Why a good night's sleep means a cleaner brain

Shakib Rahman
9 January 2014

Above: Image © istockphoto.com/MikekP

The brain can do a lot of amazing things. Recent research shows that it’s even capable of cleaning itself. The scrubbing happens overnight, while you sleep, and removes harmful chemicals that build up during the day.

Fast fact: The average adult brain accounts for about 2% of a person’s total body mass, yet it uses about 20% of the oxygen in the blood. All that oxygen is needed to fuel the intense activity that goes on inside the brain.If you’re like most people, sleep takes up about a third of your day. It’s also one of the longstanding mysteries of neuroscience (the study of the brain), since no one knows for sure why you need to sleep. Various theories suggest that it helps repair your brain, store your memories, balance your metabolism and immune system, or reduce the energy used by your body. In other words, during sleep, your brain slows down, taking time to cool off and recharge.

Your brain also needs time to clean up and repair itself. When your brain "thinks", it generates small electrical signals inside cells called neurons. Neurons, which are connected to each other, are responsible for processing information received from your body. Not only do these electrical signals need energy to work, the process also generates chemical waste, which needs to be removed.

Previously, scientists thought that brain cells mainly removed these waste chemicals by recycling them within the neurons themselves. However, Dr. Maiken Nedegaard and his team at the University of Rochester have discovered that waste chemicals are actually carried away during sleep, allowing your brain to cleanse itself. This work is done by the cerebrospinal fluid (CSF) that surrounds your brain.

Fast fact: You're born with most of the neurons you’ll need for the rest of your life. There are only two areas of the brain that actually grow new cells.During the experiment, researchers injected glowing green dye into the necks of sleeping mice. The dye quickly made its way into the brain, where it flowed around with the CSF. After a quick 30-minute nap, the mice were awoken and injected with red dye.

By studying the mice’s brains under a powerful microscope (the mice were trained to fall asleep on the microscope), the team compared the flow of red and green dyes. They found that there was more fluid moving in and out of the brain when the mice were asleep than when they were awake. This increased flow helps remove waste chemicals from the brain as it gets ready for another day of thinking.

When you call it a night, your brain cells become less active and some of them begin to shrink. This creates spaces between them, allowing the CSF to flow more freely and carry away any waste chemicals accumulated during the day. However, only one type of brain cell, called glia, seems to experience this shrinkage. Glia cells hold neurons in place while providing them with oxygen and nutrients. Glia also help store waste chemicals, preventing them from building up in the neurons.

Fast fact: Your brain contains more than 100 billion cells!Significant amounts of waste chemicals have been found in people suffering from various brain diseases, including Alzheimer's. Since age and sleep disruption have also been identified as risk factors for brain diseases, it is possible that sleep (and the brain cleaning that occurs during sleep) could play an important role in preventing them.

What’s still not clear is whether brain cleaning is the main purpose of sleep, or just a helpful side effect. In any case, there are plenty of other good reasons to get a good night’s sleep, so it’s probably not worth lying awake worrying about it!

References

General information

Sleep: The Ultimate BrainWasher? (Emily Underwood, Science/AAAS)

Scholarly publications

Xie L, et al. 2013. Sleep Drives Metabolite Clearance from the Adult Brain. Science. 342(6156):373-377. Albrecht J, et al. 2007. Glutamine in the central nervous system: function and dysfunction. Frontiers of Bioscience. 12:332-343. Matute C et al. 2005. Glutamate-mediated glial injury: Mechanisms and clinical importance. Glia. 53(2):212-224. Stover JF, et al. 2003. Neurotransmitters in cerebrospinal fluid reflect pathological activity. European Journal of Clinical Investigation. 27(12):1038-1043.

Shakib Rahman



 Shakib Rahman is a coordinator with Let's Talk Science at the UofA.  He an avid soccer player and a sports nut in general.  He also has a a passion for science, science literature and TV. In his spare time, he writes science articles, some of which you can read here at CurioCity.



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