Amputees may benefit a lot from new-age bionic phantom arms that not only make them sense the presence of a new limb, but can also provide them with amazing flexibility that could make their body attain anatomically impossible shapes, says a new study.
With practice, people with lost limbs could even learn to envisage their bodies as having changed to an entirely unnatural shape, according to Lorimer Moseley of the University of New South Wales in Sydney, Australia, and Peter Brugger of University Hospital Zurich, Switzerland.
The researchers investigated seven amputees who sensed a phantom arm.
In one task, the amputees were shown pictures of a hand and were asked to say if it was a left or right hand.
Because the hand was shown in an awkward position, the subjects had to imagine moving their phantom hand into the position shown.
In a second task, they were shown pairs of pictures of a hand in two different positions, and asked to imagine making their phantom hand move from one to the other.
In both tasks, it was quicker to make the necessary movement by doing something that would be impossible with a real hand, such as bending it back through the wrist.
The researchers timed their subjects' responses, and could tell whether they were moving their hand in an anatomically correct or anatomically impossible way.
After practising, four of the seven subjects learned how to move their phantom limbs in "impossible" ways, and were able to say how their wrist allowed them to do this.
The joints they described not only allowed them to move their phantom arms in strange ways, but also got in the way of normal movement.
Essentially, they constructed a new body image of their phantom limb.
"The brain truly does change itself," New Scientist quoted Moseley and Brugger as saying.
"The idea that just thinking about movements can change body image is quite surprising," said Henrik Ehrsson, a neuroscientist at the Karolinska Institute in Stockholm, Sweden.
Brugger expects that the findings could be used to help patients with phantom-limb pain.
An amputee might feel as if their phantom hand is always clenching a metal bar, causing pain, but the discovery increases the chance that amputees can learn to get out of such painful positions.
The study has been published in the journal Proceedings of the National Academy of Sciences.