PROJECT SUMMARY/ABSTRACT Humans are inherently social creatures, wherein social connection (SC) is essential for optimizing well-being (WB),1–3 including positive feelings, perceptions, and functioning in daily life and the absence of psychological problems and pathological distress.4,5 This is especially critical during adolescence, a sensitive developmental period with substantial and rapid changes in their general social connections (and in peer and family domains in particular).6 Social isolation (i.e. lacking SC) is one of the primary risk factors for adolescent mental and physical health problems,7–9 while having sufficient SC is a strong facilitative factor for their long-term WB and civic engagement in adulthood.7,10,11 SC is a multi-faceted construct that includes the facets of quality of, quantity of, and need for social interactions,2,12–14 each demonstrating unique influences on adolescent health and WB.14–21 However, little is known about how these facets converge and predict (or are predicted by) adolescent WB over time or the extent by which neurobiological markers of SC relate to WB.22–24 The overall objective of the project is to evaluate the integrative facets of SC quality, quantity, and need, and their reciprocal associations with adolescent WB, in daily fluctuations, long-term trajectories, and neurobiological processes. Proposed project scientific goals are to: (1) Evaluate short-term reciprocal process between SC and WB; (2) Examine the long-term reciprocity between SC constellations and WB trajectories; and (3) Identify the convergence of behavioral and neurobiological markers of SC and their prospective associations with WB. Exploratory analyses will (a) explore modulation of these processes by sex, gender, age, pubertal status, and race and (b) consider the above three goals in peer- and family- specific SC contexts. Study design: The first two goals will be addressed via an online platform to ensure a large sample of 12-17-year-old adolescents using a 14-day daily diary design nested within a longitudinal study design (N=914 enrolled; T1-T2-T3, every 0.5 year). A subset of participants (n=104 enrolled) will also complete an in-person battery (at T1 and T3) of SC experimental tasks targeting each of the three SC facets during electroencephalography (EEG) and eye tracking (ET) acquisition. To evaluate the short-term reciprocal process, we will use daily questionnaire assessments of SC and WB to examine the same-day and next-day associations between SC and WB (Aim 1). To provide a holistic consideration of the three SC facets, we will identify adolescent subgroups based upon their experience of SC quality, quantity, and need (at T1, T3, respectively) and WB trajectories (T1-T2-T3), and examine the prospective transition probabilities between SC constellations and WB trajectories (Aim 2). Lastly, we will assess the convergence of behavioral and neurobiological markers of SC (at T1 and T3) and their prospective associations with WB (Aim 3). Significance: A deeper understanding of the reciprocal relationship between SC and WB and the neurobiological mechanisms underlying these associations will be crucial for mechanism- informed prevention programming.

PROJECT NARRATIVE Social connection is an essential human aspect, yet is poorly understood despite the developmental implications on well-being and development during adolescence, especially for the current GenZ population. This project will disentangle the different elements of social connection in adolescence and its associations to well-being using multiple measurements across short-term (daily) and long-term (across months) time, as well as neurobiological assessment, across contexts. This information will help inform “when” and “who” need intervention to promote positive well-being (and prevent negative well-being) outcomes in support of healthy adolescent development.