Editor's Note: Lynette Duncan was a third-place award winner for the 1997 O & P Business News Scholarship Award. Future issues will explore some other theories of phantom pain management; however, we do not promote or advocate any particular theory or treatment. It is interesting to note that a survey conducted in 1980 by R.A. Sherman, C.J. Sherman, and N.G. Gall identified more than 50 unrelated treatments for phantom limb pain in the U.S. at that time.

Phantom limb pain is a phenomenon experienced by 50% to 80% of the amputee population. It is described as any feeling intense enough to be called painful, emitting from the amputated portion of the limb. These feelings are individual and varied. Some phantom limb pains have been described by patients as itching, mild warmth, burning, and squeezing.[1]

The pain can be infrequent, experienced less than two weeks out of the year; or it can be chronic and debilitating. A constant uncontrollable itch on the bottom of a phantom foot left an amputee suicidal.

Along the same lines of phantom limb pain is phantom sensation. Phantom sensation is the feeling that the amputated limb is still intact. One patient could still feel his amputated hand clutch a cup of coffee; another, a double arm amputee, could still feel his arms swing when he walked. There is reported a right-armed amputee who learned to play tennis with his left arm, but still had trouble serving when his phantom arm insisted on holding the racquet. [2]

Sometimes the phantom sensation can telescope to reach objects or be located in an odd position. One amputee felt his phantom arm extend from his shoulder at a right angle. He would always walk through a doorway sideways to avoid hitting his phantom arm. A phantom foot has been felt dangling beneath the residual limb and not physically connected to the body, but still unquestionably belonging to the patient. [3]

Phantom experiences are not limited only to amputees. Spinal cord injury patients also experience phantoms.

Phantom limb pain and sensation should not be confused with stump pain. Stump pain is the feeling of pain such as burning, throbbing, or shooting occurring in the residual limb.  Phantom limb pain and sensation has been addressed for close to 500 years, but the name "phantom" wasn't coined until 1866, when S. Weir Mitchell, an American neurologist, developed the name. Until quite recently, it was considered a "psychological" phenomenon

A recent survey of 2,700 amputee veterans showed that 69% had been told or their physician implied that the phantom was all in their heads. As late as the 1970s, most literature stated that phantom sensations were created from a psychiatric disturbance due to the loss. However, many studies have since shown that persons with phantom pain are no more or less likely to suffer from psychological abnormalities than the population at large. Many amputees have been sent to psychiatrists for physiological conditions. [4]

One of the oldest and more common beliefs involved the cut nerve endings in the stump. The cut nerve ends grow nodules which are known as neuromas. These neuromas continue to generate impulses. The impulses flow through the spinal cord into parts of the brain. These brain areas include the thalamus (a central way station of the brain); then onto the somatosensory areas of the cortex, the presumed centers for sensation.  This is the classical concept of the brain, where neurons fire and transmit signals from the nerve endings through the spinal column to the brain and back as sensations.

Based on this assumption, medical treatments to relieve pain have included cutting the nerves just above the neuroma at the roots.  Pathways in the spinal cord have also been cut and areas of the thalamus and cortex that receive this sensory information have been removed.  Although traditionally this has brought temporary relief to some patients, the pain usually returns. It should also be noted that this procedure never eliminated the phantom sensation, only the pain.

Recent discoveries have clearly directed the path of phantom pain and sensations to the brain; however, the exact cause and cure are still being researched and investigated. In this paper, I will explain what we know, what we think we know, and the research behind the hypotheses. It should be noted, however, that this research is still in its infancy. We do not know for sure exactly what causes phantoms. We can only hypothesize at this time.

One of the foremost hypotheses comes from Ronald Melzack, Ph.D., a professor of Psychology at McGill University and Research Director for the Pain Clinic at Montreal General Hospital. He, of course, agrees that phantoms lie in the brain, but not just in the somatosensory system. He believes far more of the cerebrum is involved. [5]

His theory draws into account that an explanation must be made for the variety of sensations a person feels, and to the extent of reality the patient feels of the phantom-even the free-floating phantoms belong to the self.

