It Takes Two to Regulate: Neural and Behavioral Synchrony Relate to Child Externalizing and Internalizing Profiles.

Parent-child interactions contribute to children's behavioral development and may buffer against psychopathology. Less is known about behavioral and neural alignment's association to development. Therefore, we examined behavioral and neural synchrony's relation to child behavioral problems. Parent-child behavioral synchrony was measured by Mutually Responsive Orientation coding, capturing coordinated routines, mutual cooperation, emotional ambiance, and harmonious communication. Functional near-infrared spectroscopy hyperscanning was used to measure parent-child neural synchrony in the temporoparietal junction (TPJ) and the dorsolateral prefrontal cortex (dlPFC). Children's externalizing and internalizing behaviors were assessed using the Child Behavior Checklist. 39 dyads (children aged 4 to 6) participated. Mutual cooperation positively related to externalizing and internalizing behaviors. Coordinated routines negatively related to externalizing behaviors. Neural synchrony between child TPJ and parent left dlPFC positively, whereas between child regions and parent right dlPFC negatively related to child externalizing behaviors. Neural synchrony between child regions and parent left dlPFC positively, whereas between child left-hemisphere and parent TPJ negatively related to child internalizing behaviors. Combining behavioral and neural synchrony did not improve model fit beyond considering each level alone. Our results suggest that distinct synchrony components uniquely relate to child psychopathology. Synchrony type matters more than amount, with flexible, turn-taking interactions being particularly beneficial.