Editing Primary somatosensory cortex

{{Short description|Region of the brain which processes touch}}
{{Infobox brain
| Name     = Primary somatosensory cortex
| Image    = Blausen 0103 Brain Sensory&Motor.png
| Caption  = Primary somatosensory cortex labeled in purple
| Image2   = File:Cerebrum lobes.svg
| Caption2 = Primary somatosensory cortex: second image.
}}

## In neuroanatomy, the '''primary somatosensory cortex''' is located in the postcentral gyrus of the [[Human brain cell|brain]]'s parietal lobe, and is part of the somatosensory system. It was initially defined from surface stimulation studies of Wilder Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann areas 3, 1 and 2, more recent work by Kaas 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 the thalamocortical projections from the sensory input fields.<ref name="Viaene 2011">{{cite journal |author= Viaene A.N.|title= synaptic properties of thalamic input to layers 2/3 and 4 of primary somatosensory and auditory cortices |journal= Journal of Neurophysiology |volume=105 |issue=1 |pages=279–292 |year=2011 |doi=10.1152/jn.00747.2010 |display-authors=etal|pmc=3023380 |pmid=21047937}}</ref>

At the primary somatosensory cortex, tactile representation is orderly arranged (in an inverted fashion) from the toe (at the top of the cerebral 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 the [[Cortical homunculus#Representation|relative density]] of cutaneous [[Mechanoreceptor|tactile 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 human [[lips]] and [[hand]]s have a larger representation than other body parts.

==Structure==
[[File:Schematic of cortical areas involved with pain processing and fMRI cropped.jpg|thumb|left|300px|Primary somatosensory cortex labeled in green '''S1''']]
=== Brodmann areas 3, 1, and 2 ===
'''Brodmann areas 3, 1, and 2''' make up the primary somatosensory cortex of the human [[brain]] (or '''S1''').<ref name=GuyEvans>{{cite web |last1=Guy-Evans |first1=Olivia |title=Somatosensory Cortex |url=https://www.simplypsychology.org/somatosensory-cortex.html |website=SimplyPsychology |access-date=22 February 2023}}</ref>  Because [[Korbinian Brodmann|Brodmann]] sliced the [[brain]] somewhat obliquely, he encountered area 1 first; however, from [[Anatomical terms of location#Directional terms|anterior]] to [[Caudal (anatomical term)|posterior]], the [[Brodmann area|Brodmann]] designations are 3, 1, and 2, respectively.

Brodmann area (BA) 3 is subdivided into two cytoarchitectonic areas labeled as 3a and 3b.<ref>{{cite book |last1=Benarroch |first1=Eduardo E. |title=Basic Neurosciences with Clinical Applications |date=2006 |publisher=Elsevier Health Sciences |isbn=0750675365 |page=440 |url=https://books.google.com/books?id=98oLRD5-KlYC |access-date=22 February 2023}}</ref><ref>{{Cite journal |last1=Sanchez-Panchuelo |first1=Rosa M. |last2=Besle |first2=Julien |last3=Beckett |first3=Alex |last4=Bowtell |first4=Richard |last5=Schluppeck |first5=Denis |last6=Francis |first6=Susan |date=2012-11-07 |title=Within-Digit Functional Parcellation of Brodmann Areas of the Human Primary Somatosensory Cortex Using Functional Magnetic Resonance Imaging at 7 Tesla |journal=The Journal of Neuroscience |language=en |volume=32 |issue=45 |pages=15815–15822 |doi=10.1523/JNEUROSCI.2501-12.2012 |issn=0270-6474 |pmc=6621625 |pmid=23136420}}</ref>

== Clinical significance ==
Lesions affecting the primary somatosensory cortex produce characteristic symptoms including: [[agraphesthesia]], [[astereognosia]], [[hemihypesthesia]], and loss of [[vibration]], [[proprioception]] and [[fine touch]] (because the third-order neuron of the medial-lemniscal pathway cannot synapse in the cortex). It can also produce [[hemineglect]], if it affects the non-dominant hemisphere. Destruction of brodmann area 3, 1, and 2 results in contralateral hemihypesthesia and astereognosis.

It could also reduce [[nociception]], [[thermoception]], and [[crude touch]], but, since information from the [[spinothalamic tract]] is interpreted mainly by other areas of the brain (see [[insular cortex]] and [[cingulate gyrus]]), it is not as relevant as the other symptoms.{{Citation needed|reason=This claim needs a reliable source. Nociception, for example, is known to project to and be heavily processed by areas 1, 3a and possibly 3b (see Vierck CJ et al. Role of primary somatosensory cortex in the coding of pain. PAIN (2012), http://dx.doi.org/10/1016/j.pain.2012.10.021) of the post central gyrus.|date=March 2013}}

==See also==
* [[List of regions in the human brain]]

==References==
{{Reflist}}

==External links==
* {{BrainInfo|ancil|1040}} - area 1
* {{BrainInfo|ancil|1041}} - area 2
* {{BrainInfo|ancil|1042}} - area 3

{{Prosencephalon}}
{{Neural tracts}}

[[Category:Cerebral cortex]]
[[Category:Brodmann areas|01]]
[[Category:somatosensory system]]
[[Category:Parietal lobe]]