Placebo in emotional processing--induced expectations of anxiety relief activate a generalized modulatory network.

Placebo analgesia and reward processing share several features. For instance, expectations have a strong influence on the subsequent emotional experience of both. Recent imaging data indicate similarities in the underlying neuronal network. We hypothesized that placebo analgesia is a special case of reward processing and that placebo treatment could modulate emotional perception in the same way as does pain perception. The behavioral part of this study indicates that placebo treatment has an effect on how subjects perceive unpleasant pictures. Furthermore, event-related fMRI demonstrated that the same modulatory network, including the rostral anterior cingulate cortex and the lateral orbitofrontal cortex, is involved in both emotional placebo and placebo analgesia. These effects were correlated with the reported placebo effect and were predicted by the amount of treatment expectation induced on a previous day. Thus, the placebo effect may be considered to be a general process of modulation induced by the subjects' expectations.