UC Davis

Caregiving behaviors serve as a central component through which circadian regulation unfolds during the first two years of life. This dissertation examines how parenting practices both shape and respond to children's evolving sleep patterns and stress physiology in Mexican-origin families. Through two complementary studies employing intensive longitudinal designs, this work illustrates how caregiving behaviors operate as critical regulatory agents of circadian rhythms of arousal in infancy and toddlerhood. Study 1 examined how maternal emotion socialization behaviors moderate daily associations between infant diurnal cortisol rhythms and nighttime sleep patterns. Using multilevel modeling with 73 Mexican-origin mother-infant dyads, results revealed that non-supportive maternal practices amplified the impact of dysregulated cortisol on sleep fragmentation, with flatter-than-usual cortisol slopes predicting increased night wakings and longer sleep onset latency. Conversely, shorter-than-usual sleep duration predicted flatter next-day cortisol slopes, particularly among infants whose mothers exhibited higher levels of non-supportive emotion socialization. These findings demonstrate how stable caregiving tendencies shape the developing coordination between physiological systems that regulate circadian rhythms of arousal. Study 2 investigated how daily variations in toddler sleep fragmentation influence bedtime parenting behaviors through daytime maternal parenting stress, with economic hardship moderating this pathway. Bayesian multilevel modeling with 92 Mexican-origin mother-toddler dyads demonstrated that greater-than-usual sleep fragmentation predicted increased parenting stress, which in turn led to more non-supportive bedtime behaviors. This stress spillover was significantly amplified among families experiencing economic hardship, suggesting financial strain heightened caregivers' stress reactivity to toddler sleep challenges. Notably, daily variations in sleep and stress predicted increases in non-supportive but not decreases in supportive behaviors, indicating differential impacts on caregiving dimensions. Together, these studies advance understanding of circadian co-regulation during early development by: (1) demonstrating how stable caregiving tendencies moderate circadian coordination of sleep and stress physiology in infancy; (2) revealing how caregiving behaviors adapt to daily regulatory challenges in toddlerhood; and (3) identifying the role of economic hardship in these caregiving processes. The within-person approach captured temporal dynamics often obscured by between-family designs, showing how daily variations in caregiving contribute to regulatory trajectories. Findings suggest interventions should target both supportive parenting promotion and non-supportive behavior reduction, particularly for economically disadvantaged families.