Our study extends previous research by showing elevated baseline arousal and comparable stress responding in SP children relative to HC children. In addition, based on the autonomic flexibility model, we provide a potential explanation for the null findings of previous studies during stress. The pattern of elevated baseline heart rates and reduced RSA point to restricted autonomic flexibility in children with SP.

The acquisition of social competence, such as showing prosocial behaviour (fulfilling others' needs) and social initiative (fulfilling own needs), constitutes one major developmental task in childhood and adolescence. Previous research suggests that in middle childhood, impaired social competences are related to childhood psychopathology, such as externalizing and internalizing disorders. As the period of preschool age is a particularly important time for both the development of social competence and early psychopathological symptoms, we conducted a systematic review to investigate the role of social competence in relation to early childhood psychopathology. Twenty-one clinical as well as subclinical studies published prior to September 2016 were included in a qualitative analysis of the relation between prosocial behaviour, social initiative, and early externalizing and internalizing symptoms in preschool age children (age 3-6). Effect sizes for each study were calculated if required information was available. Our review suggests that from early on in childhood development, externalizing symptoms are accompanied by prosocial behaviour deficits such as lower levels of helping or cooperating, whereas internalizing symptoms may be accompanied by either deficient or excessive levels of prosocial behaviour. Exhibiting social initiative such as initiating contact with others or communicating one's own needs seems to be impaired in children with internalizing symptoms. Implications for current theory and future research are discussed.

Reports of exaggerated anxiety and physiological hyperreactivity to social-evaluative situations are characteristic of childhood social phobia (SP). However, laboratory research on subjective, autonomic and endocrine functioning in childhood SP is scarce, inconsistent and limited by small sample sizes, limited breadth of measurements, and the use of non-standardized stressor tasks. We exposed 8-12-year-old children with DSM-IV SP (n=41) and matched healthy control children (HC; n=40) to the Trier Social Stress Test for Children (TSST-C) while measuring subjective anxiety, heart rate (HR) and salivary alpha-amylase (sAA) as well as salivary cortisol. The SP children showed heightened reactivity to the TSST-C on subjective anxiety compared to the HC children but not a heightened reactivity in HR, sAA or cortisol. However, the SP children showed chronically elevated HR levels throughout the whole laboratory session. Whereas subjective anxiety seems to respond specifically to social-evaluative stress in childhood SP, HR levels may be chronically elevated suggesting a more generalized autonomic hyperreactivity.

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Previous research on autonomic characteristics of social anxiety in children and adolescents has produced highly inconsistent results which may partially be due to task differences and a limited breadth of autonomic measurement. Here we investigated a sample of high (HSA) and low socially anxious (LSA) children, aged 10-12 years before, during and after a standardized evaluated speech task while acquiring a broad set of autonomic and experiential measures. During baseline, we found evidence for tonically higher sympathetic autonomic activity in HSA children, indicated by higher low frequency heart rate variability (LF) and a trend for higher LF to high frequency heart rate variability ratios (LF/HF). In response to the speech task, HSA children showed blunted cardiac responding evidenced by slower increase and delayed recovery of heart rate and a similar significant trend on LF/HF values. Self-reported anxiety, by contrast, showed enhanced reactivity from baseline to anticipation in the HSA compared to the LSA group. The results suggest a restricted cardiac flexibility in HSA children and illustrate that broad autonomic assessment during a well-structured, naturalistic task may improve our understanding of the autonomic physiology of socially anxious children. The results have implications for current theories of social anxiety.