Risk-dependent reward value signal in human prefrontal cortex
When making choices under uncertainty, people usually consider both the expected value and risk of each option, and choose the one with the higher utility. Expected value increases the expected utility of an option for all individuals. Risk increases the utility of an option for risk-seeking individuals, but decreases it for risk averse individuals. In 2 separate experiments, one involving imperative (no-choice), the other choice situations, we investigated how predicted risk and expected value aggregate into a common reward signal in the human brain. Blood oxygen level dependent responses in lateral regions of the prefrontal cortex increased monotonically with increasing reward value in the absence of risk in both experiments. Risk enhanced these responses in risk-seeking participants, but reduced them in risk-averse participants. The aggregate value and risk responses in lateral prefrontal cortex contrasted with pure value signals independent of risk in the striatum. These results demonstrate an aggregate risk and value signal in the prefrontal cortex that would be compatible with basic assumptions underlying the mean-variance approach to utility.
Additional Information© 2009 National Academy of Sciences. Edited by R. Duncan Luce, University of California, Irvine, CA, and approved March 6, 2009 (received for review September 30, 2008). We thank Peter Bossaerts, Shunsuke Kobayashi, and Krishna Miyapuram for helpful discussions. This work was supported by the Wellcome Trust, the University of Cambridge Behavioral and Clinical Neuroscience Institute funded by a joint award from the Medical Research Council and the Wellcome Trust, the Swiss National Science Foundation, the Roche Research Foundation, and the Greek Government Scholarship Foundation. R.J.D. and W.S. are supported by Wellcome Trust Program grants, and W.S. by a Wellcome Trust Principal Research fellowship. Author contributions: P.N.T., G.I.C., and W.S. designed research; P.N.T., G.I.C., and J.P.O. performed research; P.N.T. and G.I.C. analyzed data; and P.N.T., R.J.D., and W.S. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/cgi/content/full/0809599106/DCSupplemental.
Published - zpq7185.pdf
Supplemental Material - 0809599106SI.pdf