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Published March 13, 2012 | Published + Supplemental Material
Journal Article Open

Honesty mediates the relationship between serotonin and reaction to unfairness

Abstract

How does one deal with unfair behaviors? This subject has long been investigated by various disciplines including philosophy, psychology, economics, and biology. However, our reactions to unfairness differ from one individual to another. Experimental economics studies using the ultimatum game (UG), in which players must decide whether to accept or reject fair or unfair offers, have also shown that there are substantial individual differences in reaction to unfairness. However, little is known about psychological as well as neurobiological mechanisms of this observation. We combined a molecular imaging technique, an economics game, and a personality inventory to elucidate the neurobiological mechanism of heterogeneous reactions to unfairness. Contrary to the common belief that aggressive personalities (impulsivity or hostility) are related to the high rejection rate of unfair offers in UG, we found that individuals with apparently peaceful personalities (straightforwardness and trust) rejected more often and were engaged in personally costly forms of retaliation. Furthermore, individuals with a low level of serotonin transporters in the dorsal raphe nucleus (DRN) are honest and trustful, and thus cannot tolerate unfairness, being candid in expressing their frustrations. In other words, higher central serotonin transmission might allow us to behave adroitly and opportunistically, being good at playing games while pursuing self-interest. We provide unique neurobiological evidence to account for individual differences of reaction to unfairness.

Additional Information

© 2012 by the National Academy of Sciences. Freely available online through the PNAS open access option. Edited by Ranulfo Romo, Universidad Nacional Autónoma de México, Mexico City, D.F., Mexico, and approved January 19, 2012 (received for review November 12, 2011). Published ahead of print February 27, 2012. We thank Mr. Katsuyuki Tanimoto and Mr. Takahiro Shiraishi for their assistance in performing the PET experiments. We also thank Ms. Yoshiko Fukushima for her help as clinical research coordinator. A part of this study is the result of "Integrated research on neuropsychiatric disorders" carried out under the Strategic Research Program for Brain Sciences by the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT). This work was supported by a Grant-in-Aid for Scientific Research in Innovative Areas: Prediction and Decision Making (23120009); a Grant-in-Aid for Young Scientist A (23680045); a research grant from the Takeda Science Foundation; a research grant from the Casio Science Foundation; and a consignment expense for Molecular Imaging Program on "Research Base for PET Diagnosis" from MEXT. Author contributions: H. Takahashi, H. Takano, and C.F.C. designed research; H. Takahashi, H. Takano, T.I., R.A., F.K., M.Y., Y.E., and H.I. performed research; H. Takahashi and H. Takano contributed new reagents/analytic tools; H. Takahashi, H. Takano, S.O., H.M., Y.T., and K.T. analyzed data; and H. Takahashi, H. Takano, C.F.C., T.M., Y.O., M.K., and T.S. wrote the paper.

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Published - Takahashi2012p17574P_Natl_Acad_Sci_Usa.pdf

Supplemental Material - pnas.201118687SI.pdf

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