Modeling of drosophila circadian system based on locomotor activity

Due to the 24-hour lighting-dark cycle on earth, circadian rhythm regulates the biochemical and physiological processes of almost all living organisms, including plants, insects, and mammals. Maintaining the regular cyclicity of this internal clock, called entrainment, is important to the well being of an organism. For human, circadian disruption can lead to lower productivity, digestive problems, decreased sleep efficiency and other health problems. Various models have been proposed for the circadian rhythm, from empirical oscillator type models to genetic network based biochemical models. These models are used to gain insight into the mechanism governing the circadian rhythm, but may also be used to formulate light-based control strategies for its regulation. As a first step towards our eventual goal of light based circadian rhythm regulation for human, we are conducting experiments with drosophila (fruit fly), measuring the interaction between light intensity and wavelength and its locomotive activity level. Instead of the high order biochemical models proposed in the past, we consider a second order empirical oscillator model, with light intensity as input and activity as the output. By first entraining the flies in a regular rhythm and then observe the effect of light pulses, we are able to identify the model parameters based on the input/output experimental data. The model shows promising predictive capability: Our simulation shows that two blue pulses can shift the phase of drosophila circadian pacemaker by 12 hours, while the experiment result is 13.3 hours.