EEG alterations during wake and sleep in mild cognitive impairment and Alzheimer's disease

Patients with Alzheimer’s disease (AD) undergo a slowing of waking electroencephalographic(EEG) rhythms since prodromal stages, which could be ascribedto poor sleep quality. We examined the relationship between wake and sleep alterationsby assessing EEG activity during sleep and (pre-sleep/post-sleep) wakefulnessin AD, mild cognitive impairment (MCI) and healthy controls. AD and MCIshow high sleep latency and less slow-wave sleep. Reduced sigma activity characterizesnon-rapid eyemovement (NREM) sleep, reflecting sleep spindles loss. TheEEG slowing characterizes REM sleep and wakefulness of AD and MCI, withstrong correlations among the two phenomena suggesting common neuropathologicalmechanisms. Evening-to-morning variations in waking EEG revealed thegradual disappearance in MCI and AD of overnight changes in delta activity, indicatinga progressive decay of sleep restorative functions on diurnal activity thatcorrelates with the impairment of sleep high-frequency activity in AD. Our findingssupport a linkage between wake and sleep alterations, and the importanceof sleep-related processes in Alzheimer’s disease progression.