Mighty Mind : Phantom Limb

[Few weeks back I watched a DVD borrowing from Netflix named “The Secrets of Mind”. It is an interesting documentary delving into the deep of human mind, nature and consciousness. It features some work of famous neuroscientist Dr. Vilayanur Ramachandran. This post is mainly a summary of that documentary in my own language]

After the Iraq war, veterans who lost there limbs, sometimes felt unnatural sensations in their lost limbs. How would you explain such phenomenon? For a long time, it was considered as a hoax. Neuroscientists could not accept this as a true sensation because for every sensation there should have some neurons carrying small electric signals to the brain. In the case of phantom limb, this is not possible. Then what?

Dr. Ramachandran made a pioneering work in explaining phantom limb syndrome while providing treatment to one of his patients named Derick Sting. Derick used to feel vivid presence of his left arm in a strange way. When he used to go for a shave, he felt sensation in the left arm which actually does not exist. It was found in some simple experiment that when Derick’s left cheek is touched, he feels that sensation both in his cheek and in the left arm. Dr. Ramachandran got very interested. He knew that different parts of our body are mapped to some part of our brain. For example, the entire left part of the body is mapped to a strip on the right part of the brain known as somatosensory cortex. So he hypothesized that, when a limb gets amputated it looses its connection from brain and that part of the brain does not receive any signal anymore. Now, without any signal, this part becomes thirsty for some sensory signal and gets more and more sensitive to any kind of electric impulses. When some electronic impulses come to the nearby region, it actually catches that signal and gives a false signal to brain regarding a sensation on the person’s lost limb. Therefore, the postulation was the brain undergoes a massive rewiring after the amputation. Dr. Ramachandran got some scornful comments regarding his hypothesis. One strong argument was based on the dogma that the brains wiring is permanent and does not change once it is developed in the fetus. However, Ramachandran’s hypothesis got support when neural images provided support on his side.

Amputation can alter brain’s work not only in receiving signal but also transmitting. A patient used to feel extreme pain like clinching his right hand too much. But there is no right hand in his body. Ramachandran explained this phenomenon like this: When we clinch our hand, it actually sends some feedback to the brain which damps brains signal to clinch. But if the limb is amputated, it does not give any feedback to the brain and as a result brain sends more and more signal which eventually leads to extreme pain.

This problem was solved by the use of a technique named as “mirror-box“. A mirror box is a kind of apparatus where you see the image of your one hand in place of your another hand. Using this box, if a person moves his left hand, he gets an illusion that his right hand is moving. The patient was advised to put both his hands into the mirror-box and move both hands. Through this, he got a visual clue that his hand his moving. This visual information also acted as a feedback to the brain and the pain started to subside. This proved Ramachandrans theory and a very intriguing assertion that even a pain can be a construct of mind.

Interesting Follow Ups

  1. Ramachandran, V. S., Brang, David and McGeoch, Paul D.(2009) “Size reduction using Mirror Visual Feedback (MVF) reduces phantom pain“, Neurocase, 99999:1 DOI 10.1080/13554790903081767
  2. Ramachandran, VS & Hirstein, W (1998). The perception of phantom limbs: The D. O. Hebb lecture. Brain, 121, 1603-1630.
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