Deep sleep takes out trash from brain: study

By Xu Jing

CHICAGO, Jan. 21 (Xinhua) -- By examining fruit flies' brain activity and behavior, researchers at Northwestern University (NU) found that deep sleep has an ancient, restorative power to clear waste from the brain.

In the study, the researchers examined proboscis extension sleep, a deep-sleep stage in fruit flies, which is similar to deep, slow-wave sleep in humans. They discovered that, during this stage, fruit flies repeatedly extend and retract their proboscis or snout.

"This pumping motion moves fluids possibly to the fly version of the kidneys," said Ravi Allada, senior author of the study and a professor in neuroscience and chair of the Department of Neurobiology in NU's Weinberg College of Arts and Sciences. "Our study shows that this facilitates waste clearance and aids in injury recovery."

When the researchers impaired flies' deep sleep, the flies were less able to clear an injected non-metabolizable dye from their systems and were more susceptible to traumatic injuries.

This study brings us closer to understanding the mystery of why all organisms need sleep, said Allada. All animals, especially those in the wild, are incredibly vulnerable when they sleep. But research increasingly shows that the benefits of sleep, including crucial waste removal, outweigh this increased vulnerability.

"Our finding that deep sleep serves a role in waste clearance in the fruit fly indicates that waste clearance is an evolutionary conserved core function of sleep," the paper's co-authors write. "This suggests that waste clearance may have been a function of sleep in the common ancestor of flies and humans."

The study was published Wednesday in the journal Science Advances.

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