[1] Gyri and sulci create the folded appearance of the brain in humans and other mammals.

Ridges and depressions create folds allowing a larger cortical surface area, and greater cognitive function, to exist in the confines of a smaller cranium.

In embryonic development, all mammalian brains begin as smooth structures derived from the neural tube.

Pachygyria, lissencephaly, and polymicrogyria are all the results of abnormal cell migration associated with a disorganized cellular architecture, failure to form six layers of cortical neurons (a four-layer cortex is common), and functional problems.

[8] Pachygyria is used to describe brain characteristics in association with several neuronal migration disorders; most commonly relating to lissencephaly.