Sleep is something that we spend about a third of our lives doing, but do any of use have any idea what it's all about? Two thousand years ago Galen, one of the most prominent medical researchers of the ancient world, proposed that whilst we are awake our brains mode of force, its juice, would flow out to all the other parts of the body animating them but leaving the brain all dried up. He thought that when we sleep, all that moisture that filled the rest of the body would come rushing back, rehydrating the brain and refreshing the mind. That sounds completely ridiculous to us all now, but Galen was simply trying to explain something about sleep that we all deal with everyday. We all know based on our own experience that when you sleep it clears the mind, and when you don't sleep it leaves your mind feeling murky. While we know a great deal more about sleep now, compared to when Galen was around, we still haven't understood why it is that sleep, of all of our activities, has this incredible restorative function on the mind.
Sleep might be some elegant design solution to some of the brains most basic needs. A unique way that the brain meets the high demands, and narrow margins that set it apart from all of the other organs in the body. Almost all of the biology that we observe can be thought of as a series of problems and their corresponding solutions. The first problem that every organ must solve is the continuous supply of nutrients to fuel all those cells in the body. In the brain that is especially critical. Its intense electrical activity uses up ΒΌ of the body's entire energy supply, even though the brain only accounts for 2 % of 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. Blood vessels in the brain form a complex network that fills the entire brain volume. They start at the surface of the brain, then...