Melzack postulates that a network of neurons creates a neuromatrix.  Not only does the brain respond to stimuli, but it continuously generates a pattern of impulses indicating the body is one's own and is intact. He refers to this neuromatrix pattern as a neurosignature. He feels that if the brain operated in this way, signals would emit, creating a sensation of having a limb when the limb no longer existed.

For this hypothesis to work, Melzack believes the neurosignature to be quite extensive and to include at least three major neural circuits. The first is, of course, the classic sensory pathway to the somatosensory cortex via the thalamus as has been previously discussed.

A second system consists of the pathways leading through the reticular formation of the brain stem to the limbic system. This is the system responsible for emotion and motivation. He includes this system because paraplegics who suffer complete severing of the spinal column high in the upper body still report experiencing themselves in their old bodies and describe feeling much like they did before their injury, with these feelings including exhaustion, pain, and pleasure.

The third and final system stems from the cortical regions of the brain.

These regions are responsible for the recognition of self and the evaluation of sensory signals. The parietal lobe is a main player in this region. Studies have shown that patients who have suffered lesions of the parietal lobe in one hemisphere have disowned parts of their bodies. One patient pushed one of his own legs out of the hospital bed, insisting that the leg did not belong to him.

The theory involves a combination of sensory information passing through all three systems working in parallel. The information is shared between the systems, with the information converted to an integrated output which is then sent throughout the brain. This information is then processed in the matrix, which recognizes the neurosignature and the output contains the assurance that the sensation is occurring in one's own body.

The matrix of the brain, Melzack postulates, is largely prewired, dependent more on genes than on experiences. This is due to the number of patients born without limbs who still experience the phantom. This goes against a commonly held belief that those losing limbs before the age of six do not experience phantoms.

An explanation is given for the fading of phantom limb pain and sensation that sometimes occurs over time. It seems that the cerebral neurons that once responded to the amputated limbs develop increasingly strong connections with the remaining intact body parts and eventually begin to serve those areas.

Another researcher in the field of phantoms is neuroscientist Dr. Vilayanur Ramachandran of Scripps Institute in La Jolla, California. His hypothesis revolves around his research on nerve impulses. These nerve impulses or synapses travel through the brain stem signaling other synapses, thus sending the information through the thalamus and up to the somatosensory cortex. He then describes this portion of the brain as being "laid out as a French garden." He notes that nerve impulses beginning in the thumb stimulate an area of the cortex that only serves the thumb. It is located next to an area that serves only the index finger. This "garden" continues digit by digit. The arm lies next to the shoulder, then the trunk. Except for a few unusual pairings (i.e., the toes are laid out next to the genitalia), the body is laid out on the brain in an orderly fashion, with the areas with the most number of nerve endings, for instance, the hands, receiving the most area of cortex space. Ramachandran describes it as "if there exists a tiny, orderly, though distorted version of oneself-a homunculus-outlined on the pleated surface of the brain." [6]

Since the early 1960s, it was a long-held belief that the adult brain was "hardwired" and could not change after a critical growth period in infancy. This belief was centered on a Nobel Prize-winning study by David Hubel and Torsten Wiesel. This study demonstrated that a newborn kitten whose eye was patched during a critical period of neural growth would experience permanent blindness. It showed that during this period the functional eye encroached over the patched eye's allotment of cortex. The patched eye was never able to recover.

Because of the Hubel and Wiesel study, it was long believed that once the brain was "hardwired," it would be unable to change.

Ramachandran's theory suggests that when a limb is missing, the cortex remaps itself. To really explain this theory, I must first explain the two studies, both involving monkeys, from which this theory began.

The first experiment occurred at the University of California at San Francisco in the 1980s with research involving a monkey whose finger was amputated. Researchers Michael Merzenich and Jon Kass of Vanderbilt University discovered that when the fingers on either side of the amputated digit were stimulated, nerve impulses from the neighboring sections appeared to have been remapped into the vacated cortex. At that time it was noted that the distance the nerve impulse traveled across the vacated region of the cortex was the distance of an axon. When two fingers were amputated, the impulse traveled, but the distance wasn't as great. The 1980s monkey research opened a new door in this field. With this study, they began to believe a brain could adapt, but the hardwiring had to remain in place. 

