The Human Dynamic Clamp (HDC) is a new paradigm for the study of social coordination. It consists of a human subject interacting reciprocally with a Virtual Partner (VP), the dynamics of which is based on an empirically validated model of human coordination behavior. As a surrogate system for human social coordination, HDC allows realtime control and parametric manipulation of a VP’s intrinsic behavior and its coupling to humans. Subjects (n=20) were instructed to coordinate continuous finger movement inphase or antiphase with the VP, while the latter maintained either a cooperative (shared goal, in or antiphase) or competitive behavior (opposite goal), or switched between the two. Human and VP behaviors were recorded continuously, as well as subjects’ highdensity EEG used to estimate cortical sources and their dynamics, emotional (skin potential) responses and verbal reports of the VP’s intentions and humanness. Subjects accurately judged the intention of the VP (80.3% correct, 10.6% falsecooperation, 9.1% false competition) despite the confounding factor of task difficulty arising from performance of inphase (easier) vs antiphase coordination (more difficult). Source estimation in the 10Hz range suggested that right parietal cortex was associated with correct attribution of intention. Corticomotor coherence in the theta band also revealed how right parietal sources were coordinated with shared movement velocity. Self and other movement velocities were also coordinated with primary motor and visual cortices respectively. Subjects judged the VP to be human 47.3% of the time, especially during cooperative trials in the antiphase condition. Such judgment of humanness was associated with widespread functional connectivity in the frontoparietal network, along with an increase in alpha band activity over SMA and right temporal cortex. Interactions marked with high levels of emotional responses elicited a similar right temporal/insular activity in the alpha band (see companion work, Zhang et al.), while perception of cooperative partners elicited a pronounced decrease in alpha activity in left frontal superior cortex, suggesting intense cortical engagement in positive social contexts. By combining a realistic social interaction (HDC) and neuroimaging a number of key brain networks engaged in intention attribution, perception of cooperativeness, and attribution of humanness were uncovered. Knowledge of such brain networks in normal adults may lead to advances in understanding the interaction of self and other in patients suffering, e.g. from schizophrenia and depression.