Cortisol synchrony is the degree to which mother-toddler cortisol levels are mutually regulated within a dyad. Synchrony's impact on toddler development is not well understood, so this study investigated how synchronous cortisol levels (reactivity and total concentration) in mother-toddler dyads moderates the association between risk factors (i.e., maternal worry, toddler inhibition) and early internalizing symptoms. Seventy mothers and their 2-year-old toddlers provided interpretable saliva samples. Behavioral observations were made to assess the toddler's temperament at age 2, and mothers reported on their toddler's internalizing symptoms when toddlers were 2- and 3-years-old. Results suggest that mother-toddler synchrony in total cortisol concentration moderates the relation between risk factors and internalizing symptoms. Specifically, toddler inhibition and maternal worry were less associated with concurrent toddler internalizing symptoms when dyads demonstrated greater cortisol synchrony in total concentration. Further, synchrony in total cortisol levels marginally moderated the association between toddler inhibition and future internalizing symptoms, such that inhibited toddlers were less likely to demonstrate internalizing symptoms at age 3 when dyads demonstrated more cortisol synchrony. This suggests that cortisol synchrony may serve as an advantageous context that reduces the risk of developing of internalizing symptoms and augments the field's understanding of the implications of shared physiological responses within mother-toddler dyads.
Keywords: cortisol synchrony; inhibited temperament; internalizing symptoms; maternal anxiety; toddlers.