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The somatosensory cortex is a brain region associated with processing sensory information from the body such as touch, pressure, temperature, and pain.
Sensory information gets sent to the somatosensory cortex which has numerous connections with other brain areas to process this information.
The somatosensory cortex is a region of the brain located in theparietal lobeand lies behind the primarymotor cortexof thefrontal lobe.
The somatosensory cortex uses sensory information to initiate important movements that may be required to deal with particular situations.
Where is the somatosensory cortex located?
The somatosensory cortex is located in theparietal lobeof the brain, specifically in a ridge of thecerebral cortexcalled the postcentralgyrus, which lies directly behind the central sulcus (a deep fissure) and theprimary motor cortex.
Both hemispheres of the brain contain a somatosensory cortex, with each side processing sensory information from the opposite side of the body.
Somatosensory cortex functions
The somatosensory cortex processes all sensory information from your body. Key functions include:
Areas of the somatosensory cortex
The somatosensory cortex is divided into two main regions: the primary and secondary somatosensory cortex.
Primary somatosensory cortex
The primary somatosensory cortex (S1) is located in the postcentral gyrus and contains several distinct areas known asBrodmann’s areas.
Area 3 serves as the main receiving center for sensory input from thethalamusand handles initial processing.
Within this, Area 3b processes basic touch sensations, while Area 3a specifically processes information about body position.
Area 1 has specialized functions for perceiving texture, while Area 2 focuses on processing object shape and size.
Secondary somatosensory cortex
The secondary somatosensory cortex (S2) lies adjacent to S1 in the upper part of the lateral sulcus.
It receives information both from S1 and directly from the thalamus, functioning as an association area for sensory input.
S2 contains multiple representations of the body and plays a crucial role in tactile object recognition and memory.
Through its connections to thehippocampusandamygdala, S2 integrates past experiences with current sensory information. It also has a specific role in processing pain intensity through bilateral activation.
Both regions process information from the opposite side of the body, meaning the left hemisphere processes sensations from the right side of the body and vice versa. This arrangement, known as contralateral processing, is fundamental to how the somatosensory cortex operates.
Homunculus Map
Within the somatosensory cortex, parts of the body are represented on a sensory homunculus map. This means that areas within the somatosensory cortex are arranged such that a particular location receives information from a particular part of the body.
Thus, the surface area of the cortex dedicated to a part of the body correlates with the amount of sensory information from that area.
Some areas of the body are more sensitive than others and are therefore represented in the homunculus map in a distorted way, so those areas of the body take up a disproportionate amount of space.
For instance, the hands and the lips are very sensitive to sensations. So there is a large area of the somatosensory cortex dedicated to sensation in these areas.
In contrast, body parts such as the back are less sensitive to sensations and would therefore have a much smaller area represented in the cortex.
Typically, the medial portions of the sensory homunculus represent body parts such as the hips and, below, those less sensitive to sensation.
At the same time, the lateral sides have a larger surface area which would be where the areas for fingers, lips, eyes, and face would be, those which would be more sensitive to sensations.
Somatosensory Pathway
Somatosensory pathways are typically comprised of threeneurons: primary, secondary, and tertiary.
The primary neurons are the sensory receptors within the periphery of the somatosensory cortex, which can detect various stimuli such as touch or temperature.
The secondary neurons are located within the spinal cord and brainstem and act as a relay station.
These will then terminate in either the thalamus or the cerebellum.
The tertiary neurons, located within the thalamus andcerebellum, will then project to the somatosensory cortex. This will then aid in forming a sensory homunculus, a representational map of the body.
What happens if the somatosensory cortex is damaged?
Damage to the somatosensory cortex can result in mostly mild deficits, and symptoms depend on which area was damaged.
Damage could result from lesions to one or more areas, sometimes due to a stroke. Another type of lesion is multiple sclerosis (MS) which results in loss of proprioception or exteroception (sensations from stimuli outside the body).
Below are descriptions of some of the symptoms that may be experienced as a result of damage:
Numbness
Numbness can result due to damage in the cortex which then affects the receptors in the body for certain areas.
As more sensitive areas such as the hands and face have the most receptors and take up the largest amount of surface area on the cortex, these are most susceptible to numbness.
This numbness can also result in difficulties detecting the temperature of something, which could be a safety issue if an individual is unable to recognize when a surface may be scolding hot, for instance.
Inability to Localize Sensations
Damage could result in individuals being unable to pinpoint on their body where a sensation has taken place.
They may be able to identify the general area where a sensation occurred (e.g., on the left leg) but not precisely.
This general identification is possible due to other brain regions in the cerebral cortex being able to localize as well.
Similarly, someone with damage to this area would have difficulty recognizing things being traced onto their skin, such as being unable to identify what letter has been traced on a hand.
Therefore, if they close their eyes and are asked to identify an object, they may find it difficult to identify whether they are holding a book or a cup, as these may feel the same.
Inability to Judge Weight and Pressure
Another possible symptom of damage is the inability to judge the weight of objects. These individuals would not be able to identify whether an object was heavy or light after carrying it.
Likewise, people with this damage would find difficulty in judging physical pressure.
They may be able to know that pressure has been applied to their bodies but would not be able to identify the degree or severity of the pressure applied.
Phantom Limb Pain
It is relatively common for people who have had a limb amputated to experience sensations in their amputated limb. This is called phantom limb and can cause some pain to individuals suffering from it.
Studies have found that this pain correlates to changes in the primary somatosensory cortex, which is no longer receiving expected input from the amputated limb (Flor, 2003).
References
Coghill, R. R. (2009).Pain: Neuroimaging. Encyclopedia of Neuroscience, 409-414.
Flor, H. (2003). Remapping somatosensory cortex after injury.Advances in neurology, 93, 195-204.
Neuroscientifically Challenged. (2016, March 10).Know your brain: Primary somatosensory cortex. https://www.neuroscientificallychallenged.com/blog/know-your-brain-primary-somatosensory-cortex
Raju, H., & Tadi, P. (2020). Neuroanatomy, Somatosensory Cortex. StatPearls [Internet].
The Human Memory. (2020, November, 25).Somatosensory Cortex. https://human-memory.net/somatosensory-cortex/
Saul McLeod, PhD
BSc (Hons) Psychology, MRes, PhD, University of Manchester
Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.
Olivia Guy-Evans, MSc
BSc (Hons) Psychology, MSc Psychology of Education
Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.
