US scientists say they can tell whether one person trusts another, by using a brain scan.
Scans can help scientists pinpoint where functions occur
The results suggest that a brain region called the
caudate nucleus lights up when it receives or computes data to make
decisions based on trust.
The Baylor College of Medicine team based their findings
on magnetic resonance imaging (MRI) brain scans of volunteers playing a
The research is published in the latest edition of Science magazine.
During the money game, one player, designated the
"investor", received $20. They then had the option of sending some,
all, or none of the $20 to the other player, the "trustee".
According to the rules of the game, which were known by
both players, whatever money the trustee was given would triple. The
trustee then had the option of returning a portion of the new sum to
The study authors looked at what happened in the brains of both players during 10 rounds of the game.
They found the extent to which the players trusted each other with their money depended on the recent history of the exchange.
Activity in the caudate nucleus was greatest when the
investor repaid generosity with generosity and most subdued when the
investor repaid generosity with stinginess.
According to the researchers, this suggested that the
caudate nucleus receives or computes information about both the
fairness of a social partner's decision and the intention to repay that
decision with trust.
As the game went on, brain scan signs of the trustee's
intention to "trust" or "not to trust" the investor began before the
investor revealed whether were going to increase their investment or
Past studies have shown the caudate nucleus is connected
to the brain's reward pathways and that it goes into overdrive when a
reward is expected.
Lead researcher Dr Read Montague said the latest
findings might be important for understanding more general, everyday
judgments of trust, as well as conditions such as schizophrenia and
He said it could help in cases where people "have an
incapacity to model others or be sensitive to others such as in autism,
and also in people who do not know how to trust people".
His team is also investigating whether trust differs
across nationalities, comparing German volunteers with volunteers from
Professor Lyn Pilowsky, professor of neurochemical
imaging and psychiatry at London's Institute of Psychiatry, UK, said
that because of the complex function of the caudate nucleus it was
difficult to tell whether it was also the centre for trust.
This was because it is involved with ranking the order and priority of information as well as judging rewards.
"The caudate nucleus would be generally important in
this type of money game anyway because of its many functions. It's not
"It would be important to devise a test that would test only trust.
"It offers us a window into these very complex social interactions but whether it tells us something specific I do not know.
"It might be good to look back at people who had lost
function of their caudate nucleus through a stroke, for example, and
see whether they had particularly lost their sense of trust."
She said the caudate nucleus was certainly an important area of the brain involved in schizophrenia and autism.