Cerebral cortex

Lore & Background

The cerebral cortex is folded into peaks called gyri and grooves called sulci, a structure that increases surface area within the cranium. In humans, about two-thirds of the cortical surface is buried in sulci. The cortex is divided into left and right hemispheres by the longitudinal fissure, joined beneath by the corpus callosum. The six-layered neocortex makes up approximately 90% of the cortex, with the allocortex comprising the remainder. Cortical folding, or gyrification, appears during fetal development and continues after birth; in small mammals with small brains, the cortex is smooth.

Reader's Guide

The cerebral cortex is fundamental to understanding brain function, as it integrates sensory information and enables consciousness, thought, memory, and language. Its layered structure—six layers in the neocortex—allows for specialized processing, with different layers receiving and sending distinct types of signals. The cortex is organized into functional areas such as the motor cortex (in the precentral gyrus) and visual cortex (in the occipital lobe). Cortical thickness varies across species and regions, with sensory cortex generally thinner than motor cortex. Studies have found associations between cortical thickness and intelligence, though findings on conditions like migraine are mixed. Genetic disorders affecting cortical folding, such as microgyrus with four layers instead of six, have been linked to dyslexia. The cortex's folding pattern is crucial not only for fitting within the skull but also for brain circuitry and functional organization.

Did You Know?

• The cerebral cortex makes up 40% of the brain's mass.
• In humans, the cortex is thickest over the top of a gyrus and thinnest at the bottom of a sulcus.
• The line of Gennari in the primary visual cortex is a band of whiter tissue visible to the naked eye.
• African elephants, cetaceans, and hippopotamus lack a layer IV in the neocortex.