AN INTERPRETATION OF THE INTERNAL DESYNCHRONIZATIONS BASED ON DYNAMICS OF THE 2-PROCESS MODEL

Daan's two-process model is known to be one of the most powerful model s, covering various situations from free-running to sleep deprivation. In this study, bifurcation properties of the model dynamics are clari fied using a circle map. In addition, the two-process model is applied to simulate the two distinct patterns (the period-prolonged: I and th e period-shortened: II) of sleep-wake cycles during internal desynchro nizations. We propose the novel interpretation that types I and II cou ld be regarded as mutual entrainments between the body temperature rhy thm and the sleep-wake cycle with the period ratios 3.4 and 3:2, respe ctively. From the bifurcation properties of the two-process model obta ined above, the model is shown to be able to generate the respective t ype of mutual entrainment with an appropriate range of a parameter val ue, i.e, a gap between thresholds. The variable behavior of human circ adian rhythm is suggested to be systematically understood based on the bifurcation properties of the two-process model.