Researchers Study the Phantom Hand Sensation in Non-Amputees [Video]

Researchers from the Karolinska Institutet in Sweden have found that it is possible to get people who haven't lost a limb experience the "phantom limb": a sensation of the missing limb felt by amputees.

In the experiment, researchers stroked the hand of a volunteer (which was hidden from the volunteer's view using a partition) using a small paintbrush  and making a similar movement with another paintbrush mid-air in view of the volunteer.

"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. 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," said Arvid Guterstam, lead author of the study.

The entire study included 11 such experiments that helped researchers learn about people's reaction to a phantom limb.

To demonstrate that the participants' illusion of the phantom limb was real, researchers stabbed the imaginary hand using a knife and measured the participants' stress response. The experiment showed that when participants weren't looking at their own hand, they had elevated stress response than when they were looking at their hand.

The fMRI scans of the participants showed that certain brain regions were activated when the participants were subjected to the illusion of an invisible hand.

"Taken together, our results show that the sight of a physical hand is remarkably unimportant to the brain for creating the experience of one's physical self," said Arvid Guterstam.

The study is published in the Journal of Cognitive Neuroscience.

People who've had an amputation often feel some sensations in the missing limb that go away with time in most people. According to Medline Plus, some people may experience worse symptoms like aches and pain.

"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," said Dr Henrik Ehrsson, from the Department of Neuroscience and principal investigator of the study.