What is "gyrification"

Gyrification is the process of forming the characteristic folds of the cerebral cortex. The peak of such a fold is called a gyrus (plural: gyri), and its trough is called a sulcus (plural: sulci). The neurons of the cerebral cortex reside in a thin layer of ' gray matter', only 2–4 mm thick, at the surface of the brain. Much of the interior volume is occupied by ' white matter', which consists of long axonal projections to and from the cortical neurons residing near the surface. Gyrification allows a larger cortical surface area and hence greater cognitive functionality to fit inside a smaller cranium. In most mammals, gyrification begins during fetal development. Primates, cetaceans, and ungulates have extensive cortical gyri, with a few species exceptions, while rodents generally have none. Gyrification in some animals, for example the ferret, continues well into postnatal life.