THE TIMING OF DEFECATION WITHIN THE SLEEP-WAKE CYCLE OF HUMANS DURINGTEMPORAL ISOLATION

Data were collected from 14 human subjects who lived singly in an isol ation unit without temporal cues. The subjects used buttons to signal the times when they woke up, took a meal, defecated, and retired. Unde r these conditions, the ''free-running'' circadian rhythms (e.g., the sleep-wake cycles and the rhythm of body temperature) remained interna lly synchronized in 7 subjects (mean circadian period = 24.47 hr); in the remaining 7 subjects the sleep-wake cycle lengthened beyond 28 hr, desynchronizing from the rhythm of body temperature (internal desynch ronization; mean sleep-wake cycle = 33.45 hr). In all subjects, the in terval from wake-up to defecation increased with the duration of wake time (alpha); on average, the interval varied proportionally with alph a. Furthermore, the interval from the last main meal (dinner) to defec ation the following day was proportional to the sleep-wake cycle-eithe r that which included dinner but preceded the defecation, or that whic h followed the dinner but included the defecation. It is concluded tha t a lengthening of the sleep-wake cycle (and of the wake time) results in a slowing down of the processes of digestion and evacuation of the bowels, in parallel with an apparent reduction of total energy expend iture.