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Phantom Pain: Unlocking a Mystery
By Miki Fairley An accomplished amateur athlete named John had lost
his left arm just below the elbow. "When I play tennis, my phantom
will do what it's supposed to do," John said. "It'll want to throw
the ball up when I serve or it will give me balance in a hard shot.
It's always trying to grab the phone. It even waves for the check
in restaurants," he laughed.
 This experience is from Public Broadcasting
Service (PBS) online and is a case from "Ramachandran's Notebook" (
www.pbs.org).
Vilayanur Ramachandran, director of the Center for Brain and
Cognition at the University of California-San Diego and adjunct
professor of biology at the Salk Institute for Biological Studies,
San Diego, has been called a Sherlock Holmes of neuroscience. Among
his many noted accomplishments in the realm of neuroscience are the
strides he has made toward understanding phantom limb pain and
sensation. More about his ground-breaking work will be discussed
later in this article.
Pain and Sensation
A Philadelphia, Pennsylvania, physician coined the phrase
"phantom limb" shortly after the Civil War, when thousands of
soldiers underwent limb amputations, with phantom pain and
sensations arising. In one study of over 7,000 military amputees,
over 80 percent reported phantom pain. The type of pain can vary;
for instance, being felt as burning, stinging, cramping, shooting,
and twisting.
"Phantom sensation" is a feeling that the missing limb is still
present. "Just after the amputation, the phantom usually feels as
though it is the same size and shape as the amputated portion of
the limb," says LTC Richard A. Sherman, PhD, chief of the Surgical
Research Service, Madigan Army Medical Center, Tacoma, Washington,
in his book, Pain after Amputation--a Lifelong Problem?
"Most people feel that they can move and control it as well as they
could control the limb itself," he adds. "The sensations are so
real and normal that many young, traumatic lower-limb amputees
frequently try to get up and walk away a day or so after their
amputations.
"Phantom sensations normally include all the sensations you
would feel in an attached limb, including a sense of position,
temperature, itching, and very occasionally, a ring or other item
worn for many years," he continues. "The phantom frequently rests
in the last position the limb was in before it was amputated."
'Telescoping' Limb
Sherman then discusses "telescoping," noting that as time
passes, the limb's shape becomes less vivid. For example, a
below-knee amputee can at first feel the calf, ankle, and foot.
Gradually the foot "telescopes" into the end of the residual limb
so that eventually the calf and ankle seem to have disappeared.
However, telescoping doesn't happen if phantom pain is present, and
if phantom pain occurs even years after the amputation, the phantom
"grows" to its original shape and vividness, Sherman says.
John, mentioned in "Ramachandran's Notebook," had a telescoped
phantom hand, feeling as though it were attached directly to the
residual limb with no arm in between. "However, if an object such
as a teacup were placed a foot or two away from the stump, he could
try to reach for it," says Ramachandran. "When he did this, his
phantom no longer remained attached to his stump, but felt as if it
were zooming out to grab the cup.
"On a whim, I started thinking, What if I ask John to reach out
and grab this cup, but pull it away from him before he "touches" it
with his phantom? Will the phantom stretch out, like a cartoon
character's rubbery arm, or will it stop at a natural arm's length?
How far can I move the cup away before John will say he can't reach
it?...Or will the physical limitations that apply to a real arm
also apply to the phantom?'"
So Ramachandran placed a cup in front of John and asked him to
grab it. Just as John reached for the cup, Ramachandran yanked it
away. What happened?
"Ow!" John yelled. "Don't do that!...I had just got my fingers
around the cup handle when you pulled it. That really hurts!"
In the notebook, Ramachandran ponders, "Hold on a minute. I
wrench a real cup from phantom fingers and the person yells, Ouch!'
The fingers were illusory, of course, but the pain was
real--indeed, so intense that I dared not repeat the
experiment."
Brain 'Remapping'
These startling experiences illustrate the depth of the mystery
of mind and body regarding phantom pain and sensation--a mystery
that is beginning to be somewhat revealed.
According to the National Institute of Neurological Disorders
and Stroke (NINDS) of the National Institutes of Health (NIH),
"Scientists believe that following amputation, nerve cells rewire'
themselves and continue to receive messages, resulting in a
remapping of the brain's circuitry. The brain's ability to
restructure itself, to change and adapt following injury, is called
plasticity.'"
Understanding of phantom pain has improved tremendously in
recent years, NINDS notes, explaining that investigators previously
believed that brain cells affected by amputation simply died off.
They attributed pain at the amputation site to irritation of nerves
located near the residual limb.
"Now, using imaging techniques such as positron emission
tomography (PET) and magnetic resonance imaging (MRI), scientists
can actually visualize increased activity in the brain's cortex
when an individual feels phantom pain," the NINDS website ( www.ninds.nih.gov) explains. "When study
participants move the stump of an amputated limb, neurons in the
brain remain dynamic and excitable. Surprising, the brain's cells
can be stimulated by other body parts, often those located closest
to the missing limb."
In the mid-20th century, Canadian neurosurgeon Wilder Penfield,
MD, discovered that the entire surface of a person's body is mapped
on the surface of the brain, according to "Ramachandran's
Notebook." When a certain body part, such as a foot, is touched,
neurons in the part of the brain mapped for the foot respond.
Tim Pons, PhD, of the NIH, and his colleagues found that, while
working with monkeys, sensory information coming from a body part,
such as the face, could invade cells for the part of the brain
mapped for a dysfunctional body part, such as a paralyzed arm. The
brain thus began to modify Penfield's map when part of it was no
longer receiving impulses.
