Different nerve cells react to various sensations, such as touch, and these signals are ultimately transmitted to the somatosensory cortex.
The somatosensory cortex is an area of the brain that processes data from various systems in the body that are sensitive to touch. People often think of touch as a single sense, but in fact, several different sensory experiences are involved, including specific sensitivity to pain and temperature, and the proprioception system, which monitors the body’s place in space. The somatosensory system as a whole is extremely refined and highly sensitive, allowing people to detect and interpret a wide variety of sensations.
The Somatosensory System
The human brain.
Throughout the body, a network of nerve cells reacts when they experience sensations related to physical perception. Specialized cells react specifically to pain, while others fire in response to passing breezes, pressure, and a wide variety of other sensations, such as heat from the sun or the cold that comes from an open refrigerator. Impulses travel along these nerves to reach a part of the brain called the thalamus, which also handles information from other senses, such as vision and hearing, and passes the signals to the somatosensory cortex.
Location and Structure
Input from various systems of the body that are sensitive to touch is processed in the somatosensory cortex of the brain.
The somatosensory cortex is located within an area of the brain called the postcentral gyrus, a structure that forms a band around the middle of the cerebral cortex, spanning both hemispheres. It’s close to the motor cortex, which deals with the movement of different parts of the body, and it’s organized along similar lines in terms of which areas relate to which parts of the body. Different regions of the cortex correspond to the input of different groups of nerve cells; the larger parts correspond to areas such as the face, which are highly sensitive. Neurons are also organized according to the different types of sensation they respond to, some sensitive to pressure, some to temperature, some to vibration, and so on.
A neurologist may perform tests to evaluate disorders of the somatosensory cortex.
The researchers identified the precise regions where sensations are interpreted and arrived at representative human figures that proportionately show how much of the brain is devoted to sensation from various areas of the body. The technical term for such a figure is a homunculus, or “little man”, and people may refer to a particular “sensory homunculus” to make it clear that they mean a visual representation of the somatosensory system. The figure’s head and hands are very large compared to other parts of the body, such as the limbs and torso. This is because much of this region of the brain is devoted to the sensations of these parts of the body, which have many nerve endings, while the other parts have relatively few.
Neurons in the somatosensory cortex are organized according to the types of sensation to which they respond.
The somatosensory cortex is capable of reorganizing itself to some extent in response to external events. For example, if a finger is amputated, the corresponding part of the cortex can be “rewired” to respond to signals from fingers on either side. This region of the brain can also adjust according to the amount of stimulation it receives from different parts of the body. An increase in the use of certain fingers, for example, will lead to an increase in the amount of cortex that handles those parts. These are examples of neural plasticity: the ability of parts of the brain to change their function according to circumstances.
When part of this area of the brain is damaged by injury or illness, a person may have problems related to touch. This can take the form of loss of sensation in some parts of the body, insensitivity to temperature, or an inability to recognize objects by touch. When neurological problems that interfere with sensation are identified, a neurologist can perform tests to determine the source of the problem so that treatment recommendations can be made to the patient.