Scientists Picked Apart the Human Brain's Trash Disposal—and Found Something Incredible
"Hearst Magazines and Yahoo may earn commission or revenue on some items through these links."
The glymphatic system is responsible for removing waste that builds up in the brain while we sleep. First discovered in 2013, scientists are still trying to understand how it works.
In a series of new papers, experts have pieced together the mechanism that “pumps” cerebrospinal fluid through the brain, as well as how the waste traverses the barrier separating brain tissue and the bloodstream.
These discoveries could help neurologists better treat maladies such as Alzheimer’s and Parkinson’s diseases, as the build-up of waste in the brain can lead to these neurological disorders.
The human brain is one of the most complex structures nature has ever devised, and that means there’s a lot we still don’t know about the three pounds of neurons and fat that rests between our ears. Case in point, scientists only discovered how the organ removes waste from the deep brain in 2013.
Named the “glymphatic system,” this waste system uses cerebrospinal fluid to wash away waste products in the brain. It is especially good at clearing out protein aggregates called amyloids, which have been linked with neurological diseases like Alzheimer’s.
Sounds simple, right?
Sadly, brain biology is rarely so straightforward. While we know that this brainwashing (the good kind, not the bad kind) happens while we sleep, and that cerebrospinal fluid flushes out the waste, we don’t know exactly what the driving force behind this process is, or how it delivers the waste past the barrier separating the brain and the bloodstream.
Now, a series of three papers—all published earlier this year—answer these decade-long quandaries by focusing on the slow electrical waves that appear in the brain while we sleep. In a paper published in the journal Nature late this February, Washington University of St. Louis’s Jonathan Kipnis and his team found that individual nerve cells coordinate to create rhythmic waves, which essentially act as miniature pumps that move fluid through brain tissue. An additional study, conducted by scientists at MIT, provided more evidence to explain how these electrical waves remove waste.
“We knew that sleep is a time when the brain initiates a cleaning process to flush out waste and toxins it accumulates during wakefulness. But we didn’t know how that happens,” Kipnis said in a press statement. “It is critical that the brain disposes of metabolic waste that can build up and contribute to neurodegenerative diseases.”
While that answers how waste migrates from the deep brain to its outer edges, it still doesn’t put together how the waste was then entering the bloodstream (and eventually being filtered by the liver and kidneys). In another study published earlier this year, Kipnis announced the discovery of structures similar to “airport security checkpoints” that allow molecules and fluid to move across the arachnoid barrier separating brain tissue and the bloodstream.
“It’s a paradox. On the one hand, the barrier is impermeable and does not allow anything to get out of the brain,” PhD doctoral researcher Leon Smyth, a co-author of the study, said in a press statement. “On the other hand, cerebrospinal fluid must get through the arachnoid barrier, because we can detect it on the other side.”
By injecting mice with light-emitting molecules, the scientists were able to see the fluid slip through these “security gates” where blood vessels pass through the barrier. By then taking MRI scans of healthy humans, the team confirmed that a similar process is occurring in the our brains as well—and that a “clog” in these areas could prevent waste from exiting the brain, leading to a variety of neurological disorders.
Understanding this waste removal system could help those suffering from neurological conditions, and explain certain neurological symptoms that impact veterans. Jeffrey Iliff—a neurologist at the University of Washington who was part of the research team that discovered the glymphatic system in 2013—conducted a study in May that showed blast-induced traumatic brain injury can impair this system and lead to post-concussive symptoms.
The brain holds many mysteries that scientists have yet to uncover, but every new discovery brings us one step closer to providing therapy and relief to the millions who suffer from neurological conditions around the world.
You Might Also Like
