| Primary somatosensory cortex | |
|---|---|
 Primary somatosensory cortex labeled in purple | |
 Primary somatosensory cortex: second image. | |
| Anatomical terms of neuroanatomy |
Inneuroanatomy, theprimary somatosensory cortex is located in thepostcentral gyrus of thebrain'sparietal lobe, and is part of thesomatosensory system. It was initially defined from surface stimulation studies ofWilder Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same asBrodmann areas 3, 1 and 2, more recent work byKaas has suggested that for homogeny with other sensory fields only area 3 should be referred to as "primary somatosensory cortex", as it receives the bulk of thethalamocortical projections from the sensory input fields.[1]
At the primary somatosensory cortex, tactile representation is orderly arranged (in an inverted fashion) from the toe (at the top of thecerebral hemisphere) to mouth (at the bottom). However, some body parts may be controlled by partially overlapping regions of cortex. Each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite (contralateral) side of the body. The amount of primary somatosensory cortex devoted to a body part is not proportional to the absolute size of the body surface, but, instead, to therelative density of cutaneoustactile receptors located on that body part. The density of cutaneous tactile receptors on a body part is generally indicative of the degree of sensitivity of tactile stimulation experienced at said body part. For this reason, the humanlips andhands have a larger representation than other body parts.
Brodmann areas 3, 1, and 2 make up the primary somatosensory cortex of the humanbrain (orS1).[2] BecauseBrodmann sliced thebrain somewhat obliquely, he encountered area 1 first; however, fromanterior toposterior, theBrodmann designations are 3, 1, and 2, respectively.
Brodmann area (BA) 3 is subdivided into two cytoarchitectonic areas labeled as 3a and 3b.[3][4]
Lesions affecting the primary somatosensory cortex produce characteristic symptoms including:agraphesthesia,astereognosia,hemihypesthesia, and loss ofvibration,proprioception andfine touch (because the third-order neuron of the medial-lemniscal pathway cannot synapse in the cortex). It can also producehemineglect, if it affects the non-dominant hemisphere. Destruction of brodmann area 3, 1, and 2 results in contralateral hemihypesthesia and astereognosis.
It could also reducenociception,thermoception, andcrude touch, but, since information from thespinothalamic tract is interpreted mainly by other areas of the brain (seeinsular cortex andcingulate gyrus), it is not as relevant as the other symptoms.[citation needed]