In oxytocin we trust

It is essential to commencing labor contractions in pregnant women. It is implicated in behaviors related to maternal care, including milk letdown. It apparently helps to regulate social relationships in primates and other mammals.

And now, according to a study in Nature by Michael Kosfeld and colleagues (2005), oxytocin appears to be related to trust between people.

From the abstract:

Here we show that intranasal administration of oxytocin, a neuropeptide that plays a key role in social attachment and affiliation in non-human mammals causes a substantial increase in trust among humans, thereby greatly increasing the benefits from social interactions. We also show that the effect of oxytocin on trust is not due to a general increase in the readiness to bear risks. On the contrary, oxytocin specifically affects an individual's willingness to accept social risks arising through interpersonal interactions. These results concur with animal research suggesting an essential role for oxytocin as a biological basis of prosocial approach behaviour (Kosfeld et al. 2005:673).

Neuroscientist Antonio Damasio wrote an accompanying editorial.
There is also a story in the Economist on the paper. Damasio summarizes the logic of the conclusions:

Kosfeld et al. provide an engaging discussion of the possible mechanisms behind their finding. They reject the possibility that oxytocin has a nonspecific positive effect on social behaviour, because of its different influence on investors and trustees. Approach and trust possibly dominate the behaviour of investors, and that is where oxytocin works, whereas trustee behaviour is dominated by a principle of reciprocity, for which oxytocin seems irrelevant. Kosfeld et al. also reject the possibility that oxytocin merely reduces the sensitivity to risk, because in a control experiment in which the investors knew the trustee was a computer, they did not take any extra risks. The authors finally settle for an attractive pair of factors: that oxytocin overcomes the aversion to betrayal (which applies only to the investors), and that this is combined with the effects of reward that result from enhanced approach behaviour (Damasio 2005:571).

Damasio also points to some pretty interesting hypotheses about well-known pathologies, including autism and William's syndrome. The first is characterized by a relative lack of social bonding and trust; William's syndrome patients "approach strangers fearlessly and indiscriminately." He raises the question of whether this level of trust may come from excessive oxytocin release. One may alternatively ask whether it comes from an alteration in the underlying neural structures affected by oxytocin, but whether it is the first of the second, it seems likely that the trust-related mechanisms of the brain require both a structural and neurochemical input.

There has been a recent spurt of research on genes that may influence the structure or size of the brain, and their pattern of evolution in humans. These genes demonstrate the kinds of changes that may have generated the structural circuitry that underlies human behavior, although their workings are at present nearly completely unknown. But the influence of oxytocin on many aspects of human behavior illustrates an alternative route for the influence of genetic evolution. Oxytocin has multiple roles as a hormone, neuropeptide, and neurotransmitter. Instead of directly influencing the architecture of the brain, it may strongly modulate the functions of structural elements by predisposing or biasing certain kinds of outputs. Much remains to elucidate oxytocin's role, as well as that of other neuropeptides. But this kind of modulation makes it clear that the architecture of the brain must be adapted to work via the mediation of such molecules -- almost as if there were a "register shift" in the activity of certain neural substructures in response to the activity of these neuropeptides. Human brains differ from those of other primates not merely in their blueprint but also in their supply chain, as it were.

The research also points to the existence of strong subconscious influences on what might be classified as "rational" decision-making. This demonstration is not new, but it resonates as one that confounds more traditional analysis of human social bonds. Reciprocity is often conceptualized as a relation built on repeated interactions leading to trust. Humans are generally depicted within this framework as rational decision-makers who can examine their past history with other individuals (or make use of such information donated to them by other, known, individuals) and structure their future interactions accordingly. The role of oxytocin suggests that such decisions are not entirely, or perhaps even principally, made consciously. This is not to say that humans fail to make rational decisions, but instead to suggest that we have strong innate biases that reinforce certain kinds of decisions and weaken others.

Damasio's most interesting comments are in his last paragraph:

Some may worry about the prospect that political operators will generously spray the crowd with oxytocin at rallies of their candidates. The scenario may be rather too close to reality for comfort, but those with such fears should note that current marketing techniques -- for political and other products -- may well exert their effects through the natural release of molecules such as oxytocin in response to well-crafted stimuli (Damasio 2005:572).

In other words, all those pictures of babies on toilet paper advertisements are manipulating your trust. Or is that the babes in beer ads?


Damasio A. 2005. Human behaviour: brain trust. Nature 435:571-572. Nature online

Kosfeld M, Heinrichs M, Zak PJ, Fischbacher U, and Fehr E. 2005. Oxytocin increases trust in humans. Nature 435:673-676. Nature online