Can a Brain Scan Predict a Broken Promise?

A new study suggests that brain activity may give away dishonest intent!

I found a really interesting article at the Scientific American about broken promises and brain activity. I find it interesting that they call breaking a promise "being dishonest" and I suppose it's true. Anyway, here are the highlights of the article. I'm curious to hear what you guys think of it!


Last time you told someone “I’ll call you,” did you mean it? We all make promises in our daily interactions with others. On the one hand, promises such as “I’ll return your book next week” or “I won’t tell anyone” are not heavily binding, except maybe in a moral sense.

On the other hand, some of the promises we make bind us legally and financially. By saying “I do”, newlyweds promise to love and cherish each other no matter what happens for the rest of their lives; hardly anybody makes this promise intending to break it.

But imagine making a promise when in fact, you know you would benefit from not keeping it. Would you keep it anyway? Could we somehow tell in advance whether you’re going to keep it or break it? And finally, could we predict your decision by looking at what happens in your brain?

All these questions are addressed in an exciting new study performed in Switzerland and led by Thomas Baumgartner and Urs Fischbacher. While their findings, published in "Neuron," are brand new and thus need to be confirmed by further research, they suggest that it may indeed be possible to detect whether a person is about to break a promise based on brain activity, well before the promise is actually broken.

The researchers ran a brain-scanning experiment in which pairs of participants played a well-established economic game involving trust. The main objective of this study was to illuminate how brain activity differs when promises are kept and when they are broken.

Interestingly, nearly all participants fell into one of two groups – about half were honest and consistently kept their promises, and the other half consistently broke them. The researchers compared the brain activity of the honest and dishonest players. They found that while breaking their promise, the dishonest players showed greater activity in regions of the brain known to be involved in generating and regulating emotional and cognitive conflict (the anterior cingulate cortex, parts of the dorsolateral prefrontal cortex, and the amygdala).

Fascinatingly, another network of regions in dishonest players’ brains (the anterior insula, anterior cingulate cortex and inferior frontal gyrus) showed increased activity while the players were making promises that they would later break. In other words, the dishonest players showed increased brain activity in several areas not only while breaking promises, but also at an earlier stage when their behavior was indistinguishable from that of honest players.

The researchers also examined whether any brain regions showed increased activation in the honest (compared to dishonest) participants, but found no such areas. They interpret this to mean that honesty may be a human ‘baseline’ – our brains might find it more effortful to be dishonest than honest.

This interpretation is rather optimistic about human nature, as it implies that we are hardwired to be honest, and that even those who consistently act dishonestly do not find it easy to do so. However, we must remember that failing to find a difference is not the same as proving that there is no difference. Honesty-related brain activity may be too subtle for such techniques to pick up.

In this study, each of the participants tended to be either honest or dishonest. Surprisingly, although we often think of honesty as a general personality trait, the researchers found no differences, on personality measures, between participants who broke promises and those who kept them.

Does this mean honesty is simply not part of one’s personality? Or perhaps we will never be able to capture honesty with a test? After all, being honest or dishonest involves a set of cognitive and social factors which may prove too complex to pin down.

In the Baumgartner study, the researchers observed people doing what came naturally to them in a social interaction – and for about half, the experiment was enough to elicit deceptive behavior.

The study opens up a host of questions for future research. For example, is dishonesty in economic decision-making the same as dishonesty in other situations, such as social, romantic or political interactions? Are dishonest people equally dishonest in different situations? And do similar brain mechanisms underlie all types of dishonest behavior?

So next time you say "I will call you" take a moment and ask yourself if you really mean it. You may be surprised to realize that you already know whether you do... or do not. This intention, we now know, is evident in your brain activity, so if you intend to break a promise, you might want to avoid making it in an MRI scanner.