Cortical alpha rhythms in mild Alzheimer's disease. A multicentric EEG study

The study aimed at mapping (i) the distributed alpha (8-13 Hz) electroencephalography (EEG) sources specific for mild Alzheimer's disease (AD) compared with vascular dementia (VaD) in normal, elderly people (Nold) and (ii) the distributed alpha EEG sources sensitive to 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 on their mini mental state examinations (MMSE). Alpha bands were subdivided in alpha 1 (8-10.5 Hz) and alpha 2 (10.5-13 Hz) subbands. Cortical alpha 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 sources specific to the mild AD group with respect to Nold and VaD groups. On the other hand, occipital alpha 1 sources showed a strong decline in mild AD compared with the VaD group. However, this finding was “unspecific” because a certain decline of these sources was also recognized in VaD compared with Nold. Regarding issue (ii), there was a lower power of occipital alpha 1 sources in the mild AD more severely diseased subgroup. On the whole, these findings stress the reliability of modern technologies for EEG analysis as the LORETA approach to the study of cortical rhythmicity in resting mild AD.