Most living organisms have an internal clock which, among other things, controls the sleep-wake rhythm. The internal rhythm lasts approximately one day (circadian), i.e. about 24 hours, and is regulated by means of various clock genes. There is also permanent coordination with factors such as light and temperature for synchronizing the internal clock with the external day-night rhythm. A team led by neurobiologist Prof. Ralf Stanewsky from the University of Münster has now demonstrated in the Drosophila melanogaster fruit fly that a certain ion transport protein (KCC) plays a role in regulating circadian rhythms by means of light.