Deep Night Sleep Clears the Mind

Deep sleep is of great importance for brain health by preventing neurodegenerative diseases by clearing unnecessary information in the brain.

New study at Northwestern University highlights the importance of getting a deep night's sleep.

By studying the brain activity and behavior of fruit flies, researchers discovered that deep sleep has an ancient and restorative power to clear waste from the brain. These wastes include toxic proteins that can potentially lead to neurodegenerative diseases.

Senior author of the article, Dr. "Waste removal can be important for maintaining brain health and preventing neurodegenerative diseases," Ravi Allada said. Waste removal can take place while awake or asleep, but it is highly effective, especially during deep sleep, ”he said.

Allada is head of the Department of Neurobiology at Northwestern's Weinberg College of Arts and Sciences and Edward C. Stuntz Distinguished Professor of Neuroscience. He is also the deputy director of the Northwestern Sleep and Circadian Biology Center. Bart van Alphen, who works as a postdoctoral researcher in Allada's lab, is also the lead author of the article.

Although fruit flies look very different from humans, the neurons that regulate the flies' sleep-wake cycles are strikingly similar to our neurons. For this reason, fruit flies are a frequently used model organism in sleep, circadian rhythm and neurodegenerative disease studies.

In this study, Allada et al examined proboscis stretch sleep (PES) in flies, a state of deep sleep similar to deep, slow-wave sleep in humans. During this phase, the researchers found that the fruit flies repeatedly stretched and retracted their proboscis.

“This pumping action allows the fluid to move by acting as a kidney in flies,” says Allada. "We showed in our study that this plays a role in waste removal and wound repair,"

When Allada's team damaged the flies' deep sleep, the flies were less successful at removing an un-metabolizable dye that had been injected into them, and became more vulnerable to traumatic injury.

Allada said this study brings us a little closer to understanding why all organisms specifically need sleep. All animals, except those living in the wild, become highly vulnerable to threats as soon as they sleep. However, studies show that the benefits of sleep, such as removing harmful waste, are considered more advantageous compared to this increased vulnerability.

The authors of the study said, “Our findings on the function of deep sleep for the elimination of waste in fruit flies indicate that waste cleansing is an evolutionarily conserved essential feature of sleep. "Cleaning of waste can be a function of sleep in the common ancestor of fruit flies and humans."

The study was published in Science Advances on January 20.