Remember when we told you that the extreme heat produced during the eruption of Vesuvius in AD 79 may have been enough to vaporize bodily fluids and detonate skulls — possibly even turning a victim’s brain into glass? We now have new evidence that this could indeed be the case, according to a new paper in PLOS ONE reporting the discovery of preserved human neurons in the victim with the “vitrified” brain.
“The discovery of brain tissue in ancient human remains is an unusual event,” said study co-author Pier Paulo Petrone of the Federico II University of Naples. “But what is extremely rare is the integral preservation of neuronal structures of a 2,000-year-old central nervous system, in our case with unprecedented resolution. These and other results of the bioanthropological and volcanological studies underway at Herculaneum are gradually reveal details never before emphasized, enriching the complex picture of events of the most famous of the Vesuvius eruptions.”
According to Tim Thompson, a forensic anthropologist at Teesside University in the UK, brains typically don’t survive long after death. “It’s one of the first things to decompose in a standard decompositional context,” he told Ars. But it is not unprecedented.
“Brain tissue is preserved and it’s much more common than people think,” Alexandra Hayward, a graduate student in so-called “palaeoproteomics” at the University of Copenhagen in Denmark, told Ars. To date, she has found some 1,300 preserved brains dating back to the mid-16th and mid-17th centuries. The Vesuvian preserved brain studied by Petrone et al† is both very old (though not the oldest) and unusual in terms of the hypothesis proposed as to the precise mechanism by which it was preserved.
Brain made of glass?
The eruption of Vesuvius released thermal energy roughly equivalent to 100,000 times the atomic bombs dropped on Hiroshima and Nagasaki at the end of World War II, dropping molten rock, pumice and hot ash over the cities of Pompeii and Herculaneum in the United States. were especially ejected. The vast majority of victims died of asphyxiation, suffocated by the thick clouds of noxious gas and ash.
But a 2001 study in Nature, co-authored with Petrone, estimated a temperature of 500° Celsius (932° Fahrenheit) for the pyroclastic wave that devastated Pompeii, enough to kill inhabitants in fractions of a second. In 2018, we reported on Petrone’s conclusion that Herculaneum residents may have suffered a similar fate. There were fractures to the bones and “cracking and explosions” of the skullcaps, consistent with forensic cases where skulls cracked from extreme heat.
And earlier this year, we reported on Petrone’s follow-up study, with additional evidence that extreme heat has claimed many casualties. He and several colleagues completed an analysis of the skull of one victim in particular, first unearthed in the 1960s from Herculaneum. The body was found on a wooden bed buried in volcanic ash, and there was evidence of brain matter in the skull. According to Petrone et alUsually, such brain matter would be “saponified” by the extreme heat – that is, it turned into soap (glycerol and fatty acids). But this particular victim’s brain matter was vitrified, that is, fused into glass. Petrone et al† estimated that temperatures could have been as high as 520° Celsius (984° Fahrenheit), based on evidence collected from charred wood at the site.
“This suggests that extreme radiant heat could ignite body fat and vaporize soft tissue,” the authors concluded. “The detection of vitreous material from the victim’s head, proteins expressed in the human brain, and fatty acids found in human hair indicate the thermally induced preservation of vitrified human brain tissue.”
According to Petrone, this latest paper looked at the genetic expression of those previously identified proteins and also included the results of using scanning electron microscopy (SEM) to image vitrified brain and spinal cord remnants. They found that the images showed distinctive features typical of the human central nervous system, including evidence for white matter neurons and axons.
“The extraordinary discovery of perfectly preserved ancient neuronal structures has been caused by the conversion of human tissue to glass, indicative of the rapid cooling of the hot volcanic ash clouds that hit Herculaneum at the start of the eruption,” said co-author. Guido. Giordano, a volcanologist at the University of Roma Tre. The team concluded that the unique vitrification process that took place in Herculaneum kept the neuronal structures of this particular victim “frozen” and intact.
Earlier this year, Axel Petzold of University College London and several colleagues confirmed the preservation of neurocytoarchitecture in a 2,600-year-old Iron Age human skull unearthed in Heslington, York, albeit through a different mechanism than the vitrification claimed by Petrone. et al† According to Hayward, at least four recent papers have found evidence of neurons in preserved ancient brains. More than one mechanism may be at work.
Thompson told bioarchaeologist Kristina Killgrove earlier this year that he doesn’t find the evaporation theory plausible, preferring his own alternative theory — based on skeletal and collagen evidence — that the victims at Herculaneum may have essentially been “baked” by heat with a lower intensity, such as roasting a joint in the oven. Even saponification (turning into soap) is not typical, according to Hayward. She has scoured the literature on conserved brains, and of some 187 sources, only 9 percent described something resembling saponification — and only one of those was chemically confirmed.
Thompson found this last paper interesting, but also “frustrating,” especially since the authors don’t include their raw data — just a list of the proteins and related gene expressions. “There needs to be more information about the data the team recovered and more references to previously published work,” he said. “This would show that preserved brains from archaeological and historical contexts are actually not that rare. I was more interested in why brain material would be so well preserved in this particular context, while the same team has repeatedly argued that the soft tissues of the victims of Herculaneum have completely evaporated. Herculaneum is such an interesting and complicated context for conservation that that aspect needs much more research.”
“It’s interesting that this one person appears to have preserved brain tissue, while all the other victims would have essentially vaporized.”
According to Hayward, two recent paleo-proteomic studies reported hundreds of proteins, while Petrone et al† only nine recovered. “I’d be curious to know why these nine proteins were recovered and if it has anything to do with how this brain was preserved,” she said. “It’s very difficult to investigate that without access to the raw data.”
It’s not the first time data has been withheld in the field of ancient proteins, but Thompson, Hayward and her colleague Matthew Collins from the University of Copenhagen all believe this is in the community’s long-term interest. “When we analyze ancient proteomes, we usually identify only 3 percent of the questions the instruments ask,” Collins told Ars. “So when we publish a paper, we release all of the raw data. It’s publicly accessible and downloadable, and others may involve new software strategies and new analytical approaches that could reveal a lot more.”
Everyone agrees on one thing: the fusion of forensic medicine and anthropology, along with new advanced imaging and analysis tools, is a boon for such studies. Collins cites the wave of personalized medicine, which brought high-throughput genetic sequencing and proteomics into the mix. Add to that high resonance imaging technology well suited to analyzing ancient samples, and the result is a significant increase in the amount of research and resulting publications. There is also much more interdisciplinary collaboration. “We’re all bringing different methodologies and ideas to the table because we realize that only when we work together can we really understand what’s going on in these studies,” Collins said.
DOI: PLOS ONE, 2020. 10.1371/journal.pone.0240017 (About DOIs).