npr:

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.

“Some disruption to the way sleep is working could potentially be contributing to the decline in brain health,” Lewis says.

How Deep Sleep May Help The Brain Clear Alzheimer’s Toxins

GIF: Fultz et al., 2019
Caption: During deep sleep, waves of cerebrospinal fluid (blue) coincide with temporary decreases in blood flow (red). Less blood in the brain means more room for the fluid to carry away toxins, including those associated with Alzheimer’s disease.