Why do animals sleep? Why do humans "waste" a third of their lives sleeping? Researchers now reveal a novel and unexpected function of sleep that they believe could explain how sleep and sleep disturbances affect brain performance, aging and various brain disorders. Using 3D time-lapse imaging techniques in live zebrafish, they were able to define sleep in a single chromosome resolution and show that single neurons require sleep in order to perform nuclear maintenance. In this video: 3D imaging of chromosome dynamics in individual neurons in live zebrafish (green puncta - chromosomes; multi-color line - distance moved).