A follow-up fMRI study of a transferable placebo anxiolytic effect

Our previous study showed that placebo expectations can develop in a transferable manner; for example, a placebo expectation developed within an analgesic experience may lead to reduced anxiety. Considering that activities in such emotion-responsive areas as the amygdala and insula can be detected through functional magnetic resonance imaging (fMRI), we used fMRI to further study the transferable placebo anxiolytic effect. A main-effect analysis showed that activity in the amygdala and insula was reduced in the placebo condition, whereas an interaction analysis showed activity in the two regions was selectively attenuated in the placebo condition when unpleasant pictures were viewed. We also observed greater activity in the subgenual anterior cingulate cortex under placebo conditions when either emotionally negative or neutral pictures were viewed. These data suggest that the anxiety-relieving placebo effect arose from a reward-related response underpinned by the participants' expectations.