As our skin loses its youthful elasticity and starts to droop, it seems the same happens to our grey matter too.
Researchers from Newcastle University in the UK and Brazil’s Federal University of Rio de Janeiro mapped the folds of more than 1,000 brains and found male and female brains followed the same, simple law of folding.
They also found the tension on the cerebral cortex – the outer layer of neurons – decreases with age, an effect more pronounced in Alzheimer’s disease patients. The work was published in the Proceedings of the National Academy of Sciences.
All mammal brains – from mice to whales – are covered with an array of folds. Some are more creased than others – for instance, a mouse brain is mostly smooth while a whale brain looks like a massive walnut.
This folding increases the brain’s surface area, allowing it to pack in more cells. If you flattened out the creased parts of a human’s grey matter, for instance, you’d end up covering around three A4 sheets of paper.
Still, no one had seen if links between ageing, sex and diseases affected those brain folds. Does a female brain age differently to a male’s?
So Newcastle University’s Yujiang Wang and her crew examined magnetic resonance images of healthy brains to measure the total grey matter surface area and thickness of the cortex.
They found while female brains were slightly smaller, with less volume and were less folded than male brains of the same age, cortical tension dropped in the same way as both sexes aged.
And when they analysed brains from those with Alzheimer’s disease from the Alzheimer’s Disease Neuroimaging Initiative database, the change in brain folding was significantly different.
Brains seemed saggier, “akin to premature ageing of the cortex”, Wang says.
So what causes grey matter to droop?
It could be due to shifts in the underlying white matter – the connections between brain regions – or even down to the pressure of the fluid in which the brain is bathed (called cerebral spinal fluid).
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