The neural bases of placebo effects in pain

Placebo effects are beneficial effects of treatment caused not by the biological action of the treatment but by one's response to the treatment process itself. One possible mechanism of placebo treatments is that they create positive expectations, which change one's appraisal of the situation and may thereby shape sensory and emotional processing. Recent brain-imaging evidence suggests that placebo-induced expectations of analgesia increase activity in the prefrontal cortex in anticipation of pain and decrease the brain's response to painful stimulation. These findings suggest that placebo treatments can alter experience, not just alter what participants are willing to report about pain. To the extent that they involve neural systems mediating expectancy and appraisal, placebo effects in pain may share common circuitry with placebo effects in depression, Parkinson's disease, and other disorders.