Each cerebral HEMISPHERE is divided into four LOBES, of which the parietal lobe is one. It only becomes clearly defined within the brains of PRIMATES, since only in primates is there a clearly defined LATERAL (or Sylvian) SULCUS and a clearly defined central (or Rolandic) SULCUS. These major sulci form the inferior and anterior borders, respectively, of the parietal lobe.
The parietal lobe is conventionally divided into two parts: the POSTCENTRAL GYRUS lying immediately behind the central sulcus, and the remainder of the lobe, collectively designated POSTERIOR PARIETAL CORTEX (PPC). Within the postcentral strip is the primary SOMATOSENSORY CORTEX (S1), in which the different modalities of tactile sensation are represented in a largely homuncular layout (see HOMUNCULUS). This postcentral region contains BRODMANN’S AREAS 1, 2 and 3. Other purely somatosensory areas are now known to exist elsewhere in the parietal lobe, notably area S2, which is found in the upper lip of the lateral sulcus adjacent to the TEMPORAL LOBE. For information concerning parietal function, see PARIETAL CORTEX.
A.DAVID MILNER
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