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Have you ever looked at a picture or illustration of a human brain and wondered why there are so many wrinkles? Researchers have previously found that the folds are a result of the rate at which the brain's gray matter grows, as well as its thickness. Now, in a new study published in Nature Physics, scientists demonstrate how the folds develop using a 3D gel model of a fetal brain based on MRI scans. 

According to the study, folding begins in human brains around the 20th week of gestation and continues until the child is around a-year-and-a-half old. By coating and immersing the 3D gel model of a smooth brain in a solvent, the researchers at Harvard's John A. Paulson School of Engineering and Applied Sciences, in collaboration with scientists in France and Finland, were able to mimic the folding that occurs as the cortex, or outer layer of the brain, expands.

As shown in the timelapse GIF above, the solvent causes the surface of the brain to swell as it absorbs the liquid and to form folds similar in size and shape to those on a real fetal brain. The researchers say this happens because the swelling—akin to cortical expansion—causes compression, which leads to a "mechanical instability" similar to buckling. This mechanical instability causes the folds.

"I knew there should be folding, but I never expected that kind of close pattern compared to human brain," co-author Jun Young Chung said of the model, which has the "same large scale geometry and curvature" of a real brain. "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 potential dysfunction."

Image credit: Mahadevan Lab/Harvard SEAS