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| Is mirror therapy our best solution for this elusive condition? |
Written by Narik Dubash
Phantom limb phenomenon occupies a relatively unique position in both physiology and psychology. It is thought to occur in as many as 90% of amputees, often manifesting in discomfort or pain. Recurrence of visceral sensations of an appendage that no longer exists seems like a paradox. After all, if the limb and accompanying nerves no longer exist, how can sensation recur? It is a phenomenon that is becoming more widely recognised, and yet advances in medical technology have done little to improve our understanding of its pathology, let alone how to treat such a condition.
One such person to explain how and why phantom limbs manifest is prominent neuroscientist V.S Ramachandran. Ramachandran devoted much of his career to studying unique individuals whose experiences of phantom sensations defy scientific understanding. One case in particular; an individual who reported feeling corresponding sensations in his phantom limb when shaving his face led Ramachandran to believe that the brain may ‘rewire’ itself when specific functions of the brain that have otherwise become dormant are utilised in other areas.
Ramachandran’s theory is simple: the neurons involved in detecting sensation in the now missing limb have nothing to do, so they had somehow started detecting sensation in the face. This relates to brain plasticity, which is the brain’s ability to change and adapt as a result of experience.
But why did the sensation of the hand transfer to the face? That’s a long story but the theory goes that you have your whole body mapped on an area of your brain that deals with perceiving sensations. This isn’t a 1:1 representation of your body and, instead, areas that have the most sensitivity, such as your hands or face, take up a disproportionately large portion of the map. What’s more, the neurons that detect sensations for your hands are neighbouring the neurons that detect sensations for your face. Therefore, without any hand to perceive, these neurons make themselves useful by transferring their function to the neighbouring area, the face.
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| The Penfield map of the skin surface on the brain |
So, having
created a working theory on the origin of phantom limbs, Ramachandran set out
devising a treatment. His solution was simple, yet highly effective. Ramachandran
created the mirror box- an open topped box with mirrors on the panels within.
When patients place their functional limb within the box, the reflection within
simulates the missing limb and the pain and discomfort would dissipate. This,
in effect, would trick the brain. However, this method is somewhat limited as
an effective long-term treatment because of the confined space in which the
illusion can occur.
Now, though,
researchers at Aalborg University, Denmark, are utilising virtual and augmented
reality as a new form of treatment. Advances in virtual and augmented reality
technology has allowed researchers to simulate phantom limbs in more immersive,
lifelike scenarios. The principle of tricking the brain remains, but without
the confinement of the mirror box.
Besides simply
wearing a headset, patients also wear a glove on their functional limb and
several small electrodes on their residual limb. These electrodes are then
stimulated by small electrical impulses to simulate the sensation of the phantom
limb. Together, these individual elements form a complex and visceral illusion
to the patient. Patients are then asked to perform a series of tasks that
require use of both limbs in unison, such as bending a virtual rod or moving
boxes. This provides the patient not only with the visual illusion but with
tactile feedback that the mirror box simply can’t, helping to alleviate the
pain so many report after the loss of a limb.
Research
into the use of virtual reality as a viable treatment for phantom pain is still
in the early stages but so far results appear promising. Research conducted so
far indicates upwards of 85% of patients responding positively to treatment and
reporting complete remission of phantom limb sensation. However, the true
effectiveness may not be known for a while as many of the studies conducted
thus far have focussed on obtaining rich data from a handful of individuals,
rather than testing VR treatment on large volumes of patients. Naturally, with
a medical phenomenon as unique as phantom limb sensation, sufferers often
report varying symptoms and evaluating the effectiveness of a treatment takes
time, as well as a great deal of care and attention.
Phantom limb
phenomenon is likely to continue mystifying the medical field but with advances
in technology come innovative new treatments. Whether there can be a single
treatment for a condition so complex and varied remains to be seen but, perhaps
for now, virtual reality can provide individuals with a reality free of pain
and discomfort.
References:
Henriksen, B., Nielsen, R., Kraus, M., &
Geng, B. (2018). Comparison of Movements in a Virtual Reality Mirror Box
Therapy for Treatment of Lower Limb Phantom Pain. In VISIGRAPP (1:
GRAPP) (pp. 167-174).
Ambron,
E., Miller, A., Kuchenbecker, K. J., Buxbaum, L. J., & Coslett, H. (2018).
immersive low-cost Virtual reality Treatment for Phantom limb Pain: evidence
from Two cases. Frontiers in neurology, 9, 67.