Coupled hearts - effect of partner stress on cardiac synchronization

Physiological synchrony (PS), i.e., the alignment of physiological changes across individuals, is an established phenomenon characterizing social interactions. The degree to which interaction partners synchronize may depend on various relationship- and situation-specific factors. Stress profoundly affects behavior and cognition, but its effect on PS is still unknown. In a preregistered study, we thus investigated the effect of stress on PS in N= 75 romantic couples (mean age = 22.66 ±2.99, 51% female). Partners were separated upon arrival in the laboratory. In n=38 dyads (experimental condition), one partner underwent the Socially Evaluated Cold Pressor Task (SECPT) while the other partner completed a non-stressful control task; in control dyads, both partners underwent the non-stressful task. After completing the intervention separately, partners were reunited and participated in a non-verbal synchronization task, a walking task, and an unstructured social interaction. PS was operationalized by calculating cross-wavelet power of partners' heart rate trajectories. We hypothesized that PS would be altered in couples with one stressed partner compared to the non-stressed control group. Across all interaction tasks, PS was lower in dyads in the experimental than in the control condition. Our findings indicate that stress disrupts PS. In the discussion, we present possible mechanisms for this effect. Our results highlight that stress is not only an intra- but also an interpersonal phenomenon affecting interpersonal physiological processes and social interactions beyond the acute stressor.