Obstructive sleep apnea (OSA) is recurrent episodes of partial or complete obstruction of the upper airway during sleep that causes intermittent hypoxia and sleep fragmentation and potentially lead to cardiometabolic and neurocognitive sequelae. Chronic intermittent hypoxia, sleep fragmentation of OSA, and insufficient sleep have been significantly associated with higher risks of neurocognitive impairment, including mild cognitive impairment (MCI) and Alzheimer's disease. Thus, sleep and sleep apnea might be modifiable factors to neurocognitive impairment. Positive airway pressure (PAP) is the first line of treatment to maintain open airways for patients with OSA. Improving sleep, sleep apnea and circadian function could be a high-value intervention target to alleviate cognitive impairment and decline in subjects with mild neurocognitive impairment. Amyloid accumulation in brain tissue is a distinct feature of Alzheimers' disease, which is associated with potential impairment of neurocognition clinically. It predicts memory decline in initially cognitively unimpaired individuals. The study explores the associations between sleep apnea, cognitive function and cerebral imaging and the role of PAP therapy on neurocognitive trajectory in these patients with subjective cognitive impairment /mild cognitive impairment (SCI/MCI).