Online HD-tRNS over the right temporoparietal junction modulates social inference but not motor coordination

Abstract

Social interactions are fundamental to human cognition, with the right temporoparietal junction (rTPJ) playing a key role in integrating motor coordination and social inference. Transcranial random noise stimulation (tRNS) is a promising technique for modulating cortical excitability, yet its effect on dynamic social processes remains unexplored. This study aimed to establish a causal link between rTPJ and real-time social interaction by applying high-definition transcranial random noise stimulation (HD-tRNS) during the Human Dynamic Clamp (HDC) paradigm. Specifically, we investigated whether online HD-tRNS modulates motor coordination and social inference when interacting with an adaptive virtual partner (VP). Eighty right-handed participants were assigned to one of two experiments: (Exp1) a block design with active HD-tRNS and sham blocks or (Exp2) a trial-by-trial design with intermixed active and sham conditions. Participants engaged in an interactive coordination task with a covert VP that could behave cooperatively or competitively. Kinematic data and self-reported measures of perceived cooperativeness and humanness were analyzed. HD-tRNS over the rTPJ did not influence motor coordination or task performance. However, in Exp1, participants receiving active stimulation progressively attributed lower cooperativeness and humanness to the competitive VP, suggesting improved detection of competitive intent. This effect was absent in Exp2, indicating that repeated stimulation was necessary for cumulative neuromodulatory effects. Online HD-tRNS over the rTPJ does not acutely impact motor coordination but progressively modulates social inference, particularly in competitive interactions. The findings highlight the rTPJs role in self-other distinction and suggest that repeated short neuromodulation sessions can shape social perception. Significant statementSocial interactions rely on distinguishing between cooperative and competitive behaviors, a process involving the right temporoparietal junction (rTPJ). Using high-definition transcranial random noise stimulation (HD-tRNS), we tested the rTPJs causal role in real-time social inference. While HD-tRNS did not affect motor coordination, repeated stimulation progressively reduced perceived cooperativeness and humanness of a competitive virtual partner, suggesting enhanced sensitivity to competitive intent. Our findings provide insights into social perception mechanisms and suggest HD-tRNS as a potential tool for studying and modulating social cognition, with implications for conditions affecting social inference, such as autism and schizophrenia.