Shyness is often characterized by the avoidance of social contact, the fear of other people's evaluations and a lack of self-esteem. Generally, individuals with high levels of shyness are more likely to suffer from psychosomatic stress and social anxiety. However, the structural brain basis of individual shyness among healthy people has not yet been investigated with DTI (diffusion tensor imaging). Thus, in this study, we investigated the relationship between FA (fractional anisotropy), WMV (white matter volume), GMV (gray matter volume) and shyness in a large healthy sample of 318 college students. Multiple regression was used to analyze the correlations among regional FA, WMV, GMV and shyness, adjusting for age, sex, and total intracranial volume. The results showed that shyness was significantly, negatively associated with FA, WMV and GMV in a cluster that included the dACC (dorsal anterior cingulate cortex) and the MCC (middle cingulate cortex) and was significantly positively associated with the GMV in the IPL (inferior parietal lobule), an effect that may have been related to the weaker ability to regulate emotion in these participants and their state of being overly worried about others' evaluations. Finally, mediation analyses revealed that the correlation between shyness and psychosomatic stress was mediated by a region including the dACC and the MCC.
Keywords: Diffusion tensor imaging; Dorsal anterior cingulate cortex; Inferior parietal lobule; Shyness.