The cerebral cortex is a simple structure of the brain with complex functions. The neocortex, as it is called by neuroanatomists, is a thin covering of gray matter on the outer surface of the entire cerebrum. The layer is about two to three mm thick and primarily composed of two types of neurons. The surface area of the cortex of the average adult brain is around 964 in.² (2,500 cm²). The reason for this enormous surface area compared to brain size is the result of the infolding of the surface of the brain. The hills (gyri) and valleys (sulci) that are characteristic of the brain provide the greatly increased surface. In some places the fissures or large sulci are very deep and provide a sort of map for dividing the cortex into distinct regions with specific functions.

The cortext contains about 50-100 billion neurons. There are two major...