(Web Desk) - There's still so much we don't know about the human brain and that includes how some specimens remain preserved for thousands of years.
Over 4,000 human brains have been studied as part of new research into a mystery that's baffling scientists.
The study highlights that brains don't always decompose quickly after death and some remain preserved even when there's been no preservation techniques used.
This research was led by Oxford University's Alexandra Morton-Hayward. It involved a team trawling through the archaeological record of human brains.
The findings have been published in the Proceedings of the Royal Society B: Biological Sciences journal.
"Here, we collated an archive of more than 4400 human brains preserved in the archaeological record across approximately 12 000 years, more than 1300 of which constitute the only soft tissue preserved amongst otherwise skeletonized remains.
"We found that brains of this type persist on time scales exceeding those preserved by other means, which suggests an unknown mechanism may be responsible for preservation particular to the central nervous system," the researchers wrote.
One of the oldest brains in question was found preserved in a severed skull.
The skull belonged to a Stone Age person who had been decapitated and their head placed on spike in Sweden sometime between 6350 to 5000 BC.
Another of the brains was found in a prehistoric cemetery in Upper Egypt and had been preserved in a shallow sandy grave.
"The untapped archive of preserved ancient brains represents an opportunity for bioarchaeological studies of human evolution, health and disease," the researchers continued.
Some of the preserved brains had resonable explanations such as being freeze dried or volcanic preservation.
However, there were many that were the only soft tissue to survive on skeletons.
Scientists warned that preserved brains can look the same color as soil and many may have been discarded during excavations.