Edited by Susan T. Fiske, Princeton University, Princeton, NJ, and approved March 13, 2017 (received for review September 6, 2016)
Honesty affects almost every aspect of social and economic life. We conducted experiments in which participants could earn considerable amounts of money by cheating on a die-rolling task. Cheating was substantial but decreased by more than one-half during transcranial direct current stimulation over the right dorsolateral prefrontal cortex. This stimulation-induced increase in honesty was functionally specific: It did not affect other types of behavioral control related to self-interest, risk-taking, and impulsivity. Moreover, cheating was only reduced when it benefited the participants themselves rather than another person. Thus, the human brain implements specialized processes that enable us to remain honest when faced with opportunities to cheat for personal material gain. Importantly, these processes can be strengthened by external interventions.
Honesty plays a key role in social and economic interactions and is crucial for societal functioning. However, breaches of honesty are pervasive and cause significant societal and economic problems that can affect entire nations. Despite its importance, remarkably little is known about the neurobiological mechanisms supporting honest behavior. We demonstrate that honesty can be increased in humans with transcranial direct current stimulation (tDCS) over the right dorsolateral prefrontal cortex. Participants (n = 145) completed a die-rolling task where they could misreport their outcomes to increase their earnings, thereby pitting honest behavior against personal financial gain. Cheating was substantial in a control condition but decreased dramatically when neural excitability was enhanced with tDCS. This increase in honesty could not be explained by changes in material self-interest or moral beliefs and was dissociated from participants’ impulsivity, willingness to take risks, and mood. A follow-up experiment (n = 156) showed that tDCS only reduced cheating when dishonest behavior benefited the participants themselves rather than another person, suggesting that the stimulated neural process specifically resolves conflicts between honesty and material self-interest. Our results demonstrate that honesty can be strengthened by noninvasive interventions and concur with theories proposing that the human brain has evolved mechanisms dedicated to control complex social behaviors.
↵1M.A.M. and A.C. contributed equally to this work.
Author contributions: M.A.M., A.C., and C.C.R. designed research; G.U. performed research; M.A.M., A.C., and C.C.R. analyzed data; and M.A.M., A.C., G.U., and C.C.R. 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/lookup/suppl/doi:10.1073/pnas.1614912114/-/DCSupplemental.
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