Motivation and emotion/Book/2017/Oxytocin and trust

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Oxytocin and trust:
What is the effect of oxytocin on trust?
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Humans are naturally social beings. People interact and engage with others repeatedly throughout daily living. Trust is a fundamental aspect to our interactions and relationships with others (Weber, Malhotra & Murnighan, 2004). Because of this, we may wonder, what goes on within us that allows us to believe that someone is trustworthy? Have you ever wished you could trust someone more? Or, on the other hand, regretted trusting someone because they betrayed you?

This chapter will provide insight into the biological functions involved when we trust people. More specifically, one hormone called oxytocin has shown to be particularly relevant to trust, and will be the main focus of discussion. 

Key questions
  • What is oxytocin, and what functions does it have?
  • What is trust? How is it defined, and how can it be measured?
  • Based on research findings, what effect does oxytocin have on trust?
  • How do theoretical frameworks explain the effect of oxytocin on trust?
  • How has the effect of oxytocin on trust been applied?


You may have heard of oxytocin and its interesting role within the body. Current research on oxytocin has recently stimulated excitement within the scientific community, which has spread to the general public, and popular news and television (for example, see 'Oxytocin', a short episode from the ABC program "Catalyst"). You may have heard it labelled as "the love hormone", or "the trust hormone" (Bartz, Zaki, Bolger, & Ochsner, 2011). To understand why these labels may have originated, a description of oxytocin and its functions will be explored.

What is oxytocin?[edit]

Oxytocin is a peptide hormone stored in the hypothalamus and secreted by the posterior pituitary gland to influence central and peripheral functions within the body. Traditionally, oxytocin was understood as a primary hormone involved with female reproduction, due to its crucial role during childbirth and breastfeeding. Oxytocin is naturally released to facilitate contractions during labour, and lactation during nursing (Assad, Pandey & Sharma, 2016; Gimpl & Farenhol, 2001). However, oxytocin is not limited to these functions. More recently, researchers have found that oxytocin also plays a key role in a range of social behaviours.

Social functions of oxytocin[edit]

Figure 1. Oxytocin is released during intimate behaviours with partners, such as hugging, which is linked to attachment bonding in relationships.

Animal studies have observed the effect of oxytocin on maternal and nurturing behaviours. In rodent mothers, an injection of oxytocin has led to the onset of behaviours such as grooming, licking, and nest building towards its pup (Ross & Young, 2009). Oxytocin has been further linked to the formation of mother-infant bonding and attachment, through facilitation of memories attached to smells. It may also play a role in animal pair bonding, as it has appeared to stimulate formation of partner preferences (Ross & Young, 2009).

These fascinating findings from animal research has generated interest into human studies. Although there have been some inconsistencies, these effects of oxytocin on social behaviours may also be observed in humans (Bartz et al., 2011; Lim & Young, 2006). Increased oxytocin levels have been correlated with nurturing behaviour in mothers towards their infants, including frequent checking, and affectionate touch (Ross & Young, 2009).

Oxytocin is also released during sexual and intimate behaviours between romantic partners, leading to pair bonding in relationships (Ross & Young, 2009). For example, when we cuddle or kiss our partners, oxytocin is released, which influences feelings of attachment and caring for that person. This explains why oxytocin is often referred to as "the love hormone" (Bartz et al., 2011). Additionally, oxytocin has been shown to have a role in social cognition. Administration of oxytocin through a nasal spray (a common method in research) has led to improvements in recognition of familiar faces, judgement of others' emotions, and trust (Ross & Young, 2009).

The effect of oxytocin on trust has been a particularly prominent finding in current literature. Research examining the relationship between oxytocin and trust will be the primary topic of discussion for the remainder of this book chapter. Firstly, a definition of trust and how it may be measured will be explored. 


Trust is highly valued to our social relationships with others. This is apparent within personal relationships, such as friendships or love, and can be extended to economical relationships and political exchange (Weber et al., 2004). When we trust someone, our relationship with them is often more positive, and better-functioning compared to non-trusting relationships (Simpson, 2007). But how can we define trust?

