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

Abstract

BackgroundIncreasing 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.MethodsWe 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.ResultsDespite 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 (r2 = 0.3; p = 0.01), an effect that was not observed in the Non-OSA group (r2 = 0.08; p = 0.23)ConclusionsConsistent 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.

Overnight Motor Skill Learning Outcomes in Obstructive Sleep Apnea: Effect of Continuous Positive Airway Pressure

“…CPAP usage after the first night (+1.6 ± 4.9%), however, showed only slight nonsignificant overnight improvements. These results confirm previous findings of impaired overnight learning in patients with OSA [8][9][10] and extend the literature to show that this impairment is not present in patients who are receiving optimal CPAP treatment.…”

“…32,33 The current study and previous studies that have investigated overnight learning outcomes using the SFTT [8][9][10] have established an area of cognition that appears to be consistently dysfunctional in patients with OSA of a range of different severities. Furthermore, in contrast to hypoxic associated impairments, the current deficiencies in overnight learning appear to be the result of specific insults to sleep continuity, and appear to be largely rectified with treatment-related improvements in sleep quality.…”

“…[8][9][10] This study builds on this finding, showing that this impairment is not present in patients compliant with CPAP treatment. The alterations to the typical SFTT learning methodology used in the current study suggest that there are distinct intervening changes in motor performance that occur within this overnight period.…”

“…Controls showed significantly greater enhancements (+11.6 ± 4.7%) in typing speed compared to patients with OSA (−5.36 ± 3.5%) over the total overnight testing period, supporting previous studies. [8][9][10] This period represents the typically measured overnight improvement (difference between final trials of practice E10-12 to the first trials of testing in the morning M1-3). As expected, successfully treated compliant CPAP users (+8.9 ± 4.3%) also showed significantly greater enhancements in performance compared to patients with untreated OSA.…”

“…7 Recently, a number of studies have shown that patients with obstructive sleep apnea (OSA) do not demonstrate these motor skill improvements following a sleep episode. [8][9][10][11] Furthermore, this impairment has been shown to be associated with the extent of sleep fragmentation occurring during intervening sleep. 9 To our knowledge, it is still unknown if this impairment can be alleviated by effective treatment of OSA.…”