Scientists from Zurich University have discovered that the "love hormone" oxytocin can help foster trust after a betrayal.
The results of a study, which appears in the science publication Neuron, have brought the research team closer to understanding the physiological mechanism behind this response.
Whether in love, politics, family life or business, humans rely on trust to live together. Understanding what promotes trust can also be useful in treating mental problems associated with social dysfunctions, according to the researchers.
The team, led by a psychologist, a neuroeconomist and a neuroscientist, set up scenarios where subjects were called upon to trust another person in a deal that could work to their advantage – but only if the other person proved to be trustworthy.
Three years ago, the same scientists first discovered that oxytocin stimulated trusting behaviour in humans. They have now taken the research a stage further to show that the chemical messenger is also effective after trust has been broken.
Subjects who inhaled the hormone, which plays an important role in bonding, remained trusting even after having been let down.
Professor Ernst Fehr explained to swissinfo the typical trust relationship upon which the experiments were based. "It's like I lend you money and you have a productive opportunity to use that money and, let's say, triple it. The agreement is that we then share the proceeds but we have no contract; it's all based on informal understanding."
Once bitten ...
Subjects who inhaled oxytocin continued to act trustingly even after they had been "once bitten". They showed reduced activity in the areas of the brain where fear and responses to negative experiences are generated.
Oxytocin is a hormone with impressive powers. Levels of oxytocin are higher among people who claim to be in love. It is also thought to mediate other forms of pair bonding such as friendship and family relationships.
"It is released during orgasms and it's also released when women breastfeed their children," Fehr explained.
"There are all kinds of conjectures around suggesting that oxytocin is really an important hormone for bonding. It appears to play a big role in peer bonding."
The feelings of well being produced by oxytocin could also be useful in helping to heal troubled minds.
According to psychologist Markus Heinrichs, another co-author of the study, clinical trials are now underway to test the efficacy of the hormone in combination with behavioural therapy in the treatment of disorders such as social phobia and borderline personality disorders.
The scientists will continue to delve deeper into oxytocin and other substances that influence behaviour.
"We do many experiments where we apply pharmacological interventions in order to study the behavioural effects and the neural circuitry that is supposed to trigger these effects," Fehr said.
So what is to stop Barack Obama from spraying the crowd with oxytocin to improve his appeal? Fehr says there is no fear of this kind of manipulation at a mass level.
"When you inhale oxytocin you have to put the inhaler very deep into the nose. This cannot be done without the person's consent," he said.
But perhaps it could come in useful to those faced with unrequited love. That is, provided you could persuade the object of your affections to breathe deeply.
swissinfo, Clare O'Dea
Oxytocin is secreted in brain tissue and synthesised by the hypothalamus. This small region of the brain controls biological reactions such as hunger, thirst and body temperature, as well as visceral fight-or-flight reactions associated with basic emotions such as fear and anger.
In humans and animals, this chemical messenger stimulates uterine contractions in labour and induces milk production.
Elevated concentrations of the hormone have also been found in cerebrospinal fluid during and after birth, and experiments showed it was involved in the biochemistry of attachment.
Oxytocin also plays some role in orgasms for both sexes. In men, oxytocin is said to facilitate sperm transport in ejaculation.