Research reportBeyond amygdala: Default Mode Network activity differs between patients with Social Phobia and healthy controls
Introduction
The Default Mode Network (DMN) is a constellation of brain areas including the medial prefrontal cortex, the temporoparietal junction and the precuneus, which decrease their activity during a wide number of different goal-oriented tasks as compared to passive “rest” tasks [30]. The fact that some cortical regions are more active at rest (‘default mode’) than during task led to the hypothesis that during the resting state the brain remains active in an organized fashion [12].
Nonetheless, DMN can be modulated by different factors, such as the emotional state [22], [32] or the cognitive load of the active task [11]. It has been recently shown that also psychopathological conditions, such as schizophrenia [14], depression [20], [21], [34], or anxiety [41], and physical disorders, like chronic pain [3], can alter neural activity in specific DMN regions. Intriguingly, several DMN regions are also related to social cognition [18], [28]. Social cognition is defined as that mental activity through which we can understand and know the social world [28]. Mitchell [28] suggested that social cognition is one of the functions of the DMN: “… when left to its own devices, the human brain appears naturally to engage in social-cognitive thought”. In line with this hypothesis recent studies have revealed DMN abnormalities in autistic patients resulting in a lack of deactivation. These data indicate abnormal internally directed processes at rest, which might contribute to the social and emotional deficits in autism [23], [24], [25].
Social Phobia (SP) is a particular anxiety disorder in which patients experience a marked and persistent fear of social or performance situations in which the person is exposed to unfamiliar people or possible scrutiny by others [1]. Several studies have investigated the neural correlates of SP in relation to potential social anxiety triggering situations, like public speech [27] and face perception. Overall, the results of these studies indicated that when exposed to stimuli related to a social context, SP patients (SPP) show differences in neural activity not only in brain regions that play a role in modulating the emotional response, such as amygdala [4], [29], [37] and other limbic structures [2], but also in cortical areas involved in attention and perception [15], [38].
To our knowledge, there are no studies on DMN in SP. Because of the indications that DMN may be involved in processing socially relevant information and may be dysfunctional in some anxiety disorders, here we compared functional magnetic resonance imaging (fMRI) data obtained during a face perception study with emotional and neutral stimuli in SPP and in healthy control (HC) subjects to assess possible differences in DMN that may play a role in the pathophysiology of the disorder.
Section snippets
Subjects
Eight right-handed subjects (4 M/4 F; mean age ± S.D. 39 ± 7 years) with a diagnosis of SP according to the DSM-IV-TR criteria [1] and seven right-handed healthy control subjects (4 M/3 F; mean age ± S.D. 30 ± 7 years) were recruited. Subjects had no history of any psychiatric (other than SP in the patient group), neurological or medical disorders that could affect brain function or metabolism. No patient had received any pharmacological or psychotherapeutic treatment at the time of recruitment and at
Results
Detailed information on clinical and behavioural results is reported in a previous paper [15]. No differences were found in state anxiety, as assessed by STAI-x1, between pre- and post-scan sessions, and between the two groups of subjects (mean ± S.E.: HC-pre 36.3 ± 0.9; HC-post 38.4 ± 1.3; SPP-pre 35.6 ± 1.2; SPP-post 38.7 ± 1.0; HC-pre vs. HC-post, p = 0.20; SPP-pre vs. SPP-post, p = 0.06; HC-pre vs. SPP-pre, p = 0.67; HC-post vs. SPP-post, p = 0.84). In addition, the SP and HC groups showed no differences in
Discussion
The results of this study showed that the right PCun/PCC had, during task, a lower reduction in activity in the SPP as compared to HC. These data suggest an impairment of the DMN resulting in an alteration of the normal task-related activation/deactivation switch of this region. These findings are consistent with studies on autistic patients showing an impairment of the DMN [23], [24], [25] supporting the hypothesis of a pivotal role of the DMN in social cognition and in theory of mind as
Acknowledgments
This research was partially supported by the Fondazione IRIS (Castagneto Carducci (LI), Italy). The authors wish to thank Giulio Perugi, Researcher in Psychiatry at the School of Medicine, University of Pisa for his support in recruiting Social Phobia patients and Luigi Landini, professor at the Faculty of Engineering, University of Pisa (Pisa, Italy) for his support for neuroimaging at the MRI Laboratory at the CNR Research Area “S. Cataldo” (Pisa, Italy) coordinated by Massimo Lombardi. We
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