The cerebral cortex is the cerebrum's outer layer of neural tissue in humans and other mammals. It is divided into two cortices, along the sagittal plane: the left and right cerebral hemispheres divided by themedial longitudinal fissure. The cerebral cortex plays a key role in memory, attention, perception, awareness, thought, language, and consciousness. The human cerebral cortex is 2 to 4 millimetres thick.
In large mammals, the cerebral cortex is folded, giving a much greater surface area in the confined volume of the skull. A fold or ridge in the cortex is termed a gyrus and a groove or fissure is termed asulcus. In the human brain more than two-thirds of the cerebral cortex is buried in the sulci.
The cerebral cortex is composed of gray matter, consisting mainly of cell bodies and capillaries. It contrasts with the underlying white matter, consisting mainly of the white myelinated sheaths of neuronal axons. The most recent part of the cerebral cortex to develop in the evolutionary history of mammals is the neocortex, which differentiated into six horizontal layers; the more ancient part of the cerebral cortex, the hippocampus, has at most three cellular layers. Neurons in various layers connect vertically to form small microcircuits, called cortical columns. Different neocortical regions known as Brodmann areas are distinguished by variations in their cytoarchitectonics and functional roles in sensation, cognition and behavior.