The brain waves generated during deep sleep appear to trigger a cleaning system in the brain that protects it against Alzheimer’s and other neurodegenerative diseases.

Electrical signals known as slow waves appear just before a pulse of fluid washes through the brain, presumably removing toxins associated with Alzheimer’s, researchers reported Thursday in the journal Science.

The finding could help explain a puzzling link between sleep and Alzheimer’s, says Laura Lewis, an author of the study and an assistant professor in the department of biomedical engineering at Boston University.