Brain Activity Underlying the Placebo Effect

Research that conducted brain imaging during placebo studies found that both the active (opiod) treatment and the placebo (saline) treatment activated the same network of brain regions. This included the brain stem, a part of the opiod system that mediates pain relief, and the rostral anterior cingulate cortex, which is rich in opiod receptors.1 It is also a part of the body’s reward system. The researcher, Petrovic, proposed that placebos, like opiods, triggered control areas such as the anterior cingulate that exerted control over the analgesic systems of the brain stem. The analgesic systems of the brain stem then released endorphins.

Another researcher, Tor D. Wager, who also used MRI found that additional brain systems were involved in the placebo effect. The researchers administered a placebo cream while giving painful shocks or painful intense heat on the forearms of the research participants. In one experiment a warning cue, a red “get ready” sign was given just before the painful stimulus was administered. The research subjects expected pain, unless the cream was applied, in which case they expected relief. The expectation of relief activated the cognitive executive center of the brain, the prefrontal cortex. Then the pain response areas of the brain declined, and the experimental participants reported relief. These results suggest that the placebo pain relief involves an expectaton signal from the prefrontal cortex that orders the midbrain to release opiods to meet the expectation of reprieve. Absent this, the full experience of pain is perceived. Further research has pinpointed specific regions of the prefrontal cortex as drivers.

Emotions are also involved in the placebo effect. Wager and his colleagues reported in 2011 that activities in regions of the brain that perform emotional appraisal, such as the insula, orbitofrontal cortex, and amygdala accompany a robust placebo effect. Wager calls this endogenous regulation. Placebos seem to give us a better perspective on our predicament. We might reevaluate our predicament so that we believe that the pain will abate and not cause persistent disability. According to Wager, during a placebo response, “our brain is likely doing a lot of the work without our real conscious input or even in spite of our conscious desires.” That is, we unconsciously engage brain mechanisms that serve to sooth.

Ironically, this self-soothing process might require us to focus on the pain rather than something else. In another study by Wager and his colleagues published in 2012, they tried to distract people away from experimentally induced pain by having them perform another task. This other task did not help relieve the pain. But when the researchers encouraged the participants to pay attention to the heat on their arm by asking them to rate its intensity, the participants experienced greater relief. This result is consistent with “acceptance” therapies or with the “relaxation response” in which people surrender to their pain to tolerate it better.

1The facts in this blog post can be found in an article, When Pretending is the Remedy, in Scientific American Mind, March/April 2013 by Trisha Gura.

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One Response to “Brain Activity Underlying the Placebo Effect”

  1. Morgan Levy Says:

    Check out my new blog site entitled Placebo Medicine. It is about how the NEW neuroscience of the placebo effect explains complementary medicine and directs us how to properly integrate it into mainstream medicine. http://www.placebomedicine.com/

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