Later, with an fMRI scanner on, the researchers rubbed "control" and "painkiller" creams onto two different spots on each volunteer's left forearm and applied the same level of heat to each spot, 15 times.
The fake "painkiller" cream worked: volunteers said they experienced 26 per cent less pain on the "painkiller"-treated patch of their arm, compared with the "control"-treated area.
Meanwhile, the fMRI scanner witnessed the placebo effect. When skin treated with the "control" cream was heated, an area of the dorsal horn located on the left side of volunteers' lower necks lit up, suggesting increased neural activity there in response to pain. However, this signal disappeared in the "painkiller" trials.
Link via Popular Science | Image: U.S. Department of Health and Human Services