EEG spectral analysis in vascular and Alzheimer dementia

The role of EEG spectral analysis in the diagnosis of syndromes of dementia is still disputed. Since there have been few studies dealing with the profile of power spectra, the present investigation has focused on this aspect, constructing power spectra taken from 16 derivations and calculated by averaging twenty 2 sec epochs, using a serial array of frequencies from 1 to 32 Hz. The spectral analysis of the EEG, recorded under awake resting eyes closed (REC) and open (REO) conditions, was performed in 50 patients with Alzheimer's disease (AD), 37 with vascular dementia (VaD) and 36 elderly controls. Three spectral profiles were found under REC: (i) type A, showing a dominant 6.5-12 Hz peak (44% AD, 97.3% VaD), although lower than in controls; (ii) type B, lacking a dominant peak in the 6.5-12 Hz band, but characterised by high power in 1-6.5 Hz band (44% AD, 2.7% VaD); (iii) type C, corresponding to a flat, low voltage, spectrum (12% AD). Unlike controls, demented patients showed an increased REO/REC power ratio in the 6.5-12 Hz band, especially in those with type B spectra. AD patients with type B spectra had an earlier age of disease onset.