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Biology 202
2004 First Web Paper
On Serendip

The Gaps between Science and Behavior in Understanding Phantom Sensations

Debbie Yi

In March of 2003, my sister, Christine was in a horrible accident. She tripped off the
platform of the subway station near our New York City apartment and fell into the gap
between the platform and the train; as a result she lost all of the tissue and skin on and
below her knee and is today a below-knee amputee. During the 5 operations needed to
remove the tattered limb and close the wound, the vascular orthopedic surgeons were able
to successfully save her upper leg and create a "residual limb" or "stump." The limb
remained swollen and discharged blood for a couple of months, but gradually, raised
blood vessels and a neuroma, a ball of nerve fibers, formed at the end of her stump (1).

Following the accident, I spent between 5 to 10 hours with Christine everyday. I
monitored her convalescence as well as her initiation into a new life as a below-knee
amputee. Immediately after the amputation, she experienced phantom sensations in her
residual limb, which is common among amputees. It is believed that 50% to 80% of
amputees experience phantom pain (2). In an attempt to better
understand the behaviors of both my sister and her phantom limb, I researched the
scientific explanations for her behavior. To what extent is science helpful in
understanding my sister's case?

Phantom sensations vary in type and in degree. The types of different sensations felt by
amputees include warmth, itching, pressure, shocking, wetness, and the feeling that the
limb is in a certain position, among others. When they become cramping, stabbing, and
intense shocking, they are classified as phantom pains (2).

One of the original explanations of phantom sensations is rooted in the somatosensory
complex, the part of the brain presumed to cause sensation. According to this hypothesis,
neuromas continue to create impulses, and that the impulses travel through the spinal
cord and thalamus to the somatosensory cortex. After a limb is amputated, the nerve
paths still exist; therefore, stimulation anywhere along the nerve path to the homunculus
(a part of the somatosensory cortex similar to a miniature map of the human body (3)) can elicit the same sensation as when the limb did exist (2). This would imply that the brain is hard-wired and that the brain
doesn't realize that the amputated limb no longer exists.

A subsequent hypothesis initiated by Ronald Melzack proposes that the origin of
phantom limbs is in the brain and more focused in the cerebrum than the somatosensory
cortex. According to Melzack, the brain has a neuromatrix (network of neurons) that
creates impulses indicating one's own body, which he calls the "neurosignature" (2). The matrix consists of 3 subunits: the classical sensory pathway,
the limbic system which manages emotion, and the cortical systems which recognize self
and assess sensory signals.

Melzack believes that sensory signals received from the periphery are evaluated by all
three systems and generated into a single output which then receives its specific
neurosignature. The neurosignature is determined by the neurons in the matrix and their
connectivity. The connectivity is determined for the most part by genes and less so by
experience (4). According to Melzack, neuromas can generate an
input which will subsequently travel through the same neuromatrix as a traditional
external input. As a result, a similar output would be generated and the limb would be
perceived to exist.

A new train of thought among scientists is that once an appendage is severed, the
receptive fields go silent and then become active again through other parts of the body.
Vilayanur Ramachandran at the University of California in San Diego has most
extensively studied this theory of cortical reorganization. Through experimentation with
this theory, Ramachandran found that while brushing the body surface of an amputee
with a Q-tip, he was able to evoke sensations in the phantom limb. There were localized
references areas which yielded responses in the lost appendage. More specifically,
Ramachandran found an area of the chest which corresponded to a lost leg and areas of
the face and chin which corresponded to a lost arm. The localized field was not specific
to a patient; rather, Ramachandran found the field on the chin area on a majority of the
patients who had arm amputations with whom he worked with. Pressure and water on the
reference area would elicit responses in the phantom, as well (5).

Ramachandran also developed the mirror box technique. The mirror box technique
consists of a box which is halved by a mirror. The patient can only see one half of the
box. Once the patient puts his "good" leg into the box, the mirror produces a
"sterioisomeric image (5)" of the other leg. For example, if the
participant has an amputated right lower leg, he would put both legs on opposite sides of
the mirror and then the right half would be covered. The mirror mimics the left leg's
actions and the participant perceives this manipulated reflection as his right leg. When
participants kept their eyes open, 4 out of 5 patients claimed that they felt relief from
being able to move their once-phantom limb in or out of positions. This would imply that
the phantom limb is a creation of the brain and that relief can come from satisfying the
brain by maneuvering the image and making oneself believe that the phantom limb
actually exists.

In order to test each of these hypotheses, I compared the theories to my sister Christine's
actual behavior. Regarding phantom sensations, Christine most commonly feels
shocking and itching. The shocking is throughout her entire right leg, and the itching
emanates from what she perceives as her right foot. A few times, Christine has actually
felt as though her leg was wet like she had stepped in a puddle. According to the original
hypothesis on phantom sensations, neuromas can generate random signals and cause the
same sensations that had occurred prior to amputation. What would explain the feeling
of moisture covering her right foot when the neuroma at the end of Christine's stump was
not wet? It is plausible that random firings could cause feelings of shock and pressure,
but random signals have not yet been shown to cause the feeling of wetness in amputees.
This is still a mystery which science has not been able to answer.

