Mammoth Cave

Nathaniel Kleitman was a faculty member of the Department of Physiology and made significant contributions to modern sleep research. In 1938, Kleitman conducted a sleep research study with graduate student, Bruce H. Richardson, in Mammoth Cave of Kentucky over the course of 32 days. During the experiment, Richardson and Kleitman adapted to a 28-hour day under “uniform conditions of temperature, illumination, and quiet of the cave.” Their experiment demonstrated that the human bodies roughly maintains a 24 hour temperature cycle even with the absence of external cues. Kleitman wrote Sleep and Wakefulness in 1939, an account of the Mammoth Cave study findings.

Here is some news footage from that time about the experiment.

Several pieces of furniture, including a bed, inside a dark cave.
Image from the Mammoth Cave Sleep Experiment

From: Nathaniel Kleitman Papers. Box 33 Folder 3.

Special Collections Research Center. University of Chicago Library.

A man fiddles with medical equipment next to a bedridden man asleep.
Image from the Mammoth Cave Sleep Experiment

From: From the Photographic Archive. Special Collections Research Center, University of Chicago Library.

Identifer: apf8-03489

Title page of Kleitman, Nathaniel

Sleep and Wakefulness. Chicago, IL: The University of Chicago Press. 1939.

Crerar: QP 425. K63