Abstract
Clinical investigators have long theorized about the role of reward processing and positive affect in depression. One theory posits that compared to nonmelancholic depressives, melancholic depressives experience less consummatory (i.e., post-reward), but comparably low anticipatory (prior to reward), positive affect. We tested whether frontal EEG asymmetry, a putative marker of the anticipatory reward system, is present only before an individual receives a reward or also after receiving a reward (i.e., during consummatory reward processing). We also examined whether melancholic depression, a condition characterized by a deficit in consummatory reward processing, is associated with abnormal EEG asymmetries in alpha band power. Effects in other frequency bands (delta, theta, or beta) were also explored. EEG was recorded in 34 controls, 48 nonmelancholic depressives, and 17 melancholic depressives during a slot machine task designed to elicit anticipatory and consummatory reward processing. Results indicated that, for alpha, the frontal EEG asymmetry of greater relative left activity was specific to anticipatory reward processing. During the consummatory phase, individuals with melancholic depression exhibited different posterior EEG asymmetries than individuals with nonmelancholic depression (and controls at a trend level). This second finding was largely due to melancholics exhibiting relatively lower right posterior activity and nonmelancholics exhibiting relatively lower left activity. These results suggest that a posterior asymmetry may be a marker for melancholic depression and aberrant consummatory reward processing.
Highlights
Clinical investigators have long theorized about the role of reward processing and positive affect in depression
Because melancholics and nonmelancholics differed on Hamilton severity, we examined whether group differences in posterior asymmetry were due to depression severity rather than the presence of melancholia
The majority of previous investigations examining the relationship between EEG and depression have recorded EEG while participants were at rest
Summary
Clinical investigators have long theorized about the role of reward processing and positive affect in depression. This second finding was largely due to melancholics exhibiting relatively lower right posterior activity and nonmelancholics exhibiting relatively lower left activity These results suggest that a posterior asymmetry may be a marker for melancholic depression and aberrant consummatory reward processing. Consistent with D.F. Klein’s theory of anticipatory PA deficits in depression, EEG measurements of cortical activity have found that individuals with and at risk for MDD exhibit the hypothesized frontal asymmetry relative to controls (Debener et al, 2000; Gotlib et al, 1998; Henriques & Davidson, 1991; Tomarken et al, 2004; Thibodeau et al, 2006; see Reid et al, 1998 for contrary evidence).
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