Cut the Skull Dull the Mind: Early Surgery for Mental Patients
There are many hypotheses for why trephanation was done. Since some skulls show evidence of healing it is believed the medical people of the times treated battle wounds this way in order to heal the patients.
Later, the process may have been used to cure epilepsy and other mental disorders. However, medical practice during the earlier times periods all the way into the modern era of the middles ages and the renaissance period was the was a combination of superstitions and folklore. A true grasp of mental health had was not yet understood.
Mental health issues were often associated with evil spirits and demonology. Brain surgery was no exception. Another hypothesis is that trephining was also practiced to rid the brain of evil spirits. The medical practitioners of the time may have trepanned to rid the evils spirits possessing the minds of depressed and schizophrenic individuals.
Though the practice of trephaning is still practiced for very specific medical needs( trephaning the finger and toenail to release excessive blood accumulation below the nail, or some eye surgery) it has fallen out of favor among medical and mental health professionals except in a few fringe groups largely following the work of Bart Hughes, a man who called himself a doctor but never finished medical school.
Resurgence of the practice of cutting into the skill to treat mental patients
Though the practicing of trepanning had fallen out favor, psychiatrists of earlier times were at a loss to find treatments that would help mentally ill patients. The historical treatment of mentally ill individuals is not a nice one. Throughout the centuries the mentally ill have been tortured, abused, neglected, ostracized by society, blamed for producing natural disasters, famines, floods, stealing babies, witchcraft, imprisoned, and killed.
It wasn't until the later half of the 20 century that human treatments for mental ill patients were devised and utilized. Nevertheless, physicians and psychiatrists were desperate to find treatments to control the rage and violent outbursts of the most serious cases.
Montreal Neurological Institute