Phase shifting two coupled circadian pacemakers: implications for jet lag

Area of Science:

• Chronobiology
• Human Physiology
• Mathematical Modeling

Background:

• Environmental time cues, or zeitgebers, are critical for synchronizing the body's internal circadian timing system.
• Abrupt shifts in zeitgebers, such as during transmeridian flights, lead to gradual resynchronization of circadian rhythms.

Purpose of the Study:

• To explain the key features of circadian rhythm resynchronization after time zone shifts using a coupled two-oscillator model.
• To investigate factors influencing the rate and variability of circadian adjustment to new time zones.

Main Methods:

• Utilized a coupled two-oscillator mathematical model to simulate the human circadian system.
• Analyzed model performance in explaining resynchronization patterns after simulated time zone shifts.
• Examined the impact of individual model parameters, particularly pacemaker periods, on system variability.

Main Results:

• The model successfully simulated major features of circadian resynchronization, including dependence on rhythm, time zones crossed, flight direction, and zeitgeber strength.
• Intersubject differences in endogenous pacemaker periods were identified as a significant factor in the variability of circadian adjustment.
• Individualized model simulations accurately replicated case studies of sleep-wake and core body temperature rhythms during transmeridian travel.

Conclusions:

• A coupled two-oscillator model provides a robust framework for understanding circadian rhythm adjustment to time zone shifts.
• Individual differences in circadian period length are crucial for explaining variations in jet lag symptoms and adaptation.
• The model's ability to simulate real-world data highlights its potential for predicting and managing circadian disruption.