The neural bases of placebo effects in anticipation and pain

Numerous studies of experimental and clinical pain show that placebo treatments reduce reported pain and that expectancies play a key role in their effectiveness. However, very little is known about the neurobiological mechanisms of either placebo analgesia or the generation of expectancy that enables it. To address this issue, I used functional magnetic resonance imaging to quantify placebo-induced changes in pain-processing brain regions during the experience of pain. Results show placebo-induced decreases in contralateral thalamus, anterior insula, and anterior cingulate, and increases in prefrontal brain regions that may maintain expectations for pain relief. These findings are discussed in light of several proposed neuropsychological mechanisms of placebo analgesia: altered appraisal of threat, diversion of attention, and activation of descending opioid systems for spinal control. These results suggest that placebo treatment alters the appraisal process, reducing the subjective distress caused by pain.