Fluctuations of source locations of EEG activity during transition from alertness to sleep in Alzheimer's disease and vascular dementia.

Vascular dementia (VaD) differs from Alzheimer's disease (AD) in larger fluctuations of cognitive impairment, hypothetically because of deteriorated vigilance control. Vigilance levels are reflected by locations of EEG sources. Transition from alertness to sleep might be particularly sensitive to degradations of vigilance control. Twelve AD and 12 VaD patients (medication free, mean age 75.6 and 77.6 years, respectively, difference = n.s.), and 12 healthy elderly subjects (mean age 70.6 years), who served as controls, were studied (each group comprised 2 males and 10 females). A twenty-one-channel EEG was recorded from full alertness to the onset of sleep stage 2. Dipole source modeling, based on Fast Fourier Transform dipole approximation, yielded 3D source localizations in 7 EEG frequency bands. For each brain axis, means of source location differences between successive 20-second periods were calculated (fluctuation magnitude). EEG band-wise MANCOVAs (3 brain axes, 3 subject groups, covariate: age) showed differences in fluctuation magnitude between groups in the 10.5- to 12-Hz alpha(2) frequency band (p=0.0066). Post hoc ANCOVAs for the axes (3 subject groups, covariate: age) were significant on the superior-inferior axis: VaD patients had higher fluctuations than AD patients and controls, without significant difference between the latter two. Thus, larger source fluctuations in VaD might reflect the patients' decreased vigilance control, accounting for their increased fluctuations of cognitive impairment.