Abstract
Trust and trustworthiness are essential to an efficient economy and play crucial roles in social life. Previous evidence from behavioral experiments has revealed that the trustworthiness of individuals is closely related with their altruistic preference. It has been demonstrated that the ventromedial prefrontal cortex (vmPFC) is associated with decisions involving trustworthiness. Moreover, vmPFC lesion patients showed less trustworthiness and altruism than control subjects, indicating the indispensable role of this specific brain area in human social interactions. However, the causal relationship between this neural area and trustworthiness, as well as altruism, has not been fully revealed. The potential neural basis behind the behavior of trustees’ repayment has also seldom been discussed. In the present study, we aimed to provide evidence of a direct link between the neural and behavioral results through the application of transcranial direct current stimulation (tDCS) over the vmPFC of our participants. We found that activating the vmPFC could promote both the trustworthiness and altruism of our participants. We also show that enhancing the excitability of the vmPFC using tDCS increased the trustworthiness of the participants, and this promoting effect might be attributable to the enhancement of individuals’ altruistic preference. In addition, we revealed that the enhancing effect in trustworthiness and altruism might be specific to the activation of the vmPFC by applying tDCS over another brain region within the prefrontal cortex as a control site. Crucially, our findings provide direct evidence supporting the critical role of the vmPFC in cooperative behaviors in economic interactions, especially the trustees’ repayment in the trust game and the dictators’ altruistic transfer in the dictator game.
Highlights
“Trust is one of the most important synthetic forces within society” (Simmel and Wolff, 1950)
Because convergent evidence has demonstrated that individuals with greater altruism and empathy are more trustworthy than those who have less empathy toward their partners, along with our observations that the anodal transcranial direct current stimulation (tDCS) stimulation significantly increases altruistic preference as well as enhancing trustworthiness in tDCS experiments, we conclude that the ventromedial prefrontal cortex (vmPFC) is closely associated with trustworthiness and altruism and that altering the activity of a brain region shared by those traits, such as the vmPFC, could significantly improve the cooperative behavior of trustees by enhancing their altruistic preferences
Given that Experiment 2 placed the tDCS stimulation over another position within the prefrontal cortex as a control site to verify that the enhancing tDCS effects in Experiment 1 was due to the stimulation over vmPFC, rather than the stimulation over visual cortex, observations measuring trustworthiness and altruism from the anodal dorsolateral prefrontal cortex (dlPFC) and cathodal dlPFC groups were compared with those from the sham group
Summary
“Trust is one of the most important synthetic forces within society” (Simmel and Wolff, 1950). It has been demonstrated that the trustworthiness of trustees could be explained by unconditional preferences such as altruism (Andreoni and Miller, 2002; Holm and Danielson, 2005) and conditional preferences such as reciprocity (Camerer, 2003) In both between-subject and withinsubject designs, trustworthiness of individuals was consistently correlated with altruistic preferences of participants (Cox, 2004; Ashraf et al, 2006). In a clinical study, Moretto et al (2013) revealed that patients with lesions to the vmPFC were less trustworthy than control participants These fMRI or lesion case studies have failed to demonstrate a direct causal link between the neural activity in these brain regions and the trustees’ trustworthiness. The participants in their study were not playing with real person as counterparts and the potential preference inducing the changes of the participants’ trustworthiness by tDCS was not revealed in their study
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