Kleitman and Richardson's Sleep Study In Mammoth Cave
Can you change your sleep cycle?
Location of the Kleitman Experiment (Visitor Center on Right)
1925
Kleitman joins the University of Chicago as faculty and establishes the world's first sleep laboratory
June 4th, 1938
Nathaniel Kleitman and Bruce Richardson begin their experiment
July 6th, 1938
Kleitman and Richardson leave Mammoth Cave
1939
Kleitman publishes "Sleep and Wakefulness," the first major textbook on sleep, with results of the Mammoth Cave experiment
1953
Kleitman and Eugene Aserinsky discover rapid eye movement (REM) sleep and associated it with dreaming
Normal sleep--wakefulness cycles operate on a seven day, 24 hour cycle; Kleitman wanted to adjust himself and graduate student Richardson to a six day, 28 hour week.
Bath time
Kleitman and Richardson spent 32 days in the cave with a strict schedule of sleeping for 9 hours, working for 10, and 9 hours of leisure time. The absence of light and noise and a constant temperature made for a great experimental environment.
Meal time
Goal
The goal of their experiment was to determine if humans had an ingrained 24 hour cycle or if we can adjust our circadian rhythm. Measuring changes in body temperature shows a range of 1–2°F change with the highest value in the afternoon and the lowest in the early morning. This curve is not seen in infants, but develops as children adapt to rest-wakefulness cycle of 24 hours.
It is known that the body temperature curve can be shifted any number of hours, as when a person moves from the United States to China, or it can be completely inverted as when a person regularly stays up at night and sleeps in the day-time [sic]. In either case, however, the duration of the cycle remains unchanged, namely, 24 hours. It is our purpose to find how easy or how difficult it is for a grown up individual to change his body temperature curve from a 24-hour to a 21-hour or 28-hour cycle.
Image of Nathaniel Kleitman, professor of Physiology at the University of Chicago,(foreground) and Bruce Richardson, graduate student, (in bed)
Results
Because there were only two test subjects, you can't generalize this study to the entire human population. That said, Richardson did adjust to the study's sleep schedule, while Kleitman had difficulties and never acclimated; he was tired during the "days" and had difficulty sleeping through the "nights."
Richardson was approximately 20 years younger than Kleitman; this could be a factor in the ability to adjust to new sleep schedules. Additionally, individual habits, such as Richardson being a student and having a less structured sleep schedule to begin with, may impact the ability to adjust your circadian rhythm. Despite the study's limitations, Kleitman is quoted as saying:
“This experiment merely confirms previous results which I have obtained, in demonstrating that the [circadian] cycle is dependent on the activity of the individual. Some individuals can change their cycle with considerable ease; others find a cyclical change difficult to establish.”
Kleitman and Richardson leaving Mammoth Cave after the Sleep Experiment