Valuation of Reward with Long-Term Stimulant Abuse: The Specificity of Decision- Making Biases in Cocaine Addiction But Not Binge Eating Disorder

Background: Previous studies have suggested that cocaine users have higher delay discounting rates than controls when the data is analyzed using a hyperbolic model. However, there is growing evidence indicating that there are two processes in the decision associated with the delay discounting task. The aim of current study was to examine the impact of a two-parameter model in specifying the nature of several decision-making biases in cocaine users. Methods and findings: The study compared the findings resulting from a hyperbolic model and a saturating-hyperbolic model that specifies two parameters for both a delay discounting and a probability discounting task. Further, cocaine users (n=36) were compared with healthy controls (n=37); and binge eaters (n=20) were compared with non-binge eating controls (n=16) and overweight controls (n=19). The findings from the hyperbolic model replicated the results of previous studies and indicated cocaine users had higher delay discounting rates (z=-3.13, p=.002, d=0.79), but were not different from controls with respect to probability discounting rates (z=-0.68, p=0.50, d=0.16). However, when the data were analyzed with the saturating-hyperbolic function, cocaine users did not have significantly higher delay discounting rates than controls (z=-1.62, p=0.11, d=0.39). Rather, they showed significantly higher saturation indices than controls on both delay discounting task (z=-2.32, p=0.02, d=0.56) and probability discounting task (z=-2.24, p=0.025, d=0.56). This was not observed in binge eaters. Conclusion: The observed decision-making bias in cocaine users is more associated with the valuation bias of objective rewards than impatience. Chronic cocaine users tend to demand higher rewards to be satisfied. This may be due to acquired reward insensitivity after repeated exposure to cocaine. This effect does not seem to be germane to the acquisition and maintenance of binge eating.