About 170 billion cells are in the brain, and as they go about their regular tasks, they produce waste — a lot of it. To stay healthy, the brain needs to wash away all that debris.
During sleep, slow electrical waves push the fluid around cells from deep in the brain to its surface. There, a sophisticated interface allows the waste products in that fluid to be absorbed into the bloodstream, which takes them to the liver and kidneys to be removed from the body.
Iliff & Dr. Maiken Nedergaard, first proposed the clear fluids in & around the brain are part of a system to wash away waste products (AKA glymphatic system)which helps fight infection, maintain fluid levels and filter out waste products and abnormal cells.
Both systems work like plumbing in a house (Jonathan Kipnis/ Washington University/St. Louis. Water & sewage pipes - water comes in clean, and the dirty water goes out."
The lymphatic system is a network of thin tubes transporting waste to bloodstream. Brain lacks these tubes.
In sleeping animals, cerebrospinal fluid begins to flow quickly through the brain, flushing out waste. It turned out that the electrical waves were acting as a signal, synchronizing the activity of neurons and transforming them into tiny pumps that push fluid toward the brain's surface.
"Around the vein, you have a sleeve, which is never fully sealed," he says. "That's where the [cerebrospinal fluid] is coming out" and transferring waste to the body's lymphatic system.
Together, the new studies suggest that keeping the brain's waste-clearance system functioning requires two distinct steps: one to push waste into the cerebrospinal fluid that surrounds the brain, and another to move it into the lymphatic system and eventually out of the body.
Researchers know that the brain's waste-clearance system can be impaired by age, injuries and diseases that clog blood vessels in the brain.
"All of these are risk factors for Alzheimer's disease," Iliff says.
Impaired waste removal may also be a factor in Parkinson's disease, headache and even depression, Iliff says. So finding ways to help the brain clean itself — perhaps by inducing those slow electrical waves — might prevent a wide array of disorders.
