Could Chronic Hypothermia in a Human Affect the Clock System?

Hibernation-like episodes would be particularly interesting for clinical and spatial use if they could be observed and induced in humans. As animal hibernation differs from hypothermia with its control by a temperature-dependent clock, we undertook to find evidence that human hypothermia might affect the circadian clock system. We revisited Siffre’s 1962 abyss experiment. Deprived of temporal information and showing signs of chronic hypothermia, Siffre underestimated his stay underground by 22 d. We show that the temperature-dependent clock equation for classical hibernators accurately predicts Siffre’s subjective times, and we list potential conditions to be further explored for inducing hibernation-like bouts in humans.