When Do Sulci and Gyri Develop?

By 30–32 weeks most of the main sulci could be demonstrated. The fetal cortex undergoes significant development during the course of pregnancy; from a completely smooth surface at 22 weeks, it develops into a complex array of sulci and gyri resembling the adult brain by the end of gestation1,2.

How are gyri and sulci formed?

Each gyrus is surrounded by sulci and together, the gyri and sulci help to increase the surface area of the cerebral cortex and form brain divisions. They form brain divisions by creating boundaries between the lobes, so these are easily identifiable, as well as serving to divide the brain into two hemispheres.

Do all brains have gyri and sulci?

In general, larger brains have folds while smaller brains do not, even small mammals like rats or mice have smooth brains. In humans, a lissencephalic brain is one without gyri and sulci and is a result of a rare disorder that is characterised by mental abnormalities.