APA Dictionary of Psychology

n. a surgical procedure in which a disk of bone is removed from the skull with a circular instrument (a trephine) having a sawlike edge. On the basis of evidence found in skulls of Neolithic humans, trephining is believed to be one of the oldest types of surgery. Among the numerous conjectural reasons given for the practice is that it was a treatment for headaches, infections, skull fractures, convulsions, mental disorders, or supposed demonic possession. Also called trepanation. —trephine vb.