The glymphatic system of the brain was described and named in 2013 by Dr. Maiken Nedergaard, a Danish neuroscientist. The glymphatic system is a "macroscopic waste clearance system that utilizes a unique system of perivascular channels, formed by astroglial cells, to promote efficient elimination of soluble proteins and metabolites from the central nervous system.”
A 2021 study described how the glymphatic merges with the lymphatic system of the body:
The glymphatic system enables bulk movement of cerebral spinal fluid (CSF) from the subarachnoid space along periarterial spaces, where it mixes with interstitial fluid (ISF) within the parenchyma before ultimately exiting from the parenchyma via perivenous spaces and drains into the peripheral lymphatic system ...
Besides waste elimination, “the glymphatic system may also function to help distribute non-waste compounds, such as glucose, lipids, amino acids, and neurotransmitters related to volume transmission, in the brain."
The discovery of the glymphatic system – the name merging ‘glial’ and ‘lymphatic’ – surprised researchers and overturned decades of textbook teaching. A senior researcher at the U. of Virginia was quoted in 2016:
The brain and the adaptive immune system were thought to be isolated from each other, and any immune activity in the brain was perceived as sign of a pathology. And now, not only are we showing that they are closely interacting, but some of our behavior traits might have evolved because of our immune response to pathogens…
A highly significant feature of the glymphatic system, researchers stress, is the fact that “it functions mainly during sleep and is largely disengaged during wakefulness”:
The biological need for sleep across all species may therefore reflect that the brain must enter a state of activity that enables elimination of potentially neurotoxic waste products, including β-amyloid.