Early chronic stress has enduring implications for physical and mental health outcomes. Hair cortisol concentration (HCC) has emerged as a marker of cumulative cortisol exposure, yet HCC in infants is not well understood. We examined how infant HCC relates to widely used basal salivary cortisol measures, maternal HCC, and environmental context in 111 infants assessed at 6 and 12 months of age. Maternal HCC at 6 and 12 months was correlated with infant HCC at 12 months. At 12 months, infant HCC was positively associated with waking salivary cortisol concentration (SCC), evening SCC, and area under the curve (AUC), but was independent of diurnal slope. Breastfeeding was associated with lower HCC, whereas increased sleep disruption was related to flatter slope. Reduced nighttime sleep duration was related both to higher HCC and to flatter slope. A person-focused analysis indicated that the combination of high HCC and flattened slope was associated with more environmental risks, highlighting the importance of investigating the interplay between HCC and diurnal cortisol slope. Results support the validity of HCC as a marker of cumulative cortisol exposure in infancy, while emphasizing the value of including multiple cortisol measures assessing distinct aspects of Hypothalamic-Pituitary-Adrenal (HPA) function.

Callous-unemotional behaviors (CU) demonstrate meaningful individual differences in early childhood, even in nonclinical samples with low mean levels of CU, but the factors underlying this variation have not been examined. This study investigated genetic and environmental contributions to individual differences and to sources of continuity and change in CU in toddler twins (145 MZ, 169 DZ) assessed at ages 2 and 3 years. CU, as assessed by the Child Behavior Checklist 1.5-5 (Achenbach & Rescorla, 2000), was moderately stable across age (r=.45, p<.0001). Longitudinal biometric analyses revealed genetic and nonshared environmental influences on CU at both ages, with no significant contribution from shared environmental factors. Stability from age 2 to 3 was due to genetic factors, whereas change was due to both genetic and nonshared environmental influences. This genetic and nonshared environmental change was substantial, suggesting malleability of CU in early childhood. Over 50% of the genetic influences and 100% of the nonshared environmental influences on CU at age 3 were independent of those that operated at age 2. Implications of novel sources of variance across age are discussed.

Background Early callous-unemotional (CU) behaviors identify children at risk for severe and persistent aggression and antisocial behavior. Recent work suggests that fearlessness and low social affiliation are implicated in the etiology of CU behaviors, although more research is needed to clarify these etiological pathways, as well as the role of parenting. Method Using a sample of preschoolers (N = 620), we examined pathways between observed fear in response to social and non-social stimuli and observed social affiliation during social interactions at age 3 and increases child CU behaviors and oppositional-defiant behaviors from ages 3 to 5. To elucidate the role of parenting in exacerbating or buffering the relationships between low fear and social affiliation and CU behaviors, we tested whether parental harshness or low warmth moderated these pathways. Results Fearlessness and low social affiliation uniquely predicted increases in CU behaviors, but not oppositional-defiant behaviors, from ages 3 to 5. Moreover, there was evidence for differential moderation of the fear pathway by harsh parenting, such that harsh parenting predicted increases in CU behaviors in fearless children but increases in oppositional-defiant behaviors in fearful children. Conclusions Fearlessness and low social affiliation contribute to the development of CU behaviors. Harsh parenting can exacerbate the risky fearlessness pathway. Preventative interventions aimed at reducing risk for CU behaviors and persistent aggression and antisocial behavior should target socioaffiliative processes and provide parents with strategies and training to manage and scaffold rule-compliant behavior when children show low fearful arousal.

Isolating child attributes and familial characteristics that support school readiness in children on the upper half of the socioeconomic spectrum can complement existing research on lowersocioeconomic status (SES) children and facilitate a more complete understanding of how children's performance varies across the full SES spectrum. This study examined if relations between SES, two components of executive function (EF; set-shifting and inhibitory control), and school readiness vary as a function of household chaos in 564 four-year-old children, primarily from middle-to upper-middle class families in the Northeast Region of the United States. Structural equation modeling of direct and indirect effects revealed three major findings: 1) higher levels of EF were related to better school readiness regardless of level of household chaos; 2) SES had an indirect effect on school readiness through set-shifting; and 3) household chaos was negatively associated with school readiness.

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