Brain wrinkles explained by physics, study says
While scientists have long understood that brain wrinkles — the folds in the outer layer of the human brain — are needed to pack a lot of processing power into a small skull, exactly how this works remained a puzzle.
Now, a team of researchers from the United States and Europe has discovered that the brain’s telltale folds can be explained by physics, a new study in Nature Physics reports.
The physical folds of the brain create room for large numbers of neurons to be packed tightly together, allowing for shorter, faster connections between the cells. While other animals — including dolphins, elephants, chimpanzees and pigs — have folds in their brains, the human brain is the wrinkliest by far.
For the first 20 weeks of life, the brain of a human fetus is smooth. As the fetal brain grows, buckling of weak spots begins to occur. After that, folding begins and continues until the child is 18 months old, Discovery News reports. The size, shape, number, and position of brain cells during early growth all lead to the expansion of gray matter. This compresses the cortex and creates the creases.
“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,” said L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, Organismic and Evolutionary Biology, and Physics at Harvard University, in a statement.
The researchers took MRI scans of smooth fetal brains and used them to build a three-dimensional gel model. They then coated its surface with a thin layer of elastomer gel to represent the cortex and mimicked brain growth by immersing the gel brain in a solvent that caused the outer layer to swell relative to the deeper region.
Within minutes of immersion, folds began to appear on the model. Despite containing no living tissue, they were similar in both size and shape to an actual human brain. This suggests the process is governed by physical, rather than biological, principles.
A better understanding of how the folds of the brain are formed could lead to breakthroughs in diagnosing, treating and preventing certain neurological disorders, the scientists say. For example, severe under-folding or over-folding of the brain can cause a variety of problems, such as seizures, mental disability, motor dysfunction, and developmental delay.
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