Lissencephaly

In humans, lissencephaly is a neurodevelopmental disorder due to disturbed neuronal migration during the development of the cerebral cortex. It results in disturbed cortical connectivity and, consequently, a smooth cortical surface (i.e. low gyrification), with sulci being less pronounced than in the normal brain (a condition known as pachygyria) or even totally absent (agyria).

In other mammals, particularly those with small brains, lissencephaly may be the normal state of an adult brain, as is the case with beavers, manatees and platypus, for instance.