Circadian periodicity, adrenal corticosteroids, and the EEG of normal man.

Human EEG activity in the conventional frequency range of 1-30 c/s is a well-established entity. This paper illustrates a method for utilizing a conventional EEG frequency analyser to demonstrate a considerably lower frequency, circadian (about 24-h) rhythm in the EEGs of a group of human volunteers. This periodicity persists even in a group of totally sleep deprived (50 h) subjects. Plasma cortisol levels from blood samples drawn simultaneously with the EEG data also demonstrate circadian periodicity, and EEG-cortisol temporal (phase) relationships are apparent by inspection of the data collected, but could not be confirmed statistically. Evidence for the statistical significance of circadian organization of the EEGs and adrenal cortices of healthy men is provided by a phase testing technique developed for this study and discussed further in the appendix. This technique is readily applicable to further studies of periodicity in physiological functions.