Sleep and the glymphatic system

Although waste clearance, as well as protein synthesis, is fundamental to maintain brain homeostasis, the brain parenchyma lacks a classic lymphatic vessel. Therefore, there has been a longstanding question of how interstitial fluid homeostasis is maintained. In 2012, the glymphatic system was discovered as a glial-dependent waste clearance pathway in the brain. Notably, glymphatic activity is mostly active during sleep, suggesting that sleep propels the removal of brain waste. Upon discovery of a downstream meningeal lymphatic system in 2015, a growing body of evidence suggests that the disruption in the glymphatic-lymphatic system may contribute to some neurological diseases including Alzheimer's disease.