A new Northwestern University study confirms the importance of sleep.
Examining the brain activity and behavior of fruit flies, the researchers found that deep sleep has an ancient, restorative power to clear waste from the brain. This waste probably contains toxic proteins that can lead to neurodegenerative disease.
Waste disposal can be important, in general, for maintaining brain health or for preventing neurogenic diseases. Waste disposal can occur during sleep and sleep, but increases significantly during deep sleep. “
Dr. Ravi Allada, senior author of the study
The study will be published tomorrow (January 20) in the journal Science is advancing.
Allada is Edward C. Stuntz Distinguished Professor of Neuroscience and Chair of the Department of Neurobiology at Weinberg College of Arts and Sciences in Northwestern. He is also the Deputy Director of Northwestern’s Center for Sleep and Circadian Biology. Bart van Alphen, a postdoctoral fellow at Allada Laboratory, was the newspaper’s first author.
Although fruit flies look very different from humans, the neurons that govern fly sleep-wake cycles are strikingly similar to ours. For this reason, fruit flies have become a well-studied body model for sleep, circadian rhythms and neurodegenerative diseases.
In the current study, Allada and his team looked at proboscis extension sleep (PES), a stage of deep sleep in fruit flies that resembles deep slow-wave sleep in humans. The researchers found that during this stage, the fruit flies repeatedly expanded and regenerated their proboscis (or snout).
“This pumping movement is probably moving fluids to the kidney version,” Allada said. “Our study shows that this facilitates waste disposal and helps repair injuries.”
When Allada’s team attenuated deep fly sleep, flies were less able to clear an injection of non-metabolizable dye from their systems and were more susceptible to traumatic injuries.
Allada said that this study brings us closer to understanding the mystery of why all organisms need sleep. All animals – especially those in the wild – are extremely vulnerable when they sleep. But research is increasingly showing that the benefits of sleep – including critical litter removal – outweigh this increased vulnerability.
“Our finding that deep sleep plays a role in the removal of waste in the fruit fly shows that waste disposal is an evolutionarily conserved basic function of sleep,” the paper’s authors write. “This suggests that waste disposal may have been a function of sleep in the common ancestor of fly and humans.”
van Alphen, B., et al. (2021) A stage of deep sleep in Drosophila with a functional role in waste disposal. Science is advancing. doi.org/10.1126/sciadv.abc2999.