Project Summary Objective biomarkers of disease states offer significant potential for improving clinical diagnoses and care. Despite widespread increases in the incidence of infants born with neonatal abstinence syndrome (NAS), there are currently no objective clinical measures of this syndrome. NAS infants exhibit a wide range of symptoms with characteristic dysregulation of central nervous system activity including pronounced sleep disruption. Recent developments in bedside electroencephalography (EEG) have enabled researchers to continuously record neonatal brain activity across behavioral states with high temporal resolution and minimal confounding artefacts. These noninvasive and affordable recordings are readily implemented in clinical settings and thereby have great potential for characterizing healthy and disordered brain activity. In Aim 1 of this proposal, eight hours of continuous bedside EEG will be recorded from healthy infants 24 – 72 hours post-birth. Identification and assessment of basic electrophysiological characteristics of healthy sleep will occur to establish baseline metrics of typical- developing neonatal brain activity. These data will then be compared to similar EEG recordings collected from NAS infants. By comparing sleep EEG parameters across the populations and for NAS infants to assessments of NAS severity as determined by the ESC care tool (the current subjective clinical assessment of NAS), the goal is to develop novel, objective biomarkers of NAS. As a complementary approach to Aim 1, in Aim 2 bedside EEG recordings will be re-analyzed to quantify EEG complexity within healthy controls, NAS neonates, and across behavioral states. Unlike traditional EEG analyses, complexity measures are sensitive to inherent nonlinearities in brain activity and consequently reflect different dynamics of ongoing neuronal activity. As measures like Lempel-Ziv complexity and multiscale entropy have already shown widespread promise as potential biomarkers for a diverse set of brain disorders, it will also be determined whether they may serve as biomarkers for NAS. Collectively, this work will improve the diagnosis and care of NAS infants and will additionally increase our understanding of healthy neuronal communication patterns within the infant brain.