What is trust?[edit]

Figure 2. Acrobats trust each other to perform risky acts.

Weber et al. (2004) explained that interpersonal trust is a psychological state that involves interdependence, vulnerability, and intentionality between a "truster" and a "trustee". Typically, trust is based on the truster's expectation that the trustee will perform a specific, and important action. The interdependent aspect of trust means that the truster in the relationship is reliant on the trustee to cooperate effectively to perform this action. If the trustee does not cooperate, this will have strong impact on the truster. Due to this, trust also involves vulnerability, in that the truster in the relationship may be putting themselves at risk if the trustee does not cooperate in a certain way. Therefore, the trustee must make an intentional decision to cooperate and match both of their best interests (Simpson, 2007; Weber et al., 2004). 

For example, imagine that your friend asks to borrow your car for a day and you agree. You, as the truster, expect that your friend will take care of your car. This makes you vulnerable as you have little control over whether they will look after your car. If your friend brings your car back and it has been scratched and damaged, you may feel like they betrayed your trust. Your friend, as the trustee, is aware of this and intentionally takes care of your car whilst they are borrowing it. Because of this, you are likely to maintain trust in your friend.

Measuring trust[edit]

Figure 3. Diagram showing the first move in the trust game.

Trust may seem like an understandable concept, as we are all likely to have experienced it at some point in our lives. But how can we objectively measure a person’s feelings of trust in research?

"The trust game", developed by Berg, Dickhaut and McCabe (1995), has been frequently used in research as an objective experimental measure of trust among humans. In the trust game, an initial participant, the truster, is randomly paired with a second, anonymous, trustee participant. Each of them are given a certain monetary amount. The truster participant must decide whether to transfer some or all their money to the trustee participant, despite not knowing who they are. The amount that the truster participant chooses to transfer becomes tripled by the experimenter when the trustee participant receives it. The trustee participant is then given the choice of whether to send some money back to the truster participant. If the truster participant chooses to transfer money during the first move, this indicates trust, as they are willing to be at risk for the potential of reciprocity from the trustee participant. If the trustee participant sends some money back during the second move, this indicates a reciprocation of trust, as their voluntary decision mutually benefits each of them (Berg et al., 1955; Kosfeld, Heinrichs, Zak, Fischbacher & Fehr, 2005).

Some researchers have criticised that the trust game may be enabling altruism rather than trust. To test this, Brülhart and Usunier (2012), altered the monetary amounts that the trustee participant initially received to manipulate a "rich" and a "poor" participant. It was hypothesised that the truster would be more likely to transfer more money to the poor participant due to an altruistic reaction. However, this did not occur, and no differences in the amount of money transferred was found. This suggests trust, not altruism is affected during the trust game (Brülhart & Usunier, 2012). Therefore, the trust game has been maintained as a primary measure of trust in current research. 

What is the effect of oxytocin on trust?[edit]

Now that we have grasped an understanding of oxytocin and its social function, and how trust may be defined and measured, we will examine the effect that oxytocin has on trust.

Relationship between oxytocin and trust[edit]

Figure 4. Experimenters administer oxytocin through a nasal spray to examine its effect on trust.

In a preliminary study, Kosfeld et al. (2005) administered oxytocin to participants through a nasal spray, and examined how this affected their trust behaviour during the trust game. To ascertain whether oxytocin specifically affected trust, rather than general risk-taking behaviour, trust behaviour was compared to performance in a risk game that lacked an element of social interaction. Participants who received oxytocin displayed more trusting behaviour through more generous acts during the trust game, than those that received a placebo. Further, behaviour did not differ between oxytocin and control participants during the non-social risk game. From these findings, we may infer that increased levels of oxytocin enhances trusting behaviour (Kosfeld et al., 2005).

