|Time.com, 20-07-2009, door Adi Narayan||
The fMRI Brain Scan: A Better Lie Detector?
would seem that being honest is an absolute, undebatable state. A person is
either truthful or he's not. Right?
Consider this scenario: a shopkeeper mistakenly returns an
extra $10 in change to a customer. In one outcome, the customer returns the
money promptly, without pause. In another, he hesitates for just a second,
thinks about pocketing the 10 bucks, then decides to give it back.
Which is true honesty?
That is the question that Joshua Greene, 35, an assistant
professor of psychology at Harvard University is trying to answer. More
specifically, Greene is trying to identify the particular pattern of brain
activity that distinguishes people who are simply telling the truth from those
who are resisting the temptation to lie. His findings, which are based on
functional-magnetic-resonance-imaging (fMRI) data, shed light not only on the
workings of the human mind but also on the controversy over using fMRI
technology outside the lab in the detection of lies.
In a cleverly designed experiment, recently published in the
Proceedings of the National Academy of Sciences, Greene recruited 35 volunteers
and told them they would be participating in a study to find out whether people
are good at predicting the future when they are paid for it. The real purpose,
of course, was to get people to lie without asking them to lie — and image their
brains committing an act of deception.
While inside an fMRI scanner, each participant was asked to
predict the outcome — heads or tails — of about 210 coin tosses. The
participants made their predictions privately, but after each toss, researchers
asked them to reveal whether or not they had guessed accurately. A display
mounted inside the scanner flashed the questions, and participants pressed a
button in response. Each correct prediction was awarded up to $7; incorrect
predictions were awarded nothing, but there was ample opportunity to lie and
still win the money.
The researchers then divided the volunteers into groups on
the basis of their answers. Those who reported an improbably high number of
correct answers were labeled dishonest. Most of the others were classified as
honest. Researchers then averaged the fMRI data — which monitors blood flow and,
therefore, activity inside the brain in real time — for each group to try to
establish a neural signature that represented truth-telling and one that
(See the top 10 scientific discoveries of 2008.)
Compared with the lying group, honest volunteers had
relatively quiet minds — that is, they showed no distinctive activity in the
prefrontal cortex, an area of the brain responsible for planning and
decision-making. In the dishonest group, however, areas within the volunteers'
prefrontal cortices registered vigorous activity — and the activity persisted
whether they were lying or not.
What does this mean? Greene suggests that in some
circumstances, real honesty is not about overcoming the temptation to lie but
about not having to deal with that temptation in the first place. On an fMRI
image, at least, the lying brain may look no different from one that's simply
contemplating whether to lie. "Within the dishonest group, we saw no basis for
distinguishing lies from honest reports," says Greene.
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