In 1991, a new study from Timothy Pons of the National Institute of Mental Health gave new evidence that began to change what neuroscientists believe as to the way in which a brain could change, grow, and evolve. Pons' study used the twelve "Silver Spring" macaque monkeys. These monkeys had their sensory nerves from one arm cut where it entered the spinal cord.

Animal activists sued, and due to a court order, the research was put on hold while the animal rights trial was tied up in the courts. Twelve years later, it was decided that four of the monkeys had deteriorated to the point where it was in their best interest to be euthanized. Prior to their demise, Pons was allowed to plant electrodes in their cortexes in hope of seeing where 12 years of dormancy would lead. Due to the results of Merzenich's prior experiment, he expected to find a couple of millimeters of encroachment-no more than the length an average nerve axon could reach.

"We were astounded," said Pons. "Instead of a little bit of trespassing from both sides, we discovered that the face region had completely invaded the neighboring cortex. In each of the four animals, the entire hand and arm zone responded when we stimulated the face." [7]

With no stimulation or nerve input coming in from the arms for 12 years, nearly a half inch of cortex (a third of the touch map) changed its alliance to the face.

How this happened is still a mystery. Pons acknowledged, "We don't have the mechanism yet to explain it." Possible explanations suggest that new connections grew between neurons, creating links across the empty area.

This was highly speculative because until this time it was believed that adult brains could not grow any new neurological connections; they were only capable of losing them. Yet there have been even more recent studies on monkeys showing that new axons can sprout from already existing cells in the spinal cord. Pons has hypothesized that the changes in the monkeys may be a consequence of relatively modest growth occurring in more constricted places farther down the touch pathway, before they even reach the cortex. He speculates that one point could be the thalamus (the gatekeeper). Nerve impulses traveling from the face must pass through the thalamus at the same time that it is receiving information from the hands and arms. Usually they just interchange without making connections. Without input from the hand and arm, over time even a little sprouting of axons near the facial nerves passing through the limb's portion can create new synapses.

When the Pons study was announced in 1991, Ramachandran was inspired by the brain's ability to change. For years he had been working on the mystery of blind areas in eye retinas. He was puzzled by how everyone has a blind area about 15 degrees off center, yet we don't walk around with blind spots. He had suspected that this occurred due to the remapping or filling in of synapses delivered to adjacent parts of the visual cortex.

When Ramachandran read Pons' paper, it occurred to him that possible remapping or filling in is what happens to phantom limb sufferers. So in 1993, he began recruiting upper limb amputees for experiments to test his theory. He began with a teenager who had lost an arm in an auto accident only four weeks prior. Ramachandran began his test by brushing a Q-Tip along the volunteer's blindfolded face.

"Where do you feel that?" he asked.

"You are touching my face," said the teenager, "but I also feel my left thumb tingling."

"And here?" asked Ramachandran, stroking the skin above his upper lip.

"You are touching my index finger."

"Now," he said, as he moved the Q-Tip to his upper lip.

"My pinkie."

Ramachandran continued running the Q-Tip along the subject's trunk, intact arm, etc., without any response. But when he touched the Q-Tip to an area just above his stump, he received the response, "There, my thumb tingled again...now my index finger...the ball of my thumb..."

With this study Ramachandraable to neurologically locate his missing limb by touching the areas that border the cortex regions.

One was on his face, the other on his shoulder, just exactly as Pons discovered with the monkeys. This suggested that much of the same cortex encroachment that occurred with the monkeys occurs in phantom limb patients also.

This experiment was performed on six other patients. All of them experienced remapping to some degree. One patient had lost both his arm and shoulder. Ramachandran was able to trace his entire missing forequarter across his face. The shoulder was located in the jaw joint and the elbow across the elbow-like bend of his lower jaw. The hand and fingers were found on his chin.

Another patient, who was not an amputee, but one of the rare individuals who experience phantoms when his nerves were yanked from his spinal cord in an automobile accident, had water dribbled on his face. The patient claims it felt as if water was literally being poured on his arm.

