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How can a missing arm cause pain?
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The question of how intense pain can come from a limb that does not exist (or cannot feel anything) has puzzled scientists for centuries?
However, they are now beginning to unravel the mystery, and know that much of the answer lies in neurons of the brain, not the stump.
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After injury: Invading other brain areas
The touch signals from the entire surface of your body are mapped on the surface of your brain – in a strip between your two ears called your sensory cortex. The area that ‘feels’ your hand is very close to the area for your face.
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Ramachandran in his book ‘The emerging mind’ writes of a man whose right arm had been amputated above the left elbow. ‘ Whilst he was blindfolded, I touched his left cheek. He exclaimed ‘oh my god you are touching my left thumb’ ie his missing phantom thumb. He seemed as surprised as I was. Touching his upper lip produced sensations in his phantom index finger”
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It seems there was a complete map of his missing phantom hand draped over his brain’s face map.
These cortical changes might contribute to the pain from the phantom limb.
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Using mirrors to relieve phantom pain
Ramachandran wanted to test the idea that visual feedback could change the way the cortex operated, and reduce pain from phantom limbs.
He propped a mirror on a table and asked a man with a painful paralysed arm to arrange himself so that when he looked in the mirror he saw the reflection of his good arm in the position of his paralysed arm.
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The idea was to trick his visual system into believing his paralysed arm was moving.
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When the man watched the reflection of his good arm moving, he began to have the sensation that his paralysed arm was moving. That it had begun to obey his brains commands to move.
The man was able to take his arm out of its painful clenched position and reported a huge reduction in pain.
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Subsequent trials have been less effective, but Ramachandran’s ground-breaking studies may well hold the key to reducing pain from phantom limbs.
Giraux and Sirigu have shown that merely training patients to imagine their paralysed arms moving in relation to a moving arm on a screen in front of them can relieve phantom limb pain.
This astounding discovery may well be related to the latest brain scanning studies of Daniel Glaser - discussed in the dancers brain on this web site.
They suggest that these attempts to link the visual and motor systems might be
What’s next
Using the latest motion capture techniques from the film industry, scientists hope to use virtual reality arms to fool people’s brains into seeing movement in their paralysed or missing arm. It’s hoped that this will be an efficient method to reduce pain from phantom limbs.
For more information visit the Wellcome Trust’s website
Try these astounding experiments to explore how your brain perceives your body.
Vilaynur Ramachandran the world-renowned neurologist has investigated phantom limb pain using this rubber arm experiment.
Body image and a rubber arm
The Pinocchio experiment with body image
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