Context: Major depressive disorder (MDD) is associated with behavioral and neurophysiological evidence of mood-congruent processing biases toward explicitly presented, emotionally valenced stimuli. However, few studies have investigated such biases toward implicitly presented stimuli.
Objective: To investigate differential amygdala responses to sad, happy, and neutral faces presented below the level of explicit conscious awareness using a backward masking task in unmedicated participants with MDD and healthy controls (HCs).
Design: Initial cross-sectional design followed by a longitudinal treatment trial using functional magnetic resonance imaging.
Setting: Psychiatric outpatient clinic at the National Institute of Mental Health.
Participants: We studied 22 unmedicated, currently depressed people with MDD (dMDD), 16 unmedicated individuals with MDD in full remission (rMDD), and 25 HCs.
Intervention: Ten dMDD participants underwent 8 weeks of antidepressant treatment with the selective serotonin reuptake inhibitor sertraline hydrochloride.
Main outcome measures: Amygdala region-of-interest and whole-brain analyses evaluated the hemodynamic response during exposure to masked sad vs masked happy faces, to masked sad vs neutral faces, and to masked happy vs neutral faces.
Results: The dMDD participants showed greater amygdala responses than HCs to masked sad faces, whereas HCs showed greater amygdala responses to masked happy faces. The bias toward sad faces also was evident in rMDD participants relative to HCs and did not differ between dMDD and rMDD participants. This processing bias reversed toward the normative pattern in dMDD participants after sertraline treatment.
Conclusions: Emotional-processing biases occur in amygdala responses to sad faces presented below the level of conscious awareness in dMDD or rMDD individuals and to happy faces in HCs. By influencing the salience of social stimuli, mood-congruent processing biases in the amygdala may contribute to dysfunction in conscious perceptions and social interactions in MDD. Our data suggest, however, that the negative bias resolves and a positive bias develops in patients with MDD during selective serotonin reuptake inhibitor treatment.