A previous review of the neuroimaging studies in obstructive sleep apnea (OSA) called for specific attention to longitudinal studies of the treatment effects of OSA on neuroimaging. This chapter focuses on those studies where treatment effects were considered. The structural studies suggest that there are some notable changes in the structure of the human brain when continuous positive airway pressure (CPAP) is used to correct OSA. Some of these changes are even associated with cognitive changes in the expected cognitive domains and are seen with as little as only three months of treatment. The functional imaging studies together suggest that changes in brain function associated with working memory are evident when comparing treatment with no-treatment conditions in patients with OSA. Specifically, treatment often results in the recruitment of fewer cognitive resources to perform at the same level or better.