Academic journal article Cognitive, Affective and Behavioral Neuroscience

Behavioral, but Not Reward, Risk Modulates Activation of Prefrontal, Parietal, and Insular Cortices

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Behavioral, but Not Reward, Risk Modulates Activation of Prefrontal, Parietal, and Insular Cortices

Article excerpt

Risky decisions may involve uncertainty about possible outcomes (i.e., reward risk) or uncertainty about which action should be taken (i.e., behavioral risk). Determining whether different forms of risk have distinct neural correlates is a central goal of neuroeconomic research. In two functional magnetic resonance imaging experiments, subjects viewed shapes that had well-learned response-reward contingencies. Magnitude of a monetary reward was held constant within one experiment, whereas expected value was held constant within the other. Response selection, in the absence of behavioral risk, evoked activation within a broad set of brain regions, as had been found in prior studies. However, behavioral risk additionally modulated activation in prefrontal, parietal, and insular regions, within which no effect of reward risk was observed. Reward delivery, in comparison with omission, evoked increased activity in the ventromedial prefrontal cortex and the nucleus accumbens. We conclude that distinct brain systems are recruited for the resolution of different forms of risk.

Many decisions are fraught with risk. Doctors and patients must choose among potential courses of action by weighing uncertain benefits and costs, and the manner in which risk is presented guides medical decision making (McNeil, Pauker, Sox, & Tversky, 1982). When gamblers bet on dice throws, poker hands, or sporting events, they judge the relative probabilities of a set of risky outcomes (Bernoulli, 1738). Both the buying and the selling of insurance depend upon calculated actuarial information and subjective assessments of unlikely but catastrophic events (Johnson, Hershey, Meszaros, & Kunreuther, 1993). hi all of these cases, decisions must be made despite limited knowledge about the likely consequences of chosen actions.

Although the lay usage of risk reflects a single cognitive state of ambiguity or doubt, more precise conceptualizations may be possible. A seminal monograph by F. H. Knight (1921) defined risky decisions as those in which the decider has a priori or statistical knowledge about the probability of likely outcomes. (Note that such situations are fundamentally different from uncertain decisions, in the Knightian sense-i.e., those for which a probability distribution of likely outcomes is not known.) A central consideration of economic theories of decision making has been whether all forms of risk or uncertainty reflect a similar underlying subjective assessment of belief (de Finetti, 1937; Ramsey, 1931; Savage, 1954) or whether different decision processes are invoked depending on the source of risk (Ellsberg, 1961; Epstein & Wang, 1994; F. H. Knight, 1921). The recent growth of the interdiscipline of Neuroeconomics is predicated on the assumption that information about brain mechanisms can inform these sorts of economic questions (Glimcher, 2003).

In this article, we compare decisions made under two forms of risk, which we label reward risk and behavioral risk. Reward risk reflects limited knowledge about which outcome will occur (i.e., it is a continuous quantity that is probabilistically expressed). In contrast, behavioral risk reflects limited knowledge about which potential action is the optimal one to choose (i.e., it is a categorical variable that is present or absent). To use simple gambles for illustration, if one is given the option to bet with even odds on whether a roll of a standard six-sided die will be greater than 1, one should obviously take the bet. This gamble incurs reward risk (because one does not know what outcome will occur), but not behavioral risk (because one knows what bet to make). In contrast, betting on whether a coin flip will be heads or tails incurs both behavioral and reward risk. Note that although one can have reward risk without behavioral risk, the opposite is not possible: One will be unsure about one's optimal action only when potential outcomes are unknown or incomparable. …

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