Neurons assist in the removal of waste from brain during sleep

During sleep, when the body is at rest, the brain cells produce bursts of electrical pulses that cumulate into rhythmic waves -- a sign of heightened brain cell function. Cerebrospinal fluid surrounding the brain enters and weaves through intricate cellular webs, collecting toxic waste as it travels. Upon exiting the brain, the contaminated fluid must pass through a barrier before spilling into the lymphatic vessels in the dura mater -- the outer tissue layer enveloping the brain underneath the skull.

"The neurons are miniature pumps. Synchronized neural activity powers fluid flow and removal of debris from the brain," explained first author Li-Feng Jiang-Xie, PhD, a postdoctoral research associate in the Department of Pathology & Immunology. "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 -- accumulate in the brain and lead to neurodegeneration."

Researchers studied the brain of sleeping mice and discovered that neurons generate rhythmic brain waves, driving cleaning processes by facilitating fluid movement. Silencing specific brain regions halted these waves, preventing fresh cerebrospinal fluid flow and trapping waste in brain tissue.

"One of the reasons that we sleep is to cleanse the brain," said Jonathan Kipnis, Professor of Pathology & Immunology and a BJC Investigator. "And if we can enhance this cleansing process, perhaps it's possible to sleep less and remain healthy. Not everyone has the benefit of eight hours of sleep each night, and loss of sleep has an impact on health. Other studies have shown that mice that are genetically wired to sleep less have healthy brains.”

Brain wave patterns change throughout sleep cycles. Taller brain waves with larger amplitude move fluid with more force. The research could help people living with insomnia by enhancing their brain's cleaning abilities so they can function well on less sleep.

Reference: Li-Feng Jiang-Xie, Antoine Drieu, Kesshni Bhasiin, Daniel Quintero, Igor Smirnov, Jonathan Kipnis. Neuronal dynamics direct cerebrospinal fluid perfusion and brain clearance. Nature, 2024; DOI: 10.1038/s41586-024-07108-6