The skull containing the Heslington brain, as it’s called, was found in a soggy mud pit near the British village of Heslington. The skull dates back some 2,600 years ago to the British Iron Age, and it belonged to a middle-aged man who was decapitated, according to research done a few years ago. His head was buried in soil immediately afterward. Over time, the spot became a soggy, mud-filled bog.
When this skull was first uncovered, the archaeologists were shocked to find a generous amount of dark brain tissue inside, which was described as having the consistency of tofu. It’s considered to be the most well-preserved brain dating back to ancient times. Such a thing is rare, if not completely unheard of, since brain matter degrades exceptionally quickly due to its high fat content. This is due to a process known as autolysis, in which the body’s enzymes destroy cells and tissues inside the brain.
Scientists have been at a loss to explain why the Heslington brain avoided autolysis, as it doesn’t appear to have been embalmed or specially prepared for preservation prior to burial. What’s more, no other traces of biological material, such as hair, were found alongside the skull, hinting that something other than the wet, oxygen-poor environment was responsible for the preservation.
New research published in the Journal of the Royal Society Interface is finally providing an explanation. First author Axel Petzold from University College London and his colleagues studied samples of the brain from a molecular perspective, with a particular emphasis placed on the proteins—that special stuff that comprises and binds bodily tissue.
In a process that required a full year of lab work, the researchers carefully documented how proteins unfolded in the Heslington brain. In total, the scientists identified over 800 proteins, many of which still looked normal. Some of the proteins were still hardy enough to exhibit an immune response, as shown in mice.
Importantly, the proteins had become folded into tightly packed and stable “aggregates,” according to the new paper. This configuration made the proteins more durable and capable of staving off the decay associated with death. This special aggregate formation “permits for the preservation of brain proteins for millennia,” according to the study.
Key to these formations are two types of brain fibers, both of which were found to reside in the Heslington brain: neurofilaments and glial fibrillary acidic proteins (GFAP). Together, these structures have worked over time as a scaffold to keep the Heslington brain matter intact.
Petzold and his colleagues speculate that, around three months after the man died, enzymes that would normally ravage the brain were shut down. And indeed, lab experiments pointed to this possibility, showing that, in the absence of autolysis, it takes about three months for proteins to fold themselves into the the tightly wound aggregates.