Abstract
BackgroundMajor depressive disorder (MDD) is associated with a mood-congruent processing bias in the amygdala toward face stimuli portraying sad expressions that is evident even when such stimuli are presented below the level of conscious awareness. The extended functional anatomical network that maintains this response bias has not been established, however.AimsTo identify neural network differences in the hemodynamic response to implicitly presented facial expressions between depressed and healthy control participants.MethodUnmedicated-depressed participants with MDD (n = 22) and healthy controls (HC; n = 25) underwent functional MRI as they viewed face stimuli showing sad, happy or neutral face expressions, presented using a backward masking design. The blood-oxygen-level dependent (BOLD) signal was measured to identify regions where the hemodynamic response to the emotionally valenced stimuli differed between groups.ResultsThe MDD subjects showed greater BOLD responses than the controls to masked-sad versus masked-happy faces in the hippocampus, amygdala and anterior inferotemporal cortex. While viewing both masked-sad and masked-happy faces relative to masked-neutral faces, the depressed subjects showed greater hemodynamic responses than the controls in a network that included the medial and orbital prefrontal cortices and anterior temporal cortex.ConclusionsDepressed and healthy participants showed distinct hemodynamic responses to masked-sad and masked-happy faces in neural circuits known to support the processing of emotionally valenced stimuli and to integrate the sensory and visceromotor aspects of emotional behavior. Altered function within these networks in MDD may establish and maintain illness-associated differences in the salience of sensory/social stimuli, such that attention is biased toward negative and away from positive stimuli.
Highlights
A mood-congruent emotional processing bias toward negative information is a robust finding in major depressive disorder (MDD)
Depressed and healthy participants showed distinct hemodynamic responses to masked-sad and maskedhappy faces in neural circuits known to support the processing of emotionally valenced stimuli and to integrate the sensory and visceromotor aspects of emotional behavior
In a recent functional MRI study of implicit emotional processing biases in depressed and healthy participants [8] we reported that the negative bias in Major depressive disorder (MDD) is evinced by the hemodynamic responses of the amygdala to emotionally expressive face stimuli presented below conscious awareness using a backward masking technique
Summary
A mood-congruent emotional processing bias toward negative information is a robust finding in major depressive disorder (MDD). The amygdala plays a pivotal role in evaluating the behavioral salience of sensory stimuli, partly through subcortical networks that rapidly respond to stimulus features and objects processed at both conscious and non-conscious levels [18,19,20] In this role the amygdala forms part of extended anatomical networks that involve other mesiotemporal lobe structures, the sensory thalamus, the primary and associative sensory cortices, and the medial and orbital prefrontal cortex. The current study aimed to elucidate the extended functional anatomical network that participates with the amygdala in maintaining emotional processing biases in MDD, by identifying other brain regions where the hemodynamic response to masked-sad versus masked-happy face stimuli differed between depressed and healthy control participants. The extended functional anatomical network that maintains this response bias has not been established,
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