We all need to clear our heads, sometimes literally — and now scientists have learned how our neurological plumbing system works.
Every organ produces waste, and the brain is no exception. But unlike the rest of our body, it doesn’t have a lymphatic system, a network of vessels that filter out junk. Now, a new study of mouse brains suggests how ours handle waste: by rapidly pumping fluid along the outside of blood vessels, literally flushing waste away. The finding, reported Aug. 15 in Science Translational Medicine, could hint at how diseases like Alzheimer’s develop and might be treated.
“If you look at a body-wide map of the lymphatic system, you see a great big void in the brain,” said neuroscientist Jeffrey Iliff of the University of Rochester Medical Center. He and his colleagues found that puzzling, given how active the brain is and how sensitive it is to waste buildup.
Scientists long suspected that the brain’s refuse ended up in the cerebrospinal fluid, which cushions the brain inside the skull. In the 1980s, some researchers proposed that the fluid might be pumped into the brain to wash it, then pumped out again. Other researchers weren’t convinced.
Thanks to new imaging techniques that made it possible to peer inside the brain of a living mouse, Iliff’s team saw the process in action. Cerebrospinal fluid flowed along the outside of blood vessels, carried through a network of pipe-like protein structures. The fluid picked up waste that accumulated between cells, then drained out through major veins.
“These experiments validate a powerful ‘prevailing current’ of cerebrospinal fluid in brain extracellular space that effectively clears metabolic garbage,” said neurologist Bruce Ransom of the University of Washington, who was not affiliated with the study.