RecruitingDevice studyThe Effects of Successful OSA Treatment on Memory and AD Biomarkers in Older Adults StudyThe Effects of Successful OSA TreatmENT on Memory and AD BIomarkers in Older AduLts (ESSENTIAL) study is a 5-year, multicenter randomized open-label trial that will screen 400 cognitively normal older adults recruited from well-established sleep clinics at 4 academic medical centers, with newly diagnosed moderate-severe OSA. An expected 200 OSA patients will be then randomized to one of two groups: i) a 3-month OSA treatment by any combination of PAP, OAT, and positional therapy that results in an "effective" AHI4%\< 10/hour and AHI3A\<20/hour (see below); ii) a waitlist control group to receive treatment at the conclusion of the 3-month intervention period. Both groups will continue follow-up for 24 months on stable therapy to determine if sustained improvements in sleep are associated with improvement in cognitive function and AD biomarkers.