For some lying comes too easily (Image: Giorgio Majno/Getty) )

Honest people don’t have to work at not cheating. They’re not even tempted.

That’s the conclusion of the first-ever neurobiological study of honesty and cheating, which could someday help develop brain-based tests of truthfulness.

When studying honesty, neuroscientists usually ask people to either tell the truth or lie while undergoing a brain scan. This is unsatisfactory, because even the “liars” are doing as they were told, so Joshua Greene and Joseph Paxton at Harvard University came up with an alternative.


They asked volunteers to bet money on the flip of a coin. Sometimes the players had to record their predictions before the flip, and sometimes they said whether they had guessed correctly after the flip, giving them the opportunity to cheat. Some – but not all – did so, as evidenced by an abnormally high “success” rate.

Honesty test?

In each round, fMRI was used to record brain activity in the prefrontal cortex and other regions associated with decision making and behavioural control.

Honest players showed no increase in brain activity when they had a chance to cheat, suggesting that they didn’t have to make a conscious effort to be honest. In contrast, dishonest players showed increased brain activity whenever they had a chance to cheat – even when they reported (presumably truthfully) that they had lost.

In fact, Greene and Paxton found that they could predict each player’s degree of cheating from their brain activity with remarkable accuracy. If the results of this lab experiment can be generalised to real-world situations – a big if, Greene points out – then brain scans could someday be used to measure, for example, a prospective employee’s overall honesty.

But before that becomes practical, researchers would need to verify that scans can be compared reliably over time and among different test conditions or groups of subjects, says Martha Farah, a cognitive neuroscientist at the University of Pennsylvania in Philadelphia.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0900152106)