This article challenges the hypothesis that sleep and anesthesia enhance brain clearance of metabolites and toxins. Researchers measured the diffusion and clearance of fluorescent molecules in the brains of mice and found that brain clearance is not increased during sleep or anesthesia, but rather is significantly reduced. The study used a combination of in vitro and in vivo experiments to measure the diffusion coefficient of fluorescent dyes, such as FITC-dextran, and found that diffusion rates remained consistent across different vigilance states, including sleep and anesthesia. The researchers also measured brain clearance using fluorescent dyes and found that clearance was reduced during sleep and anesthesia. These findings contradict previous suggestions that sleep and anesthesia enhance brain clearance. The study also shows that the glymphatic system, which is thought to be responsible for brain clearance during sleep, does not operate more efficiently during sleep or anesthesia. The results suggest that the core function of sleep may not be to clear toxins from the brain, but rather to serve other essential functions. The study highlights the importance of understanding the mechanisms of brain clearance and the potential impact of sleep and anesthesia on these processes.This article challenges the hypothesis that sleep and anesthesia enhance brain clearance of metabolites and toxins. Researchers measured the diffusion and clearance of fluorescent molecules in the brains of mice and found that brain clearance is not increased during sleep or anesthesia, but rather is significantly reduced. The study used a combination of in vitro and in vivo experiments to measure the diffusion coefficient of fluorescent dyes, such as FITC-dextran, and found that diffusion rates remained consistent across different vigilance states, including sleep and anesthesia. The researchers also measured brain clearance using fluorescent dyes and found that clearance was reduced during sleep and anesthesia. These findings contradict previous suggestions that sleep and anesthesia enhance brain clearance. The study also shows that the glymphatic system, which is thought to be responsible for brain clearance during sleep, does not operate more efficiently during sleep or anesthesia. The results suggest that the core function of sleep may not be to clear toxins from the brain, but rather to serve other essential functions. The study highlights the importance of understanding the mechanisms of brain clearance and the potential impact of sleep and anesthesia on these processes.