A crumpled-up sheet of pinkish paper could maybe pass for a brain, if you squint. Apparently, there's a scientific reason for the resemblance.

It turns out that the folds in a simple crumpled sheet of paper are determined by the same universal physics law that controls the folding of the extremely complex tissues in the brain, scientists reported in a paper published in the journal Science. This discovery comes as the result of a longtime partnership between physicist Bruno Mota and neuroscientist Suzana Herculano-Houzel, who work together at the Federal University of Rio de Janeiro in Brazil.

"People think the brain is this mysterious thing that has to be super complex, and there must be some really fancy mechanisms controlling the number of folds," Herculano-Houzel told Tech Times.

"Well, guess what? Yes, there are very complex mechanisms that control the number of neurons and how they spread out, but once you get past that point, it's just pure physics. It's like you have a sheet of paper growing inside your skull."

Rather than depending on the number of neurons or any of these complex biological factors, the folding depends on which conformation requires the least amount of energy — a purely physical property.

That doesn't mean the folding of that outer layer of brain tissue (known as the cortex) is trivial for its biological functioning, however. The amount of folding in a brain is directly related to the speed at which signals get transmitted within that brain. If you compare two brains with the same surface area but one has more folding, it's because the more folded one has a much thinner cortex.

"The consequence of having a much thinner cortex is that it folds and because it folds, the final volume of the cortex of the cortex will be much smaller," said Herculano-Houzel. "A smaller cortex has smaller conduction time, so being small is a big advantage."

Making the connection between balls of crumpled paper and the balls of folded tissue in our skulls was completely accidental. The universal scaling law that governs the folding of paper has been known for some time, and, being a physicist, Mota was already familiar with this law. What he was not familiar with was the mathematics of the folding of the brain — until a recent meeting with Herculano-Houzel.

"When he laid eyes of the plot of total surface area against the exposed surface area of the brain, he said, 'This has the same fractal dimensions as a crumpled sheet of paper!'" she recounted.

Finding out that this scaling law was so general that it could be applied to these two vastly different objects was exhilarating, Herculano-Houzel said.

"I remember driving home that day with that equation in mind and thinking, 'I know what I'm doing this afternoon — I'm going back to kindergarten and making crumpled paper balls!'"

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