London: It is not just our skin that starts to lose its youthful firmness and elasticity as we age, but our brain too gets 'slacker', a new study has found.
Researchers from Newcastle University in the UK collaborated with the Federal University of Rio de Janeiro to investigate the way the human brain folds and how this 'cortical folding' changes with age. Linking the change in brain folding to the tension on the cerebral cortex - the outer layer of neural tissue in our brains - the team found that as we age, the tension on the cortex appears to decrease.
This effect was more pronounced in individuals with Alzheimer's disease. The research sheds light on the underlying mechanisms which affect brain folding and could be used in the future to help diagnose brain diseases. "One of the key features of a mammalian brain is the grooves and folds all over the surface a bit like a walnut - but until now no-one has been able to measure this folding in a consistent way," said lead author Dr Yujiang Wang of Newcastle University.
"By mapping the brain folding of over 1,000 people, we have shown that our brains fold according to a simple universal law. We also show that a parameter of the law, which is interpreted as the tension on the inside of the cortex, decreases with age.
"In Alzheimer's disease, this effect is observed at an earlier age and is more pronounced. The next step will be to see if there is a way to use the changes in folding as an early indicator of disease," said Wang. The expansion of the cerebral cortex is the most obvious feature of mammalian brain evolution and is generally accompanied by increasing degrees of folding of the cortical surface.
In the average adult brain, for example, if the cortex of one side - or hemisphere - was unfolded and flattened out it would have a surface area of about 100,000 square millimetre, roughly one and a half times the size of a piece of A4 paper.
Previous research has shown that folding of the cortex across mammalian species follows a universal law - that is, regardless of size and shape, they all fold in the same way. However, until now there has been no systematic study
demonstrating that the same law holds within a species.
"Our study has shown that we can use this same law to study changes in the human brain," said Wang. "From this, we identified a parameter that decreases with age, which we interpret as changing the tension on the cortical surface. It would be similar to the skin. As we age, the tension drops and the skin starts to slacken. "It has long been known that the size and thickness of the cortex changes with age but the existence of a general law for folding shows us how to combine these quantities into a single measure of folding that can then be compared between genders, age groups and disease states," said Wang. The study was published in the journal PNAS.
