The practice was believed to alleviate pressure and treat health problems localized within the head, though it was also thought to cure epilepsy, migraines, and mental disorders and were a common "fix" for more physical problems such as skull fractures. Needless to say, such exposure of the brain to airborne germs would often be fatal.
Trepanning as a practice has not been completely abandoned: it was performed as recently as 2000 when two men in the US used it to treat a woman suffering from chronic fatigue syndrome and depression.