The cells in each primary sensory cortex is arranged according to the plan of the body surface. Each region is a map of the body in which the relative areas devoted to body regions reflect the density of body innervation. Furthermore, parts of the body where we are especially sensitive to touch (like our hands and fingers) send information to a larger area of S1 than do less sensitive body regions (like our shoulder).
The attached picture shows the two homunculi (little men), which represent how we would appear if our body proportions matched cortical representations. As you can see, the hands and face far outweigh other body parts in representation due to innervation. 

Topographic Mapping

Plasticity of the sensory cortex refers to a characteristic of the cortex, that the cortical maps can change with experience. This was demonstrated in an experiment by Merzenich and Jenkins (1993), where they surgically removed the middle finger of the monkey, then found later that the region of cortex that responded to each remaining, adjacent finger expanded.

Plasticity of the Sensory Cortex

An Elite Cafemedia. (n.d.). Primary Somatosensory Cortex (In Blue). Know Your Brain: Primary Somatosensory Cortex. https://www.neuroscientificallychallenged.com/blog/know-your-brain-primary-somatosensory-cortex. 

Primary Somatosensory Cortex

Since more than half of children with Autism Spectrum Disorder (ASD) display sensory over-responsivity, are there differences in brain response, habituation, and connectivity during exposure to sensory stimuli between children with ASD and sensory over-responsivity, compared to neurotypical children?

Neurobiology of sensory symptoms in ASD (research question)

The primary somatosensory cortex (S1) is located in both hemispheres and lies in the postcentral gyrus of the parietal cortex, just behind the central sulcus dividing the parietal lobe from the frontal lobe. Each S1 receives touch information from the opposite side of the body. 
- Topographic Mapping
- Plasticity of the Sensory Cortex

Johns Hopkins University

University of Rochester

A large part of our somatosensory system is responsible for our perception of touch.
- Sensory Organ: Skin
- Dorsal Column System
- Primary Sensory Cortex
- Secondary Sensory Cortex
- Skin sensory receptors

Somatosensory System: Touch

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Skin is the largest organ in the human body. It is responsible for receiving the environmental stimuli that we process when perceiving touch and pain. The skin is made up of three separate layers.
- Epidermis
- Dermis
- Hypodermis

Sensory Organ: Skin

The dorsal column system is the pathway in which the touch receptors that have sent their axons to the spinal cord, have entered the spinal cord through the dorsal horn and turn upward, traveling to the brain along the spinal cord's dorsal column of white matter.
- Dorsal column nuclei
- Dermatome

Dorsal Column System

Primary Sensory Cortex

The secondary somatosensory cortex (S2) maps both sides of the body in registered overlay (ie. the left-arm and right-arm representations occupy the same part of the map and so forth). In recent studies, the S2 has been implicated in information integration, grounded essentially in spatial body maps, allowing humans to form complex relations between the body and the environmental space (establishing a body-in-world map). 

Secondary Sensory Cortex

Sensory neurons located in the skin that respond to various mechanical stimulations. There are 3 main groups of receptors, categorized by what type of stimulus they detect:
- Mechanoreceptors
- Thermoreceptors
- Nociceptors


Skin Receptors

There are anatomical and functional connections between auditory and somatosensory processing. For instance, hearing a rubbing sound and feeling sandpaper with the fingers activates the same part of the cortical area in the caudal auditory region.

Auditory and Somatosensory Processing

Somatosensation, commonly known as the sense of touch, is the sensory system responsible for perceiving contact with the skin.

Touch (Somatosensation)

The pathway for sensory information begins at the skin's receptors and free nerve endings. From there, signals ascend the spinal cord and are relayed through the medulla and thalamus before reaching their final destination for processing in the somatosensory cortex, which is situated in the postcentral gyrus of the parietal lobe.

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