However, this only explains the effect of manipulated oxytocin levels on trust. How do we know if oxytocin is naturally released in the body when we trust people? Expanding on Kosfeld et al.'s (2005) research, Zak, Kurzban and Matzner (2005) conducted a similar study using the trust game. Though, instead of administering oxytocin through a nasal spray, they measured the participants' naturally produced oxytocin levels within the blood. Results were consistent with Kosfeld et al.'s (2005) findings, in that displays of trust and reciprocal trust during the trust game aligned with increased oxytocin levels in the body. These findings complement Kosfeld et al’s (2005) groundwork results, and provides additional evidence for oxytocins role in increasing trust (Zak et al., 2005).

Oxytocin and betrayal of trust[edit]

If we can increase trust through oxytocin, what happens when our trust is betrayed? Does this mean we can maintain trust despite suffering a betrayal? One study by Baumgartner, Heinrichs, Vonlanthen, Fischbacher, and Fehr (2008) investigated the effect of oxytocin when trust is betrayed multiple times during the trust game, and similarly compared this to performance in the non-social risk game. In an event of betrayal during the trust game, the trustee withdraws from sending money back to the initial truster during the second transaction. Consequently, this leaves the truster feeling betrayed after not receiving a reciprocal interaction. In Baumgartner et al's (2008) study, researchers administered a nasal spray that contained oxytocin for some participants, and a placebo for the others. Participants that received oxytocin were more willing to take social risks and trust the second person during the trust game, despite experiencing betrayal previously. Further, oxytocin had no effect on whether participants were likely to engage in non-social risks during the risk game (Baumgartner et al., 2008).

It was thought that this outcome may have been due to the effect of oxytocin reducing participants fear of social betrayal. To examine this, researchers also observed activation of brain regions during the experiment using fMRI scans. The brain regions that were activated in oxytocin participants during the trust game were areas such as the amygdala, and the midbrain, that have a role in regulating and reducing the fear response. These regions were not significantly activated for the placebo participants. This suggests oxytocin may influence trust through decreasing fear of social betrayal (Baumgartner et al., 2008). 

Context dependent effects of oxytocin[edit]

From these findings, we may be thinking that it may be damaging if all it takes for us to trust anyone, even if they've betrayed us, is to use an oxytocin nasal spray. What about times when we don't want to trust someone? Imagine if this power was misused by marketing specialists, or politicians. We may end up spending all our money on useless items because we trusted the salesman that told us we needed it (Mikolajczak et al., 2010a). 

In light of this, Mikolajczak et al. (2010a) wanted to investigate whether oxytocins effect on trust was context dependent, or if it just makes us gullible. To do this, researchers added cues during the trust game that hinted that the participant they were partnered with may not be trustworthy. The truster's were given descriptions of their partners that were considered either reliable or unreliable traits. For example, a reliable partner may have been described as an academic that knows first aid, whereas an unreliable partner may have been a marketer that plays aggressive sports. Results indicated that participants that received the oxytocin spray still increased trust in the reliable partners, but they were less likely to trust unreliable partners. Thankfully, it may be concluded from this that oxytocin does not cause people to trust just anyone, and people may still be able to determine whether people should be trusted or not (Mikolajczak et al., 2010a).

The entirety of research discussed has examined has focused on the trust game. But what about trust relationships that do not involve money? Alternative contexts have also been explored to ascertain the generalisability of this effect. One study by Mikolajczak, Pinon, Lane, de Timary, and Luminet (2010b) demonstrated that oxytocin increased participants willingness to share confidential information about themselves with the experimenter. In an additional study, Lane et al. (2013) revealed that oxytocin increased sharing of personal emotions with others among both male and female participants. These findings show that oxytocin may increase trust among more intimate relationships. Furthermore, these studies may help explain the role of oxytocin during relationship attachment and pair bonding (Lane et al., 2013; Mikolajczak et al., 2010b).

Although findings on oxytocins effect on trust in alternative contexts may be of interest, researchers have had difficulty attempting to replicate these outcomes. Lane et al. (2015), conducted a subsequent study on the effect of oxytocin on sharing personal, and confidential information, with only slight differences in methodology. In contrast to previous findings, oxytocin did not have a significant effect on trust. This proposes that additional replication is needed to clarify whether oxytocin improves intimate instances of trust (Lane et al., 2015; Nave, Camerer & McCullough, 2015). 

