Download Like crumpled paper balls: the evolution of the mammalian cerebral

Like crumpled paper balls: the evolution of the mammalian cerebral cortex and its folding
Prof. Suzana Herculano-Houzel - Universidade Federal do Rio de Janeiro, Brasil
Larger brains tend to have larger and more folded cortices, and gyrification has long been
considered a mechanism that allows for larger neurons in the cerebral cortex – but why is
the cetacean cortex much more folded than predicted? Or why is the large manatee cortex
nearly smooth? Do increasing numbers of neurons necessarily cause, or require, increasing
cortical folding?
This talk will show that the degree of cortical folding scales uniformly neither with brain size
nor with number of cortical neurons, but simply with the surface area of the cortical surface
depending on its thickness, regardless of the numbers of neurons that build this surface. This
is identical to the generic folding of a self-avoiding surface, such as paper. Describing the
folding of the cerebral cortex according to the physical rules that apply to a self-similar, selfavoiding surface collapses all available mammalian species (including cetaceans, the
manatee, and lissencephalic animals) onto a single, universal scaling rule that also predicts
the transition between lissencephaly and gyrencephaly (as well as the ratio between cortical
grey and white matter). The many developmental, evolutionary and clinical implications of
this finding will be discussed.