LATERAL VIEW OF THE FOREBRAIN: FUNCTIONAL REGIONS
Some circumscribed regions of the cerebral hemisphere are associated with specific functional activities, including the motor cortex, the supplemental and premotor cortices, the frontal eye fields, the primary sensory cortex, and other association regions of the sensory cortex. Part of the auditory cortex is visible at the inferior edge of the lateral fissure (the transverse temporal gyrus of Heschl). Part of the visual cortex is visible at the occipital pole. Language areas of the left hemisphere include Broca’s area (expressive language) and Wernicke’s area (receptive language). Damage to these cortical regions results in loss of specific functional capabilities. There is some overlap between functional areas and named gyri (e.g., the motor cortex and the precentral gyrus), but there is no absolute concordance.
Some specific regions (gyri) of the cerebral cortex, such as the precentral gyrus (primary motor cortex) and the postcentral gyrus (primary somatosensory cortex), demonstrate topographic organization. Thus, information from the contralateral hand and arm are localized laterally, the body is represented more medially, and the lower extremity is represented along the midline and over the edge into the paracentral lobule. The face and head are represented in far lateral regions of these gyri, just above the lateral fissure. This has important functional implications; damage to selected regions such as the midline territory, which is supplied with blood from the anterior cerebral artery, results in somatosensory loss and paresis in the contralateral lower extremity, while sparing the upper extremity.