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    Explicit neural signals reflecting reward uncertainty
    Schultz, W ; Preuschoff, K ; Camerer, C ; Hsu, M ; Fiorillo, CD ; Tobler, PN ; Bossaerts, P (ROYAL SOC, 2008-12-12)
    The acknowledged importance of uncertainty in economic decision making has stimulated the search for neural signals that could influence learning and inform decision mechanisms. Current views distinguish two forms of uncertainty, namely risk and ambiguity, depending on whether the probability distributions of outcomes are known or unknown. Behavioural neurophysiological studies on dopamine neurons revealed a risk signal, which covaried with the standard deviation or variance of the magnitude of juice rewards and occurred separately from reward value coding. Human imaging studies identified similarly distinct risk signals for monetary rewards in the striatum and orbitofrontal cortex (OFC), thus fulfilling a requirement for the mean variance approach of economic decision theory. The orbitofrontal risk signal covaried with individual risk attitudes, possibly explaining individual differences in risk perception and risky decision making. Ambiguous gambles with incomplete probabilistic information induced stronger brain signals than risky gambles in OFC and amygdala, suggesting that the brain's reward system signals the partial lack of information. The brain can use the uncertainty signals to assess the uncertainty of rewards, influence learning, modulate the value of uncertain rewards and make appropriate behavioural choices between only partly known options.
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    Markowitz in the brain?
    Preuschoff, K ; Quartz, S ; Bossaerts, P (Editions Dalloz, 2008)
    Brain-scanning (fMRI) evidence is presented that activity in certain sub-cortical structures of the human brain correlate with changes in expected reward, and with risk. Risk is measured by variance of payoff, as in Markowitz’ theory. These brain structures form part of the dopaminergic system (which consists of the neurons that emit a crucial chemical, namely, dopamine, and the areas to which the dopamine neurons project). The dopaminergic system has been known to regulate reward expectation. We show that it is involved in risk perception as well. As such, our findings support for the human brain what recently had been discovered in the primate brain (using single-neuron analysis instead of fMRI).