This article is from the the official alt.spleen FAQ, by Andrew Stellman with numerous contributions by others.
Andrew says: NOTE: PLEASE DO NOT SEND ANY MAIL TO ME REQUESTING MEDICAL ADVICE! I AM NOT A DOCTOR, AND WILL NOT GIVE YOU ANY USEFUL INFORMATION.
Brain specialist and all-around smart guy Eli the Bearded (email@example.com) writes:
"Trephination is -- as I recall -- is use of a circular blade [similar to a core drill] to cut a hole in the skull ...Usual reasons for trephination are crude brain surgery/implants, substitute for illegal mind-altering drugs, as documented in somebody's home movie of self-trephination. Go ask about it on rec.arts.bodyart."