October 27, 2020
Written by: Claudia Lopez-Lloreda
The explosion of Mount Vesuvius in 79 AD covered many Italian towns along the Gulf of Naples, among them Pompeii and the lesser-known Herculaneum, a small town at the bottom of the mountain, with a destructive combination of fast-moving lava, ash, and hot gas. This mixture, called pyroclastic flow, engulfed thousands of people. For many years, archeologists have dug into the remains of this catastrophe to understand how these extreme conditions alter the human body. Now, researchers have discovered how pyroclastic flow may have altered the victims’ brains: by turning them into glass1.
The group of researchers, led by Pier Paolo Petrone of the University Federico II of Naples, found one victim of the volcano, a young man predicted to be in his 20s, lying face down. Based on the location where they found him, they think that he was possibly a guardian at the college. Although these small details gave interesting insight into this person’s life, modern technology, like the scanning electron microscope developed in the 1940s, allowed this group of researchers to peer into his brain.
Earlier this year, the group had described finding black glass within the skull of the victim as well as brain proteins in the New England Journal of Medicine2. Brain tissue from archeological sites are usually saponified, meaning that they turn into fatty acid salts, the main component of soap3. However, the brain found at Herculaneum was not like soap, but rather glass. It was precisely the event that killed its’ owner that made it that way. This process, called vitrification, happens when extreme heat turns something into glass.
Now in the newest study, they dug into the tissue of the same victim much further. Through this, they were able to identify main components of a central nervous system, including neurons and axons. In fact, based on the specific expression of certain proteins, they estimated that the part of the brain they were looking at was the most posterior area, the cerebellum and the spinal cord.
Using a type of microscopy called scanning electron microscopy, they imaged the frozen brain of the victim. In the study published in PLOS One this month, they found that the sample that they were viewing contained traces of a brain that once was: cell bodies that resembled neurons and tubular structures that resembled axons, the long arm-like structures that connect neurons. These axon-like structures, they noted, seemed to look like those from freshly preserved biological samples that were frozen and were similar in size to those axons protected by a protein called myelin, which provides insulation around axons.
Spinal cord axons in the mammalian central nervous system, on the other hand, are generally not myelinated (surrounded by myelin), which makes them much smaller than their myelinated counterparts in the brain. When the researchers looked at the axon-like structures in what would have been the spinal cord, they noted that these were smaller in diameter, as one might expect.
This would suggest that not only were neurons preserved, but also, they remained relatively intact. For example, they also saw that the neurons had membranes that characterize living cells as well as the smaller structures that reside within cells such as vesicles. Not only that, but they also found proteins that are typically found in the brain. One interesting protein that they found, ATP6VIF, plays an important role in maintaining the function of synaptic vesicles, which shuttle neurotransmitters, the chemicals neurons used to communicate, throughout the cell. Another protein they found called KIF26B is involved in the stabilization and organization of microtubules, which run down the length of axons and help neurons communicate with each other. This would suggest that they were indeed looking at preserved neurons.
In this case, it was the extreme heat from the volcanic eruption and the pyroclastic flow following a quick decrease in temperature that vitrified the brain. The upwards of 900-degree Fahrenheit temperatures would have destroyed any trace of fat, while the subsequent cooling would help turn the remaining brain into glass. Extreme temperatures can have other interesting consequences on the human body. For example, analyzing the body position of victims at Herculaneum led researchers to hypothesize that the eruption resulted in rapid vaporization of the soft tissues in the body, like the muscle4. The discovery of a perfectly preserved nearly 2,000 thousand year-old brain is, in itself, amazing. It also gives us insight into how people in Herculaneum might have died. In contrast to the people in Pompeii, who likely died due to falling debris and asphyxiation, these observations add evidence to the hypothesis that some of those who perished in the Mount Vesuvius eruption in Herculaneum, which was closer to the mountain than Pompeii, died because of the extreme heat that accompanied the pyroclastic flow. This depiction, although gruesome, illustrates something never before thought of: that the brain can turn into glass and be preserved for centuries.
- Petrone, P., Giordano, G., Vezzoli, E., Pensa, A., Castaldo, G., Graziano, V., … Niola, M. (2020). Preservation of neurons in an AD 79 vitrified human brain. Plos One, 15(10).
- Petrone, P., Pucci, P., Niola, M., Baxter, P. J., Fontanarosa, C., Giordano, G., … Amoresano, A. (2020). Heat-Induced Brain Vitrification from the Vesuvius Eruption in c.e. 79. New England Journal of Medicine, 382(4), 383–384.
- Fernando, S., Francisco, E., Herrasti, L., Cascallana, J. L., & Del, O. J. (2017). Saponified Brains of the Spanish Civil War. Taphonomy of Human Remains: Forensic Analysis of the Dead and the Depositional Environment, 429–437.
- Petrone, P., Pucci, P., Vergara, A., Amoresano, A., Birolo, L., Pane, F., … Graziano, V. (2018). A hypothesis of sudden body fluid vaporization in the 79 AD victims of Vesuvius. Plos One, 13(9).
Cover image: National Parks Service on Flickr.