These are the best linear algebra videos I've ever seen. The creator is now working on an introductory calculus series. He's already released the first few episodes to patrons.
Recent research shows that a major function for sleep may be to facilitate the brain’s janitorial functions. Waste products and the detritus of daily thinking can be removed during nightly sleep. This cleaning function allows our brains to work properly and may account for why we generally feel brighter and happier in the mornings.
Other organs and tissues are "cleaned" using the lymphatic system that almost works as a sewage system for the body. The lymphatic system does not extend into the brain. The so-called "blood-brain barrier" limits fluid channel exchanges between the brain and the rest of the body to protect the brain.
The extracellular fluid in the brain – the wetness between the neurons – is part of a system that essentially flushes the brain and removes waste. This has been named the glymphatic system. It was previously thought that waste products were metabolized and broken down by the neurons themselves and the results of that breakdown carried away in capillaries and ultimately removed by the kidneys.
From other sources, while you sleep the brain changes permeability to allow stuff to be flushed out. I'm sorry I can't watch this vid now so it may be having different take/information.
Coincidence. FB has over a billion daily users and each one communicates dozens of concepts per day - if each person sees numerous ads per day then it's a statistical certainty that someone, somewhere happens to get an ad that matches up with something they mentioned earlier in that day or week. This is the same reason why everyone has a story about a dream that came true.
