Dopamine prediction error responses integrate subjective value from different reward dimensions

Significance Most real-world rewards have multiple dimensions, such as amount, risk, and type. Here we show that within a bounded set of such multidimensional rewards monkeys’ choice behavior fulfilled several core tenets of rational choice theory; namely, their choices were stochastically complete and transitive. As such, in selecting between rewards, the monkeys behaved as if they maximized value on a common scale. Dopamine neurons encoded prediction errors that reflected that scale. A particular reward dimension influenced dopamine activity only to the extent that it influenced choice. Thus, vastly different reward types such as juice and food activated dopamine neurons in accordance with subjective value derived from the different rewards. This neuronal signal could serve to update value signals for economic choice. Prediction error signals enable us to learn through experience. These experiences include economic choices between different rewards that vary along multiple dimensions. Therefore, an ideal way to reinforce economic choice is to encode a prediction error that reflects the subjective value integrated across these reward dimensions. Previous studies demonstrated that dopamine prediction error responses reflect the value of singular reward attributes that include magnitude, probability, and delay. Obviously, preferences between rewards that vary along one dimension are completely determined by the manipulated variable. However, it is unknown whether dopamine prediction error responses reflect the subjective value integrated from different reward dimensions. Here, we measured the preferences between rewards that varied along multiple dimensions, and as such could not be ranked according to objective metrics. Monkeys chose between rewards that differed in amount, risk, and type. Because their choices were complete and transitive, the monkeys chose “as if” they integrated different rewards and attributes into a common scale of value. The prediction error responses of single dopamine neurons reflected the integrated subjective value inferred from the choices, rather than the singular reward attributes. Specifically, amount, risk, and reward type modulated dopamine responses exactly to the extent that they influenced economic choices, even when rewards were vastly different, such as liquid and food. This prediction error response could provide a direct updating signal for economic values.