Neurons in the brains of adult monkeys grow and make new
connections in somatosensory areas when they are massively deprived
of sensory input, according to a paper in the April 25, 2000, issue
of PNAS, the Proceedings of the National Academy of
Sciences ( www.pnas.org). This strongly suggests that
neuronal growth underlies the brain's reorganization following such
injuries, according to the writers: Neeraj Jain and Sherre L.
Florence, psychology professors at Vanderbilt University,
Nashville, Tennessee; Hui-Xin Qi, research associate; and Jon H.
Kass, psychology professor, also of Vanderbilt.
"We have suspected for some time that this is the case," says
Jain. "But, until recently, the prevailing view has been that this
kind of regenerative growth is unlikely to occur in adult brains.
Hopefully, this new insight will suggest ways to stop or reverse
phantom limb sensations..."
Ramachandran also wondered about the "mapping."
By blindfolding Tom, an upper-limb amputee, so he couldn't see
where he was being touched, Ramachandran took a Q-tip and starting
stroking various parts of his body surface and asked Tom where he
felt the sensations. For instance, he moved the Q-tip to Tom's
upper lip. To Tom, it felt that Ramachandran was not only touching
his lip, but also his missing index finger.
"I soon found a complete map of Tom's phantom hand--on his
face!" reports Ramachandran. "I realized that what I was seeing was
perhaps a direct perceptual correlate of the remapping that Tim
Pons had seen in his monkeys. For there is no other way of
explaining why touching an area so far from the stump--namely the
face--should generate sensations in the phantom hand; the secret
lies in the peculiar mapping of body parts in the brain, with the
face lying right beside the hand."
Ramachandran encountered another amazing phenomenon: "&I
also found a second, beautifully laid out map' of his missing
hand--tucked into his left upper arm a few inches above the line of
amputation. Stroking the skin surface on this second map also
evoked precisely localized sensations on the individual
fingers&"
Virtual and Augmented Reality Technology
More research has continued, with the goal of stopping phantom
pain and sensations. One promising avenue uses "virtual reality"
(VR) and "augmented reality" (AR) technology. What is the
difference? According to Jim Vallino, Department of Software
Engineering, Rochester Institute of Technology, Rochester, New
York, "virtual reality" has been defined as "a computer-generated,
interactive, three-dimensional environment in which a person is
immersed."
"Augmented reality" is an area of virtual reality in which a
composite view is generated for the user, Vallino notes on the
Rochester Institute website ( www.se.rit.edu). "It is a combination of the
real scene viewed by the user and a virtual scene generated by the
computer that augments the scene with additional information," he
explains.
Thranhardt Lecture
VR and AR research relative to phantom limb pain was a subject
of one of the Thranhardt lectures during the 2004 Annual Meeting
and Scientific Symposium of the American Academy of Orthotists
& Prosthetists (AAOP) in New Orleans, Louisiana. Presented by
Malcolm MacLachlan, PhD, of the Trinity Psychoprosthetics Group,
Trinity College, University of Dublin, Ireland, the study also
involved researchers from the Cappagh National Orthopaedic
Hospital, Dublin; IDS Ltd., Dublin; the Depart-ment of Electronic
& Electrical Engineering, University College, Dublin; MIT Media
Lab Europe, Dublin; and the Department of Psychology, Cardiff
University, Wales.
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Dr. Olga Horgan, Dublin Psychoprosthetics Group, demonstrates Ramachandran’s “Mirror Box Illusion.” Photo courtesy of Dublin Psychoprosthetics Group. |
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The discussion noted that previous research on
referred phantom sensation from body parts represented on adjoining
regions of the somatosensory cortex to the phantom limb "has been
interpreted as a dramatic indication of rapid cortical remapping'
post-amputation." Of particular interest has been evidence that
greater neural plasticity is associated with more severe phantom
limb pain, MacLachlan noted in a proceedings paper for the
lecture.
The lecture mentioned experimentally induced phantom
experiences, such as the "Mirror Box Illusion" used by Ramachandran
and colleagues. People with upper-limb amputations were asked to
place their intact arm into a box, with a mirror down the mid-line,
so that when viewed from slightly off-center, the reflection of
their arm gave the impression of having two intact arms.
However, a regular mirror reflects the image of the intact limb,
while the way the phantom is perceived and experienced may differ
greatly from both the original limb before amputation and from the
remaining intact limb.
For instance, for some persons, the phantom limb may be shorter,
longer, continuous, or have "gaps" in it, in comparison to the
original limb. This may explain why the "Mirror Box" technique was
therapeutically positive for some people, but for others had only
moderate effectiveness or none at all.
"We have developed VR technology to produce authentic phantom
limbs' by giving preeminence to people's descriptions of their own
phantom experiences and encoding these into the parameters used to
generate the virtual phantom image," MacLachlan said.
Potential Technology Applications
VR technology has the potential to reduce or remove phantom limb
pain, according to MacLachlan. Also for elective amputations,
preoperative use of AR technology "offers a unique opportunity to
enhance patients' preparation for post-amputation changes in their
physical appearance, and thus potentially reduce post-operative
shock and trauma."
A prosthesis may be invested with a person's emotional response
to their limb loss: it may come to embody ability or disability,
MacLachlan said. "We believe that there is great potential for
virtual and augmented reality to allow people to further customize
their prosthetic limbs, through trying on' a broad range of designs
prior to fitting, in order that prosthesis users can contribute
more fully to their personalized development."
He added, "Perhaps the greatest challenge to our increasingly
sophisticated technology is to consider not just the
biotechnological ramifications for body function, but also the
psychosocial implications for body image and overall
wellbeing."
For more information, visit www.tcd.ie/Psychoprosthetics 
Table Of Contents - May 2004
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