The work, which used a specialized type of magnetic resonance imaging to track pain-related brain activity, showed drops of as much as 97 percent in such activity in some brain centers. The study marks the first time that scientists have documented a link between virtual reality and pain reduction in terms of an actual physiological response.
"What this study shows is that virtual reality is not only changing the way people interpret the incoming pain, it is changing the actual activity in the brain," said Hunter Hoffman, director of the VR Analgesia Research Center at the UW's Human Interface Technology Laboratory, a facility affiliated with the university's College of Engineering.
The paper appears in the current issue of the journal NeuroReport.
The findings support those of an earlier study by Hoffman and Dave Patterson, a psychologist and pain expert at Harborview Medical Center in Seattle, in which patients were asked to rate their levels of pain while being treated for severe burns, both with and without virtual reality. Patients immersed in a virtual world during the often-excruciating therapy reported a 40-percent to 50-percent drop in pain.
"These results show converging evidence from both subjective pain reports and from objective brain activity patterns that VR reduces pain," Hoffman said. Since virtual reality can be used in addition to morphine-related medications, he added, the small but growing number of clinical and laboratory studies showing that virtual reality can reduce pain so dramatically could have broad implications for medical procedures, where excessive pain is a common problem.
To conduct the latest study, researchers attached a heating device to the top of participants' feet. The device produced a strong but tolerable level of pain for several 30-second intervals, during which participants were monitored using functional magnetic resonance imaging for activity in five brain areas associated with pain perception.
When a brain center is activated, there is a rapid momentary increase in blood flow to the area. The increase in circulation brings an increase in oxygen, which, when scanned, makes the neural center stand out in contrast to surrounding tissue. As a result, scientists can monitor activity in specific brain areas by tracking increases in blood flow.
"It's like being able to look through someone's skull and into the brain and see what's going on inside," Hoffman said.
Scans were done both while the participants were engaged in a virtual world and without virtual reality.
When in the virtual program, called "SnowWorld," participants experienced the illusion of floating down an icy canyon and could toss snowballs at snowmen, igloos, robots and penguins. For the non-virtual sessions, participants still wore the VR headgear. However, instead of being inside a virtual world, they simply saw a black cross on a white background.
In the current study, participants were also asked to fill out a form rating their levels of pain. On a scale of one to 10, with 10 being the highest, they were asked to rank such things as "time spent thinking about pain," "pain unpleasantness" and "worst pain" for both virtual reality and non-virtual reality sessions. As with the earlier study involving burn patients, there was a significant change in the conscious perception of pain when virtual reality came into play. Results showed that during VR:
* Time spend thinking about pain dropped 35 percent. * Pain unpleasantness registered a 36-percent decrease. * Worst pain dropped by about 23 percent.
That's significant, researchers say, but the actual physical changes were even more marked. Average drops in pain-related brain activity in the five sites monitored ranged from 50 percent to 97 percent, depending on the neural area observed.
"That's a drastic reduction," said Todd Richards, professor of radiology in the UW Medical Center and a co-author of the study. "The subjects' pain ratings went down and their pain-related brain activities were greatly reduced. In other words, the VR treatment reduced pain both in the mind and the brain."
The first-of-its-kind study was made possible by a new type of virtual reality helmet developed by Hoffman and Richards' team to be compatible with the magnetic resonance imaging process.
Conventional virtual reality helmets use miniature electronic computer screens, placed close to the eye, to give the impression of entering into a computer-created world. However, problems arise when trying to use such equipment near an MRI machine. MRI devices create powerful magnetic fields, which wreak havoc with the electronics in the helmet. The electronics in the helmet, in turn, tend to interfere with the brain scan.
For the new helmet, Hoffman and his colleagues simply got rid of the conventional electronics.
"Instead of electrons, we're using photons," Hoffman said. "We convert the images to light, which is then carried to the goggles via fiberoptic cables."
In addition to Hoffman and Richards, co-authors of the paper include Sam Sharar, Aric Bills and Barbara Coda, all with the UW Department of Anesthesiology; Anne Richards, UW Department of Radiology; and David Blough, UW Department of Pharmacy.
The research was funded by the National Institutes of Health and Microsoft co-founder and philanthropist Paul Allen.
Additional information about Hoffman's VR research is available on his Web site at http://www.hitl.washington.edu/people/hunter/.