Interpersonal physiological synchrony: estimation and clinical application to cardiac dynamics of parent-infant dyads ⋆

Abstract Synchrony is a key mechanism that builds up the foundations of human interactions. Quantifying the level of physiological synchronization that occurs during dyadic exchanges is essential to fully comprehend social phenomena. We present a new index to characterize the coupling of complex physiological dynamics: the optimized Multichannel Complexity Index (opMCI). We validated this approach using synthetic time series of two coupled Hénon Maps, with four different coupling levels in unidirectional and bidirectional manners. We demonstrated that the opMCI method allows to effectively discern between all coupling levels. Then, we applied the opMCI metric on heart rate variability data collected from 37 parent-infant dyads, during shared reading and playing activities, in the framework of the Shared Emotional Reading (SHER) project, with the aim of assessing the effects of early intervention in preterm babies. Two groups presented preterm infants: an intervention group, who participated in a two-month shared reading program, and a control group, who practiced shared play activities. A full-term group provided additional control data. The opMCI values were significantly higher for the intervention dyads with respect to the other groups during the shared reading task, showing that an early reading intervention program could increase parent-infant synchrony in preterm babies. Highlights Interpersonal physiological synchrony is a fundamental mechanism for the evolutionary path An ad-hoc methodological framework to assess nonlinear cardiac coupling is lacking The opMCI has been shown to be a reliable tool for assessing the degree of synchrony Early shared book reading may increase parent-infant synchrony in a clinical setting Competing Interest Statement The authors have declared no competing interest. Footnotes ⋆ This research received funding from the Italian Ministry of Education and Research (MIUR) in the framework of the ForeLab project (Department of Excellence) and the PRIN Framework Programme (Grant No 2022ZWNB37) of the project “MOONSHINE”, and from the University of Geneva, the Ernest Boninchi Foundation, the Prim’Enfance Foundation, and the Hopitaux Universitaires of Geneva (HUG) in the framework of research project Shared Emotional Reading (SHER). We updated the template, as the manuscript has been withdrawn and resubmitted to a different journal.