This week on eBay, people had a chance to bid on an authentic antique trephination kit (The item went for $7500 — emergency rooms around the bidders’ hometown have been alerted to look out for open head injuries). We found a nice overview of ancient (and not so ancient) practices of trephination (also called trepanation) at this site:
The motives for Neolithic trephining have been the subject of speculation since the first specimens were discovered in the nineteenth century. Generally, it is surmised that, on the living, it was performed for the escape or entrance of spirits. This, of course, is conjectural. It may have been done for therapeutic reasons, such as for headaches, fractures, infections, insanity, or for convulsions. It might have been done for religious reasons. It has been suggested that the motive was to acquire rondelles (the disks of bone obtained from the cutting of circular holes in the skulls)…
The following essential aspects of trephining must be accounted for in any explanation of the practice:
The practice was astonishingly widespread… It was practiced in the presence, and absence of head trauma… The practice was performed on the living and on the dead… In some skulls, the trephining was incomplete, as if the procedure was abandoned mid-operation…
…There were probably three general techniques: scraping, drilling, and cutting.
Trepanning drills have smooth wooden shafts and tips of very hard material, to cut into the bone as neatly as possible. The earliest trepanned skulls are from the Neolithic Stone Age long before the introduction of metallurgy. Their holes were cut not by a drill, but with a sharp-edged flint scraper or knife. A circular or rectangular groove was made. The practitioner would cut deeper and deeper until penetration to the dura mater was accomplished. In ancient Peru, people used knives of bronze or obsidian. They would cover the wound with a shell, a gourd, or even a piece of gold or silver.
The most common of the techniques was the bow drill. The bow was made of springy wood and had a leather thong wound around the drill several times. To perform the procedure, the operator positioned the drill tip on the head and thereby made the bore through the bone.
Drilled holes were usually roughly circular. Knife cut ones were usually more square. A few skulls have up to five holes, the longest of which measures two inches across.
It is interesting that in modern times, neurological surgery is one of the more recently developed specialties. Yet, it has this remarkable antecedent in Neolithic times. It is very unlikely, however, that Neolithic surgeons entered the brain itself. We can only conjecture as to why they did it.