Sleeping is essential for our proper functioning. While we sleep, we achieve both physical and cognitive balance and not only recover energy, but the organs and systems of the body work to control all vital functions, maintaining a good level of homeostasis, that is, a correct tendency to internal self-regulation that manages to stabilize the body.
In fact, there is still much to discover about the importance that the act of sleeping has for our survival and research in recent years has revealed more and more information. One of these investigations highlights the important capacity of sleep to eliminate toxins and waste accumulated in the brain.
For centuries, scientists have wondered how sleep affects the brain by improving cognitive abilities such as attention, memory or concentration. It was not until recent years that the properties that sleep possesses at the brain level have begun to be revealed. This is what the research team at the University of Rochester led by Dr. Nedergaard did that found how the act of sleeping allowed the brain to cleanse itself of toxic molecules.
The team members studied the brains of mice while they slept and saw how, in Nedergaard's words, brain fluids were pumped and eliminated at a very rapid rate. Using the technique of two-photon excitation microscopy, a technique that allows images of living tissues to be viewed with great depth, the researchers were able to observe how the cerebrospinal fluid flowed through the brain more fluidly, eliminating harmful substances and incorporating them through the bloodstream to the liver, where these elements would later be disposed of.
Cerebrospinal fluid is a transparent fluid that, in addition to serving as a waste eliminator, acts as a shock absorber that the brain may receive..
For this cleaning process, glial cells, cells that play a key role in the support and functioning of the brain, also have very important functions. Through the glymphatic system, glial cells control the flow of cerebrospinal fluid by swelling or shrinking for the best passage of this.
The researchers decided to check if the glymphatic system in the sleeping brain suffered any modification and through the insertion of electrodes to measure the space between the cells, they verified how these shrink until they were reduced by 60%, allowing a greater fluidity of this liquid. and achieving a better elimination of toxins.
When the animals woke up, the cells were enlarged again and the cleansing cerebrospinal fluid was reduced to almost a trickle. "It's almost like opening and closing a faucet," explained the study leader. "We were surprised by how little circulation there was in the brain when the mice were awake. (...) This suggests that the space between brain cells changes a lot between conscious and unconscious states".
According to Nedergaard, this process cannot be carried out during wakefulness because it requires a lot of energy, which would make our capacities not work properly.
This process is important, because it allows the brain to eliminate proteins that are toxic to it. This could explain why when we don't sleep well, we have such a hard time maintaining our cognitive functions properly. "It's like a car wash," explains Dr. Maiken Nedergaard, author of the study published in the journal Science.
Nedergaard's research results also relate to some extent to the connection between sleep disorders and diseases like Alzheimer's. During this disease, there is a peptide called amyloid beta that is produced in an exacerbated way in the extracellular space, forming senile plaques. During the elimination of toxins that are produced in sleep, the amyloid beta protein that has increased during wakefulness is also eliminated. This suggests that amyloid beta removal is not effective during sleep in Alzheimer's and may encourage research into the connection this disease, like many others, has with many sleep disorders.
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