THIS is the left cerebral hemisphere of an 18-month-old infant who lived some 800 years ago. Such finds are extremely rare, because nervous tissue is soft and normally begins to decompose soon after death, so this specimen is unique in that it has been far better preserved than any other. Although reduced by about 80% of its original weight, many of its anatomical features have remained intact. The frontal, temporal and occipital lobes have retained their original shape; the gyri and sulci (the grooves and furrows on the surface, respectively labelled G and S, above) are easily recognizable; and amazingly, it contains the identifiable remnants of neurons.
The paper describing this extraordinary artifact, which is due to be published in the journal NeuroImage next month, reads somewhat like a medieval murder mystery, with elements of archaeology, forensic science and neuropathology. The child’s skeletonised remains were exhumed in 1998 from a burial site in the city of Quimper, north-western France, in a wooden coffin with the head wrapped in leather and resting on a pillow. The coffin was dated by dendrochronology (tree-ring dating) to the mid- to late 13th century (1250-1275 AD), and the age of the child determined by examination of the teeth. After the remains were discovered, the brain was removed and immersed in a preservative formalin solution. Several years later, Christina Papageorgopolou of the University of Zurich’s Institute of Anatomy and her colleagues began to re-examine it.
The brain is so well preserved that the researchers were able to perform far more tests on it than were possible with similar specimens found previously. Computed tomography and magnetic resonance imaging revealed the gross anatomical features of the organ, clearly showing the central sulcus, which separates the frontal and parietal lobes, and the corpus callosum, the huge bundle of nerve fibres connecting the left and right hemispheres. The grey and white matter, which are made up respectively of cell bodies and axon bundles enveloped in fatty insulating tissue, could easily be distinguished from one another.
Small samples of tissue were taken from the motor cortex and hippocampus. Microscopic examination of the motor cortical tissue showed the grey matter and white matter in more detail (GM and WM, above), and allowed glial cells and blood vessels to be identified. The layered structure of the cortex was no longer apparent, however, and no cells were visible, although numerous darkly stained structures – possibly the remains of cell nuclei – were observed. Likewise, the typical structure of the hippocampal formation could not be identified, but nevertheless, pyramidal cells were clearly visible in that part of the brain, and had retained their characteristic shape, with the dendrites, triangular cell body, axon and terminal branches intact (below).
The pathologist who initially examined the remains diagnosed the cause of death to be a cerebral haemorrhage, but the CT and MRI scans showed no signs of haemorrhage, so the researchers could not confirm this. They did, however, find deposits of a chemical called hemosiderin on the outer surface of the brain, which indicates that bleeding did occur: following a haemorrhage, the oxygen-carrying protein hemoglobin is released from red blood cells, and is broken down by the immune system. Hemosiderin is one of the breakdown products, but takes a few days to form. Its presence on the brain’s surface, together with that of a large, circular non-depressed fracture near the top of the skull, suggests that the child died several days after a severe head trauma.
Strangely, the brain was the only soft tissue that did not perish but exactly why it is so well preserved is unclear. The researchers speculate that environmental conditions are likely to be important. Quimper is 50-60m above sea level, and located at the confluence of the Odet, Steir and Jet rivers. It is exposed to the Atlantic tide, and therefore has a combination of fresh and salt water, as well as acidic clay soil. These conditions are known to favour the formation of adipocere, a wax-like substance that is deposited when bacteria break down fatty tissues in the absence of oxygen, and which slows down the rate of decomposition or inhibits it altogether. Continuous water immersion, which promotes adipocere formation, may also have contributed to the preservation of the brain tissue.
Papageorgopoulou, C., et al. (2010). Preservation of cell structures in a medieval infant brain: A paleohistological, paleogenetic, radiological and physico-chemical study. NeuroImage 50: 893-901. DOI: 10.1016/j.neuroimage.2010.01.029.