Abstract

Major depressive disorder (MDD) is becoming increasingly understood as a recurrent and sometimes chronic disorder (Keller & Boland, 1998). Some theorists have invoked the concept of stress sensitization to explain the recurrent nature of MDD, arguing that negative cognitive structures and their products may become activated with increasingly minimal environmental cues among individuals with a history of MDD (Clark & Beck, 1999). To test this formulation, an interview-based measure of life stress was added to an existing research protocol investigating the role that cognition plays in the onset and maintenance of depression. The life stress measure assessed stressful life events occurring prior to the onset of depression, and the cognitive tasks in the protocol assessed the levels of biased perception, attention, and memory that were present during the depressive episode. Analyses were then conducted to examine the associations between severe life stress and levels of cognitive bias for all participants, and the associations between non-severe life stress and levels of cognitive bias for participants with and without extensive histories of depression. The extent to which scores from the cognitive bias tasks cohered as measures of a unitary construct was also examined.

Overall, exposure to severe life stress was significantly associated with endorsement of more sad and physical threat self-adjectives. Among individuals with more than two lifetime episodes of depression, exposure to non-severe life stress was significantly associated with greater selective attention for sad faces, endorsement of fewer sad self-adjectives, quicker reaction times to endorse sad and positive self-adjectives, recall of fewer previously-endorsed sad self-adjectives, and recall of more previously-endorsed positive self-adjectives. In general, scores from the different cognitive bias tasks did not cohere as measures of a unitary construct. These findings offer partial support for the formulation that severe life stress activates negative cognitive biases, and that such biases may become activated with increasingly minimal environmental cues among individuals with a history of depression. The implications of these findings are discussed in light of the roles that life stress and cognitive biases play in the onset of depression.