[Circadian-dependent changes in the EEG of vital elderly humans]

The study was conducted with six women and four men, 70-84 years old, without any psychopathologic signs of organic brain syndrome. Every experiment ran for five days during which closed-eye-EEGs were registered at 8 a.m., at 12 noon, at 4 p.m., and at 8 p.m. of the alert but relaxed patients and recorded on tape for computer processing. Simultaneously with every EEG registration the body temperature was measured.

As in younger persons the power of the alpha frequency band occipital exceeds the activity of the other frequency bands. But though the frequency of the dominant alpha rhythm comes with 9.5 Hz occipital on an average clearly under the normal range, there was a slight slowing down in sporadic cases. Probably old age leads to a decrease of alpha frequency, even in a state of unaffected sanity. The increase of peak frequency and body temperature during the day, well known from experiments with younger people, comes to the fore in the healthy aged as well. Of striking intensity, especially in the evening, is the beta power at the parietal and the central parts of the scalp, caused possibly by a transitory decline of vigilance. Circadian variations of the different band powers, ascertained in younger persons, are absent in the present collective.