A Circadian Rhythm in the Frequency of Spontaneous Task-Unrelated Images and Thoughts

It was hypothesized that the frequency of task-unrelated images and thoughts (TUITs) would demonstrate a circadian periodicity as a result of circadian periodicity in activation level. Six subjects were monitored for frequency of deliberate and spontaneous TUITs during a twenty minute vigilance task. The vigilance task was repeated every two hours for twenty-four hours. Spontaneous TUIT frequency was found to demonstrate a sinusoidal periodicity of twenty-two hours. TUITs were more frequent from late morning to early afternoon and less frequent from late evening to early morning. Although the times of the minimum and maximum TUIT frequencies generally correspond with previously reported periods of low and high body temperatures, both body temperature and TUIT frequency must be measured simultaneously to demonstrate the relationship.