Seasonality and Light Phase-Resetting in the Mammalian Circadian Rhythm

TL;DR

This paper develops a physiologically interpretable low-dimensional model of the mammalian circadian clock to understand how light influences phase resetting and seasonal adaptations.

Contribution

It introduces a new macroscopic model based on phase response curves that links physiological parameters with experimental observations of light effects on circadian rhythms.

Findings

Light sensitivity can be modulated by coupling forces.

Seasonal day-length affects light entrainment after-effects.

The model explains experimental phase response behaviors.

Abstract

We study the impact of light on the mammalian circadian system using the theory of phase response curves. Using a recently developed ansatz we derive a low-dimensional macroscopic model for the core circadian clock in mammals. Significantly, the variables and parameters in our model have physiological interpretations and may be compared with experimental results. We focus on the effect of four key factors which help shape the mammalian phase response to light: heterogeneity in the population of oscillators, the structure of the typical light phase response curve, the fraction of oscillators which receive direct light input and changes in the coupling strengths associated with seasonal day-lengths. We find these factors can explain several experimental results and provide insight into the processing of light information in the mammalian circadian system. In particular, we find that the sensitivity of the circadian system to light may be modulated by changes in the relative coupling forces between the light sensing and non-sensing populations. Finally, we show how seasonal day-length, after-effects to light entrainment and seasonal variations in light sensitivity in the mammalian circadian clock are interrelated.