Local and selective decrease of fast sleep spindle density in patients with Alzheimer's disease and Mild Cognitive Impairment

Patients with Alzheimer’s Disease (AD) and Mild Cognitive Impairment (MCI) show alterations of sleep spindle activity. Separating fast (13-15 Hz) and slow (11-13 Hz) sleep spindles, a selective decrease of fast spindles count has been found in AD/MCI, without slow spindles changes. However, evidences about the regional specificity of pathology-related fast spindles alterations, their relation with cognitive deterioration and the comparison between AD and MCI patients are still missing. Moreover, fast and slow spindle density in AD/MCI patients has never been investigated. In the present study, 15 AD patients, 15 amnesic MCI patients and 15 healthy elderly controls (HC) underwent a baseline polysomnographic recording (19 cortical derivations) during a single night of sleep. Spindles detection during non-rapid eye movements (NREM) sleep was performed by means of a customized algorithm. Between-groups differences in spindle density were assessed in the cortical derivations where fast and slow spindles exhibited their density peaks (parietal and frontal, respectively), established by the empirical observation of their topography. A selective parietal fast spindle density decrease in AD and MCI patients compared to HC has been observed, while no significant differences have been found between AD and MCI patients. Fast spindle density and Mini-Mental State Examination scores were positively correlated. These findings suggest the existence of a local (parietal) and frequency-specific (fast) spindle density alteration in AD, that may emerge in an early stage during the pathology development. Moreover, our results are in line with the view of altered spindle activity as a marker of cognitive deterioration.