In 1988, a cave explorer named Véronique Le Guen volunteered for an extreme experiment: to live alone in an underground cavern in southern France without a clock for one hundred and eleven days, monitored by scientists who wished to study the human body's natural rhythms in the absence of time cues. For a while, she settled into a pattern of thirty hours awake and twenty hours asleep. She described herself as being "psychologically completely out of phase, where I no longer know what my values are or what is my purpose in life."When she returned to society, her husband later noted, she seemed to have an emptiness inside her that she was unable to fully express. "While I was alone in my cave I was my own judge," she said. "You are your own most severe judge. You must never lie or all is lost. The strongest sentiment I brought out of the cave is that in my life I will never tolerate lying." A little more than a year later, Le Guen swallowed an overdose of barbiturates and lay down in her car in Paris, a suicide at age thirty-three.