The fruits of your labor: Neuromodulatory effects of effort and endocrine signals on food reward
Human Cognitive and Systems Neuroscience
Final Report Abstract
The prospect of reward can help to “fuel” instrumental action. However, opportunity costs of action such as increased effort and uncertainty of reward receipt can affect the subjective value of a reward (i.e., cost/benefit analysis). While neuroeconomic theories posit that increased effort will lead to discounting of the reward value, psychological and philosophical theories suggest that effort justification may increase the reward value in retrospect. This project aimed to improve our understanding of the effects of effort requirements on the neural processing of rewards during the stages of anticipation and consumption. Using functional magnetic resonance imaging (fMRI), we literally investigated the brain response to the “the fruit of labor” by employing a newly developed task in healthy participants sampled from a wide range of body mass index (BMI). I predicted that higher BMI would be associated with an increased sensitivity to effort requirements. In a number of detailed analyses of time series data extracted from several hubs of the feeding network, I could demonstrate that variability in brain response is a reproducible characteristic of an individual that is predictive of body weight regulation, feeding behavior, and metabolic health, thereby providing support for the critical assumption of the project during the first stage. During the second stage, I developed the “fruit of your labor” (FOYL) task to quantify the effects of effort requirements on trial-by-trial differences in behavioral approach and brain response. First, the analysis of liking and wanting ratings suggested that effort requirements do not lead to a monotonic decrease in liking, as expected based on the classical economic framework of discounting. In line with cognitive dissonance theory, however, we found that highest-effort rewards (level four) were liked more than just high-effort rewards (level three) despite of the increased opportunity costs of action. Second, we found that effort discounting in the dorsal striatum during anticipation was positively correlated with the effort bias during milkshake consumption, indicating a shared evaluation process during both stages. Critically, individuals with high BMI were grouped towards the end of the “effort discounting” dimension as hypothesized. Third, we found that hemoglobin A1C, a common indicator of glycemic control and insulin sensitivity was negatively associated with the invigoration of approach behavior by reward and the effort bias during consumption of the milkshake reward, pointing to a potential contribution to the observed effects by insulin sensitivity. Collectively, these results provide novel results on the cost/benefit analyses of instrumental behavior that may help to improve our understanding of the interdependence of overweight and obesity and a sedentary lifestyle. Moreover, the results in lean individuals provide a potential neurobiological mechanism for the so-called “IKEA effect” used to describe the increase in the subjective value of a reward by preceding effort requirements.
Publications
- (2015). Basolateral amygdala response to food cues in the absence of hunger is associated with weight gain susceptibility. The Journal of Neuroscience, 35, p. 7964-7976
Sun, X., Kroemer, N. B., Veldhuizen, M. G., Babbs, A. E., de Araujo, I. E., Gitelman, D. R., Sherwin, R. S., Sinha, R., & Small, D. M.
(See online at https://doi.org/10.1523/JNEUROSCI.3884-14.2015) - (2016). Weighting the evidence: Variance in brain responses to milkshake receipt is predictive of eating behavior, NeuroImage, 128, p. 273-283
Kroemer, N. B., Sun, X., Veldhuizen, M. G., Babbs, A. E., de Araujo, I. E., & Small, D. M.
(See online at https://doi.org/10.1016/j.neuroimage.2015.12.031)
