Life stress and blunted reward processing each have been associated with the onset and maintenance of major depressive disorder. However, much of this work has been cross-sectional, conducted in separate lines of inquiry, and focused on recent life stressor exposure, despite the fact that theories of depression posit that stressors can have cumulative effects over the lifespan. To address these limitations, we investigated whether acute and chronic stressors occurring over the lifespan interacted with blunted reward processing to predict increases in depression over time in healthy youth.

Participants were 245 adolescent girls aged 8–14 years old (Mage = 12.4, s.d. = 1.8) who were evaluated at baseline and two years later. The reward positivity (RewP), an event-related potential measure of reward responsiveness, was assessed at baseline using the doors task. Cumulative lifetime exposure to acute and chronic stressors was assessed two years later using the Stress and Adversity Inventory for Adolescents (Adolescent STRAIN). Finally, depressive symptoms were assessed at both baseline and follow-up using the Children's Depression Inventory.

As hypothesized, greater lifetime acute stressor exposure predicted increases in depressive symptoms over two years, but only for youth exhibiting a blunted RewP. This interaction, however, was not found for chronic stressors.

Lifetime acute stressor exposure may be particularly depressogenic for youth exhibiting a blunted RewP. Conversely, a robust RewP may be protective in the presence of greater acute lifetime stressor exposure.

Multiple studies have found a reduced reward positivity (RewP) among individuals with major depressive disorder (MDD). Event-related potential studies have also reported blunted neural responses to pleasant pictures in MDD as reflected by the late positive potential (LPP). These deficits have been interpreted broadly in terms of anhedonia and decreased emotional engagement characteristic of depression.

In the current study, a community-based sample of 83 participants with current MDD and 45 healthy individuals performed both a guessing task and a picture viewing paradigm with neutral and pleasant pictures to assess the RewP and the LPP, respectively.

We found that both RewP and LPP to pleasant pictures were reduced in the MDD group; moreover, RewP and LPP were both independent predictors of MDD status. Within the MDD group, a smaller RewP predicted impaired mood reactivity in younger but not older participants. Smaller LPP amplitudes were associated with increased anhedonia severity in the MDD group.

These data replicate and merge separate previous lines of research, and suggest that a blunted RewP and LPP reflect independent neural deficits in MDD – which could be used in conjunction to improve the classification of depression.

Reward processing deficits have been implicated in the etiology of depression. A blunted reward positivity (RewP), an event-related potential elicited by feedback to monetary gain relative to loss, predicts new onsets and increases in depression symptoms. Etiological models of depression also highlight stressful life events. However, no studies have examined whether stressful life events moderate the effect of the RewP on subsequent depression symptoms. We examined this question during the key developmental transition from childhood to adolescence.

A community sample of 369 children (mean age of 9) completed a self-report measure of depression symptoms. The RewP to winning v. losing was elicited using a monetary reward task. Three years later, we assessed stressful life events occurring in the year prior to the follow-up. Youth depressive symptoms were rated by the children and their parents at baseline and follow-up.

Stressful life events moderated the effect of the RewP on depression symptoms at follow-up such that a blunted RewP predicted higher depression symptoms in individuals with higher levels of stressful life events. This effect was also evident when events that were independent of the youth's behavior were examined separately.

These results suggest that the RewP reflects a vulnerability for depression that is activated by stress.