Study: Could pain be an illusion?
Pain, although it has a warning function in the body, does not always appear where there has been an injury. This has been shown by the scientists from the Jagiellonian University, who caused the subjects to incorrectly indicate the place where a painful stimulus was applied.
In some neuropsychological disorders, patients feel that their hand does not belong to them; others may experience phantom pain in the limbs that they actually no longer have. Disorders such as these lead scientists to study body awareness. One of the teams that conduct research in this field are researchers from the C-Lab Awareness Research Laboratory at the Institute of Psychology of the Jagiellonian University.
One of the methods they use to temporarily change the sense of body awareness in the healthy subjects they study is an experiment called rubber hand illusion.
This is a frequently used experiment, in which investigator places a rubber hand, for example the right one, in front of the subject. For the illusion to work, the artificial hand should be in the place where the real right hand would be. At the same time, this real right hand is covered so that the subject cannot see it. The researcher strokes the rubber hand synchronously with the real hand of the subject, which remains hidden.
"When subjects feel the touch on their hands and at the same time they see stroked rubber hand, it is thought that the spatial representation of the body changes. Because vision is our dominant sense, people begin to feel touch in the place where they see it. Then the strength of illusion is measured with questionnaires" - explained Dr. Marta Siedlecka from the Institute of Psychology of the Jagiellonian University, quoted in a release sent to PAP.
Researchers from the Jagiellonian University decided to measure the strength of pain experienced by people subjected to the rubber hand illusion. The subjects, healthy people, received pain stimuli in both - real - hands, both before and after the illusion. During the induction of pain they did not see their hands, and consequently the place and moment of administering a pain stimulus.
According to Dr. Siedlecka, the study showed that the subjects felt stronger pain in the hand that was the subject of the illusion, compared to the pain before the illusion and the pain in the other hand. It happened despite the fact that the pain stimuli given to them had the same strength. In addition, when the subjects were asked to indicate the place where they felt pain, they also showed a place closer to the rubber hand than the real hand that actually received the pain stimulus.
"It is very interesting, because it always seemed that pain is a very important stimulus for the body. It is equally important to locate it very precisely in the body. After all, it has a warning function and should motivate us to protect the body. It turned out, however, that even the perception of pain is susceptible to this kind of illusions" - said Dr. Siedlecka.
According to the Institute of Psychology of the Jagiellonian University, a lot of research has been carried out on the subject of pain sensation in persons subjected to rubber hand illusion, but their results were not always consistent, for example due to the applied methodology.
In previous studies, subjects in the experiment usually saw the place in which they received pain stimulus. Other studies show that when we know the moment of receiving pain or we see the part of the body in which we received, the pain becomes smaller. Therefore, the researchers from the Jagiellonian University decided that both hands of the subjects would be covered when the pain stimulus was delivered.
"We think that in our study the main factor causing the pain to be felt as greater was very high uncertainty of the subjects regarding what was happening on the right side of their body. They could not correctly indicate the location of their right hand; they did not see the pain stimulus and could not correctly indicate its location. This uncertainty could heighten their subjective feeling of pain" - said Dr. Siedlecka.
She explained that understanding how perceiving and experiencing the person\'s own body is related to the perceived strength of pain can help create future therapies. "By adding our contribution to other studies, we can help determine under what conditions the experience of pain may increase or decrease" - said the researcher.
More information on the article "Rubber Hand Illusion Increases Pain Caused by Electric Stimuli" published in The Journal of Pain is available at: https://www.sciencedirect.com/science/article/pii/S1526590017306855
PAP - Science in Poland
ekr/ agt/ kap/