Worth the 'EEfRT'? The effort expenditure for rewards task as an objective measure of motivation and anhedonia

Abstract

Background: Of the putative psychopathological endophenotypes in major depressive disorder (MDD), the anhedonic subtype is particularly well supported. Anhedonia is generally assumed to reflect aberrant motivation and reward responsivity. However, research has been limited by a lack of objective measures of reward motivation. We present the Effort-Expenditure for Rewards Task (EEfRT or "effort"), a novel behavioral paradigm as a means of exploring effort-based decision-making in humans. Using the EEfRT, we test the hypothesis that effort-based decision-making is related to trait anhedonia.

Methods/results: 61 undergraduate students participated in the experiment. Subjects completed self-report measures of mood and trait anhedonia, and completed the EEfRT. Across multiple analyses, we found a significant inverse relationship between anhedonia and willingness to expend effort for rewards.

Conclusions: These findings suggest that anhedonia is specifically associated with decreased motivation for rewards, and provide initial validation for the EEfRT as a laboratory-based behavioral measure of reward motivation and effort-based decision-making in humans.

Figure 1. Schematic diagram of a single trial of the Effort Expenditure for Rewards Task (‘EEfRT’).

A) Subjects begin by seeing a 1s fixation cue. B) 5s choice period in which subjects are presented with information regarding the reward magnitude of the hard task for that trial, and the probability of receiving any reward for that trial. C) 1s “ready” screen. D) Subjects make rapid button presses to complete the chosen task for 7s (easy task) or 21s (hard task). E) Subjects receive feedback on whether they have completed the task. F) Subjects receive reward feedback as to whether they received any money for that trial.

Figure 2. Partial regression plots between measures of anhedonia and proportion of hard-task choices, controlling for gender.

Figure 3. Relationship between Chapman anhedonia scores and GEE model predicted scores for trials with hard-task reward magnitudes >$3.50.

Only trials at 50% probability level showed a significant relationship between anhedonia and model fit. The relationship between anhedonia and model fit for 50% probability trials was still significant after the outlier subject with the highest Chapman score was removed (b = −.052, p = .002). The presence of two lines both yellow and blue trials reflects differences in model fit due to gender.