By Adrian Cho
Whether they’re from humans, whales, or elephants, the brains of many mammals are covered with elaborate folds. Now, a new study shows that the degree of this folding follows a simple mathematical relationship—called a scaling law—that also explains the crumpling of paper. That observation suggests that the myriad forms of mammalian brains arise not from subtle developmental processes that vary from species to species, but rather from the same simple physical process.
In biology, it rare to find a mathematical relationship that so tightly fits all the data, say Georg Striedter, a neuroscientist at the University of California, Irvine. “They’ve captured something,” he says. Still, Striedter argues that the scaling law describes a pattern among fully developed brains and doesn’t explain how the folding in a developing brain happens.
The folding in the mammalian brain serves to increase the total area of the cortex, the outer layer of gray matter where the neurons reside. Not all mammals have folded cortices. For example, mice and rats have smooth-surfaced brains and are “lissencephalic.” In contrast, primates, whales, dogs, and cats have folded brains and are “gyrencephalic.”
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