As if there wasn’t enough reason to get at least 8 hours of sleep, I got another hour of sleep. Neurons are active even during sleep. We may not realize it, but our brains use this recharging period to get rid of junk that has accumulated during our waking hours.
Sleep is like a soft reboot. We knew that slow brain waves were associated with restful sleep. Researchers at Washington University School of Medicine in St. Louis have found out why. When we are awake, our neurons require energy to facilitate complex tasks such as problem solving and committing to memory. The problem is that after ingesting these nutrients, debris remains. While we sleep, neurons use these rhythmic waves to move cerebrospinal fluid within the brain tissue, carrying away metabolic waste products in the process.
In other words, neurons need to get rid of trash so it doesn’t accumulate and potentially cause neurodegenerative diseases. “Neurons act as master organizers of brain clearance,” the WUSTL research team wrote in a recently published study. Nature.
Built-in garbage disposal
The human brain (and the brains of other higher organisms) has evolved to have billions of neurons in the brain’s functional tissue, or parenchyma, which is protected by the blood-brain barrier.
Everything these neurons do produces metabolic waste, often in the form of protein fragments. Other research They discovered that these fragments may contribute to neurodegenerative diseases such as Alzheimer’s disease.
The brain has to deal with garbage in some way, and this is called Glymphatic system (No, that’s not a typo), carries cerebrospinal fluid and moves debris from the parenchyma through channels located near blood vessels. However, the question still remained. What actually drives the Glymphatic system to do this, and how does it do it? That’s what the WUSTL team wanted to know.
To find out what tells the glymphatic system to throw away trash, scientists conducted experiments on mice, inserting probes into their brains and implanting electrodes in the spaces between neurons. is. The mice were then anesthetized with ketamine to induce sleep.
After the animals fell asleep, the neurons fired strong electrically charged currents. EEG waves under anesthesia were mostly long and slow, but corresponding waves of electrical current were evoked in the cerebrospinal fluid. The fluid then flows through the dura mater, the outer layer of tissue between the brain and skull, taking debris with it.
Just let it flow
Scientists wanted to confirm that neurons were indeed the driving force of the glymphatic system. To do so, the brains of some mice would have to be genetically modified to eliminate most of their neural activity during sleep (though not to the point of brain death), while the rest of the mice would need to be left alone for comparison. Ta.
The long, slow brain waves seen previously were not detectable in these manipulated mice. As a result, fluids are no longer pumped out to carry metabolic wastes away from the brain. This simply means that neurons must be active for the brain’s self-cleaning cycle to function.
Additionally, the researchers found that the non-genetically engineered mice had fluctuations in their brain waves, with slightly faster waves that appeared to target debris that was harder to remove (at least that’s what the researchers said). (This is a hypothesis.) It’s similar to how after washing your dishes, you need to scrub a little harder where there’s particularly stubborn residue.
The researchers also revealed why previous experiments yielded different results. The type of anesthetic used was important because flushing out the cerebrospinal fluid, which carries waste products, is highly dependent on neural activity. Anesthetics that inhibit nerve activity may affect results. Other early experiments failed because of damage caused by older, more invasive methods of implanting monitoring hardware into brain tissue. This also destroyed neurons.
“The experimental method used here largely avoids acute damage to the brain parenchyma, thereby providing a valuable strategy for further studies of neurodynamics and brain clearance,” the research team said in the same paper. There is. study.
Now that it is known that neurons operate the glymphatic system, more attention has been focused on the complexity of the process. Learning more about the accumulation and clearance of metabolic wastes may contribute to the understanding of neurodegenerative diseases. That’s definitely something to think about before falling asleep.
Nature, 2024. DOI: 10.1038/s41586-024-07108-6
