Clearance of molecules from the brain is not increased during sleep, according to new findings published in Nature Neuroscience. Researchers measured brain clearance in mice that were awake, sedated or asleep by following movement of a small fluorescent dye in the brain parenchyma. Clearance was lower in animals that were sedated or sleeping than in animals that were awake. Although molecules with larger molecular weights than the dye might behave differently, the findings seem to contradict evidence that sleep is critical for the clearance of toxic proteins and metabolites from the brain, bringing into question the importance of sleep in protecting against neurodegenerative diseases.