Major depressive disorder associated alterations in the effective connectivity of the face processing network: a systematic review

Major depressive disorder (MDD) is marked by altered processing of emotional stimuli, including facial expressions. Recent neuroimaging research has investigated how these stimuli alter the directional interactions between brain regions, however, due to methodological heterogeneity the reliability of these findings remains unclear. To address this, we systematically searched five databases: PsycINFO, EMBASE, PubMed, Scopus, and Web of Science, using a preregistered protocol (PROSPERO CRD42021271586). Of the 649 studies screened, 16 examined effective connectivity in MDD during the processing of emotional expressions. Overall, MDD patients demonstrated (1) reduced excitatory or increased inhibitory connectivity from the dorsolateral prefrontal cortex to amygdala during the processing of negatively valenced expressions, and (2) increased inhibitory connectivity from the ventromedial prefrontal cortex to amygdala during the processing of happy facial expressions. Consistencies observed across neuroimaging modalities warrant further investigation to determine the specificity of these effects. Future research examining a wider range of emotional expressions, longitudinal changes in effective connectivity, and effects of different treatments are necessary steps in clarifying the findings of this review.