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Topic Review: Quiz Time!


What did participants that received oxytocin do in Kosfeld and collegues (2005) study, during the trust game, to indicate increased trust?

Showed withdrawal
Were more generous
Reported that they liked their partner
Were less generous


In Baumgartner's study, participants that received oxytocin continued to trust after being betrayed.



From fMRI scans, brain regions that are enhanced by oxytocin in the trust game play a role in _____.

Short-term memory
Fear regulation
Social skills

Theoretical explanations[edit]

So why does oxytocin increase trust in people? Initially it was thought that oxytocin increased all prosocial behaviour. However, evidence does not typically support this, as oxytocin has additionally been linked to anti-social behaviour and emotions, such as envy and aggression (Kemp & Guastella, 2011; Shamay-Tsoory & Abu-Akel, 2016). Therefore, several researchers have proposed theoretical frameworks to attempt to explain the effect of oxytocin on trust.

Social salience hypothesis[edit]

One theory that may help clarify why oxytocin has an influence on trust is the social salience hypothesis. This theory proposed that oxytocin increases the ability to recognise and attend to salient social cues (Shamay-Tsoory & Abu-Akel, 2016). This may be understood in consideration of previously discussed studies. For example, research by Mikolajczak et al. (2010a) that showed that oxytocin increased trust when a person is perceived as reliable, though not when they seemed unreliable. The social salience hypothesis would claim that oxytocin helped participants perceive whether their partners were trustworthy, because they were attending to relevant cues in their environment that conveyed their partners trustworthiness (Shamay-Tsoory & Abu-Akel, 2016).

It has been suggested that this occurs because oxytocin facilitates communication with the dopaminergic system. Dopamine is known for its response to positive, and rewarding stimuli. However, increased dopamine activity also becomes apparent when reorienting attention to alerting or important stimuli (Shamoy-Tsoory & Abu-Akel, 2016). For instance, if you imagine that you are driving and a cat suddenly runs out in front of you, your attention is likely to rapidly switch to become focused on the cat and trying not to hit it, due to increased dopamine activity. The social salience hypothesis argues that oxytocin enhances dopamine activity to have a similar effect on the appearance of important social information, including cues that someone should not be trusted (Shamoy-Tsoory & Abu-Akel, 2016). 

Approach-avoidance hypothesis[edit]

An alternative theory that has endeavoured to understand why oxytocin increases trust is the social approach-avoidance hypothesis. This theory outlined by Kemp and Guastella (2011) suggested that oxytocin encourages approach behaviour, and inhibits avoidance behaviour in social contexts. Social approach behaviour tends to enable positive affective states, including trust, and striving towards social stimuli. Whereas, social avoidance behaviours encourage negative affective states, such as fear, and involves retracting from the social environment (Kemp & Guastella, 2010, 2011)[grammar?]. This seems plausible in light of Baumgartner et al’s (2008) research that showed that oxytocin led to increased willingness to trust others, and inhibited fear of social betrayal. Increased brain activity within the amygdala and midbrain areas for oxytocin participants may help to explain this effect, as these areas play a role in fear regulation (Baumgartner et al., 2008).

As of yet, research has not directly investigated the efficacy of each of these hypotheses. Therefore, these theories remain speculative at this time. Future research is needed to directly assess and compare these hypotheses to identify which best describes the effect of oxytocin on trust (Kemp & Guastella, 2011).

Can we improve trust?[edit]

So far, we have looked at research highlighting that the oxytocin hormone tends to increase feelings of trust, and a couple of theoretical perspectives that have tried to explain this relationship. But what does this mean? Does this mean we can improve trust in everyday life?

Applications of oxytocin and trust[edit]

Researchers have explored how oxytocin may be used to improve trust in real world applications. Two of these include couples therapy, and psychological disorders.

