The front part of the parietal lobe contains an area known as the primary somatosensory cortex, also known as the sensory cortex. You can picture the sensory cortex as being located in the middle area of the brain. The sensory cortex receives information from the spinal cord about the sense of touch, pressure, pain, and the perception of the position of body parts and their movements.

Different parts of the body are represented in different areas of the sensory cortex. In general, areas of the body that have many touch receptors on them (such as the hands, face, and legs) have large parts of the sensory cortex devoted to them, whereas areas that have few touch receptors have less parts of this cortex devoted to them. Where each part of the body is located in the sensory cortex is generally the same for all individuals.

When an arm or leg is removed from the body, the area of the sensory cortex that receives touch sensation from those areas is no longer stimulated by the missing body part. The area of the sensory cortex that is no longer being stimulated reorganizes because it is used to being stimulated and cannot handle the loss of sensations. The reorganization happens when nerves from other areas of the sensory cortex make contact with the area of the sensory cortex that is no longer being stimulated. This reorganization can lead to phantom limb symptoms, as is described in more detail below. In general, the greater the reorganization of the sensory cortex, the greater the phantom limb symptoms are.

As an example of the above, if a person loses his arm, he may actually feel that the arm is being touched when someone touches the face. This makes sense because the sensory cortex is normally organized in such a way so that the area that receives sensations from the face is located next to the area that receives sensations from the arm. So in this example, nerve cells in the sensory cortex that deal only with sensations of touch in the arm receive information about sensation of touch in the face, due to the reorganization that occurred. Thus, when the face gets touched, the brain misinterprets the sensation as if the arm was being touched.

The same type of situation can happen when the reproductive organs are touched when someone loses a leg. This is because the primary sensory cortex is normally organized in such a way so that the area that receives sensations about the reproductive organs is located next to the area that receives sensations about the leg. Thus, it is not uncommon for people that lose a leg to complain about leg pain when making love.

2. NERVE DAMAGE OUTSIDE OF THE BRAIN OR SPINAL CORD:

Damage to nerves outside of the brain and spinal cord (namely, those in the leg or arm that has been cut off) can lead to phantom limb pain. Normally, layers of body tissue protect nerve endings from electromagnetic fields that come from outside of the body. An electromagnetic field is a region around a magnet where the force of that magnet and the force of electricity can be felt. It is thought by some that electromagnetic fields can cause irritation to nerve endings.

People with arms and limbs that have been cut off do not have the protection of the nerves by normal layers of body tissue that most people do. Thus, some believe that when the unprotected nerve endings are exposed to electromagnetic fields, this causes irritation, which the brain perceives as pain and other types of discomfort. See the section on treatment for a type of fabric called Farabloc that is used to treat this possible cause.

HOW CAN PHANTOM LIMB BE TREATED?

Getting rid of phantom limb pain is very difficult. In fact, only about 1% of patients with phantom limb that are treated have an improvement in symptoms that lasts more than a year. However, there are some treatments that have shown some promise. No one treatment for phantom pain has been shown to be effective, which is why many doctors suggest combining multiple forms of treatment. As was mentioned earlier, however, phantom limb tends to decrease slowly over time.

As was mentioned above in our section on possible causes of phantom pain, there is a fabric known as Farabloc that is used to treat this condition. The idea behind this treatment is that the specially made fabric can reduce the irritation to the nerves by decreasing exposure to electromagnetic fields (see above for definition).

Another form of treatment for phantom limb is biofeedback. Biofeedback is a technique in which body processes (such as temperature sensation and muscle tension) are made perceptible to the senses in order to control them with the power of thought. By controlling these factors, phantom pain can be reduced. Relaxation techniques, such as hypnosis, are also used to reduce phantom limb symptoms. Hypnosis is a technique in which a person is placed in a mental state that resembles sleep and is given suggestions (such as "you feel less pain now") that the person will accept.

Surgery on the brain, spine, and remaining limb have also been attempted to decrease phantom pain, without much success. Various pain medications and techniques that block nerve impulses have generally not been found to be very helpful either. Phantom pain characterized by burning has responded better to treatments that increase blood flow in the part of the arm or leg that remains. This is because the burning sensations are thought to be due to decreased blood flow. Phantom limb pain characterized by cramping has responded better to treatments that prevent the remaining part of the arm or leg from cramping. Phantom limb pain characterized by shooting pains are harder to treat.

Electrically stimulating the nerves in the stump (a procedure known as transcutaneous electrical nerve stimulation or TENS) can sometimes provide relief of phantom limb symptoms. Exercise, use of the stump, and fitting the stump with an artificial limb can be helpful as well. If nothing works to decrease the pain, a device (known as a dorsal column stimulator) can be used. A dorsal column stimulator stimulates nerves by tiny electrical impulses that are sent through small electrical wires placed on the spinal cord.

WHAT ELSE IS PHANTOM LIMB KNOWN AS?

Phantom limb is also known as pseudesthesia, pseudoesthesia, and stump hallucination.

WHAT IS THE ORIGIN OF THE TERM, PHANTOM LIMB?

The term, "phantom limb" was first used after the Civil War by Silas Weir Mitchell, a famous physician from Philadelphia in the 19th century. The condition became noticeable after the Civil War because many soldiers lost limbs on battle. Phantom comes from the Latin word "phantasma" meaning "something that haunts or disturbs the mind." Limb comes from the Old English word "lim" meaning "major branch of a tree." This came to eventually refer to arms and legs, which resemble the major branch of a tree. Put all the words together and you get "something that haunts or disturbs the mind (about) an arm or a leg."