A convergent behavioral-neural profile of parental dysregulation and the link between parent-child brain-state similarity and child negative affect

Parent-child neural similarity is often interpreted as a marker of attunement, but its developmental significance may not be uniformly positive across family environments. We tested whether the parent's own emotional and regulatory profile, measured both behaviorally and neurally, moderates the developmental significance of parent-child neural similarity. Applying a hidden Markov model (HMM-MAR; K = 6 states) to whole-brain fMRI timeseries from 32 parent-youth dyads who separately watched the same emotional film, we derived per-dyad measures of brain-state similarity. Parent-child dyads showed greater brain-state similarity than parent-shuffle null pairs (d = -0.55, p = .004), indicating dyad-specific alignment beyond responses shared across viewers of the same film. Parent self-reported internalizing showed only a weak direct relation to child negative affect (r = .31, p = .085). However, the association between neural similarity and child negative affect depended on parent internalizing (b = 5.62, p = .018; R^2): stronger parent-child similarity predicted higher child negative affect when parents reported higher, but not lower, internalizing. A parallel interaction emerged when parent internalizing was replaced by a neural index of the parent's own state dynamics (parent neural-state unpredictability, Htrans; b = 5.95, p = .004), indicating that the effect reflects the parent's broader regulatory profile rather than a single measurement modality. Both interactions were clearest in the primary model and only partially robust across model orders and parcellations. These findings suggest that dyadic neural similarity should be interpreted in context: resembling a parent with a dysregulated profile may confer risk rather than protection.