Interpersonal coordination with a virtual outgroup increases motor preparation demands but it is not modulated by mPFC inhibition

Racial differences lead to immediate implicit stereotyping that may influence intergroup interactions and reinforce implicit prejudices, ultimately contributing to discrimination and social inequality. Studies indicate that racial biases can reduce sensorimotor resonance and empathy toward out-group members, identifying the medial prefrontal cortex (mPFC) as part of a network involved in the regulation of racial stereotyping. Despite these findings, the specific impact of racial biases in influencing individuals' ability to coordinate actions with others and the role of mPFC in mediating in-/out-group interactions remain insufficiently understood. To deepen the comprehension of the neural mechanisms underlying these processes, we investigated whether: i) interfering with mPFC and its related network activity modulates the expression of racial biases measured through affective misattribution procedure (AMP); ii) this interference consequently affects coordination during joint actions with racial out-group and in-group partners. Participants performed a joint action task, synchronizing their grasping movements with virtual partners representing racial in-group or out-group members. Before task execution, continuous theta burst stimulation (cTBS) was applied to interfere with the activity of mPFC (Experiments 1 and 3) or left ventral Premotor Cortex (vPM) (Experiment 2), with Vertex being an active control site. We observed that stimulating mPFC did not affect either racial bias as measured through AMP or individuals’ interaction abilities when coordinating with out-group or in-group members. However, participants’ motor preparation times increased when interacting with a partner from a racial out-group compared to the in-group, regardless of the stimulation site. These findings highlight the critical role of partner racial membership in influencing social categorization and motor abilities during interpersonal interactions while limiting the role of mPFC in mediating inter-group motor coordination as measured in the present study.