How the Cerebral Cortex Got Its Folds

August 22, 2014
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Known empirical scaling laws for gray-matter volume and thickness are mapped on a g2 vs. R/T diagram. Corresponding simulations for spherical brain configurations, with images shown at a few points, show that the surface remains smooth for the smallest brains, but becomes increasingly folded as the brain size increases. [From T. Tallinen, J.Y. Chung, J.S. Biggins, and L. Mahadevan, "Gyrification from constrained cortical expansion," PNAS 2014 | doi:10.1073/pnas.1406015111]

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The convolutions of the human brain are a symbol of its functional complexity and correlated with its information processing capacity. Conversely, loss of folds is correlated with loss of function. But how did the outer surface of the brain, the layered cortex of neuronal gray matter, get its folds?

Professor L. Mahadevan and colleagues from University of Jyväskylä (Finland), SEAS, and Cambridge University (UK) argue in an upcoming article in PNAS that these folds arise due to a mechanical instability of a soft tissue that grows nonuniformly. They present numerical simulations and physical mimics of the constrained growth of the cortex which show how compressive mechanical forces sculpt it to form characteristic sulci and gyri, consistent with observations across species in both normal and pathological situations.