A mixed methods study on the emergence of nonverbal and heart-rate synchrony during single music therapy sessions in neurorehabilitation

Background
Recent advancements in neuroimaging have increasingly linked neurology and music therapy. Music therapy has been shown to enhance functional abilities in neurorehabilitation, including gait, upper extremities, speech, and cognition. This study aimed to understand the mechanisms of music therapy by focusing on the behavioural and relational aspects, specifically dyadic nonverbal synchrony (NVS) and physiological heart-rate synchrony (HRS) between patients and therapists. NVS, linked to empathy, is quintessential for building a positive therapeutic relationship. Higher NVS correlates with improved relational quality, self-efficacy, and symptom reduction. HRS is associated with therapeutic progress, occurring at empathetic moments, suggesting a connection between heart-rate synchrony and shared emotional states. This study explored the emergence of NVS and HRS during music therapy in neurorehabilitation and identified key characteristics of dyadic interactions.

Research Questions
The research questions presented are:
1. Did NVS emerge during the non-structured conversations before and after the music intervention?
2. Did HRS emerge during music intervention?
3. What can be observed on a dyadic therapy interaction level in segments of high and low synchrony of heart rates during the music intervention?

Methods
In this mixed-methods study, eleven in-patients without verbal or physical limitations participated with a music therapist in single sessions at a neurorehabilitation facility in Lower Austria. As the choice of instruments would predetermine the movements, NVS was compared during the non-structured conversations 2 minutes before and after the music intervention. The data was quantified and determined (10sec segments, ± 2 sec lag) with the applications Motion Energy Analysis (MEA) and rMEA. Heart rate was sampled with electrocardiogram sensors at 1000Hz, and HRS was quantified and determined (30sec segments, ± 2 sec lag) using rMEA. Subsequently, qualitative content analysis was adopted to examine the therapeutic interaction during the four highest and lowest HRS segments.

Results
The analysis revealed that NVS post-intervention was significantly above chance, and a significant increase in both NVS and patient leading. Similarly, HRS during the music intervention exceeded chance and positively correlated with its duration indicating an optimal duration of 25 minutes. Differences in therapeutic interactions were observed between high and low HRS segments. In high HRS segments, patients showed greater empowerment and external awareness, dyads listened more to each other and demonstrated increased relaxation, connection, and physical attunement.

Conclusion
Music intervention seemed to have effectively increased NVS and promoted patient empowerment, as reflected by the increased patient leading, which is a crucial factor for reducing drop-out rates. The differences observed in HRS may be attributed to variations in the dyadic interactions. Given the importance of patient participation in neurorehabilitation, a high HRS is thus beneficial and hence, the importance of the duration of music intervention.

This study explored the innovative application of NVS and HRS analysis within a neurorehabilitation setting, which may prove useful in future research involving patients with verbal or physical limitations, such as those with disorders of consciousness. Moreover, this study underscored the significance of the music intervention duration, an important aspect of health policy that impacts both patients and clinicians.