By Roger Highfield

The study investigated people, mostly women, who have “borderline personality disorder”, which means they are unable to hold down stable relationships.

The study, where patients played idealised games in a brain scanner[…]

The wider implications are that game playing, in this case of a game that probes the extent to which people trust each other, can provide new insights into mental disorder, how to diagnose it accurately and to treat it too.

While playing the “trust game,” in which money is exchanged between an investor, who decides how much money to invest, and a trustee, who decides how much of the investment to repay, the scientists found an unusual signature in a part of the brain, called the anterior insula, one which responds to norm violations and provides our sense of equity.

The find, based on scanning more than 600 people, including 55 with borderline personality disorder, the biggest study of its kind, is reported by Prof Fonagy with Prof Read Montague at Baylor College of Medicine in Houston and colleagues.

However, the researchers found that the patients with the disorder were much less likely to maintain the level of trust required for both parties to make the most money.

In particular, they appeared not to be able to mend or repair breaches of trust by being extra-generous in the face of slight meanness and repaying larger amounts of money.

The brain scanning results showed that the activity in the anterior insula region of the patients’ brains did not seem to be responding to the high initial investments (which signified a high level of trust), from the lower ones (which signalled distrust).

Thus it seems some of the social dysfunction, including the apparent ingratitude of these patients that tries the patience of many mental health professionals, may arise from abnormalities in the insula, a brain region involved in cooperation and social exchange.

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