Neurons Help Flush Neurodegeneration-Contributing Metabolic Waste in the Brain During Sleep, Study Finds

Neurons have been found to be miniature pumps that power the fluid flow and removal of brain debris during sleep.

The Brain During Sleep

Sleep is quite paradoxical. While it appears to be a tranquil activity, it actually juxtaposes with the bustling activity of the brain, which is far from dormant during sleep. When one is asleep, the cells of the brain make electrical pulse bursts that cumulate into rhythmic waves. This indicates increased brain cell function.

Slow brain waves have been linked to refreshing and restful sleep. Now, scientists have discovered that brain waves aid in flushing out metabolic waste from the brain during sleep. Single nerve cells coordinate in order to produce rhythmic waves that push fluid through brain tissue that is dense. In the process of doing so, tissue gets washed.

Cleaning Brain Waste

Li-Feng Jiang-Xie, PhD, the study's first author and a postdoctoral research associate from the Department of Pathology & Immunology at the Washington University School of Medicine in St Louis, explains that the neurons serve as miniature pumps. Synchronized activity of neurons powers the flow of fluid and removal of brain debris.

If such a process can be built on, there is a chance of preventing or delaying neurological conditions, such as Parkinson's and Alzheimer's disease, wherein surplus waste builds up in the brain and results in neurodegeneration.

Such findings were noted in the "Neuronal dynamics direct cerebrospinal fluid perfusion and brain clearance" study.

Brain cells orchestrate body movements, feelings, and thoughts. They also form dynamic networks that are important for problem solving and memory formation. However, to do such tasks, neurons need fuel. Their nutrient consumption leads to the creation of metabolic waste in the process.

Jonathan Kipnis, PhD, who is a BJC Investigator and Alan A. and Edith L. Wolff, Distinguished Professor of Pathology & Immunology, explains that it is crucial for metabolic waste to be disposed of in the brain. This waste can accumulate and contribute to neurodegeneration.

Kipnis explains that they knew that sleep is a period wherein the brain prompts a cleaning process for flushing out toxins and waste that the brain accumulates when awake. However, they did not know that this actually takes place. Such findings could lead to the discovery of possible therapies and strategies for speeding up the removal of waste before grave consequences result.

However, the task of cleaning the brain is not easy. The cerebrospinal fluid that surrounds the brain goes in and weaves through intricate webs of cells. It gathers waste as it moves. As it exits the brain, the contaminated fluid must move through a barrier before entering the dura mater's lymphatic vessels.

Upon examining sleeping mouse brains, the researchers observed that neurons fuel the cleaning process by releasing electrical signals coordinately to generate rhythmic brain waves. The researchers determined that such waves pushed the movement of the fluid.

They silenced certain brain regions to ensure that neurons from those regions did not produce any rhythmic waves. Without such waves, the cerebrospinal fluid that is fresh could now flow through the regions that were silenced and trapped waste could not leave the tissue.

Jiang-Xie explains that they think the process of brain-cleaning is similar to dishwashing. Kipnis also notes that brain-cleansing is one reason for sleep. If such a cleaning process can be enhanced, it could be possible to sleep less and stay healthy.

The scientists are not interested in knowing why these cells fire waves with altered rhythmicity in sleep and which brain regions are most vulnerable to the accumulation of waste.