PROJECT SUMMARY Sleep is increasingly understood as a critical contributor to brain health and development. Problems with sleep are present in more than 90% of youth with anxiety, predict worsening symptoms, and do not resolve following treatment-related remission of anxiety, leaving these youth at ongoing risk (for review see McMakin et al., 2015). Yet, we have few testable models for exactly how and why sleep-related problems impact mental health in young people, making it hard to understand risk pathology and intervene with precision. Both sleep and anxiety are heterogeneous and vary significantly across development, further complicating the picture. Models that draw from the known roles of sleep for cognitive and affective functions (e.g., memory consolidation, emotion regulation) to explain how disruptions in these processes could drive specific symptoms during sensitive periods of development are needed to move the field forward. To this end, our ongoing R01 aims to test our theoretical model whereby disruptions in key features of sleep neurophysiology (e.g., macro-arousals, spindle activity) impact emotional reactivity and memory processing to drive negative overgeneralization (Aims 1 and 2). We also examine whether this sleep-dependent process is modifiable (Aim 3). Despite methodological complexity and a global pandemic, we are nearing completion of data collection for Aims 1 and 2 (96%; n=192/200) with results supporting key features of our model. The supplement is requested to support the critical completion of Aim 3 (n=60) in which we turn our attention to the potential to modify these processes. Specifically, we will use targeted memory reactivation during sleep to manipulate which memories are selected for consolidation. If we can successfully modify memory selection and this leads to changes in sleep microstructure coincident with a reduction in negative overgeneralization, we will not only gain support for causality within our model but also, we will be well-positioned for intervention work.