I'll just leave this article here.
http://www.somethingawful.com/news/h...percent-brain/
Favorite quote: "Only a few parts of the brain are actually switched on, like the part that controls eating spaghetti, governs our ability to understand spaghetti, and allows us to see spaghetti."
They also break the brain down into what I believe is the most comprehensive representation of neurological functions I've ever seen.