Is it Worth the Effort? Novel Insights into Obesity-Associated Alterations in Cost-Benefit Decision-Making

Abstract

Cost-benefit decision-making entails the process of evaluating potential actions according to the trade-off between the expected reward (benefit) and the anticipated effort (costs). Recent research revealed that dopaminergic transmission within the fronto-striatal circuitry strongly modulates cost-benefit decision-making. Alterations within the dopaminergic fronto-striatal system have been associated with obesity, but little is known about cost-benefit decision-making differences in obese compared with lean individuals. With a newly developed experimental task we investigate obesity-associated alterations in cost-benefit decision-making, utilizing physical effort by handgrip-force exertion and both food and non-food rewards. We relate our behavioral findings to alterations in local gray matter volume assessed by structural MRI. Obese compared with lean subjects were less willing to engage in physical effort in particular for high-caloric sweet snack food. Further, self-reported body dissatisfaction negatively correlated with the willingness to invest effort for sweet snacks in obese men. On a structural level, obesity was associated with reductions in gray matter volume in bilateral prefrontal cortex. Nucleus accumbens volume positively correlated with task induced implicit food craving. Our results challenge the common notion that obese individuals are willing to work harder to obtain high-caloric food and emphasize the need for further exploration of the underlying neural mechanisms regarding cost-benefit decision-making differences in obesity.

Keywords: cost-benefit decision-making; obesity; physical effort; reward; voxel-based morphometry.

Figure 1

Schematic representation of the novel cost-benefit decision-making task (A). Across all subjects, likelihood of choosing to grip decreases over task blocks (40 trials each) (B) and is dependent on both effort and reward magnitude (C). Subjects exerted effort more often for money than for fruit and sweet snacks (D). Subjects decided fastest to expend effort in trials with low effort and high reward magnitudes and decided slowest to reject these offers (E). Men decided faster in trials involving monetary reward than in food reward trials (F). Depicted values are corrected for factors and covariates within the respective GEE model. Asterisks indicate significance within the respective GEE model reported in the Results Section.

Figure 2

An interaction between reward category and obesity revealed that obese compared with lean subjects less often chose to grip for sweet high-caloric snacks, but performed similarly with respect to fruits and money as rewards. Obese subjects also more often decided to grip for money and for fruits than for sweets, this effect was not apparent in lean subjects. Depicted values are corrected for factors and covariates within the respective GEE model. Asterisks indicate significance within the respective GEE model reported in the Results Section.

Figure 3

Chronic stress (A) and punishment sensitivity (B) correlated negatively with the likelihood of choosing to exert effort. Depicted values are corrected for factors and covariates within the respective GEE model.

Figure 4

A four-way interaction between reward category, obesity, gender, and body dissatisfaction showed that obese men's cost-benefit decisions regarding sweet snacks were negatively correlated with their self-reported body dissatisfaction (D). No such association was observed for lean women (A), lean men (B), and obese women (C). Depicted values are corrected for factors and covariates within the respective GEE model. Asterisks depict significance within the GEE model.

Figure 5

Obese subjects had lower gray matter volume in bilateral PFC compared with lean participants (A). NAcc volume positively correlated with severity of implicit food craving (B,C).