To be awake and alert requires intactness of at least one of the cerebral hemispheres, as well as the upper brainstem from the middle of the pons and above (see Chapter 42, Examination of the Comatose Patient).

Cognition is a general term referring to mental abilities, such as memory, language, orientation, knowledge, and other aspects of intellectual functioning. Some cognitive abilities have well-recognized neuroanatomic localization, such as language to the dominant cerebral hemispheric cortex (see Chapter 6, Language Testing) or memory to the medial temporal lobes and thalami (see Chapter 7, Memory Testing); most other cognitive functions, however, although known to involve the cortex, are not clinically localizable to a specific neuroanatomic area.