The homeostasis of NREM Slow Wave Activity in Alzheimer's disease and Mild Cognitive Impairment

Introduction: The modulation of delta EEG activity between eveningand morning wakefulness is considered an indirect marker of theregulation of the homeostatic sleep need, and it has been recentlyfound altered in patients with Alzheimer's disease (AD) and individualswith Mild Cognitive Impairment (MCI). This finding points to analteration of the homeostatic process during sleep in AD/MCI andsuggests an impact of the neurodegenerative process on the homeostaticregulation of NREM Slow Wave Activity (SWA). Therefore, theaim of this study is to assess overnight changes in NREM SWAtopography in AD/MCI patients, comparing these groups withhealthy controls (HC).Method: 44 AD (17 M; 73 ± 7.02 y), 50 MCI (25 M; 72 ± 6.80 y), and48 HC (29 M; 69 ± 6.26 y) performed a single night of polysomnographicrecording (19 EEG derivations, EOG, and EMG). The spectralpower of the frequency bins in the SWA range (0.5–4.75 Hz) duringNREM sleep was computed. Then, the ratio between the first and thesecond half of the night during NREM sleep has been assessed in eachcortical derivation on each SWA frequency bin. One way analysis ofvariance (ANOVA) was performed to compared macrostructural variablesand overnight changes in NREM SWA activity between AD,MCI, and HC.Results: A significant difference between groups on the 1st versus2nd half of the night ratio of NREM SWA was found at 2 Hz in rightparieto-occipital derivations, at 3 Hz in temporal, parietal, and occipitallocations, and at 4 Hz in frontal, temporal, parietal, and occipitalderivations. In all these frequency bins and locations, AD and MCIindividuals showed reduced overnight changes in NREM SWA comparedwith HC, without differences between the clinical groups.Conclusion: The present finding suggests local alterations of thehomeostatic regulation of NREM SWA in MCI/AD patients. Suchalterations appear stable in different stages of the disease and specificfor areas particularly involved in AD pathology and high-frequencydelta activity (2–4 Hz). Future studies should replicate this result anddescribe its possible relationship with AD biomarkers.