anesthetic "lidocaine" cream to one arm, and a "control" cream to the other, making sure to tell the subjects which cream was which. The researchers applied a hot stimulus for 20 seconds to the skin where the each cream was applied. Participants said the "lidocaine" cream reduced pain by an average of 26 percent.
The placebo effect, of course, is the well-known phenomenon in which patients who think they are getting medical treatment report that they feel better, even when they get only a sugar pill or other fake therapy [Los Angeles Times]. To test the limits of the placebo effect, researchers applied an
This would all be fairly straightforward had the researchers not been lying to their test subjects. You see,
neither cream had active ingredients. They also primed a response by turning down the painful heat for the painkiller cream in a first test run, and so tricked volunteers into thinking that the cream would work the next time. But actual tests with an MRI scanner on involved the same level of heat for both creams. Volunteers nonetheless reported less pain with the painkiller cream [Popular Science].
The fMRI data backed up the participants' pain perception. Normally when a person experiences pain, the dorsal horn area of the spinal cord near the lower neck will appear to be on fire with activity,
but the fMRI scans showed nerve activity was reduced significantly when subjects believed they were getting the anesthetic [Reuters]. The researchers say this indicates that "psychological factors" can have an effect on pain outside of the brain. They hope to develop new treatments that can exploit the placebo effect's painkiller effect.
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Image: flickr / fbaett