fMRI proves honest people don’t even think about lying

August 5, 2009

Honest people don't struggle with themselves about whether they should tell the truth when given the opportunity to lie, as shown in an fMRI brain study of truth telling and prevarication from Harvard University behavioral scientists.

Honest people don't struggle with themselves about whether they should tell the truth when given the opportunity to lie, as shown in an fMRI brain study of truth telling and prevarication from Harvard University behavioral scientists.

Using a unique study approach, the researchers found honest individuals displayed little to no additional neural activity in control-related brain regions when telling the truth, but liars did.

"Being honest is not so much a matter of exercising willpower as it is being disposed to behave honestly in a more effortless kind of way," said Joshua Greene, lead author of the study and an assistant professor of psychology at Harvard. "This may not be true for all situations, but it seems to be true for at least this situation."

When it comes to lie detection there are two prevailing theories: the "will" theory hypothesizes honesty results from an active resistance to temptation, and the "grace" theory hypothesizes honesty results from a lack of response to temptation, the researchers said. Since the participants who were honest didn't show any additional neural activity, this study suggests the grace theory is more accurate.

Thirty-five subjects attempted to predict the outcomes of random computerized coin flips while they underwent fMRI. They were financially rewarded for accuracy and punished for inaccuracy (Proc Natl Acad Sci USA 2009; e-pub ahead of print). In the "no opportunity" condition subjects recorded their predictions in advance. In the "opportunity" condition, subjects made their predictions privately and were rewarded based on self-reported accuracy, which allowed them to cheat.

Greene and colleagues hid the actual goals of the experiment from participants by telling them it was intended to study paranormal abilities to predict the future. Participants were led to believe the opportunity for dishonest gain was known to the researchers, but it was an unintended byproduct of the study. They were told they were expected to behave honestly.

Honest subjects displayed little to no additional brain activity when reporting their prediction of the coin toss. Researchers assessed honesty based on whether a subject's number of correct responses was statistically feasible. Individuals with improbably high levels of accuracy were classified as dishonest.

Dishonest participants' brains were active in control-related brain regions both when they chose not to lie and when they decided to lie. The control-related brain regions include the dorsolateral prefrontal cortex and the anterior cingulate cortex.

"An overall dishonest pattern of response appears to involve additional cognitive control, but it's not clear what those control processes are doing," Greene said. "It's not clear if they are suppressing the urge to lie, suppressing the urge to tell the truth, or something else that is not specifically associated with lying or telling the truth."

This study suggests it is possible to detect real dishonesty using fMRI. But detecting individual lies may be even harder than expected because refraining from lying may not look much different from lying, according to Greene. One conclusion from this: fMRI is still not ready to be used as a lie detector test by authorities.