hide
Free keywords:
-
Abstract:
Introduction:
Correct interpretation of emotional signals is crucial for successful social interactions. In the auditory domain, such signals can be expressed verbally (semantic information) and nonverbally by modulation of speech melody (prosody). Behavioral experiments documented an impaired identification of vocal emotions in patients with major depressive disorder (MDD), with deficits occurring both during perception of positive and negative emotional prosody [1]. Furthermore, a mood congruent bias could be shown for patients with unipolar depression which resulted in altered evaluation of prosodic stimuli [2]. So far, no neuroimaging studies on processing of emotional acoustic information in major depressive disorder are available.
Methods:
In this study, we investigated the neural correlates of disturbed perception of emotional information expressed by prosody in patients with MDD using functional magnetic resonance imaging (fMRI). We presented adjectives varying with respect to their emotional semantic content (positive, neutral and negative) which were spoken in happy, neutral or angry prosody. It was the task of the participants to either exclusively judge the valence (i.e., how positive or negative the emotional information was perceived) of the prosody or the semantic content (control task) on a five-point scale. This design enabled us to localize stimulus-dependent networks (comparison of emotional and neutral prosody) as well as task-dependent brain areas (comparison of judgment of prosody versus judgment of semantic content).
Results:
We found differences between MDD patients and healthy controls in the evaluation of emotional prosody. Specifically, we found depressed patients to give less intense ratings for positive emotional prosody than healthy controls. We did not find this difference in the evaluation of negative content, implying a reduced experience of positive information and a perceptual bias towards positive emotions in depressed patients. At neural level, we found activation differences between MDD patients and healthy controls, with patients showing stronger activation levels when processing emotional content as compared to healthy controls. Further, stronger activation in the left amygdala was found during the evaluation of emotional prosody, but not during the evaluation of semantic content (see Fig.1). No such differences were found in the voice areas. Subject depression scores were related to their neural responses, with higher levels of depression, yielding stronger activation in the left amygdala during the evaluation of emotional prosody.
Conclusions:
Our findings argue for a subcortical anatomical substrate underlying the observed mood congruent bias in MDD during judgement of vocal emotions. Therefore, our results add importantly to the understanding of processing emotional content in major depression disorder.
