One day you might not have to ask someone to lend a helping hand–because you’ll have a third arm of your own. At least, that’s a possible application of a mental trick scientists performed on 154 healthy volunteers: These men and women were made to feel as if they had three arms.

To pull off this ruse, the researchers placed a prosthetic arm next to a volunteer’s two real arms, and they touched the subject’s right hand and the rubber hand in exactly the same place at the same time. Because the taps were synchronized, the volunteer’s brain was tricked into feeling them both. According to Science Daily:

“What happens then is that a conflict arises in the brain concerning which of the right hands belongs to the participant’s body,” says Arvid Guterstam, one of the scientists behind the study. “What one could expect is that only one of the hands is experienced as one’s own, presumably the real arm. But what we found, surprisingly, is that the brain solves this conflict by accepting both right hands as part of the body image, and the subjects experience having an extra third arm.”

To prove that the test subjects really were having three-arm experiences, the scientists threatened both the fake and real hands with a knife, and determined that the subjects’ palms sweated the same amount in both circumstances. In other words, they had the same stress levels regardless of whether a real hand or the prosthetic was in danger.

As for applications, the researchers surmise that similar techniques could help someone paralyzed on one side to gain a feeling of ownership over a prosthetic. “It is also conceivable that people with demanding work situations could benefit of an extra arm, such as firemen during rescue operations, or paramedics in the field,” the study’s leader, Henrik Ehrsson, told Science Daily. Hey, what about the rest of us?

See Ed Yong’s post on Not Exactly Rocket Science for more details…

Related Content:
80beats: In a Sensory Hack, What You Touch Affects What You See
80beats: Virtual Reality Gives Out-of-Body-and-Into-Someone-Else’s Experience
80beats: DARPA’s Next Prosthetic Arm Will Connect to Your Brain
Not Exactly Rocket Science: The Quantum Leap effect – creating a body-swapping illusion

Image: Guterstam et al.

One Egyptologist isn’t ready to close the book on the tale of two toes. Once thought to be mere ornamentation for the afterlife, the artificial toes found on two ancient Egyptian mummies may actually be the earliest known prosthetic limbs.

The fake toes in question are the Greville Chester and Tabaketenmut toes. The Greville toe dates to before 600 BC and is made of cartonnage (similar to papier mâché); the Tabaketenmut toe could date as far back as 710 BC and is made mostly of wood, though researchers believe it also contains leather, and it even has a hinge for flexibility.

Jacky Finch, an Egyptologist at the University of Manchester, UK, had a hunch that these artificial toes weren’t just for looks. Not only were the toes rigorously correct in their anatomy, but they also showed signs of wear and tear–which prompted an experiment that has been over 2,000 years in the making.

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It’s a happy ending for Oscar. While lazing in the sun, the British cat lost his two hind paws in a tragic combine harvester accident. But after receiving two bionic paws from Noel Fitzpatrick, a veterinary surgeon based in Surrey, the lucky black cat can now continue crossing many paths.

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Wii rehab might sound like radical intervention for video game addicts, but it’s actually effective physical therapy for patients recovering from strokes, injuries, or surgeries. Otherwise tedious strength and coordination exercises go by a little easier if they involve waving a wireless controller to play virtual bowling, tennis, and golf. But it doesn’t stop there. The next step in video game rehab is “Air Guitar Hero,” which would allow amputees to rock out with the immensely popular Guitar Hero game using a mechanical arm wired to their chest muscles.

As part of a DARPA initiative for prosthetics research, scientists are now able to reroute the nerves that once controlled an amputee’s arm to the chest muscles, where electrodes can then pick up the electromyographic signals to control a mechanical arm. But the process of learning how to accurately control a prosthetic arm, not to mention individual fingers, using only twitches of the chest, can be a slow and discouraging one. So researchers at Johns Hopkins University hacked a Guitar Hero controller so that its color-coded frets could be controlled with signals from the electrodes.

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