An EEG power index (eyes open vs eyes closed) to differentiate Alzheimer's from vascular dementia and healthy ageing

EEG differential power patterns between Alzheimer's (AD, 50 patients) and vascular (VaD, 37 patients) dementia and between these two and 36 healthy ageing subjects, were studied in the 6.5-12 Hz band of the ongoing EEG recorded during the rest eyes closed (REC) and eyes open (REO) conditions. From the EEGs (16 electrodes, 10-20 international system except for Fz, Ct, Pt), a 6.5-12 Hz band, wider than the alpha range (alpha-like), was chosen and processed to include the highest theta frequencies characterising the occipital dominant activity in dementia. A global and occipital EEG Power Index (PI) was calculated and used considering the absolute powers during REC and REO. The MANOVA was used to compare the figures. Bearing in mind that the higher the PI value the greater the difference between the 6.5-12 Hz EEG band powers of REC vs. REO, the results were as follows: (i) in the patients with Alzheimer's and vascular dementia the global and occipital PIs were significantly lower than those in controls; (ii) in the patients with Alzheimer's dementia the same PIs were significantly lower that those of the patients with VaD; (iii) healthy elderly subjects showed significantly lower powers in the 6.5-12 Hz frequencies at T5 and O1 in REO as compared to dementia patients. The pathophysiological implications and the clinical applications of these results are discussed.