Seminar by Xiaochan Xu

Quantitative Investigation of Sleep Patterns in Drosophila

Xiaochan Xu (Integrated Life Sciences)

Sleep is one of the most universal physiological states shared among species. It has an irreplaceable role in maintaining physical health and brain activity. The fruit fly, Drosophila melanogaster, has been used successfully as a model organism for molecular and genetic dissection of sleeping behaviors. However, most previous studies were based on qualitative or semi-quantitative characterization of the sleep patterns. In order to provide new angles and insights into the complex behavior of sleep and to fully understand the underlying mechanism, more quantitative methods and studies have to be developed and carried out.

Here we set up a continuous tracking method with infrared cameras to track the activities of flies. The device can monitor the movement of tens of flies at the same time with high spatial and temporal resolution. We were able to obtain very accurate statistics on the rest and sleep patterns of single flies and analyze their behavior. Our experimental results and data analysis revealed a general quantitative law of sleep in flies: the rest statistics obeys a power law distribution and the sleep statistics obeys an exponential distribution. That is, when resting the fly will start to move again with a probability that decreases with the time it has rested, while in sleeping the fly will wake up with a probability that is independent of how long it has slept.

We also explored the effects of gender, age, sensation system defects, mating experience and other factors on the sleep pattern. Through genetic screening, we have identified a number of genes that may play a role in the mechanism of the quantitative sleep pattern. We developed a mathematical model to account for the observed behavior, which suggests that the quietness threshold for the brain to fall asleep and the stability of the brain at every stage of the sleep state are most important factors for the generation of the quantitative sleep law.

Our results provided a new method for evaluation of sleep pattern and laid the basis for a quantitative investigation of sleeping behavior. The sleep law revealed here also opens a new door for the studies of sleep mechanism and function.