Non-amputees experience phantom limb sensation

Non-amputees experience phantom limb sensation

Non-amputated individuals can actually experience the illusion of having a phantom hand, according to a new study in the Journal of Cognitive Neuroscience.

The research was conducted by neuroscientists at the Karolinska Institutet in Sweden who explained that the sensation of having a physical body is not as obvious as some people may assume. Nearly all patients who have had an arm or leg amputated feel a phantom limb - a realistic sensation that the missing limb is still attached to the body.

According to the experts, the healthy participants in the study were able to experience a perceptual illusion of having an invisible hand.

For the purpose of the investigation, the participants sat at a table with their right arm behind a screen so that it was not visible to them. The right hand of the volunteers was then touched by the researchers with a small paintbrush, while they imitated the same movement with a different paintbrush up in the air so that it was visible to the subjects.

Arvid Guterstam, lead author of the research, said:

"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."

The illusion resulted in increased stress responses

Eleven experiments were included in the study, which consisted of 234 participants, to investigate in detail the illusory experience.

In order to show that the illusion really did work, the scientists took a knife and made a stabbing motion towards the empty space where the invisible hand supposedly was. The investigators measured the subjects' stress responses to the perceived threat.

While experiencing the illusion, the participants' stress responses were increased; but when the illusion was broken, the stress responses were absent.

In a different trial, the subjects closed their eyes, and with their left hand, rapidly pointed to their right hand - or to where they perceived it to be.

The participants would point to the location of the invisible hand instead of their real hand after experiencing the illusion for a while, the authors explained.

The illusion caused increased brain activity

Additionally, functional magnetic resonance imagine (fMRI) was used to measure the brain activity of the volunteers.

The researchers found that when subjects perceived the invisible hand illusion, it resulted in increased activity in the same areas of the brain that are usually active when people watch their real hand being touched or when individuals experience a prosthetic hand as their own.

"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," Arvid Guterstam explained.

The findings can aid to future research on pain in amputees

This study will hopefully offer insight into investigations in the future on phantom pain in amputees, the authors said.

A recent study by Oxford University showed that changes in the brain following amputation is associated with phantom pain.

Dr. Henrik Ehrsson, principal researcher and docent at the Department of Neuroscience, concluded:

"This illusion suggests that the experience of phantom limbs is not unique to amputated individuals, but can easily be created in non-amputees. 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."

The research was funded by the Swedish Foundation for Strategic Research, the European Research Council, the Human Frontier Science Program, the McDonnell Foundation, and Söderbergska Stiftelsen.

Scientists create phantom sensations in non-amputees (Video Medical And Professional 2020).

Section Issues On Medicine: Medical practice