Previous studies suggested that self-focused attention (SFA), implicated in social anxiety disorder (SAD), correlates with heightened activity in the right frontopolar area (rFPA), which is the right prefrontal cortex just behind the forehead. Transcranial static magnetic field stimulation (tSMS) is a non-invasive brain stimulation method capable of temporarily suppressing brain function beneath the magnet. We explored whether tSMS on individuals with tendencies toward SAD elicited (1) suppressing rFPA activation during the resting-state and (2) reducing SFA during a subsequent speech task. Twenty-three university students with social anxiety performed two speech tasks. Between tasks, the tSMS group received neodymium magnet stimulation while the sham group received fake magnet stimulation on the rFPA for 20 min. Resting-state rFPA activities was measured using functional near-infrared spectroscopy (fNIRS), while SFA (body sensations and observer perspective), field perspective, and detached mindfulness (DM) perspective were assessed via questionnaires during both speech tasks. The observer perspective means SFA to self-imagery from others’ viewpoint, while the field and DM perspectives mean appropriately focusing on the external environment. The results indicated that tSMS intervention decreased rFPA activity from pre- to post-intervention rest. Then, tSMS reduced SFA to bodily sensations and increased DM perspective from pre- to post-intervention speech, especially in those with high levels of social anxiety. Furthermore, tSMS enhanced the field perspective regardless of social anxiety tendency. The results suggest that tSMS may suppress overactivity in rFPA, reduce SFA to body sensation, and increase adaptive attention in highly socially anxious individuals. Our study suggests the possibility of the clinical application of tSMS for treating SAD.

Abstract

The strategies for social interaction between strangers differ from those between acquaintances, whereas the differences in neural basis of social interaction have not been fully elucidated. In this study, we examined the geometrical properties of interpersonal neural networks in pairs of strangers and acquaintances during antiphase joint tapping. Dual electroencephalogram (EEG) of 29 channels per participant was measured from 14 strangers and 13 acquaintance pairs.Intra-brain synchronizations were calculated using the weighted phase lag index (wPLI) for intra-brain electrode combinations, and inter-brain synchronizations were calculated using the phase locking value (PLV) for inter-brain electrode combinations in the theta, alpha, and beta frequency bands. For each participant pair, electrode combinations with larger wPLI/PLV than their surrogates were defined as the edges of the neural networks. We calculated global efficiency, local efficiency, and modularity derived from graph theory for the combined intra- and inter-brain networks of each pair. In the theta band networks, stranger pairs showed larger local efficiency than acquaintance pairs, indicating that the two brains of stranger pairs were more densely connected. Hence, weak social ties require extensive social interactions and result in high efficiency of information transfer between neighbors in neural network.

In this research to assess emotions from biometric signals, participants are asked to evaluate the emotions they subjectively experienced in order to confirm whether the assumed emotions were actually elicited. However, the evaluation of emotions is not routinely performed in daily life, and it is possible that this evaluation may alter biological signals. In fMRI studies, evaluation has been shown to activate the amygdala, which is said to be related to emotional expression. However, electroencephalography (EEG) studies do not take into consideration the effects of such evaluations, and it is unclear how these evaluations affect emotion-related brain activity observed in EEG. We hypothesized that emotion evaluations would amplify emotions and c alter Frontal Alpha Asymmetry (FAA), which has been shown to be related to emotional pleasantness and unpleasantness. We suspect this is because in order to evaluate one's emotions, one must pay attention to one's internal state, and this self-focused attention has been found to enhance the subjective emotional experience. We measured a 29-channel EEG when presented with unpleasant and highly arousing images from the International Affective Picture System (IAPS) from 40 healthy male and female participants. The results revealed that FAA was significantly lower in the condition in which participants rated their own emotions compared to the condition in which they did not. Similar to fMRI studies, this result indicates that emotion-related brain activity is amplified on an EEG. This paper provides a cautionary note regarding the use of such evaluations in EEG emotion estimation studies.