This post is inspired by Jeff Iliff, a neuroscientist who gave a TED Talk on how sleep cleans and refreshes our brains. Watch the video here.
Iliff’s bio from UW Medicine:
Dr. Jeffrey Iliff focuses on neurodegeneration and traumatic brain injury research at the VA Puget Sound and at the UW Alzheimer’s Disease Research Center. Dr. Iliff’s work has probed the ‘glymphatic’ system, a brain-wide network of perivascular spaces that facilitates the clearance of waste products, including amyloid beta and tau, from the brain interstitium during sleep.
How the Ancients Thought About Sleep
Two thousand years ago a physician and philosopher named Galen concluded that sleep must originate in the brain. He proposed that a brain that is more active during the day will have a better sleep at night.
Iliff says that “Galen, one of the most prominent medical researchers of the ancient world, proposed that while we’re awake, our brain’s motive force, its juice, would flow out to all the other parts of the body, animating them but leaving the brain all dried up, and he thought that when we sleep, all this moisture that filled the rest of the body would come rushing back, rehydrating the brain and refreshing the mind.”
As you will see, Galen wasn’t too far off.
Organs and Waste Management
Iliff says “so almost all the biology that we observe can be thought of as a series of problems and their corresponding solutions.” Organs have two key problems to solve. The first problem is that all cells require a constant supply of nutrients to function properly. The circulatory system solves this nutrient logistics problem by using blood vessels that stretch out to every part of the body. They act as pipes to deliver the nutrients.
The second problem is that as cells consume nutrients, they produce waste. That waste, like dishes piling up in your kitchen sink, needs to be washed and cleared. The body’s lymphatic system solves this problem. The lymphatic system is like a set of plumbing pipes that are operated in parallel to the blood vessels. They flush out and dispose of the waste byproduct from the spaces between the cells.
Nutrient delivery is critical in the brain because it actively uses up 25% of our body’s entire energy supply. But the lymphatic system does not operate in the brain! The brain is the only organ in the body that does not rely on the lymphatic pipes to clear its waste.
Sleep is Beautifully Designed
Iliff’s research sought out to understand what clears waste in our brains. If there are no lymphatic pipes to flush out the waste, how does our brain solve the waste problem? What his team found was that the brain’s solution “was really unexpected, it was ingenious, but it was also beautiful.”
The brain contains cerebrospinal fluid (CSF) that is used to help flush out the waste. The brain is cramped, and it lacks space for both blood vessel pipes and lymphatic waste removal pipes. To solve this space problem, evolution designed a practical and simple solution using the blood vessels that supply nutrients to the far reaches of the brain. The CSF runs along the blood vessels. This logistical flow of CSF only happens when we are sleeping! As we sleep, our brain cells shrink allowing more CSF to flush away all of the waste that has accumulated throughout the day.
Galen was not too far off. What Galen didn’t know is that when waste is not removed and it accumulates between our brain cells, it may contribute to a higher risk of brain diseases like Alzheimer’s. Mounting evidence of the power of sleep.
