 Sleep is important for maintaining a healthy extracellular environment in the brain, as it allows for the removal of toxic proteins from the brain via the glimphatic system. This process is enhanced during non-rapid eye movement, NREM, sleep in both mice and humans, as well as in birds. However, in birds, the paradoxical state of rapid eye movement, REM, sleep appears to be associated with decreased waste clearance, potentially due to increased brain activity during REM sleep. This article was authored by Giannina Ungurian, Medi Barrosi, Leonard Boga, and others.