One more reason to get a good night's sleep
5,561,766 views | Jeff Iliff • TEDMED 2014
00:00
Sleep. It's something we spend about a third of our lives doing, but do any of us really understand what it's all about?
00:08
Two thousand years ago, 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. Now, that sounds completely ridiculous to us now, but Galen was simply trying to explain something about sleep that we all deal with every day. See, we all know based on our own experience that when you sleep, it clears your mind, and when you don't sleep, it leaves your mind murky. But while we know a great deal more about sleep now than when Galen was around, we still haven't understood why it is that sleep, of all of our activities, has this incredible restorative function for the mind.
01:06
So today I want to tell you about some recent research that may shed new light on this question. We've found that sleep may actually be a kind of elegant design solution to some of the brain's most basic needs, a unique way that the brain meets the high demands and the narrow margins that set it apart from all the other organs of the body.
01:30
So almost all the biology that we observe can be thought of as a series of problems and their corresponding solutions, and the first problem that every organ must solve is a continuous supply of nutrients to fuel all those cells of the body. In the brain, that is especially critical; its intense electrical activity uses up a quarter of the body's entire energy supply, even though the brain accounts for only about two percent of the body's mass. So the circulatory system solves the nutrient delivery problem by sending blood vessels to supply nutrients and oxygen to every corner of our body.
02:08
You can actually see it in this video here. Here, we're imaging blood vessels in the brain of a living mouse. The blood vessels form a complex network that fills the entire brain volume. They start at the surface of the brain, and then they dive down into the tissue itself, and as they spread out, they supply nutrients and oxygen to each and every cell in the brain.
02:33
Now, just as every cell requires nutrients to fuel it, every cell also produces waste as a byproduct, and the clearance of that waste is the second basic problem that each organ has to solve. This diagram shows the body's lymphatic system, which has evolved to meet this need. It's a second parallel network of vessels that extends throughout the body. It takes up proteins and other waste from the spaces between the cells, it collects them, and then dumps them into the blood so they can be disposed of.
03:06
But if you look really closely at this diagram, you'll see something that doesn't make a lot of sense. So if we were to zoom into this guy's head, one of the things that you would see there is that there are no lymphatic vessels in the brain. But that doesn't make a lot of sense, does it? I mean, the brain is this intensely active organ that produces a correspondingly large amount of waste that must be efficiently cleared. And yet, it lacks lymphatic vessels, which means that the approach that the rest of the body takes to clearing away its waste won't work in the brain.
03:42
So how, then, does the brain solve its waste clearance problem? Well, that seemingly mundane question is where our group first jumped into this story, and what we found as we dove down into the brain, down among the neurons and the blood vessels, was that the brain's soluti