Objective assessment of the degree of dementia by means of EEG

The aim of the study was to elaborate a method to estimate the degree of cognitive impairment in Alzheimer's disease from the EEG quantitative indicators. We examined 38 unmedicated patients with a diagnosis of Alzheimer's disease, with various stages (mild, moderate, and severe) of dementia. The EEG recordings were evaluated both visually and by means of computer analysis. The EEG spectra and coherences in 6 frequency bands were calculated in 16 EEG derivations. Among various EEG indicators, a decrease in the alpha coherence and an increase in the delta coherence was found to be most significantly correlated to the degree of dementia. Combining 6 variables from the spectrum and coherence analysis by means of the multiple regression model, a high correlation (r = 0.87) between a set of EEG variables and the Mini-Mental State Examination score could be obtained. The results suggest that the EEG can supplement the clinical examination by providing an independent assessment of the degree of dementia. The results also suggest that the EEG coherences are of particular interest in dementia, being an indicator of the signal transfer between various parts of the brain cortex.