It's no secret that sleeping recharges the brain in a vital way, but the tricky part is the central question: How? A fresh theory announced Thursday by a lab in Rochester, N.Y., is startlingly simple.
Sleep drives a garbage truck through the brain, literally removing bits of physical waste material and allowing a cleaner brain to think better the next day.
And the garbage truck won't operate while we're awake.
"Garbage truck" isn't a cute phrase invented by a newspaper. These are the words used by the research journal Science, which reports the findings of the team of Maiken Nedergaard and Lulu Xie, neuroscientists at the University of Rochester Medical Center.
The brain uses a stream of fluid running through microscopic channels to carry off waste, they found.
What it takes away is a collection of toxins that build up while we're awake, including one substance that forms a "plaque" in the brain cells of people with Alzheimer's.
A parallel fluid system called the lymphatic system operates in the rest of the body, but not in the brain. Medical thinking has been that brain cells somehow break down and recycle their waste.
Instead, they say the brain's waste removal system "amounts to a plumbing system that piggybacks on the brain's blood vessels and pumps cerebral spinal fluid through the brain's tissue, flushing waste back into the circulatory system where it eventually makes its way to the general blood circulation system and, ultimately, the liver." Nearly all animals sleep in some fashion, the researchers write, "but this period of dormancy has significant drawbacks, particularly when predators lurk about. This has led to the observation that if sleep does not perform a vital biological function, then it is perhaps one of evolution's biggest mistakes."
Instead, Nedergaard concludes that the cleanup process uses energy that isn't available when the mind is awake: "You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can't really do both at the same time."
The discovery came from tracking coloured dye through the brains of living, healthy mice. The waste-transport system operated at a very low level when the mice were awake, but much more actively when the mice slept.
They also found that brain cells shrink during sleep, creating space for the fluid to flow around them.
That adds yet another reason why sleep is important to health, they concluded: "Almost every neurodegenerative disease is associated with the accumulation of cellular waste products."
They believe this opens new avenues to explore in the treatment of brain diseases.
0 comments:
Post a Comment