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Oxytocin and the Biological Basis for Interpersonal and Political Trust

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Abstract

Political scientists have documented the many ways in which trust influences attitudes and behaviors that are important for the legitimacy and stability of democratic political systems. They have also explored the social, economic, and political factors that tend to increase levels of trust in others, in political figures, and in government. Neuroeconomic studies have shown that the neuroactive hormone oxytocin, a peptide that plays a key role in social attachment and affiliation in non-human mammals, is associated with trust and reciprocity in humans (e.g., Kosfeld et al., Nature 435:673–676, 2005; Zak et al., Horm Beh 48:522–527, 2005). While oxytocin has been linked to indicators of interpersonal trust, we do not know if it extends to trust in government actors and institutions. In order to explore these relationships, we conducted an experiment in which subjects were randomly assigned to receive a placebo or 40 IU of oxytocin administered intranasally. We show that manipulating oxytocin increases individuals’ interpersonal trust. It also has effects on trust in political figures and in government, though only for certain partisan groups and for those low in levels of interpersonal trust.

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Notes

  1. However, Muller and Seligson (1994) find that interpersonal trust is an effect rather than a cause of democracy.

  2. There are two players in the trust game: decision-maker 1 (DM1) and decision-maker 2 (DM2). Both are endowed with equal amounts of money. After instruction, DM1 is prompted to take an integer amount of his monetary stake, including zero, and transfer it to DM2. The selected transfer is removed from DM1 s account, and tripled in the account of DM2. DM2 is then informed of the transfer and the total in his account, and prompted to return any amount from zero to his account total back to the DM1 in his dyad. The sub-game perfect Nash equilibrium of this game is for DM2 to return nothing, and subsequently for DM1 to send nothing, though this rarely happens (Smith 1998; Zak et al. 2005).

  3. In this game, a proposer is endowed with $10 and a responder has nothing. The proposer is asked to make an offer of a split of the money to the responder; if the responder accepts the offer, the money is paid, but if the offer is rejected, both parties get nothing.

  4. However, some research (Levi and Sherman 1997; Weingast 1997) shows that the causal arrows work in the other direction. Since we conduct an experiment, the post-treatment measures cannot affect pre-treatment measures.

  5. Furthermore, this type of relationship would also be supported by existing literature in political science. Democrats are more trusting and supportive of expanding government, while Republicans champion limited government (e.g., Cook and Gronke 2005; Corey and Garand 2002; Rudolph and Evans 2005). Given Democrats' greater propensity to trust an active government, they may be more affected by OT for these types of questions.

  6. Partisanship is also more relevant as a moderating factor given the dependent variables we are considering.

  7. Only males are in the subject pool because one possible risk factor of taking OT intranasally is a spontaneous abortion. In females, the effects of OT also vary over the menstrual cycle.

  8. Participants’ identities were masked throughout by assigning them an alpha-numeric code. All data were collected by computer and there was no deception of any kind.

  9. Asians out-number whites (34 %) among undergraduates at the institution. The presence of Latinos is similar to the national population (15 %), while African Americans are under-represented (3 %). This racial and ethnic make-up is certainly not the norm in the U.S. and therefore may limit the extent to which the results travel to the U.S. population.

  10. The p-values associated with the relevant test between the placebo and OT condition for each measure are as follows: age (p = 0.54); height (p = 0.40); weight (p = 0.46); income (p = 0.94); ideology (p = 0.29); Democrat (p = 0.45); Republican (p = 0.73); pre-treatment trust (p = 0.97); and, race and ethnicity (p = 0.61).

  11. This is similar to the question typically used on the National Election Study. Instead of choosing between the response options of “most people can be trusted” or “you can’t be too careful in dealing with people,” subjects indicated their level of agreement with the statement that most people can be trusted. Please see supplementary Table A in the supplemental document for summary statistics on all of our variables.

  12. We use a one-tailed test since we expect a positive effect of OT on interpersonal trust. However, the effect is also significant using a two-tailed test, though only at p < 0.10. We also find similar effects if we just run a difference in means test on interpersonal trust between the OT and placebo, though the effects are outside of standard significance levels (p = 0.11, one-tailed). Even though it was not part of our expectations for interpersonal trust, we explored whether partisanship moderated the effects of OT and did not find this to be the case.

  13. We are left with 19 Democrats on placebo and 17/18 on OT, 10 Republicans on placebo and on OT, and 12 Independents on placebo and 18/19 Independents on OT.

  14. As we noted earlier, it would also have been good to have pre-treatment measures for all of our dependent variables but we were unable to do this due to limited space on the survey.

  15. In the few instances where we find a sign opposite of expectations, we use a two-tailed test.

  16. In a model without the interaction term, OT increases trust in Clinton among Democrats.

  17. In the model without interaction terms, OT leads to a drop in trust toward Edwards among Republicans and an increase in trust among Independents.

  18. Only one factor emerged with an eigenvalue over 1 and both measures had similar weights.

  19. Previous work on OT infusion has tested for racial or ethnic differences in response to OT and no effects have been found (Morhenn et al. 2008; Zak et al. 2005a, b; Zak et al. 2007). As another check for external validity, we ran all of our analyses using race and ethnicity dummy variables and in only two cases do we find that the Asian dummy variable is statistically significant and its inclusion washes away the effect of OT. This is in the analysis of trust in George Bush and trust in Mitt Romney among Democrats.

  20. This stimuli brings to mind the iconic image of authoritarian regimes. Such displays may therefore not only convey the power of the regime, but foster bonds of trust with the public in these societies.

  21. It is important to note that the temporal effects of any OT-induced changes in trust remain unclear. An individual’s feelings of trust may return to previous levels as OT is metabolized. Alternatively, feelings held during hormonally spiked experiences may be encoded and permanently alter beliefs.

  22. This is based on studies from our lab. Since it is a non-result, it is unpublished.

  23. See for example the Pew Center for People and the Press, “The Gender Gap: Three Decades Old, as Wide as Ever.” Accessed on December 17, 2012, at http://www.people-press.org/2012/03/29/the-gender-gap-three-decades-old-as-wide-as-ever/.

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Acknowledgments

This study was funded by a grant to Paul J. Zak from the John Templeton Foundation. We thank the anonymous reviewers and editors for helpful feedback.

The experiments comply with the current laws of the United States. All of the procedures were approved by the Institutional Review Boards of the universities involved.

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Authors and Affiliations

  1. School of Politics and Economics, Claremont Graduate University, 160 East Tenth Street, Claremont, CA, 91711, USA

    Jennifer L. Merolla, Guy Burnett & Kenneth V. Pyle

  2. Center for Neuroeconomic Studies and School of Politics and Economics, 160 East Tenth Street, Claremont, CA, 91711, USA

    Paul J. Zak

  3. Division of Endocrinology, Diabetes and Hypertension, Geffen School of Medicine, UCLA, 200 Medical Plaza, Suite 530, Los Angeles, CA, 90095-7073, USA

    Sheila Ahmadi

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  1. Jennifer L. Merolla
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  2. Guy Burnett
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Correspondence to Jennifer L. Merolla.

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Merolla, J.L., Burnett, G., Pyle, K.V. et al. Oxytocin and the Biological Basis for Interpersonal and Political Trust. Polit Behav 35, 753–776 (2013). https://doi.org/10.1007/s11109-012-9219-8

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