Editors' ChoicePlacebo Effect

Pleasure or Pain: A Matter of Perception

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Science Translational Medicine  21 Oct 2009:
Vol. 1, Issue 3, pp. 3ec11
DOI: 10.1126/scitranslmed.3000508

The placebo effect is a common medical phenomenon that occurs when an individual reports pain relief or shows an improved response to taking nothing other than a sugar pill. Scientists have long wondered about the neurological basis of these influential, but apparently psychological beliefs in the effects of a drug. Now, Eippert and colleagues show, upon administration of a placebo, direct evidence that the central nervous system curbs nociception—the ability of neurons to process pain as a result of a physical or an emotional, unpleasant stimulus. Using a preexisting placebo analgesic paradigm, Eippert et al. examined the blood-oxygen level dependent (BOLD) responses to painful heat stimulation in human spinal cords, using functional magnetic resonance imaging. With this experimental approach, they located the BOLD responses to pain in a very precise region of the spinal cord on the same side as the stimulus. But when the individual had taken a placebo medication these responses were reduced by nearly three times, showing that the placebo drug reduced the neural response to the painful stimulus. The authors suggest that descending neuronal pathways from the central nervous system act on the more local pain responses in the spinal cord and may confer analgesic effects as a result of natural opioids produced in the brain. This work establishes how psychological effects on human nociception can be measured with functional magnetic resonance imaging technology and, in doing so, identifies a precise site of action for the placebo effect. The malleability of the pain response suggests that the placebo effect might be harnessed for the development of more effective treatments for the various forms of pain.

F. Eippert et al., Direct evidence for spinal cord involvement in placebo analgesia. Science 326, 404 (2009). [Abstract]

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