"We found that brain preservation isn't a rare anomaly, it's a novel chemical pathway," first study author Alexandra Seviour, a doctoral researcher of paleobiology at the University of Oxford, told Live Science in an email about the new work, published June 19 in the Journal of Proteome Research. "Under the right conditions, preservation actually arises from decay itself: the same reactions that degrade tissue can also weld the breakdown products together into something far tougher."
Mummification, freezing, and even saponification (where body fat turns into a greasy substance called grave wax) can all preserve soft tissues, sometimes for millennia. Usually, these processes conserve the structures of multiple body parts, including the internal organs and skin. But bizarrely, around one-third of the archaeological brains recovered don't fit this model, and a shrunken mass of protein is the only surviving tissue left among a cluster of bones.
The preserved brain of an adult whose burial was found in Bristol. The brain is coated with clay from a waterlogged grave. (Image credit: Alexandra Morton-Hayward)
Burying mice
Seviour's team hypothesized that this specific burial environment, combined with the brain's unique structure and chemistry, divert the normal decay pathway away from total breakdown — instead stabilizing the brain's proteins via a different chemical sequence. To test this theory, they buried mouse carcasses in four different water and oxygen conditions and evaluated their decay pathways over a period of six months.
Overall, their analysis yielded more than 1.26 million protein decay trajectories, enabling the team to draw patterns about how and when the chemistry diverged under the different conditions. Early analysis showed that the initial steps of decay were fairly similar, but that after a few weeks, oxygen levels became the controlling factor, with more oxygen leading to faster and more widespread decay. Conversely, wet, low-oxygen conditions favored the formation of toughened protein structures, which resisted further decomposition and preserved the remaining brain tissue.
Brain tissue is particularly well-adapted to this localized and self-limiting pathway, Seviour added: it's rich in metals that promote free-radical chemistry, packed with membranes where radicals can accumulate, and contains many "redox-active" amino acids that can absorb free radicals to form crosslinks. The physical barrier of the skull also likely plays a part, restricting the exchange of fluid and oxygen compared with the rest of the body, the researchers said.
Related storiesRichard Evershed, an organic geochemist at the University of Bristol who was not part of the study, was impressed by the team's comprehensive analysis. Evershed believes it would be fascinating to expand this to other proteins found in the archaeological record.
But the implications of the work extend beyond archaeology. "For medicine, the more unexpected finding is that the molecular fingerprint of these decay-resistant peptides closely resembles the fingerprint seen in neurodegenerative diseases like Alzheimer's," Seviour said. One interesting future direction will therefore be to explore how far this similarity extends and whether preserved brains could ultimately help scientists understand the progression of these devastating diseases.
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