The cerebral cortex is a dense aggregation of neuron cell bodies that ranges from 2 to 4 mm in thickness and forms the surface of each cerebral hemisphere. Most of the cerebral cortex is neocortex, consisting of six layers with different populations of neurons. In addition to the laminar organization, there is a perpendicular columnar organization as well. This is especially well studied for the visual cortex, which has columns that receive only visual information from the right eye adjacent to columns that receive only visual information from the left eye. Distinct higher cortical functional areas are devoted to memory, judgment, the planning of complex activities, the processing of language, mathematical calculations, and the construction of an internal image of an individual’s surroundings. The cerebral hemisphere that controls language is called the dominant hemisphere , is the left hemisphere in about 95% of humans, and includes Broca and Wernicke areas. Damage to either area leads to one of the two classic types of aphasia, Broca aphasia or Wernicke aphasia. Parietal association cortex in the nondominant hemisphere mediates spatial relationships and related selective attention. Damage leads to contralateral neglect and associated symptoms. Prefrontal association cortex mediates the most distinctly human intellectual traits, such as judgment, foresight, a sense of purpose, a sense of responsibility, and a sense of social propriety. Damage leads to a constellation of deficits that are classically described for Phineas Gage.