Frequency analysis of the resting awake EEG in mild senile dementia of Alzheimer type.

Spontaneous resting electroencephalograms (EEGs) were recorded from 40 subjects with senile dementia of Alzheimer type (SDAT) and 40 individually matched elderly controls at entry into a longitudinal study of SDAT. All of the demented subjects had only a mild degree of dementia, and all were still living in the community. Several measures of EEG activity were calculated, based upon the power spectra of the EEG samples from left and right occipital-to-vertex derivations. Paired t tests showed significant differences between demented and control group means for measures of theta and beta activity, but not for measures of alpha and delta activity. A significant decrease in the 'average mean frequency' in demented subjects was attributed to the combination of decreased beta and increased theta activity. The earliest changes in the resting EEG in SDAT are increased theta and decreased beta power. These changes are not identical to those reported in normal aging, in which a decrease in alpha activity accompanies the changes in theta and beta.