cerebral cortex

The cerebral cortex is the thin, wrinkled outer sheet of the brain, the part you picture when you imagine a brain. It is only a few millimeters thick, about the depth of a few stacked coins, yet it is where much of our perceiving, thinking, planning, and deciding takes place. Because it is packed with the cell bodies of neurons, it has a grayish color, which is why it is often called gray matter.

Its surface is folded into bulges called gyri and grooves called sulci. This folding lets a large sheet of tissue pack into a small skull, the way crumpling a sheet of paper lets it fit inside a cup. The deepest grooves divide each half of the brain into four broad regions called lobes, the frontal, parietal, temporal, and occipital lobes. Across most of this surface the cortex is built from six stacked layers of cells, an arrangement called the neocortex, with bundles of connecting fibers, the white matter, running beneath it.

Different patches of cortex tend to specialize, with some areas leaning toward vision, others toward hearing, touch, movement, or language. This handling of more complex, higher-level tasks is often called higher cognition. But no patch works alone: they are wired together into networks, so even a simple act like naming a picture lights up many regions at once.