Speaker: Wolfram Schultz, Ph.D.
Dopamine Neurons and The Economics of Reward Value and Risk
Time: 5:00 pm – 6:30 pm Reception to follow
Date: Monday, March 5th, 2018
Location: NYU Rosenthal Pavilion 60 Washington Square South, 10th floor New York, NY 10012
Rewards induce learning (positive reinforcement), approach behavior, economic decisions and positive emotions (pleasure, desire). We investigate basic neuronal reward signals during learning and decision-making, using behavioral and neurophysiological methods.
The phasic dopamine reward prediction error 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 generalization and reward context. The second component codes reward value. Although the first component detects punishers by their physical impact, none of the activations reflects the aversive nature of punishers. Dopamine activity also shows slower, heterogeneous and inconsistent changes related to widely ranging behavioral events not easily conceptualized by formal behavioral theories. A much slower, basically tonic dopamine neurotransmission is compromised in Parkinson’s disease and often subjected to pharmacological tests.
Our recent experimental economics studies reveal that monkeys are risk-seeking with small rewards and risk neutral and then risk avoiders with larger rewards. Specifically structured behavioral tests allow us to estimate formal economic utility functions from certainty equivalents assessed during choices under risk (Von Neumann-Morgenstern utility). The animals’ choices are meaningful in satisfying first, second and third order stochastic dominance, which defines rational choices governed by value, symmetric (variance) risk and skewness risk, respectively. The biological plausibility of the theoretical construct of risk is evidenced by explicit neuronal risk signals in the orbitofrontal cortex. The utility itself is coded in dopamine neurons as utility prediction error that incorporates risk into subjective value. Consistent with this neuronal signal, the dopamine response satisfies first- and second-order stochastic dominance. These data unite concepts from animal learning theory and economic decision theory at the level of single reward neurons.