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Amputees learn a physiologically impossible movement of their phantom limb



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For those who missed ABC’s Australian coverage – here is the link to our article just published in the PNAS with extracts and news coverage.

Interdependence of movement and anatomy persists when amputees learn a physiologically impossible movement of their phantom limb

G. Lorimer Moseley  and P. Brugger


The feeling we have of our own body, sometimes called ‘body image’, is fundamental to self-awareness. However, by altering sensory input, the body image can be modified into impossible configurations. Can impossible movements of the body image be conjured solely via internally generated mechanisms, and, if so, do the structural characteristics of the body image modify to accommodate the new movements? We encouraged seven amputees with a vivid phantom arm to learn to perform a phantom wrist movement that defied normal anatomical constraints. Four reported success. Learning the impossible movement coincided in time with a profound change in the body image of the arm, including a sense of ownership and agency over a modified wrist joint. Remarkably, some previous movements and functional tasks involving the phantom arm became more difficult once the shift in body image had occurred. Crucially, these introspective reports were corroborated by robust empirical data from motor imagery tasks, about which amputees were naïve and to which assessors were blind.

These results provide evidence that: a completely novel body image can be constructed solely by internally generated mechanisms; that the interdependence between movement repertoire and structural constraints of the body persists even when the structural constraints imparted by the body do not-the body image we construct still constrains imagined movements; and that motor learning does not necessarily need sensory feedback from the body or external feedback about task performance.

For the full article see PNAS October 26, 2009, online edition

Science Blogs did a great write up of this: Phantom limbs can contort into impossible configurations

Or as reported in Reuters Health News: Amputees defy anatomy, learn to move phantom limbs:

The findings show that the brain can alter how we perceive our bodies all by itself, without input from our senses… and raise the possibility of using similar strategies to treat certain movement problems and pain syndromes.

Our sense of our own body, sometimes called our “body image,” is something we take for granted, Dr. G. Lorimer Mosely of the University of Oxford in the UK and Dr. P. Brugger of University Hospital Zurich in Switzerland note in their report in the Proceedings of the National Academy of Sciences. But this image can be altered in many neurological or psychiatric conditions, they add, and can even be manipulated in healthy people.

The findings suggest that “the brain truly does change itself,” Mosely and Brugger say.  The findings raise the “speculative, but not outrageous” possibility that patients could cope with movement problems due to stroke, back pain, or pain in other regions of the body, by being trained to change the image of that body part…

ABC Science: Phantom limbs make impossible moves

The experiment shows that the brain can create a completely new way of working the body and it can do that without any external feedback… In the near future, the findings could potentially be used to help guide amputees experiencing acute pain in phantom limbs to internally adjust their body image in a way that will remove the pain..”

and ScienceNews: Redefining self, phantom self

It is very surprising that anybody — amputees or not — can learn impossible movements just by thinking about it,” comments neuroscientist Henrik Ehrsson of the Karolinska Institutet in Stockholm.

Treatment of people with phantom limb pain usually requires starting a new conversation between the brain and the environment, typically accomplished through visual feedback… The work suggests that people with a distorted body image — such as those with anorexia — may be able to alter their self-image by imagining a change to the body… and those getting neural reconstructive surgery may be able to practice using their new body parts by simply imagining their use…

Postscript: see also write up in the New Scientist: Lost limb leads to flexible new body image

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