Hypoactivation of ventromedial frontal cortex in major depressive disorder: an MEG study of the Reward Positivity.

Background: The Reward Positivity (RewP) is sensitive and specific electrophysiological marker of reward receipt. These characteristics make it a compelling candidate marker of dysfunctional reward processing in major depressive disorder. We previously proposed that the RewP is a nexus of multiple aspects of reward variance, and that a diminished RewP in depression might only reflect a deficit in some of this variance. Specifically, we predicted a diminished ventromedial contribution in depression in the context of maintained reward learning. Methods: Here we collected magnetoencephalographic (MEG) recordings of reward receipt in 43 individuals with major depressive disorder (MDD group) and 38 healthy controls (CTL group). MEG allows effective source estimation due to the absence of volume conduction that compromises electroencephalographic recordings. Results: The MEG RewP analogue was generated by a broad set of cortical areas, yet only right ventromedial and right ventral temporal areas were diminished in MDD. These areas correlated with a principal component of anhedonia derived from multiple questionnaires. Compellingly, BA25 was the frontal region with the largest representation in both of these effects. Conclusions: These findings not only advance our understanding underlying the computation of the RewP, but they also dovetail with convergent findings from other types of functional source imaging in depression, as well as from deep brain stimulation treatments. Together, these discoveries suggest that the RewP may be a valuable marker for objective assessment of reward affect and its disruption in major depression.