PROJECT SUMMARY/ ABSTRACT Pediatric obstructive sleep apnea (OSA) is a common and progressive syndrome accompanied by severe cognition, mood, and daytime behavioral issues, as well as poor school performance, presumably stemming from compromised neural tissue, induced by intermittent hypoxia and perfusion changes. However, it is unclear whether the brain tissue injury is in acute or chronic condition, and whether myelin is preferentially affected than axons, an essential step to understand, since interventions for neural repair/recovery differ for acute vs chronic and myelin vs axonal injury. Also, it is unclear whether accompanying brain changes in pediatric OSA have functional consequences, resulting to cognitive or mood deficits. In addition, intermittent hypoxia triggers a cascade of injurious processes affecting endothelial cells, but unclear whether regional cerebral blood flow (CBF) is reduced in pediatric OSA. Treatment methods for pediatric OSA include tonsillectomy and/or adenoidectomy, and it is unclear whether brain tissue changes, regional CBF, and neural responses to cognitive challenge improve post-treatment. Using diffusion tensor imaging (DTI) and diffusion kurtosis imaging (DKI)-based procedures, acute and chronic tissue changes and axonal status and myelin integrity can be assessed. Regional brain CBF can be assessed by validated arterial spin labeling (ASL) imaging, and regional neural activity to cognitive challenge can be examined with blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (MRI). Thus, using 28 treatment-naïve, pediatric OSA and 28 control children, the specific aims are to; determine the nature and types of brain tissue injury, using DTI and DKI measures, in untreated pediatric OSA over healthy controls; identify regional brain CBF, using ASL imaging, and neural responses to cognitive challenge, using BOLD functional MRI in pediatric OSA over healthy children; assess cognitive (by the differential ability scale II and NEPSY II) and emotion functions (by the child behavior checklist) in pediatric OSA compared to control children, and examine relationships between brain injury and cognitive and emotion dysfunctions in pediatric OSA; and examine whether brain tissue changes, reduced CBF, and altered neural responses to cognitive challenge reverse, and cognition and mood signs improve after adenotonsillectomy at 6 months in pediatric OSA. In summary, the nature and types of brain injury, regional CBF changes, and neural responses to cognitive challenge, and whether brain tissue changes, altered CBF, and diminished neural responses, as well as mood and cognitive functions recover after adenotonsillectomy in pediatric OSA will be examined. Evaluation of pathological characteristics is essential to assess the mechanisms of damage, and to suggest intervention strategies before and after surgery. The findings will also help guide potential treatments to rescue/restore brain tissue (e.g., nonstero...