PROJECT SUMMARY Evidence in adults and youth suggests that sleep disturbances precede and predict the onset of depression and may serve as an important marker of depression. Various types of sleep disturbances, including disruptions of sleep continuity and abnormal sleep architecture, have been identified as markers of depression in adults, but have been virtually unexplored as markers of early childhood depression. Early childhood depression symptoms have become widely recognized as a significant public health concern as they are associated with functional impairments and heightened risk for depression across the lifespan. However, these symptoms often go unreported and underdiagnosed because they are difficult for caregivers and clinicians to identify. Research is needed to identify markers of early childhood depression as early as age 3 years or before, to improve our capacity for the earliest possible identification of young children struggling with, and at risk for, depression. This K23 proposal will examine sleep disturbances as a plausible marker of early childhood depressive symptoms in a prospectively examined sample of young children, oversampled for familial risk for depression. This proposal leverages an exceptional opportunity to add measures to a NIMH-funded study following a large, high-risk cohort of mother-infant dyads annually from birth through age 3. This K23 proposal will add comprehensive measures of sleep (i.e., sleep diaries, actigraphy, and polysomnography) at age 3 years to examine a) which specific features of objectively measured sleep (during both day and night) at age 3 best correlate with early childhood depression symptoms, b) whether misalignments in circadian rhythm – “chronodisruptions” – are associated with early childhood depression symptoms, and c) whether sleep disturbances in infancy and toddlerhood precede the onset of depression symptoms at age 3. This project has the potential to greatly inform our understanding of both the sequalae of sleep disturbances in early childhood, as well as identify a plausible marker of early childhood depression. Completion of the proposed project will provide the applicant with needed training and expertise in 1) the collection and analysis of PSG data in early childhood, 2) the developmental psychopathology of early childhood depression, 3) the quantification of chronodisruption in early childhood, and 4) advanced statistical analysis techniques. A rich training environment and a multidisciplinary team of mentors in each of these areas is detailed. The described research and training activities will enable the candidate to become an independent scientist investigating the role of sleep disturbances in the development of psychopathology across early childhood.