Skip To Content
Cambridge University Science Magazine
We spend one third of our life sleeping, which sometimes seems like a waste of time.  But somehow we clearly need it! If you ask my friends, they will tell you that you don't want to be around me when I'm lacking sleep. And this is not only anectodal evidence, but studies have demonstrated that sleep-deprived people will show loss of memory, poor decision making, confusion, and irritability.,, So yes, sleep is essential, but we still don’t know why this is the case. Scientists studying sleep mostly agree that sleep has multiple functions like memory consolidation or energy regulation.

But recent research from Maiken Nedergaard’s lab in Rochester (USA) demonstrates a completely new function for sleep. We have billions and billions of brain cells, which are very active they produce a lot of waste. But during the day, your brain needs to focus all his resources on functioning; it is too busy working hard and can't take the trash out. So waste accumulates during the day. How does the brain deal with it? Well, there is recycling, as much as the brain can because resources are precious, but some waste still needs to be taken out.

To understand how it works, you need to visualize the brain as a town where cells are households. There are big motorways and roads coming in with supplies (blood vessels carrying food and oxygen) and there are other roads and motorways that take the trash out. These are called the glymphatic system. The glymphatic sytem is a network of little rivers containing cerebrospinal fluid; the sources are on the surface of the brain, and the flow goes toward the inside of the brain then down to the spinal cord.

So you have supplies coming in and waste out. In between, it's a bit like a city center. During the day, we all know that roads are very busy in the city center, producing traffic jams. But at night, traffic is minimal, leaving a lot of space to move around and the waste can reach the exit roads quickly. In the brain, it's the space in between the cells that expands, so the waste can easily reach the glymphatic system and be flushed away. So sleep is the big cleaner of your brain!

This cleaning of the brain is highly important because some waste can be toxic and if it accumulates can lead to neurodegenerative diseases like Alzheimer. Sleep is also very important for mental health: sleep problems can be the first symptoms of disorders, lack of sleep can exacerbate symptoms and proper sleep patterns can help in their management.

To conclude, you're not wasting time when you're sleeping but disposing of the waste. Enjoy your sleep tonight!

Reference: Xie et al., “Sleep Drives Metabolite Clearance from the Adult Brain”. Science 18 October 2013:

Vol. 342 no. 6156 pp. 373-377, DOI: 10.1126/science.1241224