Why the brain has so many folds

By Ashley Abbott

導讀:你了解大腦嗎？這是一篇有關大腦的文章。“

Iknow the human brain is an incredible thing,the most complex object in the known universe.But,honestly,it’s not much to look at.Just a big,gray,foldy lump.And what’s with all those folds?Why does the brain look a lot like a scrunched up piece of paper?”

Our brains,and the brains of some other animals,have a lot more in common with a balled up piece of paper than you might think.

First,though,it’s worth mentioning that not all brains look the same.Some animals,including rats and mice,have smooth brains.No folds or wrinkles.Humans and other animals,such as pigs,have brains with many folds.

Scientists at the University of Rio de Janeiro have been trying to figure out what accounts for the folds.One idea postulated that as brains evolve and the more neurons they have,the more folds are required to allow neurons to form connections.But elephants have nearly twice as many folds in their brains yet have fewer neurons than we do,so that theory seems improbable.

The researchers have,however,determined that how human brains fold follows the same physical principles guiding folds and creases resulting from crumpling a sheet of paper.That’s interesting because it enabled the scientists to reason that the two main factors determining a brain’s shape are the surface area and thickness of the outer layer cortex.The larger the cortex surface area,the more folds a brain will have.But greater thickness results in fewer folds.

Same goes for a piece of paper.

“我知道人腦非常不可思議，是已知的宇宙世界中最復雜的構造。但是，說實話從表面看根本看不出來，只是一個體積較大的灰色有溝壑的團狀物。這些溝壑究竟是什么呢？為什么大腦看起來就像一張揉成一團的紙？”

事實上你可能不知道，我們的大腦與個別動物的大腦一樣，和揉成一團的紙有許多相似之處。

首先，值得一提的是并非所有大腦都長得一樣。一些動物，例如老鼠，他們的大腦就很平整，并沒有溝壑和褶皺。人類的大腦與豬等其他動物的大腦都有許多溝壑。

里約熱內盧大學的科學家試圖找出溝壑的成因。目前有一個理論認為隨著大腦進化，產生越來越多地神經元，就需要更多的溝壑讓神經元連接起來。但大象的溝壑幾乎是人類的2倍多，但神經元卻比我們少得多，因此這項理論并不成立。

但那些科學家從揉成團的紙中推論出，人腦形成溝壑與紙的折疊和起皺遵循同樣的物理學規律。這很有意思，科學家通過2個要素推論出大腦的形狀是由外皮質層的表面積和厚度決定的。外皮質層的表面積越大，大腦的溝壑就越多。而厚度越大，溝壑就越少。

紙張也是同樣的原理。