Tetradic Dynamics of Dyadic Sensorimotor Coordination: A Multiscale EEG Hyperscanning Study

How do leader and follower roles shape the brain mechanisms that support coordinated action between people? This question has therapeutic relevance for conditions such as schizophrenia and autism spectrum disorder, where the capacity for reciprocal social coordination is a defining vulnerability. Here, we propose a tetradic framework and examine sensorimotor coordination in 16 healthy adult pairs (15 included in EEG analyses) using dual-brain EEG hyperscanning and a 2x2 within-subject design crossing Role (Leader/Follower) and Condition (Mirroring/Matching). Mirroring required resonance with a partner's movement; Matching required its controlled transformation. This contrast was designed to dissociate automatic from controlled coordination. Behaviourally, Mirroring produced a robust Follower reaction-time advantage: pooling an independent behavioural-only cohort (combined N=64) revealed a smaller Leader advantage, consistent with role-dependent attention-inhibition gating. At the neural level, tonic power and significant phasic condition clusters were greater during Matching than Mirroring, while role-dependent phasic clusters suggested an anticipatory sequence around Leader responses and post-response gating and rebound around Follower responses. Information-theoretic decomposition identified Leader-unique predictive information in superior temporal regions and a separate frontal-pole interaction, Follower-unique predictive information in insular and superior frontal regions, sparse Synergy in the right rostral anterior cingulate cortex, and Redundancy spanning multiple cortical regions. These findings characterize tetradic coordination within dyads as a multiscale, role-asymmetric architecture in which top-down predictive control and bottom-up adaptive regulation are functionally dissociable. The tetradic framework provides a scaffold for this dissociation, and the role-specific signatures it reveals may offer candidate biomarkers for clinical populations in whom interpersonal coordination is disrupted.