Trepanation is the practice of removing a piece of the skull to expose part of the brain. It's one of the oldest known surgical procedures, dating back at least to 6500 BC. It's still practiced today, for medical reasons and also voluntarily to achieve enlightenment. Ten years ago, I wrote an article for bOING bOING Digital about Peter Halvorson, a guy who drilled a hole in his head to yield a permanent high. Peter is now the director of the International Trepanation Advocacy Group. For even more on trepanation through the ages, check out "An illustrated history of trepanation" newly posted to the Neurophilosophy blog. From the article:
In the earliest European trepanned skulls, the holes were made by scraping the bone away with sharp stones such as flint or obsidian; later, primitive drilling tools were used to drill small holes arranged in circles, after which the piece of bone inside the circle was removed. The late Medieval period saw the introduction of mechanical drilling and sawing instruments, whose sophistication would continue to increase for several hundred years.
There is a great deal of speculation about why ancient civilizations used trepanation, as it was - and still is - carried out in the absence of head trauma. However, it is almost certain that all those who used it did so because they somehow linked the brain with behaviour. Some anthropologists suggest that trepanation was performed as part of tribal or superstitious rituals. Other researchers believe that the procedure was used as a treatment for conditions such as headaches, epilepsy, hydrocephalus and mental disorders. These were presumably attributed to possession by evil demons, such that a hole in the skull would have provided the spirits a passage for escape. Although the reasons for trepanning and the instruments used for the procedure differ with time and from culture to culture, the result is always the same: a hole in the head, usually made when the individual was fully conscious and, often, unanaesthetized.