Reduced hedonic capacity in major depressive disorder: evidence from a probabilistic reward task

Abstract

Objective: Anhedonia, the lack of reactivity to pleasurable stimuli, is a cardinal feature of depression that has received renewed interest as a potential endophenotype of this debilitating disease. The goal of the present study was to test the hypothesis that individuals with major depression are characterized by blunted reward responsiveness, particularly when anhedonic symptoms are prominent.

Methods: A probabilistic reward task rooted within signal-detection theory was utilized to objectively assess hedonic capacity in 23 unmedicated subjects meeting DSM-IV criteria for major depressive disorder (MDD) and 25 matched control subjects recruited from the community. Hedonic capacity was defined as reward responsiveness - i.e., the participants' propensity to modulate behavior as a function of reward.

Results: Compared to controls, MDD subjects showed significantly reduced reward responsiveness. Trial-by-trial probability analyses revealed that MDD subjects, while responsive to delivery of single rewards, were impaired at integrating reinforcement history over time and expressing a response bias toward a more frequently rewarded cue in the absence of immediate reward. This selective impairment correlated with self-reported anhedonic symptoms, even after considering anxiety symptoms and general distress.

Conclusions: These findings indicate that MDD is characterized by an impaired tendency to modulate behavior as a function of prior reinforcements, and provides initial clues about which aspects of hedonic processing might be dysfunctional in depression.

Fig. 1

Schematic illustration of task design. For each trial, the subjects’ task was to decide whether a short (11.5 mm) or a long (13 mm) mouth was presented by pressing either the ‘z’ or the ‘/’ key of a PC keyboard. The reinforcement allocation and key assignments were counterbalanced across subjects.

Fig. 2

(A) Response bias, and (B) mean hit rates (averaged across the three blocks) for the more frequently rewarded (rich) stimulus and the lean stimulus for healthy control subjects (n = 25) and MDD subjects (n = 23). Error bars represent standard errors.

Fig. 3

(A) Probability of misclassifying a lean stimulus (i.e., lean miss rate) as a function of whether the preceding correct identification of a rich trial had been rewarded or not. (B) Probability of misclassifying a rich stimulus (i.e., rich miss rate) as a function of which stimulus was rewarded in the immediately preceding trial. Error bars represent standard errors; arrows and asterisks denote significant findings in post-hoc analyses.

Fig. 4

Scatterplot and Pearson correlation between the MASQ Anhedonic Depression (AD) score and rich miss rates (i.e., selecting “lean” when a rich stimulus was actually presented) for trials following non-rewarded correct identification of rich stimuli (r = 0.519, p = 0.011) within the MDD subjects (n = 23). MASQ: Mood and Anxiety Symptom Questionnaire (Watson et al., 1995).