Published on December 13, 2018 | Updated on January 29, 2019

CORTEX conference by Wolfram Schulz

February 26th, 2015

Phasic dopamine signals coding subjective value and formal economic utility

Rewards induce learning (positive reinforcement), approach behaviour, economic decisions and positive emotions (pleasure, desire). We investigate basic neuronal reward signals during learning and decision-making, using behavioural and neurophysiological methods. The phasic dopamine signal is composed of two components, resembling two-component responses in main sensory neurons. The early dopamine response component detects events indiscriminately and is influenced by physical impact, novelty, reward generalisation and reward context. The second component constitutes the reward prediction error response. Although the first component detects punishers by their physical impact, none of the components codes the aversive nature of punishers. Our behavioural studies reveal that monkeys are risk seeking with small rewards and risk neutral and then risk avoiders with larger rewards. The animals' choices are meaningful in satisfying first and second order stochastic dominance. Quantitative behavioural tests allow us to assess the common currency relationship of dopamine responses to subjective value derived from risk, different rewards and temporal discounting. Neuronal satisfaction of both forms of stochastic dominance suggests meaningful processing of value under risk and incorporation of risk into subjective value. Assessment of economic utility goes one step further and determines subjective value as mathematical function of objective value (of liquid reward). The dopamine reward signal follows closely the nonlinear utility function and thus codes a prediction error in economic utility. These data unite concepts from animal learning theory and economic decision theory at the level of single reward neurons.