Theories Disagree

One of the most remarkable observations was the short amount of time it took for this remapping to occur. The first volunteer had only lost his arm four weeks prior. Because of this, Ramachandran disagrees with Pons' neuron-sprouting theory, because there just isn't enough time for sprouting to   occur. Ramachandran believes that hidden circuits already exist and, as long as normal stronger inputs occur, the hidden circuits remain dormant. When input stops, the hidden circuits allow for the expansion of one cortical area into another one.

Pons has openly disagreed with Ramachandran's theory, saying that there is no evidence of latent circuits waiting to be unmasked. As I mentioned earlier, there is no known cause as yet for phantoms. There is only speculation and theory. We do know that phantoms are physiological, not psychological. There is mystery waiting at the cortex. More studies need to be performed before relief can be found for many phantom sufferers.

In the meantime, here are some suggestions for alleviating phantom pain.

As stated, at this time there is no cure; surgical cutting of the nodules brings only temporary relief. A recent survey suggests that less than 1% of the respondents found permanent relief from a number of different treatments attempted. [8]

The LEAPS organization adds that some persons who have not found help through home remedies have found help through self-hypnosis, biofeedback, and chiropractic.

As you can tell by these suggestions, none are based on the latest facts stemming from the neurological basis for phantom sensations. Many are based on the theory that phantom pain is caused by circulation constriction.

Many studies on blood flow and temperature during phantom pain sensation and stump pain relative to the intact limb have been performed over the years. It has been reported that many times during stump and phantom pain there is a remarkable difference in the bloof flow and temperature stemming from the stump and that of the intact limb.

These studies have also shown a relationship between the rate of change and the intensity of the pain.

The researchers insist that this does not mean that the rate of blood flow (circulation) causes phantom and stump pain. It could be that the pain subsequently causes the change in blood flow and temperature. [9]

These studies have also led to temperature biofeedback. The patients learn to tell when their blood flows change; thus they attempt to increase blood flow in the stump by attempting to relax, thus dilating the peripheral blood vessels. This increases blood flow to the cool area, thus decreasing the pain's intensity. Researchers state that although this helps some people, circulation is not the cause. If it were, all phantom pains would be stopped, not just some.

Other methods of pain relief include stimulation of the stump with electric currents, acupuncture, and hypnosis. Some patients have found relief from medication that is used to counteract epilepsy.

Another interesting method of pain control that has helped some patients was developed by Dr. Ramachandran, who was mentioned earlier. He developed a mirror box. When an amputee places his remaining limb in the box, the mirrors trick the mind into seeing the missing limb. This has allowed patients to feel like they are actually moving their missing limb. Patients whose pain is such that they feel their fingers clenching into their palms are now able to place their intact arm into the box and let it manipulate their phantom arm, thus moving their phantom fingers away from their palm. This box has actually helped some people. [10]

Due to the cortex research discussed in this paper, we know that the above suggestions are not the cure, although many people have been helped by them. Until a cure is found, anything is worth trying.

Research is continuing and leading us deep into the brain. The research in just the last few years has demonstrated the plasticity of the brain. Not only is this good for phantom limb sufferers, but also for those who suffer from any ailment involving the brain. We are getting closer; but as yet, the exact cause and cure remain a mystery.

Footnotes

1. Phantom Limbs, Ronald Melzack, Scientific American Vol. 266, No. 4, page 120
2. 2. James Shreeve, Touching the Phantom, Discover, June 1993, Vol. 14 No. (not listed)

3. Roger W. Davis, M.D., Phantom Pain and Stump Pain, American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation, Vol. 74, January 1993

4. Lt. Col. Richard A Sherman, Ph.D., and John G. Arena, Ph.D., Phantom Limb Pain: Mechanisms, Incidence, and Treatment, Critical Reviews in Physical and Rehabilitation Medicine 4 (1,2): 1-26 (1992)

5. Melzack

6. Shreeve

7. Touching the Phantom, James Shreeve, Discover, June 1993, Vol. 14,No. 6, page 35

8. Sherman and Arena

9. Roger W. Davis, M.D.

10. Shannon Brownlee, Karen Mitchell, US News and World