Researchers at the Washington University School of Medicine in St. Louis have discovered that neurons are still active during sleep, taking advantage of the recharging period to get rid of waste that accumulates during waking hours. Neurons use slow brainwaves to move cerebrospinal fluid through brain tissue, carrying out metabolic waste in the process. This process helps prevent accumulation of waste and potentially contribute to neurodegenerative diseases. The glymphatic system, which carries cerebrospinal fluid, moves debris out of the parenchyma through channels near blood vessels. To determine what powers the glymphatic system to dump the trash, the researchers performed experiments on mice, inserting probes into their brains and planting electrodes in the spaces between neurons. They then anesthetized the mice with ketamine to induce sleep. The researchers found that the long, slow brain waves seen before were undetectable in the engineered mice, indicating that neurons had to be active for the brain's self-cleaning cycle to work. The researchers also found that previous experiments produced different results due to the type of anesthetic used and injuries caused by older and more invasive methods of implanting monitoring hardware into brain tissues.
