The placebo effect -- a handy and inert tool used in research to study the effect of medical treatments -- may not only work on your brain, among other things, to tame pain. German researchers believe the power of the placebo may be felt in your spinal cord.

Scientists applied painful heat to the arms of 13 healthy men, then told them they were being treated with two creams, one a placebo and the other containing a "painkiller." However, both creams contained inactive ingredients. The first time the sham painkilling cream was used, scientists cut down the intensity of the heat by more than half to give patients the feeling that the "real" product actually worked. When testing the real placebo, however, scientists kicked up the temperature to 80 percent of their patients' average pain threshold to trick them.

Using specialized functional magnetic resonance imaging (fMRI) scanner, researchers applied both creams in separate spots on each patient's left forearm, then turned on the heat in each spot 15 times.

When the skin where the fake painkiller was applied with heat, patients reported a lessening of pain by 26 percent, and no responses from the fMRI scanner. When the other control product was used, however, the fMRI recorded signaling in the region of the spine known as the dorsal horn, implications that neural activity had increased in response to pain.

Researchers speculate the signaling picked up by the fMRI in the spine may be triggered by higher brain areas releasing natural opioids that dampen pain.

Science, Vol. 326, No. 5951, p. 404, October 16, 2009

Popsci October 16, 2009

Reuters October 15, 2009

New Scientist October 16, 2009