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Why You Trust Your Friends Even When They're Ripping You Off

Your brain wants to trust. We're wired for social connection--not just casual meet and greets, but genuine connection--and trust is what makes it work. Without taking a leap of faith and trusting at least one other person at a deep enough level, life takes on a reverberating hollowness.

But here's the problem - that same drive to trust, essential though it is, also makes us natural born suckers. And neuroscience has become adept at finding the brain mechanisms underlying our suckerdom.

Researchers from Dartmouth College set up an experiment in which they told participants they'd be playing a computer-based investment game with either a close friend or a stranger (to make the setup?convincing, they asked participants to bring a close friend to the study). The game involved making investments that required trusting the other player to reciprocate fairly. ?What was actually happening, unknown to the participants, is that the games were manipulated by the researchers?using a?computer algorithm designed to reciprocate only 50% of the time.

The researchers used?MRI?to image?the participants' brains while the game was going on to find out which brain areas showed the greatest level of activity given a few different conditions. They found heightened activity particularly in two brain areas--the ventral striatum and medial prefrontal cortex--when participants were playing with their close friends as compared to strangers. The ventral striatum plays a major role?in how the brain processes rewards (when, for example,?we're expecting to receive or achieve), and the medial prefrontal cortex plays a major role in our ability to "read" others' mental states. This ability, sometimes called mentalization, is how we clue into what someone is thinking during social interaction - our brain's closest thing to mind reading. Taken together, greater activity in these two areas indicates that a person believes he or she is receiving, or about to receive, a satisfying social reward. Social rewards (in brain parlance) are what motivate us to engage in social activity?-?they're a significant driver for forging trust bonds.

What the research team found is that they could accurately predict when a participant would make a more trusting decision in the game based on elevated activity in those two brain areas. And here's the kicker: even when the participants found out that both their friends and strangers were only reciprocating half the time (which is to say, the algorithm was only reciprocating half the time) they still made more trusting decisions when playing with their friends. Knowledge of unfairness didn't squelch their brains' trust signal.

The takeaway is that ?even when faced with knowledge that may call our trust into question. The social reward our brain is wired to seek outweigh