Phantom limbs make impossible moves

'It's all in the mind', takes on a whole new meaning with research revealing that phantom limbs can be taught to do physiologically impossible tasks.

The research could have ramifications for how we view the interaction between mind and body, and how amputees perceive limbs where there are none.

Clinical neurologist with the Prince of Wales Medical Research Institute, Dr Lorimer Moseley, says it shows for the first time that body images can be formed independent of any outside sensory input.

"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," he said.

Dr Moseley's work, done with Swiss neuroscientist Dr Peter Brugger, appears this week in the journal Proceedings of the National Academy of Science.

Rewiring the brain

When we try to identify an image of a left or right hand we mentally rotate our hands to adopt the position shown. Dr Moseley and Dr Brugger took advantage of this innate ability, measuring how long it took.

By showing images of the hand at two extremes of an impossible wrist movement, it was possible to determine that those manipulating phantom limbs were envisaging a shortcut movement that is anatomically impossible.

But those with real limbs were unable to operate their envisaged wrist in the same way and took the long route. This may be because of the continuous feedback from the existing limb.

The amputees who envisaged the shortcut simultaneously reported a profound change in the internal image of the wrist - they now perceived a wrist that would allow the movement.

"The brain's sense of how to implement this movement depended on the brain reconstructing the limb in order to let this movement happen according to the normal principles of physics," Dr Moseley says.

Dr Moseley says that they were surprised to find that afterwards, the amputees had difficulty envisaging their phantom limbs doing the more routine tasks again.

The researchers believe this implies that our body image must obey Newton's laws, and we may make adjustments to ensure they continue to do that even when the mind is making the rules for itself.

More broadly, it demonstrates that profound changes can occur to body image and self awareness that are independent of outside input. ...

But what is the practical significance of being able to teach imaginary wrists to do impossible things?

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, says Dr Moseley.

via Phantom limbs make impossible moves - ABC News (Australian Broadcasting Corporation).