The duration of re-entrainment of circadian rhythms after phase shifts of the Zeitgeber A theoretical investigation

Abstract A model equation for circadian rhythms describes all known general results under constant conditions and under the influence of Zeitgebers. This equation is used for computing influences of phase shifts of the Zeitgeber on circadian rhythms. A phase shift of the Zeitgeber corresponds to the shift of local time as a result of long-distance flights in eastward or westward direction. The theoretical results of four types of six-hour phase shifts and of four types of 12-hour phase shifts are compared with corresponding results of animal and human experiments. The duration of re-entrainment to the shifted Zeitgeber is of especial practical interest, because the shifted subject is less efficient during re-entrainment. This duration depends, for instance, on the direction of the phase shift and on the natural period of the shifted subject. For practical purposes, rules for shortening the duration of re-entrainment are derived from the theoretical results.