Science News / Imagination Medicine

By | December 10, 2008

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Believing is relieving

People receiving a placebo in a clinical trial often respond as though they are getting a real drug. At the University of Michigan in Ann Arbor, neuroscientist Jon-Kar Zubieta studies this phenomenon in the laboratory.

Earlier work by Zubieta and colleagues has shown that the anticipation of pain relief discharges opioids from pain control centers in the brain. Opioids are part of the brain’s pain-relief strategy and are activated by stress. Other chemical messengers, such as dopamine, join in too. In the nucleus accumbens, dopamine is released when the brain sees a reward coming, such as food or sex. Dopamine drives the reward response, and Zubieta wondered whether dopamine also participates in the placebo effect. …

The scientists then administered the “pain relief” (which did not include, in fact, any actual drugs, only placebo) and exposed participants to pain by injecting low-concentration saltwater into a large jaw muscle for 20 minutes. PET images were taken of the participants’ brains during the exposure. Pain lessened for some and strengthened for others—just what happens in clinical trials, the researchers reported in the February Archives of General Psychiatry.

In participants whose pain symptoms improved, the nucleus accumbens released dopamine and opioids. In those who reported more pain and discomfort, the brain shut down dopamine and opioid release through the same pathways.

But even in such tightly controlled laboratory experiments, not all people respond to placebos, and not all respond the same way. In another experiment, the same volunteers played the monetary incentive delay task, a gambling game. Reward was expected, but not reward in the form of relief from pain. Using fMRI, the researchers monitored neural activity and found that indeed the nucleus accumbens was activated during anticipation of monetary reward. And in each person, that activation was proportional to the person’s capacity for a placebo-generated release of dopamine during the pain experiments, the team reported in 2007 in Neuron. …

via Science News / Imagination Medicine.

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