The cerebral cortex is the outer layer of the cerebrum of the brain and also covers the cerebellum. It is about 2-4 mm thick and consists of six separate layers. It is almost entirely made up of neurons. It plays a major role in memory, attention, awareness, thought, language and consciousness.
Because it takes on a grey color when preserved, the cortex is usually referred to as "grey matter", even though in a living brain it has no distinct color.
In large mammals, particularly humans, the cortex is intricately folded to provide it with more surface area. It is believed that this characteristic is a key feature in establishing mammalian intelligence.