Some victims of repeated betrayal continue, much to the dismay of their friends, to reconcile with the one who hurt them. But a new study reveals that the length of a relationship can affect which region of the brain is used to make decisions, shedding light on how trust works.

The study, conducted by sociologists in California and appearing in the journal Proceedings of the National Academy of Sciences, involved an online experiment in which each subject received $8.

The subject could either keep the money or give it to an anonymous partner.

What the subjects did not know was that the "partner" was actually a computer, programmed to sometimes betray the subject early in the game and sometimes later.

If the subject gave the money away, the value would triple, and the "partner" had the choice to keep all the money - thus committing an act of betrayal - or give half back to the subject.

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The team of researchers found that if the subject was betrayed earlier, he or she would be more likely to keep the money, compared with when the "partner" committed a betrayal much later - after the team had established a relationship of sorts.

The researchers then carried out the same experiment in a laboratory, hooking up the subjects to fMRI scanners.

During this repeated study, they found that when a subject suffered an early betrayal, the anterior cingulate cortex - an area of the brain associated with learning, planning and problem solving - as well as the lateral frontal cortex - an area associated with feelings of uncertainty - became more active.

Additionally, an early betrayal resulted in the subjects taking more time to make a decision, which the researchers say suggests they were putting more conscious thought into whether or not to give their "partner" the money.

The researchers say:

"Differential activation in the controlled social cognition system and the automatic social cognition system indicate that decision making is less controlled and more automatic following a later as opposed to an earlier trust breach."

Being deceived early in a relationship, say the researchers, prompts this kind of careful, controlled decision making when mulling over whether or not to continue trusting the deceiver.

By contrast, when the subjects were betrayed much later in the game, the lateral temporal cortex - associated with habitual decision making - became more active and they did not take quite as much time to make decisions. Use of this area of the brain, say the researchers, increases the likelihood of forgiveness.

Dr. Oliver Schilke, one of the authors of the study, told Medical News Today:

"Although our experiment obviously was conducted in an artificial laboratory setting using an investment game originally invented by behavioral economists, our findings may generalize to various real-life contexts."


"For example, it may speak to interpersonal relationships between coworkers, between an employee and her boss, or even between intimate partners. Our results imply that people may be more 'forgiving' if a breach occurs at a point in time when people have known each other for a while, as opposed to when it occurs right after getting to know a person."

Dr. Schilke also noted that their results "have implications for interorganizational relationships, such as strategic alliances, where trust and trust recovery play important roles."