Placebo reins in pain in brain

Pain relief provided by a substance with no active ingredients, called a placebo, may have neural as well as psychological origins. Men who reported relief from a painful jaw after receiving a placebo injection also showed signs of enhanced activity of a brain substance that regulates stress and suppresses pain, say Jon-Kar Zubieta of the University of Michigan in Ann Arbor and his coworkers in the Aug. 24 Journal of Neuroscience.

The scientists administered an intravenous salt solution, which they described to volunteers as a pain reliever, to seven men who also received a jaw injection that caused a moderately painful muscle spasm for about 20 minutes. Another seven men received the jaw injection but not the placebo.

In brain scans of the placebo group only, positron-emission tomography and molecular-imaging techniques revealed pronounced activity at brain-cell receptors for chemical messengers known as endorphins. Prior studies had linked endorphins to pain relief.

Men who reported the greatest relief from the placebo injections exhibited the most-intense responses at endorphin receptors in the brain, Zubieta’s group reports.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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