Effort, anhedonia, and function in schizophrenia: reduced effort allocation predicts amotivation and functional impairment

Abstract

One of the most debilitating aspects of schizophrenia is an apparent interest in or ability to exert effort for rewards. Such "negative symptoms" may prevent individuals from obtaining potentially beneficial outcomes in educational, occupational, or social domains. In animal models, dopamine abnormalities decrease willingness to work for rewards, implicating dopamine (DA) function as a candidate substrate for negative symptoms given that schizophrenia involves dysregulation of the dopamine system. We used the effort-expenditure for rewards task (EEfRT) to assess the degree to which individuals with schizophrenia were wiling to exert increased effort for either larger magnitude rewards or for rewards that were more probable. Fifty-nine individuals with schizophrenia and 39 demographically similar controls performed the EEfRT task, which involves making choices between "easy" and "hard" tasks to earn potential rewards. Individuals with schizophrenia showed less of an increase in effort allocation as either reward magnitude or probability increased. In controls, the frequency of choosing the hard task in high reward magnitude and probability conditions was negatively correlated with depression severity and anhedonia. In schizophrenia, fewer hard task choices were associated with more severe negative symptoms and worse community and work function as assessed by a caretaker. Consistent with patterns of disrupted dopamine functioning observed in animal models of schizophrenia, these results suggest that 1 mechanism contributing to impaired function and motivational drive in schizophrenia may be a reduced allocation of greater effort for higher magnitude or higher probability rewards.

Figure 1

Percentage of hard task choices as a function of probability and reward magnitude.

Figure 2

Percentage of hard task choices as a function of reward magnitude, plotted separately for individuals with schizophrenia and healthy controls. The values in parenthesis are the effect size of the group difference at each reward magnitude.

Figure 3

Percentage of hard task choices as a function of reward probability, plotted separately for individuals with schizophrenia and healthy controls. The values in parenthesis are the effect size of the group difference at each reward magnitude. Note, the group X probability interaction was significant, though the group difference at the 88% probability condition was trend level.

Figure 4

Graphs illustrating the relationships between SLOF community and work function and the percentage of hard task choices in the 88% probability and high reward conditions. Correlation values are on each group, with * = p<.05 and ** p<.01.