The human brain is easily confused, when circumstances suit it, according to a team at Stockholm’s Karolinska Institute.
Here a volunteer undergoes a series of tests with a plastic arm placed next to her right arm.
Research scientist, Arvid Guterstam, says when the stroking turns into something more threatening the brain overcomes any confusion by responding in the same way for the plastic arm as it does for the real one.
Guterstam says, “The brain surprisingly solves this conflict by accepting both right hands as ones own and the participants experience that they have two right hands – a third artificial arm belonging to their body.”
In 154 tests, the results showed that subjects only showed the stress response when there was the illusion of the prosthetic being a third limb and no response when the right arm was replaced with a left arm or a prosthetic foot.
Associate Professor at the Department of Neuroscience Henrik Ehrsson says, “We were surprised to find that you can actually experience a third arm like three upper limbs which shows that the body image is much more plastic and dynamic than we originally thought.”
Ehrsson says the next step in the project would be to understand the brain mechanisms that produce this feeling.
“We need to understand if we can voluntarily control a third arm, that you can at the same time move three arms simultaneously in a skilled manner. We don’t know if that’s possible but there are some experiments in monkeys that are controlling robotic hands that suggest that it may be possible through plasticity in the brain,” said Ehrsson.
Already damaged limbs are being replaced by robotic prosthetics that can be controlled by the amputee’s thoughts. But the team say in the future we may be able to feel the replacement, as though it were a part of ourselves.
Bottom line: Neuro-scientists have shown it is possible to make healthy volunteers experience the feeling of having three arms. The research, which is at an early stage, could be useful in the future development of prosthetics, making the amputee believe their artificial limb is part of their body.