The study provides the first direct evidence that the brain's own pain-fighting chemicals, called endorphins, play a role in the phenomenon known as the placebo effect -- and that this response corresponds with a reduction in feelings of pain.

Previous studies at U-M and elsewhere have shown that the brain reacts physically when a person is given a sham pain treatment, which they believe will help them.

But the new study is the first to pinpoint a specific brain chemistry mechanism for a pain-related placebo effect. It may help explain why so many people say they get relief from therapies and remedies with no actual physical benefit. And, it may lead to better use of cognitive, or psychological, therapy for people with chronic pain.

The results will be published in the August 24 issue of the Journal of Neuroscience by a team from the U-M Molecular and Behavioral Neurosciences Institute (MBNI). The research was funded by the National Institutes of Health.

"This deals another serious blow to the idea that the placebo effect is a purely psychological, not physical, phenomenon," says lead author Jon-Kar Zubieta, M.D., Ph.D., associate professor of psychiatry and radiology at the U-M Medical School and associate research scientist at MBNI. "We were able to see that the endorphin system was activated in pain-related areas of the brain, and that activity increased when someone was told they were receiving a medicine to ease their pain. They then reported feeling less pain. The mind-body connection is quite clear."

The findings are based on sophisticated brain scans from 14 young healthy men who agreed to allow researchers to inject their jaw muscles with a concentrated salt water solution to cause pain. The injection
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23-Aug-2005