Generalized harmonic analysis reveals a frequency modulated timer regulates mammalian hibernation

Mammalian hibernators decrease basal metabolism and body temperature (Tb) to minimize energy expenditure in harsh seasons. During hibernation, Tb drops to low temperature (<10 °C) and remains constant for days, known as deep torpor. Spontaneous interbout arousals interrupt torpor bouts, when Tb recovers to euthermic state ∼37 °C. Torpor-interbout arousal event repeats during hibernation. Little is known about mechanisms governing Tb fluctuation during hibernation. Here, we analyzed Tb fluctuation across Syrian hamsters’ hibernation cycle using generalized harmonic analysis and discovered a model with frequency modulation quantitatively reproducing Tb fluctuation. This analysis identified that an unexpectedly longer period of 120–430 days modulates period of several days, generating Tb fluctuation. We propose that concerted action of two endogenous periods governs torpor-interbout arousal cycles during hibernation. ### Competing Interest Statement The authors have declared no competing interest.