The neural substrates of affective processing toward positive and negative affective pictures in patients with major depressive disorder.

Previous studies examining neural responses to emotional stimuli in individuals with major depressive disorder (MDD) have indicated increased responses within the left amygdala to sad faces, and increased activity within the visual cortex and striatum to expressions of happiness. Using functional magnetic resonance imaging (fMRI), the current study measured neural responses to neutral, positive and negative pictures of the International Affective Picture System in 15 healthy individuals and 15 patients with MDD. Depressed individuals demonstrated lower activity in the right hippocampus and the right insula to negative affective pictures, whereas they showed lower activity in the right anterior cingulate cortex and the left insula to positive pictures. However, within the MDD group, the severity of depression correlated with the activity of the left amygdala, bilateral inferior orbitofrontal areas, and the left insula to negative pictures, whereas there were no clear indications of association between specific cerebral regions and positive pictures. Our findings indicate that preferential decreases in the left amygdala in response to negative pictures might be involved in the processing of emotional stimuli in depressed individuals. Also, these findings suggest that the bilateral inferior orbitofrontal cortices and left amygdala may be preferentially recruited in MDD patients, but not in healthy individuals.