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A new Northwestern University study reaffirms the importance of getting a good night’s sleep. By examining fruit flies’ brain activity and behavior, the researchers found that deep sleep has the power to clear waste from the brain. This waste potentially includes poisonous proteins that may lead to neurodegenerative (神经退化) diseases. “Waste clearance could be important, in general, for maintaining brain health or for preventing neurodegenerative diseases,” said Dr. Allada, senior author of the study. “Waste clearance may occur during wake and sleep but is greatly strengthened during deep sleep.”

Although fruit flies seem very different from humans, the neurons (神经元) that govern flies’ sleep-wake cycles are strikingly similar to our own. For this reason, fruit flies have become a well-studied model organism for sleep and neurodegenerative diseases.

In this current study, Allada and his team examined Proboscis (针状喙) Extension Sleep, a deep-sleep stage in fruit flies, which is similar to deep, slow-wave sleep in humans. The researchers discovered that, during this stage fruit flies repeatedly extend and move back their proboscises. “This kind of movement moves fluids possibly to the fly version of kidneys (肾),” Allada said. “Our study shows that this promotes waste clearance and aids in injury recovery.”

When Allada’s team disturbed flies’ deep sleep, the flies were less able to clear the waste from their systems and were more likely to be influenced by injuries.

Allada said this study brings us closer to understanding the mystery of why all organisms need sleep. All animals, especially those in the wild, are incredibly weak when they sleep, but research increasingly shows that the benefits of sleep, including crucial waste removal, are greater than this increased weakness.