Research shows that our hearts beat in sync when we think about trusting each other.
Trust is a crucial part of society, building complicated links between individuals, companies and even nations, but behavioural scientists have struggled to find a way to measure the physiological signs of trust. A new study suggests that our hearts might hold a clue: the heart rates of people who think about trusting one another start to beat in sync.
Researchers from Aarhus University in Denmark studied the heartbeats of 37 pairs of participants as they solved four building tasks using Lego toys. The researchers then studied the heartbeats of a further 20 pairs of participants as they solved the same four building tasks, with an additional ‘trust-building’ game between each task. The researchers found that the heartbeats of these pairs sped up and were more strongly synchronised compared to the heartbeats of pairs who did not play the trust game.
“This is the first time that anyone has shown that trust between two people can be seen in heart rhythms and we have no idea why it happens,” said Panagiotis Mitkidis, co-author of the study and assistant professor at the Centre for Interacting Minds at Aarhus University.
People often imitate one another’s body language or tone of voice during a conversation, but much less is known about our involuntary reactions. “We hypothesised that trust will sync hearts, as physiological coordination may be a marker of a trust building process,” said Mitkidis.
Games of trust
The trust-building game, known as a Public Goods Game (PGG), encourages participants to think about how they trust one another. To play the game, participants are given a sum of money and asked to contribute a portion of their money to a collective pool. This collective pool is then multiplied by some factor and shared out equally among all participants, even those who chose not to contribute. The best outcome for everybody is reached when everybody contributes all of their money, but the best individual outcome is reached by not contributing (since a non-contributing participant will have a share of the collective pool plus their own money).
The participants in this study were very trusting, with most people contributing the full amount to the collective pool. When asked, they often said that they expected their fellow participants to also contribute the maximum amount.
It is not clear, however, if it was the act of thinking about trust, or the high level of trust, that caused the synchronisation.
“For us it was not so much a matter of high contributions. We basically wanted, by adding the PGG, to make people pay attention to each other and form some kind of strategy instead of just building,” said Mitkidis.
The researchers do not know what would have happened to participants’ heartbeats if, for example, a pair had played the PGG but chosen not to contribute their money. It is an issue that has wider implications. “I think it is a very interesting question though—what does synchrony really catch? A match between two people or a positive match between two people?”
There is a hint that the latter option is correct. Participants who said that they expected their partners to contribute the most money into the collective pool showed higher rates of heart synchronicity.
Mapping the heartbeat
The researchers then analysed participants’ heartbeats. They mapped the heartbeats from each pair together and looked for how synchronised the two heartbeats were. To reduce the chances that two heartrates were randomly beating in sync, the researchers looked for synchronised heartbeats that were constant over a longer time.
The results show that the pairs who played the trust-building game had a much higher level of heartrate synchronisation than the pairs who did not play the game.
While the research suggests that trust has a physiological response in our heartbeats, it can’t say which phenomenon comes first: trust or heartbeat synchronisation. The two effects could happen more or less simultaneously, as both participants reach a shared physiological state. Alternatively, the heart rate change could be an unspoken offer of trust, something the researchers call a “handshake”, which is then confirmed by a matching heart rate.
Either way, this research confirms what romance novels have seen telling us for decades: we really should listen to our hearts on matters of trust.
Mitkidis, P., McGraw, J., Roepstorff, A., & Wallot, S. (2015). Building trust: Heart rate synchrony and arousal during joint action increased by public goods game Physiology & Behavior, 149, 101-106 DOI: 10.1016/j.physbeh.2015.05.033