Synonyms

Cerebral hemisphere

Definition

The surface of each cerebral hemisphere is divided into four lobes (frontal, parietal, temporal, and occipital), named for the bones that lie above them. The lateral surface of the parietal lobe is behind the central sulcus and above the lateral fissure. It lies between the frontal and occipital lobes and above the temporal lobe. The parietal lobe is involved in somatosensation, vision, and attention. There are four main gyri (postcentral, intraparietal, supramarginal, and angular) and two sulci (central and postcentral).

Current Knowledge

The lateral surface of the parietal lobe is divided into three functional areas, the postcentral gyrus, which contains primary somatosensory cortex, the superior parietal lobule, and the inferior parietal lobule, which contains parts of the supramarginal and angular gyri. The primary somatosensory cortex extends down the face of the postcentral gyrus and provides a map of the contralateral body representation for somatosensation. This cortical region receives input from the somatosensory regions of the thalamus and represents information about touch, pain, temperature, and a sense of limb position (proprioception). Damage in the primary somatosensory cortex of one hemisphere results in a contralateral loss of fine tactile discrimination and proprioception. However, general tactile and pain sensation remain intact. The superior parietal lobule mediates complex aspects of spatial orientation, perception, and attention. The dorsal occipital region of the parietal lobe is part of the “where” visual pathway and contributes to the analysis of motion and spatial relationships between objects. The inferior parietal lobule (usually of the left or dominant hemisphere), along with parts of the temporal lobe is involved in language comprehension. Unilateral damage to the angular gyrus can lead to defects in reading (alexia) or naming objects (anomia), or an inability to write (agraphia) or draw simple figures (agraphia). Unilateral damage (usually the right hemisphere, referred to as the nondominant hemisphere) results in a disturbance of personal and extrapersonal space or sensory neglect. Patients with this syndrome exhibit a profound neglect for the contralateral half of their body or external world. Damage can result in apraxia, a defect in making specific movements such as dressing, or constructional apraxia, difficulty in constructing simple figures, and neglect on one side of the body.

Cross-References