Neurons help to flush out waste from the brain during sleep

Neuronal dynamics guide brain waste clearance for Cerebrospinal fluid perfusion.

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Sleep is peaceful, but the brain is busy. During rest, brain cells stay active and create electrical pulses that form rhythmic waves. This activity shows that the brain is working hard even during sleep. Why does this happen?

During deep sleep, slow brain waves help clear waste from the brain. Researchers at Washington University School of Medicine in St. Louis discovered that rhythmic waves produced by nerve cells help move fluid through the brain, cleaning it.

First author Li-Feng Jiang-Xie, Ph.D., a postdoctoral research associate in the Department of Pathology & Immunology, explained, “These neurons are miniature pumps. Synchronized neural activity powers fluid flow and removal of debris from the brain. If we can build on this process, there is the possibility of delaying or even preventing neurological diseases, including Alzheimer’s and Parkinson’s disease, in which excess waste – such as metabolic waste and junk proteins – accumulates in the brain and leads to neurodegeneration.”

Brain cells control thoughts, feelings, and movements, creating networks important for memory and problem-solving. But to do these tasks, they need energy, which creates waste. Jonathan Kipnis, a professor at Washington University, explains that “the brain needs to get rid of this waste to prevent diseases. During sleep, the brain cleans itself by flushing out toxins. Kipnis hopes these findings can lead to new ways to remove harmful waste from the brain before it causes problems.”

Cleaning the brain is a difficult task. Fluid around the brain collects waste as it moves through intricate networks of cells. This fluid should pass through barriers before it can leave the brain. Researchers studied sleeping mice and discovered that neurons and brain cells work together to create rhythmic waves. These waves help move the fluid and clean the brain.

The researchers silenced some brain areas from making rhythmic waves. This blocked fresh fluid from flowing through those areas, catching waste in the brain. Kipnis suggests that sleeping helps to clean our brains. If we can improve this cleaning, we could sleep less and still be healthy. 

Some people don’t sleep for eight hours every night, which can affect their health. Studies show that mice that naturally sleep less still have healthy brains. It could be because they clean their brains better. Kipnis wonders if we could help people with insomnia by improving their brain’s cleaning ability so they need less sleep.

Brain waves change during sleep, with taller waves moving fluid more forcefully. Researchers want to know why tides vary during sleep and which brain regions are most affected by waste buildup. 

Neurobiologist Jiang-Xie likens brain cleaning to washing dishes: starting with slow, rhythmic movements to clear soluble waste, then faster, more minor activities for stubborn debris. The brain might adjust its cleaning based on the type and amount of waste present.

This study concluded that neuronal activity during sleep is essential for flushing out the brain, highlighting the importance of quality sleep for brain health.

Journal reference: 

  1. Jiang-Xie, LF., Drieu, A., Bhasiin, K. et al. Neuronal dynamics direct cerebrospinal fluid perfusion and brain clearance. Nature. DOI: 10.1038/s41586-024-07108-6.
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