Whether it's due to an accident, combat or disease - losing a limb affects your body and mind.
In fact, many amputees say they can still feel the presence of a missing arm or leg.
It's known as a phantom limb.
Researchers are looking at how limb illusions could impact amputees.
"You don't go back to the same person, you kind of reinvent yourself,” said Mike Morgan, an amputee who lost his arm in an accident.
Morgan is one of 1.7 million Americans living with a lost limb. Swedish researchers believe he could be helped by tricking the brain.
"Our results demonstrate that the human brain has the ability to represent three arms simultaneously,” said Dr. Arvid Guterstam of the Karolinska Institute in Sweden.
Here's how it works: a rubber arm is placed next to a participant's right arm...the illusion won't work with the left. Then the two hands are simultaneously stroked by a brush.
In less than a minute, the participant feels like she has two right arms.
"It's really weird because you see the brushing and you feel it on both hands,” said one participant.
Neuroscientists also threatened the fake hand with a kitchen knife to measure the physiological reaction.
"You see this stress response,” said Dr. Guterstam.
The results could lead to new advances in prosthetics for amputees or rehabilitation options for stroke patients.
"For instance a stroke patient, paralyzed on one side of the body could maybe experience an extra robotic arm helping them out on the paralyzed part of the body,” Dr. Guterstam said.
A precious gift for people like Morgan.
"The first thing I would do if I got my arm back would be, I’d give my kids a hug with two hands so I could feel it."
The third-arm illusion only works with the right arm because it seems to rely on the area of the brain that controls your right arm.
In earlier illusion projects at the Karolinska Institute, scientists were able to make people perceive the bodies of mannequins and other people as their own.
Researchers say that study could be useful in virtual reality and robot technology.
CREATING THE ILLUSION: Researchers at the Karolinska Institute in Stockholm conducted an unusual experiment aimed at creating the illusion - and physical sensation - of having a third arm. While the traditional "phantom limb" experiments used mirrors to trick people into thinking a prosthetic arm was their own, this experiment put the fake one right out on the table next to the real thing. In five separate laboratory experiments, 154 volunteers were seated with their hands on a table and a rubber arm was placed next to their right arm. A sheet covered their shoulders and elbows, creating the illusion that the person had three arms. ( Source: Science Daily)
STUDY FINDINGS: 7 out of 10 participants experienced the sensation of having a third hand. The reason may be that the visual illusion creates a conflict for the brain. But instead of settling on just one arm as the real thing, the brain accepts both right hands as part of the body, causing the subjects to experience the sensation of having a third arm. To prove that the prosthetic arm was truly experienced as a third arm, the scientist 'threatened' either the prosthetic hand or the real hand with a kitchen knife, and measured the degree of sweating of the palm as a physiological response to this provocation. The results demonstrated that the subjects had the same stress response when the prosthetic hand was threatened as when the real hand was, but only during the periods when they experienced the third arm illusion. For instance, there was no stress reaction when the prosthetic right arm was replaced with a left arm or a prosthetic foot. ( Source: The New York Times )
HELPING THE ONES IN NEED: Approximately two million people in the United States are living with amputations, according to the Amputee Coalition, a national advocacy group. The results of the study may benefit patients by creating new applications in prosthetics research.
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Department of Neuroscience