The distinctive wrinkles on the brain are caused by the expansion of the cortex and the compression resulting from it.
Humans have unique wrinkles on their brains, which are not found in most of the animals. In humans, brain wrinkle or folding begins to evolve right from the start, around the 20th week of fetus stage and completes when the child is just about a year and a half.
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These distinctive folds are likely developed to fit a large cortex into a small skull, but how the brain gets its folds, it was a mystery – until now.
Several hypotheses have been proposed in this regard but none was able to justify experimentally. A team of researchers from Harvard John A. Paulson School of Engineering and Applied Scientists has now probably brought forward an accurate explanation about brain folding. They have found that mechanical instability associated with buckling is the likely cause of brain folds.
Researchers created a 3D gel model of a smooth and unfolded fetal brain, based on MRI scans. Then, they covered it with a layer of elastomer gel to replicate cortex and dunked it into a solvent which caused model brain to swell. The resulting compression produced the network of wrinkles similar to seen in real human brain.
“We found that we could mimic cortical folding using a very simple physical principle and get results qualitatively similar to what we see in real fetal brains,” said lead author L. Mahadevan. “This simple evolutionary innovation with iterations and variations allows for a large cortex to be packed into a small volume and is likely the dominant cause behind brain folding, known as gyrification.”
The number, size, shape and position of neural cells during brain growth all expand cortex or gray matter and put it under compression. It leads to a mechanical instability that causes distinctive twists and turns on brain.
“The geometry of the brain is really important because it serves to orient the folds in certain directions. Our model, which has the same large scale geometry and curvature as a human brain, leads to the formation of folds that matches those seen in real fetal brains quite well,” said Jun Young Chung, co-author of the study.
He added. “When I put the model into the solvent, I knew there should be folding but I never expected that kind of close pattern compared to human brain. It looks like a real brain.”
These findings could help understand the inner workings of the brain and offer more insight into disorders linked to the folding of the brain.
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“Brains are not exactly the same from one human to another, but we should all have the same major folds in order to be healthy,” said Chung. “Our research shows that if a part of 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.”