Concepts of placebo, dating back to medieval times, are becoming increasingly important today for understanding the efficacy and limitations of pain management therapies. For example, we most recently discussed in Pain-Topics UPDATES major influences of placebo effects in acupuncture [here] and transcutaneous electrical nerve stimulation (TENS) [here] as therapies for pain. With the newly reported discovery that the unconscious mind may play a key role in placebo effects, researchers have proposed a novel mechanism that helps to further explain the power of placebos and their sinister sister, nocebo.
Writing online in the Proceedings of the National Academy of Sciences (PNAS), Karin Jensen, PhD — of Massachusetts General Hospital and the Program in Placebo Studies at Beth Israel Deaconess Medical Center/Harvard Medical School — and colleagues report a novel study that demonstrated how placebo and nocebo (negative placebo) effects may rely on brain mechanisms that are not dependent on conscious awareness [Jensen et al. 2012]. They enrolled a total of 40 healthy volunteers (24 female, 16 male; median age 23) in 2 experiments: