In January 2020, History and Archaeology Online reported how forensic anthropologist Dr Pier Paolo Petrone had discovered an astounding effect of the temperatures of the pyroclastic surges of Vesuvius’s eruption in 79AD on one of its victims from Herculaneum. An investigation of the skull from human remains found in the College of the Augustales showed that the temperatures that destroyed the town were so extreme they had vitrified the victim’s brain — or turned it to glass.

Now, in a new study published in the American scientific journal PLOS ONE, Dr Petrone reveals the unprecedented discovery of human neurons in the remains of this vitrified brain and spinal column. It is a discovery that has implications for our understanding of how Herculaneum was destroyed in 79AD — and how lives could be saved in future eruptions.

Vitrified Human Brain 

In the 1960s, archaeologists discovered human remains in a side room of the Collegium Augustalium or College of the Augustales in Herculaneum. When Dr Petrone examined the remains — a young man in his early 20’s who may have been the Collegium’s caretaker — he found “a glassy material” in the skull. This material turned out to be the remains of the victim’s brains, which were vitrified or turned to glass by the high temperatures of the pyroclastic surges that ultimately destroyed Herculaneum. 

This discovery in itself was unique — not only in Herculaneum but other archaeological sites. However, Dr Petrone’s investigations did not end there, and further examination of the vitrified human brain has revealed further unprecedented discoveries.

2000-Year-Old Brain Neurons

“The discovery of brain tissue in ancient human remains is an unusual event,” explained Dr Petrone, “but what is extremely rare is the integral preservation of neuronal structures of a 2000 years ago central nervous system, in our case at an unprecedented resolution”.

Dr Petrone and his team discovered these “neuronal structures” after investigating the vitrified brain and spinal tissues using a scanning electron microscope and an image processing tool based on a neural network. Their research revealed that several preserved features of the dead man’s central nervous system — namely the brain neurons and axons.

Neurons are nerve cells, the essential units of the brain and central nervous system responsible for receiving and responding to stimuli from the outside world. Each neuron forms a network via a biological “cable” or axon, which transmits electrical impulses between the neurons. The state of preservation of these features in the vitrified brain was exceptional — the same standard as a frozen biological specimen. 

Using Archaeology to Save Lives

The survival of such intricate features from a 2000-year-old human central nervous system is fascinating in its own right. However, the conditions that allowed that survival shed further light on the circumstances that destroyed life in Herculaneum during the early hours of the second day of Vesuvius’s eruption — details that could save lives in the future.

 Scientists already know that the town and its inhabitants were exposed to a series of pyroclastic surges, with temperatures reaching around 500 degrees centigrade. However, the survival and state of preservation of the neuronal tissues reveal more exact details about those temperatures. 

 “Vitrification is a natural process that occurs when a liquid drops below its glass transition temperature, which depends largely on the cooling rate and the viscosity of the liquid,” explain Dr Petrone in the new PLOS ONE paper. “The preservation of this vitrified material implies that the brain was not destroyed during exposure by the hot pyroclastic flows and that time was allowed for its rapid cooling and transformation into glass before the final burial beneath further meters of hot pyroclastic debris.”

What this means is that the hot surge that ended the life of the man in the Collegium was followed by a sudden cooling that turned his brain to glass— thus preserving his central nervous system. This fact suggests that there were gaps between the surges when the temperature dropped. It is these cooler episodes in the eruption sequence that could be critical when saving future lives.

“This is a unique feature of the volcanic process, “Dr Petrone told History and Archaeology Online,” as it could provide relevant information for possible interventions by civil protection authorities to be implemented during the initial stages of a possible next eruption. The study of the vitrified brain may save lives in the future.”

 Sources

 Petrone, P et al. Preservation Of Neurons in an AD79 Vitrified Human Brain PLOS ONE