April 12, 2013
Illusionary Limb Study Investigates Phantom Pain In Amputees
[ Watch the Video: Scientists Create Phantom Sensations in Non-Amputees ]
redOrbit Staff & Wire Reports - Your Universe Online
Writing in the Journal of Cognitive Neuroscience, lead author Arvid Guterstam and colleagues describe how they were able to create a “perceptual illusion” in which healthy study participants experienced the sensation of having a phantom hand.
In the experiment, one of 234 volunteers recruited for the study sat at a table with his or her right arm placed behind a screen so that he or she could not see it. In order to create the illusion, the researcher touched the participant´s right hand with a small paintbrush. At the same time, the investigator mimicked the exact same movements with a second paintbrush in mid-air in such a way that the volunteer would be able to clearly see it.
“We discovered that most participants, within less than a minute, transfer the sensation of touch to the region of empty space where they see the paintbrush move, and experience an invisible hand in that position,” Guterstam said in a statement. “Previous research has shown that non-bodily objects, such as a block of wood, cannot be experienced as one's own hand, so we were extremely surprised to find that the brain can accept an invisible hand as part of the body.”
To prove that the illusion actually worked, the researchers took a knife and make a faux stabbing motion towards the empty space supposedly occupied by the invisible hand. The test subject´s sweat response to that activity was measured, and the researchers found that each individual´s stress responses were elevated while experiencing the illusion but remained steady when that illusion was broken, the researchers explained.
The experiment was one of 11 to explore the illusionary experience. In another one of those 11 experiments, the participants were asked to close their eyes and then quickly point to where the perceived their right hand to be. After spending some time experiencing the illusion, the test subjects were more likely to point at the location of the invisible hand rather than the location of their actual body part.
Each study participant also had their brain activity measured using functional magnetic resonance imaging (fMRI). The researchers found that receiving the phantom hand resulted in increased activity in the same areas of the brain which are typically active when their actual hands are being touched, or when individuals experience a prosthetic hand as their own.
Guterstam said that their findings “show that the sight of a physical hand is remarkably unimportant to the brain for creating the experience of one's physical self.” He and his colleagues are also hopeful that their work will lead to advances in future research into the phantom pain phenomenon experienced by amputees.
“This illusion suggests that the experience of phantom limbs is not unique to amputated individuals, but can easily be created in non-amputees,” explained principal investigator, Dr. Henrik Ehrsson, a cognitive neuroscientist and an associate professor at the Karolinska Institutet´s Department of Neuroscience. “These results add to our understanding of how phantom sensations are produced by the brain, which can contribute to future research on alleviating phantom pain in amputees.”