Development of infant physiological self-regulatory capacities across the first year of life: the role of parenting
Tuladhar, Charu Tara
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Sleep and cortisol function are two physiological self-regulatory processes that codevelop during infancy. Dysregulation of each system is linked to enduring health problems, so it is critical to understand factors contributing to the development of physiological self-regulation. However, it is not clear how infant sleep and cortisol interact with each other or with the parenting context. This project examined (1) the interplay of infant sleep and cortisol; (2) how cortisol interacts with parent characteristics in relation to infant sleep; and (3) whether consistent parenting buffers infant cortisol dysregulation. Study 1 (86 parent-infant dyads) investigated whether average nighttime sleep onset and duration predicted cumulative cortisol exposure, indexed by hair cortisol concentration (HCC). As hypothesized, infants who fell asleep earlier at night had lower HCC regardless of their family income and household chaos. Additionally, I expected that sleep characteristics on one night would predict total salivary cortisol exposure (AUCg) the next day, and that salivary cortisol at bedtime would predict sleep the same night. Partially supporting expectations, time-based analyses revealed that infants with lower cortisol on a particular evening fell asleep earlier the same night. In Study 2 (84 parent-infant dyads), I hypothesized that the link between parent characteristics (i.e., bedtime parental involvement and parental sensitivity) and infant sleep would differ by AUCg. Falling asleep independently predicted earlier sleep onset only for infants with dysregulated cortisol, whereas bedtime parental involvement did not predict sleep for infants with well-regulated cortisol. Infants with emotionally warm and appropriately responsive parents fell asleep earlier at night only if their cortisol was well-regulated. Utilizing archival data of 82 mother-infant dyads, Study 3 assessed consistency in parenting behaviors (i.e., smiles and laughter, and positive vocalizations), cortisol, and socioeconomic status (SES). As hypothesized, higher-SES infants experienced consistency, whereas lower-SES infants experienced inconsistency, in maternal smiles and laughter across 6 to 12 months of infancy. Contrary to expectations, inconsistent parenting did not predict cortisol. Findings highlight the intricate relation between two vital physiological processes codeveloping in the first year of life – sleep and cortisol regulation – and the role cortisol plays in moderating how parenting characteristics contribute to infant sleep.