It takes time to synchronize: the emergence of dyadic heart-rate synchrony during music therapy in neurorehabilitation.

Heart-rate (HR) synchrony between individuals has been linked to emotional contagion and shared experience. Research in psychotherapy has also associated this type of synchrony with therapists demonstrating more empathic and attentive behavior, as well as progress and alliance ratings. Using dyadic HR data, session videos and notes, this paper investigated the emergence of dyadic HR synchrony during music therapy (MT) interventions in a neurorehabilitation setting between 11 in-patients (mean age 51 years ± 6.48) and one music therapist (43 years) who were selected by convenience sampling. HR synchrony during moments of interest (MOI; mean duration 76 ± 20.7 s) within the MT intervention period (mean duration 25.62 ± 7.34 min), as selected by the music therapist was explored. Focus was also given to the leading characteristics during HR synchrony, as well as the relationships between HR synchrony and nonverbal (NV) synchrony before and after the MT intervention, along with the association with patients' therapy readiness. We found that dyadic HR synchrony occurred beyond chance but significant associations to the patient's therapy readiness and NV synchrony could not be demonstrated. However, there was a very strong association between HR synchrony and the duration of the MT interventions, especially the 20-25 min block, suggesting that a certain duration may be needed for HR synchrony to emerge. HR synchrony during MOI segments was not significantly higher than the MT intervention average but more than half of them overlapped with the four highest and lowest HR synchrony segments, which could suggest that MOI segments may be detected physiologically. The ability to access previously hidden dyadic physiological changes and understanding the impact of MT intervention duration on HR synchrony could have important.