NREM sleep EEG oscillations and overnight memory: Investigating the impact of untreated obstructive sleep apnea and the effect of CPAP treatment

Abstract

Obstructive sleep apnea (OSA) is a sleep breathing disorder which disrupts sleep architecture. Consequences associated with OSA include excessive daytime sleepiness and impaired cognition and memory. Continuous positive airway pressure (CPAP) is currently the ‘gold standard’ treatment for OSA. It restores sleep architecture, partially reverses sleep microarchitecture abnormalities, and improves performance in cognitive domains. Slow waves and sleep spindles during NREM sleep are putatively involved in overnight memory consolidation. Deficits in sleep spindles and altered SWA have been observed in patients with untreated OSA. However, these NREM EEG oscillations and their relationship with overnight memory consolidation have not been examined in older adults with OSA. Furthermore, SWA dynamics across the night in OSA patients before and after CPAP have not been examined using high-density EEG. The first study demonstrates that older adults with OSA had deficits in sleep spindles but showed preserved overnight memory consolidation relative to controls. The second study describes a novel methodological approach for defining sleep cycles, previously developed in healthy people with non-disrupted sleep architecture, in people with OSA to examine SWA dynamics. The final study employed this new approach to examine the effect of CPAP treatment on SWA and its dynamics in moderate to severe OSA patients using high-density EEG. Overall, this thesis adds to the literature by demonstrating that older adults with OSA have spindle deficits but preserved memory consolidation and highlighting the potential beneficial effects of CPAP on restoring SWA dynamics. In addition, the novel methodology developed provides future scope to explore the dynamics of SWA across different sleep-disordered populations who have disrupted sleep architecture.