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Expectations about pain can affect its intensity |
| TheallIneed.com/NC&T/WFUBMC |
"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," said Tetsuo Koyama, M.D., Ph.D, a post-doctoral fellow and lead author of the study.
The study involved 10 normal, healthy volunteers who had a heat stimulator applied to their legs while their brains were being scanned with functional magnetic resonance imaging (fMRI), a technology that shows which areas of the brain are being activated.
In a training session, researchers taught participants to expect three different levels of painful heat stimuli after a timed interval. A seven-second interval signaled a heat level that caused mild pain (115 degrees Fahrenheit), a 15-second interval signaled a heat level that produced moderate pain (118 degrees) and a 30-second interval signaled a heat level that produced severe pain (122 degrees). Since the heat stimuli were on for only 20 seconds, none of them were hot enough to cause burns or damage to the skin.
One or two days after training, participants underwent 30 different heat trials that were monitored with fMRI. About a third of the time, the researchers mixed the signals for the pain levels, so that participants were expecting one temperature, but actually received either a higher or lower temperature.
When participants expecting moderate pain were exposed to the severe heat level, their ratings of pain intensity were 28 percent lower than on the trials where they were expecting a high level of pain and actually received it. All 10 subjects had diminished pain intensity when they expected lower levels of pain.
"Expectations of decreased pain powerfully reduced both the subjective experience of pain and activation of pain-related brain regions," said Robert Coghill, Ph.D., the senior author of the study and a neuroscientist at Wake Forest University School of Medicine, which is part of the Medical Center.
Brain regions activated during expectations of pain overlapped partially with those activated during pain, which suggests that there is are crucial brain regions that allow expectations to shape the processing of information from the body.
"We don't experience pain in a vacuum," Coghill said. "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."
He said that the identification of brain regions that can allow cognitive factors such as expectations to shape incoming sensory information may lead to increased acceptance of cognitive and behavioral treatments for pain by patients, physicians and insurers.
"We need to find ways to optimize these treatments," Coghill said. "Pain needs to be treated with more than just pills. The brain can powerfully shape pain, and we need to exploit its power."
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