Neurobiology of sleep apnea and cognitive impairment.

Obstructive sleep apnea (OSA) has a broad and clinically important effect on cognition, most often impairing attention, executive function, memory, processing speed, and visuospatial ability, while language and immediate recall are relatively preserved. A substantial proportion of adults referred to sleep clinics already meet criteria for mild cognitive impairment at initial evaluation, particularly in moderate-to-severe OSA. This cognitive burden reflects multiple interacting mechanisms. Intermittent hypoxia promotes oxidative stress, mitochondrial dysfunction, and hippocampal injury through recurrent ischemia-reperfusion cycles. Sleep fragmentation disrupts slow-wave and REM sleep, impairing memory consolidation and glymphatic clearance. Neuroinflammation, endothelial dysfunction, and structural brain changes, including hippocampal atrophy, white matter hyperintensities, and reduced frontoparietal connectivity, may further compound injury over time. REM-related hypoxemia appears especially important for cerebrovascular injury and memory impairment. Measures such as hypoxic burden and oxygen desaturation indices may better capture brain risk than the apnea-hypopnea index alone. Older age, APOE ε4 genotype, obesity, hypertension, diabetes, depression, and prior cerebrovascular disease increase vulnerability and should guide screening and treatment priorities. Cognitive assessment in OSA should be domain-sensitive rather than based only on a single global cutoff. Effective therapy, especially positive airway pressure with adequate REM-period coverage, can improve alertness and selected cognitive outcomes, although attention may remain impaired despite improved oxygenation. In children, OSA can disrupt memory consolidation and working memory, and adenotonsillectomy often leads to only partial cognitive recovery. Cognition should therefore be considered a primary treatment outcome in both clinical care and future research.