London: Along with our skin that loses the firmness and elasticity of the youth, our brain too starts to sag as we age, researchers say.

A recent study found that as humans age, their brain folds and the tension on the cerebral cortex -- the outer layer of neural tissue in our brains -- appears to decrease. 

Previous research has shown that this 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.

"Our study has shown that we can use this same law to study changes in the human brain," said lead author Yujiang Wang from the Newcastle University in Britain.

However, this effect was more pronounced in individuals with Alzheimer's disease, the researchers said.

"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," Wang added. 

The study also found that male and female brains differ in size, surface area, and the degree of folding.

Indeed, female brains tend to be slightly less folded than male brains of the same age. Despite this, male and female brains are shown to follow exactly the same law, the researchers said.

The study sheds light on the underlying mechanisms which affect brain folding and could be used in the future to help diagnose brain diseases, the researchers observed.

"More work is needed in this area but it does suggest that the effect Alzheimer's disease has on the folding of the brain is akin to premature ageing of the cortex," Wang noted in the paper that appeared in the journal PNAS.