EEG power spectra and cognitive change in geriatric psychiatry: a longitudinal study.

Elderly patients with senile dementia of the Alzheimer type (SDAT), multi-infarct dementia (MID) and functional psychiatric illness, along with elderly control subjects, were studied longitudinally at 6 monthly intervals over a 2 year period, with cognitive testing and EEG power spectral analyses being carried out on each occasion. There was no significant change in the EEG power over time although a significant regression effect was noted for cognitive performance in the SDAT group. A number of between-group differences were apparent. The SDAT patients had more delta and theta power and less alpha power than those with MID and the latter group had a higher percentage of delta and theta power than the functional patients. The functional patients and normal subjects were differentiated from each other by a number of EEG power variables. The implications of these findings with respect to differential diagnosis in geriatric psychiatry are discussed.