Editor's Pick: There is a paradox in sleep in which the apparent tranquility coexists with the busy activity of the brain. The night is quiet, but the brain is far from dormant.
There is a paradox in sleep. Its apparent tranquility coexists with the hectic activity of the brain. The night is quiet, but the brain is far from dormant. During sleep, brain cells produce electrical impulses that accumulate into rhythmic waves – a sign of increased brain cell function.
But why is our brain active when we're resting?
Slow brain waves are associated with restful, refreshing sleep. Now, scientists at Washington University School of Medicine in St. Louis have discovered that brain waves help flush waste products out of the brain during sleep. Individual nerve cells coordinate to produce rhythmic waves that push fluid through dense brain tissue, rushing to the tissue in the process. These neurons are miniature pumps, and synchronized neural activity powers fluid flow and the removal of brain debris.
"If we can build on this process, it is possible to delay or even prevent neurological diseases, including Alzheimer's disease and Parkinson's disease, in which excess waste products such as metabolic waste and junk protein accumulate in the brain, leading to neurodegeneration," said Li-Feng Jiang-xie, first author and postdoctoral researcher in the Department of Pathology and Immunology. ”
The findings were published Feb. 28 in the journal Nature.
Brain cells coordinate thoughts, sensations, and body movements, forming dynamic networks that are essential for memory formation and problem-solving. But to accomplish this energy-hungry task, brain cells need fuel. In this process, they take nutrients from their diet to produce metabolic waste.
*Senior author, Distinguished Professor of Pathology and Immunology, BJC Investigator Dr. Jonathan Kipnis, said: "It is critical that the brain processes metabolic waste products that may contribute to neurodegenerative diseases. We know that sleep is when the brain initiates the cleansing process, and the brain flushes out waste and toxins that accumulate while awake. But we don't know how this happened. These findings may point us to strategies and potential ways to accelerate the removal of destructive waste and remove it before it leads to dire consequences. ”
But cleaning up a dense brain is not a simple task. The cerebrospinal fluid surrounding the brain enters and weaves through a complex web of cells, collecting toxic waste during transportation. To flow out of the brain, the contaminated fluid must pass through a barrier and then flow into the lymphatic vessels in the dura mater – the outer layer of tissue that surrounds the brain under the skull. But what drives fluids in and out of the brain?
When the researchers studied the brains of sleeping mice, the researchers found that neurons produce rhythmic waves in the brain by emitting electrical signals in a coordinated manner to drive cleaning work, Jiang-Xie explained. They determined that this wave drove the motion of the fluid.
The team silenced specific brain regions so that neurons in those areas did not produce rhythmic electrical waves. Without these brain waves, fresh cerebrospinal fluid cannot flow through the silent brain area, and trapped waste products cannot leave the brain tissue.
One of the reasons we sleep is to cleanse our brains," Dr. Kipnis emphasizes: "If we can intensify this cleansing process, it may be possible to sleep less and stay healthy." Not everyone has the benefit of 8 hours of sleep per night, and sleep deprivation has an impact on health. Other studies have shown that rats that were born with less sleep had healthier brains. Could it be because they are more efficient at cleaning up waste from the brain? Can we help insomnia sufferers by improving the cleansing ability of people's brains and getting them to sleep less? ”
Brainwave patterns change throughout the sleep cycle. It is important to note that higher brain wave amplitudes are greater and the force to move the fluid is greater. Researchers are now interested in understanding why neurons emit radio waves at different rhythms during sleep, and which areas of the brain are most susceptible to waste buildup.
Neurobiologist Jiang-Xie explains: "We think that the cleaning process of the brain is similar to washing dishes. For example, you start with a large, slow, rhythmic wiping motion to clean up the soluble waste scattered on the plate. Then you reduce the range of movements and increase the speed of those movements to remove particularly sticky food waste from the plate. Although the amplitude and rhythm of your hand movements varies, the overall goal is the same: to remove different types of waste from the plate. Perhaps the brain adjusts the cleaning method according to the type and amount of waste. ”
*：nature
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