PROJECT SUMMARY/ABSTRACT Respiratory sinus arrhythmia (RSA) activity can be used as a biological indicator of emotion regulation abilities. Emotion regulation is critical for a range of child outcomes from academic achievement to psychosocial adjustment. Extensive research has demonstrated the harmful effects of negative parent-child interaction on children’s developing emotion regulation. However, there is some evidence that parent-child coordination of RSA activity, typically during positive interaction, promotes child emotion regulation. Little research has examined the association between parent-child RSA during negative interaction and children’s developmental outcomes. Therefore, the goal of this project is to test the hypothesis that parent-child RSA coordination during negative interaction (measured as mutual negative affect) prolongs children’s experience of negative affect in the moment and hinders, rather than promotes, children’s emotion regulation development over time. This goal will be accomplished using previously-collected dynamic time-series data for parents with children aged 2-4 years (N = 200 dyads; PI Lunkenheimer). This study will examine the association between parent-child biobehavioral coregulation and children’s emotion regulation in the short-term (predicting moment to moment child affect expression) and long-term (predicting year to year child emotion regulation abilities). Novel second- by-second assessments of parent-child RSA coordination and dyadic affective states will be used in accordance with dyadic, dynamic, coregulatory theories of child emotion regulation development. These theories were largely untestable until the recent emergence of methodological and statistical strategies in social psychology (e.g., RSASeconds, Hidden Markov Models) that maximize the use of the available second- by-second data without needing to aggregate over longer periods of time. Incorporation of these methods for answering the present research questions will greatly improve our understanding of dyadic coregulatory processes that support children’s emotion regulation development. Results of this project can then be used to improve assessment targets for parenting interventions, beyond what can be gleaned from behavioral assessments at the level of the individual. Training in cognitive/affective neuroscience, risk and protective factors for child emotion regulatory development, and dynamic multi-level modeling during the award period will aid the PI in executing the current project. Upon completion of this research and training plan, the PI will be well-prepared for a career as an academic researcher in the field of developmental psychopathology.