Sept. 6, 2005 -- Doctors who say, "This won't hurt a bit" before a painful prod or poke may be delivering a pre-emptive dose of pain reliever.
A new study suggests that low expectations about impending pain can actually lower a person's perception of it.
"We found that expectations have a surprisingly big effect on pain. Positive expectations produced about a 28 percent decrease in pain ratings -- equal to a shot of morphine," says researcher Tetsuo Koyama, MD, PhD, a postdoctoral fellow at Wake Forest University Baptist Medical Center, in a news release.
In addition, researchers say the findings suggest that positive thinking about pain can reduce both the perception and processing of pain in the brain.
"Expectations of decreased pain powerfully reduced both the subjective experience of pain and activation of pain-related brain regions," says researcher Robert Coghill, PhD, a neuroscientist at Wake Forest University School of Medicine, in the release.
Positive Thinking May Be Powerful Pain Reliever
In the study, researchers told the 10 healthy participants to expect three different levels of pain after a designated signal during an experiment in which heat was applied to their legs: mild pain (115 degrees Fahrenheit), moderate pain (118 degrees), and severe pain (122 degrees). The heat was applied for only 20 seconds, which was not long enough to cause burns or damage the skin.
While the heat stimulator was applied to their legs, researchers used magnetic resonance imaging (MRI) to study which part of the brain was being activated.
During the experiment, researchers mixed up the pain signals in about one-third of the 30 different trials so that participants were expecting one temperature and received either a higher or lower one.
The results showed that when people expected moderate pain and were exposed to the severe heat, their pain ratings were 28% lower than when they expected severe pain and got it. All 10 participants experienced lower pain intensity when they expected lower levels of pain.
The brain scans showed that regions activated during the pain-expectation phase overlapped partially with those activated during the experience of pain. Researchers say those results suggest that the brain allows expectations of pain to shape the processing of actual pain signals from the body.
"We don't experience pain in a vacuum," says Coghill. "Pain is not solely the result of signals coming from an injured body region, but instead emerges from the interaction between these signals and cognitive information unique to every individual."
The results appear in the current online edition of the Proceedings of the National Academy of Sciences.