Using one-dimensional maps to understand circadian oscillators and jet lag.

Dr Casey Diekman, New Jersey Institute of Technology.

The normal alignment of circadian rhythms with the 24-hour light-dark cycle is disrupted after rapid travel between home and destination time zones, leading to sleep problems, indigestion, and other symptoms collectively known as jet lag. We have developed a new tool, called an entrainment map, to study the process of reentrainment to the light-dark cycle of the destination time zone in a model of the human circadian pacemaker. Using this 1-dimensional map, we are able to determine conditions for existence and stability of 1:1 phase-locked solutions between the intrinsic circadian oscillator and the external light-dark forcing. The map is also ideally suited to calculate the amount of time required to achieve entrainment as a function of initial conditions and the bifurcations of stable and unstable periodic solutions that lead to loss of entrainment. We calculate the reentrainment time for travel between any two points on the globe at any time of the day and year. We then use entrainment maps to explain several properties of jet lag, such as why most people experience worse jet lag after traveling east than west. We also show that the change in daylength encountered during north-south travel in the winter or summer can cause jet lag even when no time zones are crossed, contrary to the conventional wisdom that jet lag only occurs after east-west travel across multiple time zones. Finally, I will discuss how entrainment maps can be used to explore other examples of circadian misalignment due to night shift work, social jet lag, or non-24-hour sleep-wake disorder.