Abnormalities in automatic and strategic encoding of emotional information in current and remitted major depression: An ERP investigation

Abnormal processing of emotional information has been implicated in the etiology and manifestation of major depressive disorder (MDD; Beck, 1967). It is proposed that automatic activation of affectively imbalanced semantic networks represents a trait feature of MDD, whereas strategic processes (e.g., categorization and elaboration) may modulate the expression of abnormal automatic responses to emotional information depending on the disease state. This hypothesis was tested in three intentional free recall studies using event-related brain potentials (ERPs) indexing automatic (P2 and P3a) and strategic (P3b, late positive component [LPC], and slow wave [SW]) cognitive processes. Study 1 investigated whether abnormalities in automatic and strategic processing of normative emotional information depend on current phase of the disorder. ERP amplitudes were examined in current MDD, remitted MDD, and control groups during two categorization tasks designed to maximize automatic semantic identification (perceptual categorization) and strategic evaluation (affective categorization). Study 2 investigated contributions of automatic and strategic processes to self-referential memory biases. ERP amplitudes were examined in current MDD, remitted MDD, and control individuals while they were making judgments whether an emotional word describes them (self-referential categorization) or former president Clinton (other-referential categorization). Study 3 investigated whether individuals with MDD exhibit abnormal sustained strategic elaboration of emotional information, as indexed by the SW, during unstructured encoding of emotional self-relevant information. Decreased ERP amplitudes during automatic processing of normative and self-referent positive relative to negative and/or neutral stimuli were observed in individuals with current and remitted MDD. Similar processing biases and abnormal patterns of lateralization in response to negative stimuli were observed during strategic categorization and sustained encoding of normative and self-referent stimuli in the current MDD group. Remitted MDD participants demonstrated increased amplitudes during strategic categorization of positive relative to negative self-referent stimuli. Finally, control participants demonstrated positive ERP biases during automatic and strategic self-referent categorization and sustained encoding. These findings support the main hypothesis suggesting that abnormal automatic processing of emotional stimuli represents a trait-dependent feature of MDD, while abnormalities in strategic processes emerge primarily during acute episodes of the disorder. These results are discussed in the context of cognitive and neurobiological theories of depression.