Amputees are not the only people who have phantom sensations; those with spinal cord injuries, peripheral nerve injury, diabetic neuropathy, and stroke survivors all report similar feelings (4). In each of these instances, deafferentations of the nerves occur, thereby destroying pathways for information to reach the brain. It is research on such patients that will enable researchers to find therapy and medication to alleviate phantom sensations and pain.
One structure commonly implicated in phantom limb syndrome is the motor cortex. The motor cortex is the region of the brain that sends information to motorneurons by representing a map of the body in the brain. Some researchers believe that the nerve cells that served the amputated limb reorganize after amputation to be used by other parts of the body. Others, however, suspect that the brain reorganizes, yet continues to represent the entire limb even after amputation. Data on both of these possibilities exist. Researchers have been able to produce phantom sensations "by stimulating the region of the thalamus found to represent the phantom limb" (5). To counter these effects, it has been suggested that the production of anti-growth factor be stimulated. This would, in turn, prevent new growth and discontinue the effects of the removed limb (5).
Yet, phantom pain can occur by touching other areas of the body (6). Brain imaging has shown that new connections are formed so that "the cortex reorganizes and the neurons that were responding to... input start to respond to other parts of the arm" (6). One may surmise from the research that indeed some sort of reorganization of neurons is taking place to best adapt the body to its new circumstances. Phantom pain is central pain and, therefore, does not respond to substances that block peripheral pain. One researcher suggests that the only way to treat phantom pain is by lesioning the brain centers (6). This is the path that one man took to alleviate his chronic pain after six years of narcotics treatment. In a five-hour surgery, his physician cauterized his spine in 92 places, successfully relieving the pain (7).
Other treatments for phantom pain are subhypnotic propofol testing and extradural cortical stimulation to the primary motor cortex (8). Both of these treatments rely on evidence found from experiments involving the parietal lobe, which is the area of the brain where one processes the most abstract neural functions such as body sensations (including pain) and logic. In more the more extreme cases, such as the man mentioned above, neurectomy, rhizotomy, dorsal root entry zone lesions, chordotomy, and thalamotomy may also be possible routes in pain relief (3). There is also an indication, however, that simple activities such as stroking, tapping, or squeezing the limb, exercising the limb, wearing a prosthesis, shrinker, or ace bandage all may help alleviate phantom pain.
New research is pointing to phantom pain and its associations with spasticity as a means for treatment. GABA, an inhibitory neurotransmitter, is used to treat spasticity and may be a viable option for the treatment of phantom limb pain as well, because of its anti-nociceptive capability (4). Nonciceptors are the receptor cells that respond selectively to noxious stimulation. When anti-nociception is induced (through a drug called baclofen), it reduces the pain threshold, whereas analgesia suppresses the actual pain sensation (4). Baclofen is particularly effective for patients suffering from deafferentation (amputees and spinal cord injury patients) and may be an option other than surgery for those suffering from phantom pain.
Stemming from ideas in phantom limb research, questions of the body's self-awareness arise. Those describing phantom limb tell of definite outlines and movements coming from a part of the body no longer there. Spatial mechanisms in the brain must be interacting in some way with movement mechanisms even after amputation (9). The implications of these ideas are far reaching. If an adult's brain can reorganize to accommodate to a new situation, the possibilities for research in neural flexibility expands immensely. In addition, treatment for phantom pain may be more accessible to patients in the future and prepare those in medicine with ways to prevent the pain (3) and treat these patients.
1) The Cheshire Medical Center Guide for Amputees
2) Poster presented at the Fifth International Conference on Functional Mapping of the Human Brain
4) Spinal Cord Community website
5)Scientists discover phantoms in the brain
6) Vanderbilt University research website