Where wrinkly skin gets a bad rap, a wrinkly brain gives you supercomputer abilities. But how those furrows in our grey matter form had scientists scratching their heads – until now.
A paper published in Nature Physics shows a 3-D printed brain buckling as it “grows”, forming the characteristic corrugations.
Like scrunching up a flat piece of paper to fit in a small space, the brain’s wrinkles maximise its cortex – the outer layer of the brain that does the heavy-duty processing. The surface area of the folded cortex is almost triple that of a smooth brain.
In human foetuses, the folding starts at around six months. How? One theory is brain cells are biochemically programmed to grow in a folded pattern.
Another is that the cortex expands faster than the rest of the brain, and physically has no other choice but to wrinkle.
So an international team tested the second theory by building a 3-D printed polymer gel model of a smooth foetal brain.
They coated their model, based on MRI data, with a thin polymer layer that absorbed liquid and expanded like a fast-growing cortex.
This “brain”, dunked into solvent, wrinkled up like a human brain despite lacking living tissue. “I knew there should be folding but I never expected that kind of close pattern compared to human brain,” said Jun Young Chung, co-first author of the paper.
Computer models showed that as the foetal brain grew, its shape created weak points in the cortex. These buckled and folded as the cortex expanded.
Computer models showed that as the foetal brain grew, its shape created weak points in the cortex. These buckled and folded as the cortex expanded.
Not all human brains look the same, and neither did the team’s 3-D model. Over multiple experiments, the smaller wrinkles in the model’s surface took on different shapes and sizes – just as they do in brains of different people.
Large wrinkles, on the other hand, consistently formed in the same places in the 3-D model – just as they do in human brains.
The work lays groundwork for studying developmental brain disorders.
“Our research shows that if a part of the brain does not grow properly, or if the global geometry is disrupted, we may not have the major folds in the right place, which may cause dysfunction in the brain,” said Chung.
