Seven people who had an arm that had been amputated above the elbow were encouraged to learn a particular arm movement that defies biomechanics — turning a hand that’s bent 90 degrees at the wrist the last quarter of a full turn that the hand won’t do. The study participants practiced by imagining that they were moving the phantom limb for five minutes per hour every day until they had achieved the impossible movement or had given up (this took one to four weeks depending on the individual). Four of the participants were successful in feeling the sensation of the impossible movement, the researchers report.
“This shows that body image is constructed in a dynamic manner — it can be changed,” says V.S. Ramachandran, director of the Center for Brain and Cognition at the University of California, San Diego. Previous work by Ramachandran and others has shown that the sensation of a perpetually clenched and painful wrist that often accompanies a phantom limb can be relaxed with a mirror-based therapy: the patient clenches and then unclenches the remaining hand while looking at a boxed mirror that makes it appear both arms are intact. By visualizing both hands unclenching, the patient feels a release in the phantom limb.
To corroborate that the individuals had really learned the new movement (after all, the scientists couldn’t see the phantom limbs) the researchers had them perform a task known as left-right hand judgement before and after their training. The ability to twist the phantom wrist in a new way allowed the participants to react to this task faster than they could before they had learned the impossible move.
Each of the participants who achieved the impossible move also described developing a new wrist joint that allowed the impossible movement. And three of the four reported that moves that were previously possible for the phantom limb were now difficult with their new wrist.
Saturday, October 31, 2009
New wrist joints
At Science News, Rachel Ehrenberg on phantom limbs (link courtesy of GeekPress):