Cerebral cortex: A thin mantle of gray matter about the size of a formal dinner napkin covering the surface of each cerebral hemisphere. The cerebral cortex is crumpled and folded, forming numerous convolutions (gyri) and crevices (sulci). It is made up of six layers of nerve cells and the nerve pathways that connect them. The cerebral cortex is responsible for the processes of thought, perception and memory and serves as the seat of advanced motor function, social abilities, language, and problem solving.

The embryonic development of the cerebral cortex is under the control of a number of genes. In the first trimester of fetal life, neurons arise in a region lining the cerebral cavity. Precursor cells in this "proliferative zone" give rise to neurons that migrate up and out into the cortex, forming its layers. Other cell types arrive from different areas to complete the structure.

Much can go wrong in this process and result in congenital malformations of the cerebral cortex. Much can also go wrong with the cerebral cortex after birth. Nerve cells in the cerebral cortex are known to die in Alzheimer disease and in many other brain diseases.

The word "cortex" is Latin for the bark of a tree. The plural of cortex is cortices. The adjective is cortical.