Take a moment to rub the top of your skull. Pretty smooth and sturdy, right? What a great place to store 86 billion neurons! Aren't you glad there are no holes in it?
A quarter-inch of solid bone (0.28 inches for women), a thin layer of skin, and -- with any luck -- some hair is all that separates the outside world from your precious brain, the nucleus of your nervous system and the center of your psyche. The protection is sufficient for the hazards of everyday life; an occasional clunk to the noggin' is of little to no concern. But with a little motivation -- and the aid of a drill or pick -- one could easily unlock the squelchy pink organ encased within.
This fact was not lost on our ancestors. Medicine men of pre-Inca, Peruvian civilizations would often use their sacred knives to puncture the skulls of tribe members afflicted with serious headaches. Like letting the air out of a brimming balloon, the procedure was thought to release evil, pain-inducing spirits locked within. Of course, at the same time it let in dust particles and microbes, which often led to infection. The spirits appreciated the fresh air, though.
