Depressive symptoms and depressed mood affect cognitive processing of emotional information : evidence from psychophysiological and behavioral studies

Abstract

Depression is a severe mental health disorder. Many empirical studies using experimental static stimuli, such as pictures, have reported alterations in the processing of emotional information in depression. However, the way depressed people react to dynamic emotional stimuli has not yet been researched in depth. It is also unclear how depressed mood in healthy people influence the processing of emotional information. This doctoral thesis investigates these issues. In three studies, the measurements of electrical brain activity (event-related potential (ERP)), physiological reactivity (electrodermal activity (EDA)), and behavioral responses (facial electromyography (EMG); valence rating), were applied. Study I investigated the cognitive and affective processing of ironic conversations in depressed and non-depressed individuals. The results showed greater brain responses (N400 and P600) to ironic than to non-ironic punchlines in both groups, indicating increased cognitive effort in interpreting ironic meanings. A right-hemisphere dominant P600 modulation to irony was found specifically in the depressed group. However, no depression-related alterations were found in facial EMG specifically related to irony. Study II explored the intersubject synchrony of dynamic valence ratings (i.e., the similarity of ratings) across depressed and non-depressed participants when viewing amusing, sad, and fearful movie clips. The results showed that the synchrony of valence ratings to sad movies across depressed participants was lower compared to the controls, which may reflect less stimulus-dependent processing in depression when viewing mood-congruent stimuli. Study III investigated how depressed mood, which was induced with sad music and statements, affected brain responses by measuring the preattentive detection of changes in facial expressions in healthy participants. The induced depressed mood affected the encoding of face structure, which was indexed by the brain’s smaller amplitude of N170 differential responses in depressed mood rather than neutral mood. In sum, this dissertation shows evidence that depressive symptoms affect the cognitive processing of different types of dynamic emotional stimuli, and it also provides the first evidence of the effect of depressed mood on healthy participants’ preattentive face perception.