Oxytocin Increases Trust in Humans
Oxytocin has been coined “the love hormone” because it plays a significant role in our social attachments and interactions. A lesser-known benefit of oxytocin is its ability to inspire trust in and among people. The connection between oxytocin and trust seems logical when you consider how oxytocin affects animal behavior.
Scientists credit oxytocin with enabling animals to bypass their natural inclination to avoid being close to other animals and instead allow approach.
Two studies conducted by researchers at the University of Zurich demonstrate the link between oxytocin and trust in humans. The first double-blind study, led by Michael Kosfeld Ph.D., compared the trust levels of 2 groups of participants: 1 group was administered oxytocin in the form of a nasal spray, and the other was given a placebo.
Participants competed in two financial trust games, one of which they played with another human, and in the other they competed against a computer. The game features an investor and a trustee. The investor must decide whether he wants to entrust his money to the trustee, or keep it all to himself. 
Handing it over to a trustee doubles the amount of money, but involves risk. The trustee then gets to decide how she wants to divvy up the money: Does she want to halve it, or keep it all for herself? This truly was a game of financial risk, as participants played with monetary units that were converted to real money at the study’s end.
The results confirmed the scientists’ suspicions: 45% of those given oxytocin exhibited the highest trust levels, whereas the placebo group showed high trust levels in only 21% of participants. These trust levels were not present when individuals played against the computer, thereby ruling out the possibility that oxytocin may enhance risk-taking as a whole, and narrowing the hormone’s influence down to social risk-taking among people.
The second double-blind study, led by neuroscientist Thomas Baumgartner, not only demonstrated oxytocin and trust had a great effect, but also showed exactly how it influences the brain. Using functional magnetic resonance imaging (fMRI), scientists were able to see how oxytocin influences trust behavior and what happens in the brain when that trust dissolves.
Forty-nine people were administered either the oxytocin nasal spray or a placebo. They participated in the same trust game with humans, and then what was termed a financial risk game with a computer. The experiment was bisected into a pre and post feedback stage. In between the two stages, participants in both groups were told that 50% of their investments had gone sour.
This translated to betrayal in the trust game and a bad gamble in the financial risk game. Investors given the placebo at the start of the game reduced the amount of money they gave to trustees, thereby decreasing the rate of trust significantly. Investors given oxytocin, however, invested at the same rate of trust despite the betrayal.
These different behavioral responses also registered as different neural responses in the brain. Oxytocin encouraged decreases in 2 areas of the brain: the amygdala and the candate nucleus. Abundant in oxytocin receptors, the amygdala is responsible for triggering emotional and fear learning.
The caudate is responsible for reward-related reactions and learning how to trust.
Based on these results, researchers concluded that oxytocin reduces the fear mechanism that activates the fear of deception (amygdala) and overrides the need for positive feedback that can influence our future ability to trust (caudate).
Once again, these results were only evidenced in the trust game, not the risk game played with the computer, thus indicating that oxytocin’s effect on trust only applies to actual people.
Further research is needed to explore oxytocin and trust and how this hormone can be used to strengthen our trust in others and even treat mental disorders that specifically relate to deficiencies in social behavior.
