Abstract
Intergroup bias, which is the tendency to behave more positively toward an in‐group member than toward an out‐group member, is pervasive in real life. In particular, intergroup bias in trust decisions substantially influences multiple areas of life and thus better understanding of this tendency can provide significant insights into human social behavior. Although previous functional magnetic resonance imaging studies showed the involvement of the right temporoparietal junction (TPJ) in intergroup trust bias, a causal relationship between the two has rarely been explored. By combining repetitive transcranial magnetic stimulation and a newly developed trust game task, we investigated the causal role of the right TPJ in intergroup bias in trust decisions. In the trust game task, the counterpart's group membership (in‐group or out‐group) and reciprocity were manipulated. We applied either neuronavigated inhibitory continuous theta burst stimulation (cTBS) or sham stimulation over the right TPJ before performing the trust game task in healthy volunteers. After the sham stimulation, the participants' degrees of investments with in‐group members were significantly higher than those with out‐group members. However, after cTBS to the right TPJ, this difference was not observed. The current results extend previous findings by showing that the causal roles of the right TPJ can be observed in intergroup bias in trust decisions. Our findings add to our understanding of the mechanisms of human social behavior.
Highlights
We interact with people who share common group identities, such as nations, religions, and political parties, and we find ourselves interacting with others who belong to different groups (Akerlof & Kranton, 2000; De Dreu et al, 2010; Fiske, 2002; Levine, Prosser, Evans, & Reicher, 2005; Tajfel, Billig, Bundy, & Flament, 1971)
Because we aimed to examine the causal impact of the right temporoparietal junction (TPJ) on intergroup trust bias, we manipulated the counterparts' group membership and reciprocity
The right TPJ plays a key role in social cognition, such as perspective taking (Krall et al, 2016; Schurz, Tholen, Perner, Mars, & Sallet, 2017; Tei et al, 2014), FIGURE 3 Right temporoparietal junction (TPJ) in intergroup trust bias. (a) Amounts invested in the trust game task after sham stimulation and continuous theta burst stimulation. *p < .05, **p < .01. (b) The 2 × 2 × 2 repeated-measures analysis of variance revealed the presence of a stimulation condition × group membership interaction effect (F [1, 20] = 4.87, p = .039)
Summary
Groups are a pervasive feature of our social lives. We interact with people who share common group identities, such as nations, religions, and political parties, and we find ourselves interacting with others who belong to different groups (Akerlof & Kranton, 2000; De Dreu et al, 2010; Fiske, 2002; Levine, Prosser, Evans, & Reicher, 2005; Tajfel, Billig, Bundy, & Flament, 1971). It may lead to severe outcomes, such as excessive competition, discrimination, and violent protest (De Dreu & Kret, 2016; Romano et al, 2017) This tendency to extend trust toward in-group members improves group functioning and enables the individual to fit into a group (Balliet et al, 2014; Baumgartner, Schiller, Rieskamp, et al, 2013). The tendency brings a wide variety of advantages, such as safety and security the group provides against outside threats, inclusion in potentially beneficial exchanges with others, and social support (Balliet et al, 2014; Baumgartner, Schiller, Rieskamp, et al, 2013) Impairments in such group psychology undermine social inclusion and fitting in (Balliet et al, 2014; De Dreu & Kret, 2016). An improved understanding of intergroup trust bias can provide significant insights into social cognitive functioning and its impairments in psychiatric disorders
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