If a person hides their own hand and focuses on a rubber hand instead, they may perceive it as part of their own body under certain conditions. What sounds like a gimmick could one day be used to help patients who suffer from chronic pain: Researchers at the Clinic for Psychosomatic Medicine and Psychotherapy at the LWL University Hospital in Bochum, Germany, have shown that pain caused by heat is experienced as less severe thanks to the rubber hand illusion. They published their findings in the journal PAIN Reports from April 2025.
Heat creates illusion
The rubber hand illusion occurs when the hidden hand and the rubber hand are touched at the same time, for example with a brush. In the experiment outlined here, the illusion was not evoked through touch, but through a heat stimulus and simultaneous illumination with red light:
In the first step, the researchers determined the individual pain threshold for heat pain in all 34 right-handed test participants. The participants then placed their left hand behind a screen so that they could no longer see it. The hand hidden by the screen was placed on a thermode head, a small plate that can be heated under controlled conditions. Instead of their left hand, a rubber hand was placed in front of the participants, which could be illuminated with red light from below. The test participants' right hand was placed on a slider which they used during the experiment to continuously rate the painfulness of the heat on their left hand.
The researchers carried out several test runs in which they heated the thermode to several temperature levels just below the respective pain threshold, exactly at the pain threshold and just resp. significantly above it. The rubber hand was simultaneously illuminated with red light. “The heat stimulus on the left hand with simultaneous red illumination of the rubber hand evoked the illusion,” explains study supervisor Professor Martin Diers, Head of the Research Section Clinical and Experimental Behavioral Medicine. A survey of the test participants confirmed these findings after each series of experiments. In the control condition, the researchers conducted the experiment with a rubber hand rotated by 180 degrees.
The intensity of pain decreases
“We showed that the perceived pain intensity was reduced in the rubber hand illusion condition compared to the control condition,” says Martin Diers. “We assume that the mechanism behind the rubber hand illusion is the multisensory integration of visual, tactile (here nociceptive) and proprioceptive information. The findings suggest that when people perceive the rubber hand as part of their own body, this reduces their perception of pain.” Another factor could be the phenomenon of visual analgesia, which has also been shown in other studies: A pain stimulus is perceived as less intense if the person can see the relevant part of the body while it is occurring. “However, we still don’t fully understand the neural basis for this phenomenon,” admits Diers.
In future, the findings could possibly be used in the treatment of pain. One conceivable field of use would be the treatment of complex regional pain syndrome, for example, in which patients typically experience pain and swelling in the hand.
