The concept of a placebo effect, by which patients get better from the mere illusion of treatment, has intrigued scientists since it was first proposed in 1955. Since then debate has centered on whether it truly exists and, if it does, how it works. Findings published today in the journal Science offer fresh evidence in support of the existence of a placebo effect and suggest how a brain influenced by this effect changes its response to pain.

Tor D. Wager of the University of Michigan and his colleagues used functional magnetic resonance imaging (fMRI) to study the brains of volunteers who were exposed to harmless but painful stimuli such as small electric shocks or heat. In some cases, the researchers told participants that a pain-relieving cream had been applied to their skin. When these subjects were shocked, they reported less pain on average than did participants lacking the "anti-pain" cream. Subjects under the influence of the placebo effect also exhibited increased brain activity in an area known as the prefrontal cortex, and decreased activity in well-known pain-sensing regions such as the thalamus, the somatosensory cortex and parts of the cerebral cortex.

The results support the hypothesis that the placebo effect does not interfere with the bodys ability to sense pain but instead affects how the brain modulates its interpretation of the bodys signals. Paradoxically, the placebo findings could aid the development of novel therapeutic treatments for pain. Remarks Casey: "One could imagine compounds that would activate these control systems specifically."