If the brain is hard-wired but occasionally malleable to experiences, what type of
experience would interrupt the hard wiring? On numerous occasions, Christine has
tripped and tried to maintain her balance by landing on her right leg and has
unfortunately crashed down on her residual limb. Her brain tells her that she still has a
right lower leg, but when she looks down at her leg it is not there. In split-second
decisions, such as trying to break a fall, Christine instinctively tries to land on her right
leg. If the brain cannot be re-wired to recognize that her lower leg no longer exists, what
type of life experience merits resculpting of the neuromatrix? Is this a matter of habit
rather than a faulty neuromatrix?

According to Ramachandran's theory, sensations are referred to different locations
following amputation of a limb. The Q-tip method was intriguing and to test its findings,
I blindfolded Christine and brushed a Q-tip along her chest. If the chest was a reference
area for the lost leg, Ramachandran's theory could possibly explain phantom wetness.
The Q-tip method did not arouse any sensations in Christine's phantom limb. In addition,
the wet Q-tip test did not yield any results.

Proponents of the principles behind Ramachandran's mirror box technique believe that
phantom sensations are attributed to the brain. If the principles are valid, my sister
should receive a sense of satisfaction in believing that her limb receives the attention it
needs. For example, when her leg is itchy, if she can convince her brain that her leg is
being scratched, even though it is not, she should feel a sense of relief. In trying to
mimic what the mirror box provides for participants, I recommended the following
technique to Christine: I asked her to imagine that her leg was still intact and to scratch
where the foot would be located when the foot was itchy (when Christine has phantom
sensations and pains, she can envision where the feeling is radiating from). This method
provided no relief for Christine. Instead, she tapped and rubbed the bottom of her stump.
Since that method was unsuccessful, I asked her to monitor her own actions when she had
the itchy sensation in her phantom limb. Typically, when she is wearing her prosthesis,
she will unconsciously scratch the part of the prosthetic leg which corresponds to the part
of her leg or foot which feels itchy. She noticed that she would reach down, scratch, and
then realize afterwards that her leg was prosthetic when there was no relief from her
scratching. In Christine's case, Ramachandran's hypothesis was incorrect. Even when
she was "tricked" into believing her prosthetic leg was her own right leg, scratching it
offered no solace.

Although I have studied only Christine's case extensively, I asked other amputees to
contribute their own experiences while I was conducting my research. Three additional
amputees reported that the Q-tip test did not work and that nurturing the prosthesis did
not provide any relief for phantom pain. This leads me to believe that there is a gap
between the scientific explanations for phantom sensations and what I have witnessed in
Christine's behavior towards her phantom limb.

One of the hypotheses that seems reasonable for Christine's case is in the same vein as
Melzack's theory and is credited to Timothy Pons of the National Institute of Mental
Health. His studies indicate that other locations which were previously dormant along
the nerve path of an amputated limb are unmasked and that a "neural reorganization (6)" occurs following amputation. In addition, since Ramachandran
did have many successful case studies in both his aforementioned projects, the Q-tip test
and the mirrored box technique, it is plausible that Ramachandran's science helps to
understand the behavior of a certain population of amputees.

At this point in time, each scientific explanation for phantom limbs, sensations, and pains
seems to have credit-worthy aspects, as well as flaws in trying to understand phantom
sensations for amputees as a whole. Aforementioned research leads to further questions
as to what extent the brain is pre-wired. Christine's behavior seems to exhibit that there
is a lack of communication between the physical reality and conscious and subconscious
understandings, though experiences of amputees differ. It may therefore be worthwhile
for scientists to study phantom limbs on an individualized basis. The origin of phantom
sensations could be dependent upon the type of injury or the specific cause for
amputation. Comparing each explanation to Christine's actual behavior leads me to
believe that different amputees experience phantom sensations for diverse reasons and
that varying sensations are potentially caused by different mechanisms, as well.


1) Amputee-Related Terms, A glossary of amputee-related terms

2) Electromyography webpage, An overview of specific phantom pains

3) Neurological Theories , An interesting discussion on
phantom limbs in a less technical voice

4) "Phantom Limbs," Scientific American, April 1992, 120-126
~ A good foundation for understanding phantom limbs

5) Phantom Limb Disorder , A thorough overview of phantom limbs and
phantom sensations and research regarding the topics

6) Touching the Phantom , A fascinating description of the research
of Melzack, Pons, and Ramachandran

Further Reading

BBCi Website
, BBC interview with Vilayanur Ramachandran

Mirror Box Technique, A description of the mirror box technique

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