When research does not synchronize: Comprehensive analyses show no mother–child physiological coupling

Biobehavioral synchrony refers to covariation in physiological signals between interacting partners and is widely hypothesized to support co-regulation, bonding, and early socio-emotional development. This assumption is particularly salient for children born preterm, who often experience reduced early physical contact and prolonged neonatal separation, potentially shaping later caregiver–child attunement. Here we present a large-scale, systematic investigation of mother–child physiological synchrony in 102 dyads (70 preterm 5-year-olds and 32 matched full-term controls). Heart rate was recorded across eight interaction paradigms spanning passive viewing to face-to-face play. We applied the major commonly used analytic approaches, combined with rigorous surrogate-data controls and multiverse analyses, to assess the robustness of synchrony estimates. Across all paradigms, metrics, and analytic variants, synchrony in real dyads never exceeded that observed in pair-shuffled or segment-shuffled surrogate data. Patterns were virtually identical in full-term and preterm groups, and no reliable variability in synchrony remained that could be related to indices of prematurity. Together, these findings challenge the view that autonomic synchrony is a robust or ubiquitous feature of early social interaction and reveal substantial methodological fragility in current synchrony research. Our results underscore the need for more rigorous analytical frameworks and raise critical questions about when - and whether - physiological synchrony genuinely emerges in caregiver–child relationships.