Untreated Sleep-Disordered Breathing: Links to Aging-Related Decline in Sleep-Dependent Memory Consolidation

Background: Increasing age is associated with a decline in cognition and motor skills, while at the same time exacerbating one's risk of developing obstructive sleep apnea (OSA). OSA-related cognitive deficits are highly prevalent and can affect various memory systems including overnight memory consolidation on a motor sequence task. Thus, the aim of our study was to examine the effect of aging on sleep-dependent motor memory consolidation in patients with and without OSA. Methods: We studied 44 patients (19-68 years) who had been referred by a physician for a baseline polysomnography (PSG) evaluation. Based on their PSG, patients were assigned either to the OSA group (AHI>5/h), or control (Non-OSA) group (AHI<5/h). All subjects performed the Psychomotor Vigilance Task (PVT) and the Motor Sequence Learning Task (MST) in the evening and again in the morning after their PSG. Results: Despite similar learning in the evening, OSA subjects showed significantly less overnight improvement on the MST, both for immediate (OSA -2.7%+/- 2.8% vs. controls 12.2%+/- 3.5%; p = 0.002) and plateau improvement (OSA 4.9%+/- 2.3% vs. controls 21.1%+/- 4.0%; p = 0.001). Within the OSA group, there was a significant negative correlation between overnight MST improvement and age (r(2) = 0.3; p = 0.01), an effect that was not observed in the Non-OSA group (r(2) = 0.08; p = 0.23) Conclusions: Consistent with previous research, healthy sleepers demonstrated a higher degree of sleep-dependent overnight improvement on the MST, an effect not mitigated by increasing age. However, the presence of untreated obstructive sleep apnea is associated with an aging-related cognitive deficit, otherwise not present in individuals without OSA. As other research has linked the presence of OSA to a higher likelihood of developing dementia, future studies are necessary to examine if the inhibition of memory consolidation is tied to the onset of neurodegenerative disease.