The cerebral cortex is the outermost sheet of neural tissue of the cerebrum of the brain in some vertebrates. It covers the cerebrum and cerebellum, and is divided into left and right hemispheres. The cerebral cortex plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It consists of up to six horizontal layers, each with a different composition in terms of neurons and connectivity. The human cerebral cortex is 2 to 4 millimetres (to in) thick.