The somatosensory cortex processes inputs from various body systems sensitive to touch, including pain, temperature, and proprioception. It is located in the postcentral gyrus and can reorganize itself in response to external events. Damage can cause problems with touch sensation.
The somatosensory cortex is an area of the brain that processes inputs from various body systems that are sensitive to touch. People often think of touch as a one-way sense, but in reality, several sensory experiences are involved, including specific sensitivity to pain and temperature, and the proprioceptive system, which monitors the body’s position 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
Throughout the body, a network of nerve cells react when they experience sensations related to physical perception. Specialized cells react specifically to pain, while others activate in response to passing breezes, pressure, and a wide variety of other sensations, such as the heat of the sun or the chill from an open refrigerator. Impulses travel along these nerves to a part of the brain called the thalamus, which also handles information from other senses, such as vision and hearing, and relays signals to the somatosensory cortex.
Location and structure
The somatosensory cortex is located within an area of the brain called the postcentral gyrus, a structure that forms a band around the center of the cerebral cortex, encompassing both hemispheres. It is close to the motor cortex, which deals with the movement of different parts of the body, and is organized along similar lines in terms of which areas relate to which parts of the body. Different regions of the cortex correspond to inputs from different groups of nerve cells; the largest parts correspond to areas such as the face, which are highly sensitive. Neurons are also organized according to the different types of sensations they respond to, some sensitive to pressure, some to temperature, some to vibration, and so on.
Researchers have identified the precise regions where sensations are interpreted and have developed representative human figures that show proportionally 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 “sensory homunculus” specifically to clarify that it is 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 sensations from these parts of the body, which have many nerve endings, while the other parts have relatively few.
Reorganization
The somatosensory cortex is able to reorganize 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 finger signals on either side. This region of the brain can also adjust 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 dealing with these parts. These are examples of neural plasticity: the ability of parts of the brain to change their function depending on circumstances.
Effects of damage
When part of this area of the brain is damaged due to injury or disease, a person may experience problems relating to their sense of touch. This can take the form of loss of sensation in parts of the body, numbness to temperature, or an inability to recognize objects by touch. When neurological problems that interfere with sensation are identified, a neurologist may conduct tests to determine the source of the problem so that treatment recommendations can be made to the patient.
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