Depression, one of the most widespread mental disorders, is associated with considerable alterations in emotional functioning. It is unclear whether these alterations are associated with clinical depression or exist already at preclinical stages. Here, in clinically healthy individuals, a combination of neuroticism and introversion was used as a predisposition to depression (PD) scale. Participants were presented with pictures of emotional facial expressions and performed the gender discrimination task, while their electroencephalogram (EEG) was recorded. The affective processing bias (i.e., longer reaction time and higher error rate for angry faces) was found in low, but not in high PD scorers. High PD scorers also showed reduced theta synchronization and enhanced alpha desynchronization in the test interval and higher delta and theta power in the interstimuli interval. The latter effect implies that activity of emotional circuits, which is mirrored in low-frequency oscillations, is tonically increased in predisposed-to-depression individuals, thus precluding an adequate response to external emotional cues. This results in unspecific general activation reflected in enhanced alpha desynchronization and in disrupted ability to differentiate incoming emotional information.
Keywords: Electroencephalogram; Emotional facial expressions; Implicit emotion processing; Predisposition to depression; Theta and alpha oscillations.