Couples therapy[edit]

Figure 5. Couple turned away from each other to indicate conflict.

Couples that frequently conflict with each other typically exhibit reduced psychological and physical well-being, and lower satisfaction with their relationships (Ditzen et al., 2009). Considering this, researchers have examined whether oxytocin could potentially increase prosocial interactions, including trust, among couples in conflict to help improve their quality of life. Ditzen et al. (2009) explored this, and administered oxytocin nasal spray to both partners in heterosexual couples experiencing conflict. They found that oxytocin significantly increased the ratio of positive to negative interactions for both partners, which is suggested to be an important predictor for satisfactory relationships in long-term. Improved trust was one indicator of positive interactions among couples. Couples also demonstrated reduced stress and anxiety and increased accessibility of positive memories of their relationship. These findings may be promising for reducing couple conflict in therapy. However, this study only investigated this on one occasion. Therefore, it is uncertain whether this effect of oxytocin may continue over time (Ditzen et al., 2009). 

Psychological disorders[edit]

It has been additionally postulated that oxytocin may help alleviate symptoms for psychological disorders that involve social deficits. Individuals with high-functioning autism spectrum disorders tend to have a reduced capacity to recognise and respond to social cues. These individuals have also shown reduced oxytocin levels in comparison to people without the disorder (Andari et al., 2010). A study by Andari et al. (2010) explored how oxytocin affected social interactions during a simulated ball game for adults with autism. Participants presented better social interactions by attending and reacting to social cues, and reported enhanced trust towards their ball game partners. These results suggest oxytocin may have a therapeutic effect for social impairments in high-functioning autism spectrum disorders. However, more research is needed to ascertain oxytocins long-term capacity to improve social behaviours in people with autism (Andari et al., 2010).

Another psychological disorder that may be assisted with oxytocin is social anxiety disorder. Social anxiety has been characterised by recurring avoidance and withdrawal from social situations (Kosfeld et al., 2005). Given that oxytocin has been theorised to reduce withdrawal behaviour, and facilitate approach behaviour in social interactions, it has been investigated in relation to treatment for social anxiety disorder (Kemp & Guastella, 2011). A randomised control trial by Guastella, Howard, Dadds, Mitchell and Carson (2009) revealed that participants with social anxiety disorder that received oxytocin showed a reduction in symptoms although this effect was not maintained over time, suggesting oxytocin may not be suitable for treatment until additional research establishes its efficacy (Guastella et al., 2009). 

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Topic Review: Quiz Time!


The social salience hypothesis proposed that oxytocin enhances attention to social cues through _____ activity.



The approach-avoidance hypothesis suggests oxytocin ______ approach behaviour, and ______ avoidance behaviour in social contexts.

Encourages; encourages
Encourages; inhibits
Inhibits; encourages
Inhibits; inhibits


What effect does oxytocin have on individuals with autism?

Improved social interactions
Improved mood
Improved attention


From understanding theory and research, we may conclude that oxytocin can improve trust. This effect may even allow us to continue trusting after we've been betrayed, on the condition that we do not perceive untrustworthy social cues. However, it is important to remember that the effect of oxytocin on trust is strongest in contexts involving money, as research in alternative contexts have been inconsistent. Clearly, this topic is still in development, and more research is needed to establish its reliability across settings, and time. If this is achieved, oxytocin may have a number of therapeutic implications, including for couples therapy, and for individuals with autism and social anxiety disorder.  

See also[edit]


Andari, E., Duhamel, J., Zalla, T., Herbrecht, E., Leboyer, M., & Sirigu, A. (2010). Promoting social behavior with oxytocin in high-functioning autism spectrum disorders. Proceedings of the National Academy of Sciences, 107(9), 4389-4394.

Assad, N., Pandey, A., & Sharma, L. (2016). Oxytocin, functions, uses and abuses: a brief review. Theriogenology Insight - An International Journal of Reproduction in All Animals, 6(1), 1.

