Ultradian Rhythms in Task Performance, Self-Evaluation, and EEG Activity

Many studies have shown the existence of cycles of approximately 90 to 100 minutes (corresponding to Kleitman's basic rest-activity cycle) and several hours ('slow ultradian rhythm' cycles). EEG power spectra, mood, performance, and self-evaluation of performance were measured every 15 minutes for 9 hours for 10 male university students. Principal component analysis was applied to extract ultradian fluctuations in EEG activity, task performance, and subjective variables. The analysis indicated two common temporal fluctuations: one in behavioral and subjective variables, and the other in EEG activity. Spectral analysis indicated that the former fluctuated at a rate of 12 cycles per day (corresponding to the basic rest-activity cycle), and the latter comprised both a slower (6 cycles per day) and a faster (10 to 18 cycles per day) cycle, supporting the multioscillator hypothesis of ultradian rhythm.