Tired of reaching for a bottle of pills to quell your chronic pain? Maybe you should strap on a virtual reality headset. In an experiment described last week in Psychological Science, scientists showed how bogus visual feedback created by virtual reality can actually trick the brain into boosting or reducing a person's range of pain-free movement. The study highlights the ways in which sensory perceptions, and not just physical signals, can make us feel pain—and how that effect can be manipulated to design new therapies.
To test this notion, Daniel Harvie at the University of South Australia and his colleagues put chronic neck pain sufferers through a series of twists and turns, first with no equipment and then fitted with Oculus Rift headsets. The headsets were programmed to show indoor and outdoor scenes, and they used gyroscopes to monitor the wearer's head movements. The patients were then told to turn their heads left or right until they felt pain.
When patients turned their heads just a bit, they sometimes perceived that they were moving much further, or vice versa. If participants moved their heads within a normally non-painful range, they experienced pain when the headset's visuals made them think they'd performed a much greater rotation. Similarly, the volunteers often experienced no pain when the headsets made it appear to them that they'd performed smaller, normally pain-free turns—even if they moved into a normally painful pose. The results suggest that chronic sufferers create an association between movement and pain, so that the mere visual suggestion of motion its own signal of danger to the body.
“It is important to recognize here what pain actually is,” Harvie says. “Pain is not a linear result of messages from the body. Rather, pain is one of the brain's protective responses, produced when, after evaluating all of the evidence, it decides that body tissue is in danger and that we need warning. In this case, because of the association between pain and movement, learned through past experience, visual signals of movement themselves have become signals of threat to the body and therefore, triggers of pain.”
Virtual reality has been used previously for other types of pain research. In 2014 Swedish scientists detailed in the journal Frontiers in Neuroscience how virtual reality helped phantom limb pain, which plagues some 70 percent of amputees. Muscle signals from a patient's stump were recorded by electrodes and processed by a software program that enabled each patient to control a virtual limb just by thinking about it. The treatment caused a reduction in phantom pain, perhaps because the illusion tricked the brain into thinking that the missing limb was again part of the body.
Harvie sees similar potential for developing future pain treatments based on his team's research, such as training the brain to target the cues it interprets as danger signals.
“Movement is a common example of something that is often associated with pain when we have an injury, and might therefore become a 'learned' signal of danger and trigger of pain, even after injury healing,” he says. “If we can teach the brain anew that movement and other learned triggers are actually safe, then their ability to contribute to pain will be extinguished.”