The practice, also known as trepanation or trepanning, has been carried out since ancient times and has been thought to cure all sorts of conditions we would now know as mental or neurological disorders – such as epilepsy or psychosis.
It is thought that it was carried out to release ‘evil spirits’ or similar from the head, by creating a way for them to escape.
The practice hasn’t died out, however. It is occasionally practised by peoples outside the reach of modern medicine, and some people in industrialised countries do it as a form of body modification for its supposed consciousness modifying properties.
In fact, there’s a whole trepanning subculture on the internet.
For example, the Body Modification EZine has an article about someone who undertook a trepanning procedure (warning, if you’re a bit squeamish, the article and images are a bit icky):
I awoke the next morning still very much wanting to move forward with the operation. I thought to myself, “The key to more consciousness is sitting in the next room over. How can I know this and not unlock the door?” I explained my sincere desire to my girlfriend, and though she was still apprehensive, she agreed to try to be there for me if it was really what I wanted to do.
We had coated every wall of a room in plastic sheeting, had a placement tray ready (a sterilized tray to set the instruments on), had the drill sterilized and ready to go, autoclaved bits set out, etc and proceeded to trepan me. One person was to do the drilling and another was to help by passing instruments, turning the drill off and on, by holding a light in the right place at the right time, and by irrigating the wound every so often.
UPDATE: Grabbed from the comments page (thanks Anders!)…
Personally I need trepanation like I need a hole in my head (sorry,couldn’t resist), but there is actually a trepanation advocacy group called ITAG their site is at www.trepan.com (Warning: site uses excessive amounts of flash, a possible side effect of trepanation?) which has documents and videos on the procedure and it’s supposed benefits that are both enlightening and a little scary.