Parietal Fast Sleep Spindle Density Decrease in Alzheimer's Disease and Amnesic Mild Cognitive Impairment

Abstract

Several studies have identified two types of sleep spindles: fast (13-15 Hz) centroparietal and slow (11-13 Hz) frontal spindles. Alterations in spindle activity have been observed in Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI). Only few studies have separately assessed fast and slow spindles in these patients showing a reduction of fast spindle count, but the possible local specificity of this phenomenon and its relation to cognitive decline severity are not clear. Moreover, fast and slow spindle density have never been assessed in AD/MCI. We have assessed fast and slow spindles in 15 AD patients, 15 amnesic MCI patients, and 15 healthy elderly controls (HC). Participants underwent baseline polysomnographic recording (19 cortical derivations). Spindles during nonrapid eye movements sleep were automatically detected, and spindle densities of the three groups were compared in the derivations where fast and slow spindles exhibited their maximum expression (parietal and frontal, resp.). AD and MCI patients showed a significant parietal fast spindle density decrease, positively correlated with Minimental State Examination scores. Our results suggest that AD-related changes in spindle density are specific for frequency and location, are related to cognitive decline severity, and may have an early onset in the pathology development.

Figure 1

Whole range (11–15 Hz), fast (13–15 Hz), and slow (11–13 Hz) spindle density topographical scalp maps in AD patients, amnesic MCI patients, and HC. The maps are based on the 19 derivations of the 10–20 system (electrodes positions indicated by black dots). Values are color-coded and plotted at the corresponding position on the planar projection of the hemispheric scalp model. Values between electrodes were interpolated (biharmonic spline interpolation). Values are expressed in terms of number of spindles divided by artifact-free NREM sleep minutes.

Figure 2

Whole range (11–15 Hz), fast (13–15 Hz), and slow (11–13 Hz) spindle density of AD patients (black bars), amnesic MCI patients (gray bars), and HC (white bars) in the cortical derivations where the maximum mean density values were observed for fast (Pz) and slow (F3 and F4) spindles. Error bars represent the standard errors. Asterisks indicate between-groups statistically significant differences (p ≤ 0.05) after post hoc unpaired t-tests.

Figure 3

Scatterplots of the individual correlations between Minimental State Evaluation (MMSE) scores and (a) whole range (11–15 Hz) and (b) fast (13–15 Hz) spindle density at Pz cortical derivation (p ≤ 0.05). Pearson's r and relative p values are reported for each scatterplot.