Dysfunction of processing task-irrelevant emotional faces in major depressive disorder patients revealed by expression-related visual MMN.

We compared the pre-attentive processing of emotional faces in major depressive disorder (MDD) patients and matched healthy controls as indexed by the visual mismatch negativity (vMMN) elicited by emotional faces presented in upright and inverted orientations. Compared with standard neutral faces, infrequent emotional faces elicited posterior negativities between 100ms and 350ms. Early vMMN was smaller, while late vMMN was absent in the MDD group, as compared with the normal group. Face inversion decreased the vMMN in the normal group but had no effect on MDD patients. These data suggest the functional dysfunction of pre-attentive expressional information processing in MDD patients, coupled with the disorder of high-level perceptual strategy of processing emotional faces.