Simulation of the Circadian Response to Time Zone Transitions by a Van der Pol Oscillator

Abstract

When a Zeitgeber advance shift is increased from about 6 to 12 hours, the response of the entrained circadian body temperature rhythm changes from a phase advance to a phase delay. The shift at which this transition occurs is called “critical shift” in this context. In general, it is not an integer number of hours. The term critical is to describe an unstable equilibrium. That is the state of a pendulum which stands upright and will swing by more than 180° in either direction towards its stable equilibrium due to any infinitesimal force.