Salience Network Functional Connectivity Predicts Placebo Effects in Major Depression

Recent neuroimaging studies have demonstrated resting-state functional connectivity (rsFC) abnormalities among intrinsic brain networks in major depressive disorder (MDD); however, their role as predictors of treatment response has not yet been explored. Here, we investigate whether network-based rsFC predicts antidepressant and placebo effects in MDD. We performed a randomized controlled trial of two week-long, identical placebos (described either as having active fast-acting, antidepressant effects or as inactive) followed by a 10-week open-label antidepressant medication treatment. Twenty-nine participants underwent an rsFC functional magnetic resonance imaging scan at the completion of each placebo condition. Networks were isolated from resting-state blood oxygen level-dependent signal fluctuations using independent component analysis. Baseline and placebo-induced changes in rsFC within the default mode, salience, and executive networks were examined for associations with placebo and antidepressant treatment response. Increased baseline rsFC in the rostral anterior cingulate within the salience network, a region classically implicated in the formation of placebo analgesia and the prediction of treatment response in MDD, was associated with greater response to 1 week of active placebo and 10 weeks of antidepressant treatment. Machine learning further demonstrated that increased salience network rsFC, mainly within the rostral anterior cingulate, significantly predicts individual responses to placebo administration. These data demonstrate that baseline rsFC within the salience network is linked to clinical placebo responses. This information could be employed to identify patients who would benefit from lower doses of antidepressant medication or nonpharmacologic approaches or to develop biomarkers of placebo effects in clinical trials.