Placebo Acts on Brain to Relieve Pain

The placebo effect may be all in your head–in your brain, that is. New research suggests that placebo treatments can influence activity in pain-sensitive parts of the brain.

The placebo effect may be all in your head–in your brain, that is. New research suggests that placebo treatments can influence activity in pain-sensitive parts of the brain. “We may have more control over our minds and experiences than we think we have,” lead author Dr. Tor D. Wager at Columbia University in New York told Reuters Health. Most people have heard of the placebo effect, in which people who are given an inactive drug or therapy experience an improvement in their symptoms. Researchers often compare new drugs to placebo to gauge the true benefit of a therapy. The effect of placebo treatments on pain has been controversial, according to Wager. Researchers have disputed whether placebos in clinical trials actually affect pain or simply reflect participants’ tendency to report what they or other people expect them to feel, Wager told Reuters Health. But the results of the study suggest, Wager said, “that placebo treatments in pain actually affect the feeling of pain, not simply your desire to comply with physicians’ or experimenters’ expectations.” Wager and his colleagues measured brain activity in response to pain in two sets of experiments. During several rounds of experiments, people were given an identical cream; sometimes researchers described it as an experimental pain reliever, other times they said it was an inactive cream. “We found that placebos decrease the brain’s response to pain in areas that seem to code for the magnitude of pain experience,” Wager said. “This suggests that the experience of pain really is altered.” The results are reported in Friday’s issue of the journal Science. In a region called the anterior cingulate, activity decreased early in pain, which may be related to how uncomfortable the pain is, Wager said. The Columbia researcher noted that changes occurred later in pain in the thalamus and insula, which may reflect how bad the experience is for a person. “In each of these areas, the greater the placebo decreases observed in the brain, the more pain relief due to the placebo a person reports,” Wager said. As for how a placebo can change the brain’s coding of pain, Wager said that this requires a person’s belief in the placebo to be translated into changes in pain pathways. In the study, Wager’s team found that the anticipation of pain while taking a placebo produces increases in activity in parts of the brain that are related to control of attention and that link stimuli with rewards. “We think these areas are maintaining expectations of pain relief and that they may influence pain signals in at least two ways,” Wager said. One way, he said, is by increasing activity in a part of the brainstem that produces morphine-like chemicals that can block pain signals coming into the brain. A second way, and probably the one with the greater effect, Wager said, is that expectations can have a direct effect on activity in parts of the brain that may track the emotional significance of pain. “So, although the incoming pain signals may be modified slightly, the interpretation of the threat value and potential harmfulness of pain may be modified quite a bit,” according to Wager. (SOURCE: Reuters Health, Science, Feb, 2004.