Deep within burial caves in south-central Peru, archaeologists have uncovered a collection of 1,000-year-old skulls bearing the signs of the complex surgical procedure known as trepanation. 

Practiced by civilizations throughout history and into today, the procedure involves removing a portion of the skull with the help of a hand drill or scraping tool.

Writing in the American Journal of Physical Anthropology, the scientists say they unearthed 32 individuals dating back roughly 1,000 years. In all, 45 separate trepanation procedures are evident.

"When you get a knock on the head that causes your brain to swell dangerously, or you have some kind of neurological, spiritual or psychosomatic illness, drilling a hole in the head becomes a reasonable thing to do," said co-author Danielle Kurin, a visiting assistant professor in the Department of Anthropology at University of California, Santa Barbara and a specialist in forensic anthropology.

According to the researcher, the procedure first appeared in the south-central Andean highlands between 200-600 AD and was used in that area of the world until the Spanish put an end to it about 1,000 years later.

"For about 400 years, from 600 to 1000 AD, the area where I work - the Andahuaylas - was living as a prosperous province within an enigmatic empire known as the Wari," she said. "For reasons still unknown, the empire suddenly collapsed."

And upheaval, she noted, can bring a whole host of issues with it.

"But it is precisely during times of collapse that we see people's resilience and moxie coming to the fore," she said. "In the same way that new types of bullet wounds from the Civil War resulted in the development of better glass eyes, the same way IED's are propelling research in prosthetics in the military today, so, too, did these people in Peru employ trepanation to cope with new challenges like violence, disease and depravation 1,000 years ago."

The study shows that various approaches to the dangerous procedure were used, including scraping, cutting and hand drilling - and all around the same time period. "It looks like they were trying different techniques, the same way we might try new medical procedures today," she said.

Some of the cases were clearly successful, as evidenced in signs of bone regrowth at the surgical site. It could take years for the bone to grow, however, and some might have a retained a hole through his or her life.

"These ancient people can't speak to us directly, but they do give us information that allows us to reconstruct some aspect of their lives and their deaths and even what happened after they died," she continued. "Importantly, we shouldn't look at a state of collapse as the beginning of a 'dark age,' but rather view it as an era that breeds resilience and foments stunning innovation within the population."