Phantom limbs learn impossible tricks

Oct 28, 2009 by Lin Edwards weblog
The fact that the representation of the face lies adjacent to the representation of the hand and arm in the cortical homunculus is crucial to explaining the origin of phantom limbs. Image: Wikimedia Commons

(PhysOrg.com) -- New research has shown that body images can be formed independently of external sensory inputs, and that the phantom limbs of amputees can be trained to carry out tasks that would be impossible for real limbs.

The researchers, Dr Lorimer Moseley, a clinical neurologist currently at the Prince of Wales Medical Research Institute in Randwick, Australia, and Dr Peter Brugger, a Swiss neuroscientist from the University Hospital in Zurich, wanted to find out if it would be possible to change our purely by thought. They also wondered whether or not the image created would obey the normal laws of physics if the body part did not actually exist.

Before the experiment the scientists used what is known as a left-right hand judgment test to measure reaction times. In this test the subjects were shown images of hands at extremes of an impossible movement of the wrist and measured the time taken for them to decide whether the image was of a right or left hand. Earlier studies have demonstrated that the reaction time corresponds to how long the actual movement to the position shown would take, since the movement is made in the imagination.

They then asked participants to practice imagining they were rotating the hand through 360 degrees as if it was joined to the arm via pivot. The subjects, all amputees with vivid phantom arms and hands, practiced five minutes an hour every day until they had learned, or until they had given up.

Four of the seven amputees were able to imagine and feel the impossible movement. They reported that at first they felt as though they were watching someone else's hand, but as they learned their perception of their wrist changed to one that would allow the movement, and the rotating wrist felt like part of their own body.

After the experiment their reaction times on the left-right hand judgment test were measured again. Those who had learned to mentally make the impossible movement were faster than before.

Moseley said the experiment showed the brain can create a physiologically impossible way of working the body without feedback from outside, and that body image and self awareness can change dramatically without external inputs. He also said they were surprised to learn that after the experiment two of the amputees found it difficult to imagine their phantom limbs carrying out normal tasks, but this suggests the limbs were adhering to a new set of physics rules.

Moseley said the findings may find practical application in the future in training amputees who experience pain in their phantom limbs to change their body image in a way that will remove the pain. There is also a possibility people with movement problems caused by stroke or intense pain could be trained to change their image of the body part to help reduce the pain or improve movement, and that patients with distorted body image (such as anorexia) could learn to imagine a changed body.

The paper was published this week in the Proceedings of the National Academy of Science.

More information: Interdependence of movement and anatomy persists when amputees learn a physiologically impossible movement of their , G. Lorimer Moseleya and P. Brugger, Published online before print October 26, 2009, doi: 10.1073/pnas.0907151106

© 2009 PhysOrg.com

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User comments : 4

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LariAnn
3 / 5 (2) Oct 28, 2009
Could it also be that the "phantom limb" phenomenon is evidence of the existence of a non-physical aspect to being that is not limited by physics? I'm curious as to how much more these ephemeral appendages can be trained to do, such as stretch out as though made of gum rubber, or divide into two or more independently movable appendages.
Simonsez
5 / 5 (1) Oct 28, 2009
Careful there LariAnn, you are suggesting that physics cannot explain everything, and that just will not sit right with some folks who frequently like to comment here. :)

I have to agree though, the findings suggest that the mind--the conscious mind, I should say--is not limited to three dimensions bound by the the DNA-painted picture of the human body. I would like to see more research done into phantom limbs and, as a parallel, research into cybernetics (which currently consists of neural shunt to connect to computer).
fixer
1 / 5 (1) Oct 28, 2009
This is a well known phenommena, most guys immagine that one particular part of their body is larger than life.
I am not sure this article should be classed as science so much as science fiction.
zevkirsh
5 / 5 (2) Oct 29, 2009
it is already well known that the observed neurological patterns exhibited by people using tools reflects an activity pattern that resembles what one would observe if the tool were temporarily 'part of the motor cortex'
the ability to use tools and integrate them seemlessly into the body reflects an underlying plasticity of the brain.

what is the difference in the brains of someone who
a) wakes up with amputated limbs
b) wakes up with a broken leg
c) wakes up and puts on a pair of stilts for fun
d) wakes up and puts on a pair of unused and uncomfortable offbalance sneakers.
....probably very little. the motor cortex would probably exhibit massive flexibility in all cases.

i know i'm no neurologist, but the fact so many observations of neuropathology have contributed SO MUCH to neuroscience , shows that observation and intuition still have a massive role to play in understanding the brain, not just intracellular recordcings, ekg's, mri's and other neurorecording techniques.

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