The social, decoupled self: interpersonal synchronization of breathing alters intrapersonal cardiorespiratory coupling

People synchronize their periodic behavioural and physiological rhythms with each other during social interaction. While this interpersonal synchronization has largely been associated with positive effects such as social bonding, some evidence suggests that it may also impair self-regulation and disrupt intrapersonal coordination. Because respiration and heart rhythms are weakly coupled within individuals, we investigated whether synchronizing breathing with another person alters intra-personal cardiorespiratory coupling. Across two experiments, participants synchronized their breathing reciprocally (bidirectional interaction), unidirectionally with a confederate, or with pre-recorded breathing signals, while respiration and electrocardiography (ECG) were continuously measured. Relative phase analyses revealed that bidirectional breathing synchronization induced in-phase synchronization of heart rhythms between individuals. Critically, interpersonal synchronization coincided with cardiorespiratory decoupling: respiration and heart rhythms became more out of phase during interaction compared to resting baselines and the unidirectional condition. Moreover, stronger interpersonal respiratory synchronization predicted greater intra-personal cardiorespiratory decoupling. These findings provide the first evidence that interpersonal physiological synchronization entails a trade-off with intrapersonal physiological coupling, perturbing the phase relationship within one's own physiological system. We propose that aligning one's physiological rhythms with others strengthens self-other coupling but weakens intrapersonal coupling, pointing to a physiological mechanism of self-decoupling during social interaction.