A relationship between the oxytocin receptor gene (OXTR) and behavioral and attitudinal trust has been suggested, but the nature of this relationship has not yet been established. We obtained behavioral trust data from 470 Japanese participants (242 women) aged 20–59 years, together with their levels of general trust and personality traits (NEO-FFI). Saliva buccal swabs were collected from 411 of these 470 participants and used for genotyping of OXTR rs53576. Our participants were found to have more AA alleles (40%) than GG alleles (12%). The GG men were more trusting and also rated higher on attitudinal trust than AA men, and this difference did not diminish when personality traits were controlled for. However, this pattern was not observed among women. In addition, controlling for attitudinal trust reduced the difference in behavioral trust among men to a non-significant level, but the difference in attitudinal trust remained significant when behavioral trust was controlled. These results indicate that the OXTR genotype affects attitudinal trust as part of an individual’s relatively stable disposition, and further affects behavioral trust through changes in attitudinal trust.

This study examined the association between salivary oxytocin (sOT) levels and generosity in preschoolers. Fifty preschoolers played two dictator games (DG) by deciding how to allocate 10 chocolates between themselves and another child, who was either from the same class as the participant (ingroup member), or an unknown child from another class (outgroup member). sOT levels were assessed in saliva collected from the children immediately prior to the DG tasks. While sOT levels were negatively associated with allocations made to both ingroup and outgroup members by boys, among girl sOT levels were positively related to allocations made to ingroup members, and unrelated to allocations made to outgroup members. These results suggest sex differences in the association between salivary oxytocin and generosity.

Previous studies have shown that genetic variations in rs53576, a common variant of the oxytocin receptor gene (OXTR) resulting from a single nucleotide polymorphism involving an adenine (A)/guanine (G) transition, are associated with attitudinal trust in men. However, the pathway from gene to behaviour has not been elucidated. We conducted the present study to determine whether amygdala volume mediates the association between OXTR rs53576 genotypes and attitudinal trust. Our results revealed that the left amygdala volume was significantly smaller in GG men than in AA and AG men, whereas it was significantly smaller in AA and AG women than in GG women. In addition, the left amygdala volume was negatively associated with attitudinal trust in men, whereas there was no such association in women. We also found a significant mediation effect of the left amygdala volume on the association between OXTR rs53576 genotypes and attitudinal trust in men. The results of our study suggest that the left amygdala volume plays a pivotal role in the association between OXTR rs53576 genotypes and attitudinal trust in men.

Oxytocin (OXT) is known to play an important role in trust, whereas the involvement of other peptide hormones has not been evaluated. In this study, we focused on microsatellite polymorphisms in the intron of the arginine-vasopressin receptor 1a ( AVPR1a ) gene and examined whether the association between the repeat lengths in the intron of AVPR1a is associated with trust and reciprocity in humans. Four-hundred and thirty-three participants played the trust game, answered the attitudinal trust question, and their buccal cells were collected. Results showed that men with a short form of AVPR1a tend to send more money to the opponent, even if there is a possibility of being betrayed by the opponent. Additionally, people with a short form of AVPR1a tended to return money to the opponent who trusts them. However, attitudinal trust was not associated with AVPR1a . These results indicate that arginine-vasopressin receptor 1a plays an important role in trust and reciprocal behaviors.

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