Dopaminergic Modulation of Decision Making and Subjective Well-Being

Abstract

The neuromodulator dopamine has a well established role in reporting appetitive prediction errors that are widely considered in terms of learning. However, across a wide variety of contexts, both phasic and tonic aspects of dopamine are likely to exert more immediate effects that have been less well characterized. Of particular interest is dopamine's influence on economic risk taking and on subjective well-being, a quantity known to be substantially affected by prediction errors resulting from the outcomes of risky choices. By boosting dopamine levels using levodopa (l-DOPA) as human subjects made economic decisions and repeatedly reported their momentary happiness, we show here an effect on both choices and happiness. Boosting dopamine levels increased the number of risky options chosen in trials involving potential gains but not trials involving potential losses. This effect could be better captured as increased Pavlovian approach in an approach-avoidance decision model than as a change in risk preferences within an established prospect theory model. Boosting dopamine also increased happiness resulting from some rewards. Our findings thus identify specific novel influences of dopamine on decision making and emotion that are distinct from its established role in learning.

Keywords: decision making; dopamine; reward prediction error; subjective well-being.

Copyright © 2015 Rutledge et al.

Figures

Figure 1.

Task design and performance on placebo and l-DOPA. A, In each of 300 trials, subjects made choices between safe and risky options. In 100 gain trials, the worst gamble outcome was zero. In 100 loss trials, the best gamble outcome was zero. In 100 mixed trials, both gamble outcome gains and losses were possible. Chosen gambles were resolved after a brief delay period. Subjects were also asked after every 3–4 choice trials “how happy are you at this moment?” and indicated their responses by moving a slider. B, On average, subjects (n = 30) gambled most in gain trials, less in mixed trials, and least in loss trials on both placebo and l-DOPA. Error bars indicate SEM. C, Subjects did not gamble more in mixed and loss trials on l-DOPA compared with placebo, but did gamble more in gain trials. *p < 0.05. D, Subjects who received higher effective drug doses chose more gain gambles on l-DOPA than placebo (p < 0.01).

Figure 2.

Choice behavior and economic decision model fits. A, Parametric model based on prospect theory explained choice behavior. Error bars indicate SEM. B, Parameter estimates were similar on placebo and l-DOPA. C, Gain gamble value was determined relative to the value of the certain option. Deciles 1–2 corresponded to lower expected reward for the gamble than the certain option. Decile 3 corresponded to equal expected reward for the gamble and certain option. Deciles 4–10 corresponded to higher expected reward for the gamble than the certain option. As gain gamble value increased, subjects gambled more on both placebo and l-DOPA, as expected. D, Average model fit across subjects for the prospect theory model, which cannot account for the observed difference in choice behavior on l-DOPA compared with placebo.

Figure 3.

Approach–avoidance model fits. A, Our approach–avoidance model incorporates an additional value-independent, valence-dependent effect on choice probability that accounts for the increased gambling on l-DOPA across gamble value deciles. B, Risk aversion parameters αgain and αloss for both placebo and l-DOPA sessions were <1, indicating risk aversion in the gain domain and risk seeking in the loss domain. Approach–avoidance parameter βgain was positive (“approach”) and βloss was negative (“avoid”) in placebo and l-DOPA sessions. Error bars indicate SEM. *p < 0.05. C, βgain was higher on l-DOPA than placebo, indicating an increased tendency to choose gain gambles independent of value. D, Subjects that received higher effective drug doses had a greater increase in βgain on l-DOPA than placebo (p < 0.05).

Figure 4.

Choice behavior and approach–avoidance model fits for mixed and loss trials. A, Mixed gamble value was determined by the ratio of the potential gain to the potential loss. As mixed gamble value increased, subjects gambled more, as expected. B, Average model fit across subjects for the approach–avoidance model. C, Subjects who received higher effective doses did not have a larger change in the number of mixed gambles chosen on l-DOPA than placebo (Spearman's ρ = 0.02, p = 0.91), a relationship that would be negative if l-DOPA decreased risk taking. D, Loss gamble value was determined relative to the value of the certain option. As loss gamble value increased, subjects gambled more, as expected. E, Average model fit across subjects for the approach–avoidance model, which can account for the low probability of gambling for even the highest gamble values in placebo and l-DOPA sessions. F, Subjects who received higher effective doses did not have a larger change in the number of loss gambles chosen on l-DOPA than placebo (Spearman's ρ = 0.19, p = 0.32), a relationship that would be negative if l-DOPA decreased risk taking.

Figure 5.

Happiness ratings across sessions. A, l-DOPA did not affect the mean or SD of happiness ratings. Error bars indicate SEM. B, Mean happiness ratings were uncorrelated across placebo and l-DOPA sessions (p = 0.27). C, SD of happiness ratings was correlated across placebo and l-DOPA sessions (p < 0.001). D, l-DOPA did not affect initial or final happiness ratings or how happy subjects remembered being the day after the session (all p > 0.2). Error bars indicate SEM. E, Mean happiness ratings were correlated with how happy subjects remembered being the day after the session (both Spearman's ρ > 0.5, p < 0.01). F, Remembered happiness was uncorrelated between placebo and l-DOPA sessions (Spearman's ρ = −0.21, p = 0.27).

Figure 6.

Rewards and expectations explain momentary subjective well-being. A, B, Happiness ratings and cumulative task earnings across subjects (n = 30) on placebo (A) and l-DOPA (B) (placebo: r2 = 0.49 ± 0.25; l-DOPA: r2 = 0.45 ± 0.25). Happiness model fits are displayed for the model in C. Subjects completed 300 choice trials and made a rating after every 3–4 trials for a total of 90 ratings. C, The computational model that best explained momentary happiness had positive weights for certain rewards, gamble EVs, and gamble RPEs. Error bars indicate SEM. D, An alternative computational model included separate positive and negative RPE terms. E, F, In trials with potential gains but not losses, happiness was higher after gamble wins than losses on both placebo and l-DOPA (both p < 0.05). Happiness was higher after the small rewards from low-value gain gambles on l-DOPA compared with placebo (E), but not for the large rewards from high-value gain gambles (F). Error bars indicate SEM. *p < 0.05.