Scientists: Brain Has Built-In Waste Removal System

A unique peek inside the human brain may help explain how it clears away waste like the kind that can build up and lead to Alzheimer's disease. Brain cells use a lot of nutrients, which means they make a lot of waste. Scientists have long thought the brain has special plumbing to flush out cellular trash, especially during sleep—they could see it happening in mice. But there was only circumstantial evidence of a similar system in people. Now, researchers have finally spotted that network of tiny waste-clearing channels in the brains of living people, thanks to a special kind of imaging, per the AP. "I was skeptical," said Dr. Juan Piantino of Oregon Health & Science University, whose team reported the findings on Monday in the journal Proceedings of the National Academy of Sciences. "We needed this piece to say this happens in humans, too."

• Snooze factor: The brain is remarkably active during sleep. One reason seems to be that's the time it does a deep clean—and that's gotten attention because chronic sleep deprivation is considered a risk factor for dementia.

• Cleansing process: More than a decade ago, scientists at the University of Rochester first reported finding a network they dubbed the "glymphatic system." Cerebrospinal fluid uses channels surrounding blood vessels to get deep into tissue and move waste until it exits the brain. When mice were injected with a chief Alzheimer's culprit named beta-amyloid, it cleared away faster when the animals were sleeping. It's not clear exactly how that network works, although some research has shown the pulsing of blood vessels helps move the waste-clearing fluid where it needs go.

• Piantino's experiment: It's been hard to find that system in people. Regular MRI scans can spot some of those fluid-filled channels but don't show their function. So Piantino's team injected a tracer into five patients who were undergoing brain surgery and needed a more advanced form of MRI. The tracer "lit up" under those scans, and sure enough, 24 to 48 hours later, it wasn't moving randomly through the brain but via those channels, just as prior research found in mice.
• Uses: It's a small but potentially important study that the university's Dr. Maiken Nedergaard predicted will increase interest in how brain waste clearance connects to people's health. It could also lead to tests that check how better sleep or other treatments might really spur waste clearance and improve health. Additional larger studies in healthy people are needed, and Piantino wants to find an easier, more noninvasive test. "We cannot study all these questions by injecting people," he said.

(More brain stories.)