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Credit: Axel Petzold

2,600-year-old human brain is so well preserved it could almost be a horror movie prop

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Jan 10, 2020

There was a reason the ancient Egyptians got rid of the brain right away during the mummification process, and it wasn’t just because they thought it was incapable of thinking.

Brain tissue usually decomposes way too fast to keep around. Emphasis on usually. After 2,600 years, a disembodied head unearthed near Heslington in northern England revealed a brain that had survived longer than some mummies have. The missing body means that the man this brain belonged to was probably either sentenced to execution or killed as part of a gruesome ritual. That much was easier for neurologist Axel Petzold and his research team to assume than how the brain had stayed intact for so long.

“The preservation of the ancient brain tissue remains enigmatic because of rapid decomposition and autolysis after death,” Petzold and colleagues said in a study recently published in the Journal of the Royal Society.

Credit: Axel Petzold

This brain has been baffling scientists since it was first dug up in 2008. It is already unique in that it is is the only brain preserved this well that is also uncontaminated by any other bodily tissues. Petzold’s team has now made headway (no pun intended) in discovering how it was the only soft tissue preserved in the unidentified skull. Brain tissue decomposes and putrefies right after death. In the process of autolysis, enzymes called proteases and phospholipases, degrading the tissue by breaking apart its lipids and proteins of that tissue. Something strange happened here, though — there was an outside factor that froze the effects of these enzymes.

“The proteases of the ancient brain might have been inhibited by an unknown compound which had diffused from the outside of the brain to the deeper structures,” he said, adding that “Chemically, preservation might have been possible by an acidic compound similar to what is known from the soft tissue preservation of the bog bodies.”

Bog bodies, the relics of executed or ritualistically murdered victims that have been unearthed from the peat bogs of northern and western Europe, are so well-preserved — brains included in some specimens — because of tannins. Tannins preserve the subtle flavors in wine and do the same for human tissues. As the sphagnum moss in a bog dyes, the carbohydrate polymer sphagnan binds nitrogen to prevent bacteria from growing. It seems like this brain has all the qualifications to be part of a bog body, except that there were no tannins or sphagnan found in the tissue.

You may never put wine near your lips again after finding that out about tannins.

Petzold and his team compared the decomposition rate of tissue from the Iron Age brain to tissue from a modern brain over the course of a year. Analysis through mass spectrometry, which converts molecules to ions and measures the ratio of mass to charge, singled out hundreds of different proteins, most of which were expected. The team also sought out antibodies that proved those proteins had an immune response. It was the stability and binding abilities of proteins, possibly caused by mutation, that had a part in preserving this brain. Protein aggregates (the result of proteins clumping together) could be what ultimately kept it in such eerily great condition.

“These long-term data from a unique ancient human brain demonstrate that aggregate formation permits for the preservation of brain proteins for millennia,” said Petzold , also noting that “The aggregates from the ancient brain were larger and considerably more resistant to incubation with [decomposers] as those from recent human or animal brains.”

Even though the exact cause of such am amazing preservation remains a mystery, Petzold’s team was onto something else. Protein aggregation is often a culprit in neurodegenerative diseases such as Alzheimer’s. Understanding how that relates to the preservation of neural tissues may eventually lead to medical breakthroughs that were previously thought to be impossible.

The one downside of this postmortem is that nobody will ever know whose head it was which was hacked off and thrown in a pit, because the DNA of the tissue had degraded. Maybe his body will mysteriously surface someday.

(via Journal of the Royal Society)

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