic individuals are notorious for their controlled goal-directed aggressive behavior. Yet, during social challenges, they often show uncontrolled emotional behavior. Healthy individuals can control their social emotional behavior through anterior prefrontal cortex (aPFC) downregulation of neural activity in the amygdala, with testosterone modulating aPFC-amygdala coupling. This study tests whether individual differences in this neuroendocrine system relate to the paradoxical lack of emotional control observed in human psychopathic offenders. Emotional control was operationalized with an fMRI-adapted approach-avoidance task requiring rule-driven control over rapid emotional responses. Fifteen psychopathic offenders and 19 matched healthy control subjects made approaching and avoiding movements in response to emotional faces. Control of social emotional behavior was required during affect-incongruent trials, when participants had to override affect-congruent, automatic action tendencies and select the opposite response. Psychopathic offenders showed less control-related aPFC activity and aPFC-amygdala coupling during trials requiring control of emotional actions, when compared with healthy control subjects. This pattern was particularly pronounced in psychopathic individuals with high endogenous testosterone levels. These findings suggest that reduced prefrontal coordination underlies reduced behavioral control in psychopathic offenders during emotionally provoking situations. Even though the modest sample size warrants replication, the modulatory role of endogenous testosterone on the aPFC-amygdala circuit suggests a neurobiological substrate of individual differences that is relevant for the advancement of treatment and the reduction of recidivism.

Generalized social anxiety disorder: A still-neglected anxiety disorder 3 decades since Liebowitz's review

In the 3 decades since Liebowitz's review of 'a neglected anxiety disorder,' controversy and challenges have remained in the study of social anxiety disorder (SAD). This review examines evidence around the classification and subtyping of SAD, focusing on generalized SAD. Substantial discrepancies and variation in definition, epidemiology, assessment, and treatment of generalized SAD exist as the international literature on it has grown. In East Asian cultures in particular, study of taijin kyofusho has been important to a broadened conceptualization of SAD into generalized SAD. Despite important progress with biological and other studies, many challenges in the understanding of generalized SAD will remain in the years to come.

Neuroimaging and Anxiety: the Neural Substrates of Pathological and Non-pathological Anxiety

Advances in the use of noninvasive neuroimaging to study the neural correlates of pathological and non-pathological anxiety have shone new light on the underlying neural bases for both the development and manifestation of anxiety. This review summarizes the most commonly observed neural substrates of the phenotype of anxiety. We focus on the neuroimaging paradigms that have shown promise in exposing this relevant brain circuitry. In this way, we offer a broad overview of how anxiety is studied in the neuroimaging laboratory and the key findings that offer promise for future research and a clearer understanding of anxiety.

Neural sensitivity to social reward and punishment anticipation in social anxiety disorder

An imbalance in the neural motivational system may underlie Social Anxiety Disorder (SAD). This study examines social reward and punishment anticipation in SAD, predicting a valence-specific effect: increased striatal activity for punishment avoidance compared to obtaining a reward. Individuals with SAD (n = 20) and age, gender, and education case-matched controls (n = 20) participated in a functional magnetic resonance imaging (fMRI) study. During fMRI scanning, participants performed a Social Incentive Delay (SID) task to measure the anticipation of social reward and punishment. The left putamen (part of the striatum) showed a valence-specific interaction with group after correcting for medication use and comorbidity. The control group showed a relatively stronger activation for reward vs. punishment trials, compared to the social anxiety group. However, post-hoc pairwise comparisons were not significant, indicating that the effect is driven by a relative difference. A connectivity analysis (Psychophysiological interaction) further revealed a general salience effect: SAD patients showed decreased putamen-ACC connectivity compared to controls for both reward and punishment trials. Together these results suggest that the usual motivational preference for social reward is absent in SAD. In addition, cortical control processes during social incentive anticipation may be disrupted in SAD. These results provide initial evidence for altered striatal involvement in both valence-specific and valence-nonspecific processing of social incentives, and stress the relevance of taking motivational processes into account when studying social anxiety.

Oxidative imbalance and anxiety disorders

The oxidative imbalance appears to have an important role in anxiety development. Studies in both humans and animals have shown a strong correlation between anxiety and oxidative stress. In humans, for example, the increased malondialdehyde levels and discrepancies in antioxidant enzymes in erythrocytes have been observed. In animals, several studies also show that anxiety-like behavior is related to the oxidative imbalance. Moreover, anxiety-like behavior can be caused by pharmacological-induced oxidative stress. Studies using knockout or overexpression of antioxidant enzymes have shown a relationship between anxiety-like behavior and oxidative stress. Related factors of oxidative stress that could influence anxious behavior are revised, including impaired function of different mitochondrial proteins, inflammatory cytokines, and neurotrophic factors. It has been suggested that a therapy specifically focus in reducing reactive species production may have a beneficial effect in reducing anxiety. However, the neurobiological pathways underlying the effect of oxidative stress on anxiety symptoms are not fully comprehended. The challenge now is to identify the oxidative stress mechanisms likely to be involved in the induction of anxiety symptoms. Understanding these pathways could help to clarify the neurobiology of the anxiety disorder and provide tools for new discovery in therapies and preventive strategies.

Advances in the neuroimaging of panic disorder

Models of the neuroanatomy of panic disorder (PD) have relied on both animal work on fear and on clinical data from neuroimaging. Early work hypothesised a network of brain regions involved in fear processing (e.g. the amygdala), but more recent work has also pointed to the involvement of other cortical areas and other brain circuitry (e.g. the insula and anterior cingulate cortex). Studies investigating functional and structural brain connectivity in PD may ultimately shed light on the extent to which the neuroanatomy of PD is localised versus distributed, and on how current treatments alter this neuroanatomy.

Multivariate classification of social anxiety disorder using whole brain functional connectivity

Recent research has shown that social anxiety disorder (SAD) is accompanied by abnormalities in brain functional connections. However, these findings are based on group comparisons, and, therefore, little is known about whether functional connections could be used in the diagnosis of an individual patient with SAD. Here, we explored the potential of the functional connectivity to be used for SAD diagnosis. Twenty patients with SAD and 20 healthy controls were scanned using resting-state functional magnetic resonance imaging. The whole brain was divided into 116 regions based on automated anatomical labeling atlas. The functional connectivity between each pair of regions was computed using Pearson's correlation coefficient and used as classification feature. Multivariate pattern analysis was then used to classify patients from healthy controls. The pattern classifier was designed using linear support vector machine. Experimental results showed a correct classification rate of 82.5 % (p < 0.001) with sensitivity of 85.0 % and specificity of 80.0 %, using a leave-one-out cross-validation method. It was found that the consensus connections used to distinguish SAD were largely located within or across the default mode network, visual network, sensory-motor network, affective network, and cerebellar regions. Specifically, the right orbitofrontal region exhibited the highest weight in classification. The current study demonstrated that functional connectivity had good diagnostic potential for SAD, thus providing evidence for the possible use of whole brain functional connectivity as a complementary tool in clinical diagnosis. In addition, this study confirmed previous work and described novel pathophysiological mechanisms of SAD.