Bartz, J., Zaki, J., Bolger, N., & Ochsner, K. (2011). Social effects of oxytocin in humans: context and person matter. Trends in Cognitive Sciences.

Baumgartner, T., Heinrichs, M., Vonlanthen, A., Fischbacher, U., & Fehr, E. (2008). Oxytocin shapes the neural circuitry of trust and trust adaptation in humans. Neuron, 58(4), 639-650.

Berg, J., Dickhaut, J., & McCabe, K. (1995). Trust, reciprocity, and social history. Games and Economic Behavior, 10(1), 122-142. doi:10.1006/game.1995.1027

Brülhart, M., & Usunier, J. (2012). Does the trust game measure trust? Economics Letters, 115(1), 20-23. doi:10.1016/j.econlet.2011.11.039

Ditzen, B., Schaer, M., Gabriel, B., Bodenmann, G., Ehlert, U., & Heinrichs, M. (2009). Intranasal oxytocin increases positive communication and reduces cortisol levels during couple conflict. Biological Psychiatry, 65(9), 728-731.

Gimpl, G., Fahrenhol, F. (2001). The oxytocin receptor system: structure, function, and regulation. Physiological Reviews. 81 (2) 629-683

Guastella, A., Howard, A., Dadds, M., Mitchell, P., & Carson, D. (2009). A randomized controlled trial of intranasal oxytocin as an adjunct to exposure therapy for social anxiety disorder. Psychoneuroendocrinology, 34(6), 917-923.

Kemp, A., & Guastella, A. (2010). Oxytocin: prosocial behavior, social salience, or approach-related behavior?. Biological Psychiatry, 67(6), e33-e34.

Kemp, A., & Guastella, A. (2011). The role of oxytocin in human affect. Current Directions in Psychological Science, 20(4), 222-231.

Kosfeld, M., Heinrichs, M., Zak, P., Fischbacher, U., & Fehr, E. (2005). Oxytocin increases trust in humans. Nature, 435(7042), 673-676.

Lane, A., Luminet, O., Rimé, B., Gross, J., de Timary, P., & Mikolajczak, M. (2013). Oxytocin increases willingness to socially share one's emotions. International Journal of Psychology, 48(4), 676-681.

Lane, A., Mikolajczak, M., Treinen, E., Samson, D., Corneille, O., de Timary, P., & Luminet, O. (2015). Failed replication of oxytocin effects on trust: The envelope task case. Plos One, 10(9), e0137000.

Lim, M., & Young, L. (2006). Neuropeptidergic regulation of affiliative behavior and social bonding in animals. Hormones and Behavior, 50(4), 506-517.

Mikolajczak, M., Gross, J., Lane, A., Corneille, O., de Timary, P., & Luminet, O. (2010a). Oxytocin makes people trusting, not gullible. Psychological Science, 21(8), 1072-1074.

Mikolajczak, M., Pinon, N., Lane, A., de Timary, P., & Luminet, O. (2010b). Oxytocin not only increases trust when money is at stake, but also when confidential information is in the balance. Biological Psychology, 85(1), 182-184.

Nave, G., Camerer, C., & McCullough, M. (2015). Does oxytocin increase trust in humans? A critical review of research. Perspectives on Psychological Science, 10(6), 772-789.

Ross, H., & Young, L. (2009). Oxytocin and the neural mechanisms regulating social cognition and affiliative behavior. Frontiers in Neuroendocrinology, 30(4), 534-547.

Shamay-Tsoory, S., & Abu-Akel, A. (2016). The social salience hypothesis of oxytocin. Biological Psychiatry, 79(3), 194-202.

Simpson, J. (2007). Psychological foundations of trust. Current Directions in Psychological Science, 16(5), 264-268.

Weber, J., Malhotra, D., & Murnighan, J. (2004). Normal acts of irrational trust: motivated attributions and the trust development process. Research in Organizational Behavior, 26, 75-101.

Zak, P., Kurzban, R., & Matzner, W. (2005). Oxytocin is associated with human trustworthiness. Hormones and Behavior, 48(5), 522-527.

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