Neurophilosophy has a fascinating article on the recent archaeological discovery of numerous ancient Incan skulls of which over 1 in 6 showed signs of trepanation – an ancient form of brain surgery where a hole was drilled in the skull.
What’s surprising is just how common it was. 66 skulls from Incan burial sites had a total of 109 trepanation holes. Some, like the one pictured, obviously needed a significant amount of skill and practice to complete.
And with this many examples, the archaeologists could make some fascinating inferences about the purpose and success of these operations:
Andrushko and Verano argue that the Incas performed trepanation primarily to treat head injuries incurred during battle, because the holes are most often found at the front of the skull to the left, consistent with injuries caused by a right-handed opponent during face-to-face combat, and because adult males are overrepresented in the sample. The procedure was evidently used to treat mastoiditis (an infection of the region of the temporal bone behind the ear) as well.
The authors also show that the success rate of the procedure improved with time, as the Inca empire progressed and made advances in medicine. The earliest specimens, dated to around 1,000 A.D., showed no signs of bone growth around the perforations, suggesting that the procedure was often fatal. But specimens dating to around 400 years later suggest a survival rate of around 90%.
Link to Neurophilosophy article on prehistoric Inca neurosurgery.