There is a paradox in the dream. Its apparent tranquility is juxtaposed with the bustling activity of the brain. The night is quiet, but the brain is far from asleep. During sleep, brain cells produce bursts of electrical pulses that build up into rhythmic waves, a sign of increased brain cell function.
But why is the brain active when we are at rest?
Slow brain waves are associated with restful, refreshing sleep. And now, scientists at Washington University School of Medicine in St. Louis have discovered that brain waves help clear waste from the brain during sleep. Individual nerve cells coordinate to produce rhythmic waves that propel fluid through dense brain tissue, washing the tissue in the process.
“These neurons are miniature pumps. Synchronized neuronal activity drives fluid flow and waste removal from the brain,” explained first author Li-Feng Jiang-Xie, PhD, a postdoctoral research associate in the Department of Pathology and Immunology. “If we can harness this process, there is a chance to delay or even prevent neurological diseases, including Alzheimer’s and Parkinson’s disease, in which excess waste, such as metabolic waste and junk proteins, builds up in the brain and leads to to neurodegeneration.”
The findings are published on February 28 in Nature.
Brain cells orchestrate thoughts, feelings, and body movements, forming dynamic networks essential for memory formation and problem solving. But to perform tasks that require so much energy, brain cells need fuel. Your consumption of dietary nutrients generates metabolic waste in the process.
“It is critical that the brain clears out metabolic waste that can accumulate and contribute to neurodegenerative diseases,” said Jonathan Kipnis, PhD, Alan A. and Edith L. Wolff Distinguished Professor of Pathology and Immunology and BJC investigator. Kipnis is the lead author of the article. “We knew that sleep is a time when the brain begins a cleansing process to remove waste and toxins it accumulates during wakefulness, but we didn’t know how that happens. These findings could point us toward potential strategies and therapies to speed up removal of harmful waste and eliminate it before it can have dire consequences.
But cleaning the dense brain is not an easy task. Cerebrospinal fluid surrounding the brain enters and weaves through intricate cellular networks, collecting toxic waste as it travels. Leaving the brain, the contaminated fluid must pass through a barrier before spilling into the lymphatic vessels of the dura mater, the outer layer of tissue that surrounds the brain under the skull. But what drives the movement of fluid into, through and out of the brain?
By studying the brains of sleeping mice, researchers found that neurons drive cleaning efforts by firing electrical signals in a coordinated manner to generate rhythmic waves in the brain, Jiang-Xie explained. They determined that such waves drive the movement of the fluid.
The research team silenced specific brain regions so that neurons in those regions would not create rhythmic waves. Without these waves, fresh cerebrospinal fluid would not be able to flow through the silenced regions of the brain and trapped waste would not be able to leave the brain tissue.
“One of the reasons we sleep is to cleanse the brain,” Kipnis said. “And if we can improve this cleansing process, it may be possible to sleep less and stay healthy. Not everyone has the benefit of sleeping eight hours a night, and lack of sleep has an impact on health. Other studies have shown than mice that “are genetically programmed to sleep less and have healthy brains. Could it be because they clear waste from their brains more efficiently? “Could we help people living with insomnia by improving the cleaning abilities of their brains so they can cope with sleeping less?”
Brain wave patterns change throughout sleep cycles. It is noteworthy that taller brain waves with greater amplitude move fluid more strongly. Researchers are now interested in understanding why neurons fire waves with different rhythmicity during sleep and which regions of the brain are most vulnerable to waste buildup.
“We think the brain’s cleaning process is similar to washing dishes,” explained neurobiologist Jiang-Xie. “You start, for example, with a large, slow, rhythmic wiping motion to clean soluble debris scattered across the plate. Then you decrease the range of motion and increase the speed of these motions to remove particularly sticky food debris. of the plate. Despite the variation in amplitude and rhythm of the hand movements, the general goal remains the same: to remove different types of debris from the dishes. Perhaps the brain adjusts its cleaning method depending on the type and the amount of waste”.