Mapping distributed sources of cortical rhythms in mild Alzheimer's disease. A multi-centric EEG study

The study aimed at mapping (i) the distributed electroencephalographic (EEG) sources specific for mild Alzheimer's disease (AD)
compared to vascular dementia (VaD) or normal elderly people (Nold) and (ii) the distributed EEG sources sensitive to the mild AD at different stages of severity. Resting EEG (10- 20 electrode montage) was recorded from 48 mild AD, 20 VaD, and 38 Nold subjects. Both AD and VaD patients had 24- 17 of mini mental state examination (MMSE). EEG rhythms were delta (2- 4 Hz), theta (4- 8 Hz), alpha 1 (8- 10.5 Hz), alpha 2 (10.5- 13 Hz), beta 1 (13-20 Hz), and beta 2 (20- 30 Hz). Cortical EEG sources were modeled by low resolution brain electromagnetic tomography (LORETA). Regarding issue i, there
was a decline of central, parietal, temporal, and limbic alpha 1 (low
alpha) sources specific for mild AD group with respect to Nold and VaD
groups. Furthermore, occipital alpha 1 sources showed a strong decline
in mild AD compared to VaD group. Finally, distributed theta sources
were largely abnormal in VaD but not in mild AD group. Regarding
issue ii, there was a lower power of occipital alpha 1 sources in mild AD
subgroup having more severe disease. Compared to previous field
studies, this was the first investigation that illustrated the power
spectrum profiles at the level of cortical (macroregions) EEG sources in
mild AD patients having different severity of the disease with respect to
VaD and normal subjects. Future studies should evaluate the clinical usefulness of this approach in early differential diagnosis, disease staging, and therapy monitoring.