Can a Brain Scan Predict a Broken Promise?

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














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Promises, Promises Image: Kuzma

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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. Player A, who was outside the MRI scanner, had to decide whether to keep or give away a certain amount of money -- say, $1 -- to Player B, who lay in the scanner.

If Player A decided to give the money to Player B, the amount would be increased five times (to $5). Once entrusted with the money, Player B could choose to either split it with Player A, so that each ended up with equal shares, or to keep it all.

Before Player A decided whether to hand over the money, player B made one of four promises: That if given the money, he would always, mostly, sometimes or never share it. The twist, however, was that once given the money, Player B could break his promise and keep the entire amount. Player A therefore faced a dilemma: to trust or not to trust the promise.

The main objective of this study was to illuminate how brain activity differs when promises are kept and when they are broken. Therefore, Player B’s brain activity was measured at three points during each game: When he made his promise; while he waited for player A to decide whether to trust him; and finally when he decided whether to keep his promise to share or not.

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.


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  1. 1. Elan 12:53 AM 2/2/10

    Are we in the same Journal Club? We just discussed this article a few days ago! ;)

    One thing though: it was mentioned above, but in my opinion not very clearly. If A trusts B and gives him one "money unit", B receives TEN. B then either keeps 10, or splits the money, A and B then both receive 5.
    The text above makes it seem as if 1 MU will be 5, not 10, which could be split in two.
    I know it's just one little detail, but imho this does add up a little to the moral dillema the trustee is facing.

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  2. 2. jtdwyer 08:53 AM 2/2/10

    Monitoring brain activity to determine intention might reveal individual pathological malevolence and self-interest, but does not assess the ability of the promise-giver to fulfill the promise. In addition, interactions with large organizations involve direct exchanges with minions who may have the best intentions, but whose organization has no intention of sacrificing its own self-interest in order to fulfill a promise made. I wouldn’t get too excited about this unless you’re in personnel or law enforcement.

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  3. 3. KS in reply to Elan 09:45 AM 2/2/10

    The numbers are in fact correct here. In the study, A gets 2 MUs that are then increased by a factor of FIVE, which makes 10MUs. So if we take e.g. 1 dollar and increase this by a factor of 5, we get 5 dollar. Greetings.

    See the paper: A receives an endowment of 2 [TWO] money units (MUs) at the beginning of each trial (&) If A trusts B and sends his endowment (case 1), the experimenter increases the amount sent by a factor of five [FIVE], so that B receives 10 MUs.

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  4. 4. MCMalkemus 02:22 PM 2/2/10

    Here's another question: can a brain scan be fooled, like a polygraph can?

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  5. 5. Iahmad 01:44 AM 2/3/10

    I wonder what will be the scan pattern of war criminals like Bush, Blair and many more when they were lying outright while proposing to attack Iraq and other nations.

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  6. 6. Spiff 03:36 PM 2/3/10

    Holley Molley! Keep this scanner away from Congress 'cause it will blow up!
    Spiff

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  7. 7. laligam 08:19 PM 2/4/10

    what about the other circumstances,due to which One may not be able to keep a Promise?Can that also be predicted?

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  8. 8. verdai 08:55 PM 2/22/10

    yes! them liars are detectable!
    even if for now one must have the intuition or the second-sight, the day will come when we all will be able to know and hate them by various means.

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