EEG topography alterations in wakefulness and sleep in patients with mild cognitive impairment and Alzheimer's disease

Objective: Mild Cognitive Impairment (MCI) represents a preclinical stage of Alzheimer’s disease (AD). It is crucial have a set of biomarkers to contribute to an early detection of AD before the clinical onset. EEG longitudinal studies in MCI show the potential usefulness of resting EEG-based biomarkers for this purpose, but studies that evaluate sleep and wakefulness together are still missing. The aim of the present study was to evaluate EEG topography of MCI subjects which later converted (AD-C) or notconverted to AD (AD-NC). Method: Twenty-five MCI were enrolled for recording across one night and two different circadian phases (20 pm, 8 am) wake EEG recordings. Patients were re-assessed after a period of 20 months. Eleven subjects converted to AD and fourteen remained stable in MCI condition. Standard 10–20 recordings were then analyzed by Fast Fourier Transform analyses. Results: Wake EEG revealed increased theta and decreased beta 2 power in AD-C compared to AD-NC. In NREM, MCI-C showed increased frontal delta and decreased alpha sigma and beta activity. In REM MCI-C had higher frontal delta power and lower posterior beta activity. Conclusion: MCI who converted to AD show a specific EEG topography, resembling the typical slowing of AD patients. For this reason, they are possible candidate as early predictors of the conversion to AD.