US researchers claim to have developed a brain scanning technique reliable enough to identify when criminals lie.
Could this one day be part of criminal investigations?
The University of Pennsylvania School of Medicine, Philadelphia, team say monitoring the frontal lobe area of the brain shows when people are lying.
Nature magazine reports the scientists say the area is more active when people are not telling the truth.
But other experts said laboratory research would not translate to real-life situations.
The researchers use functional magnetic resonance imaging (fMRI) scans to look at which areas of the brain were active in particular circumstances.
In the study, which is also set to be published in the journal Neuroscience, volunteers were given an envelope with two cards and $20.
They were told they could keep money if they lied convincingly in tests.
Once inside the fMRI scanner, they were asked to press a button if cards flashed up on a screen in front of them matched one they had.
They were asked to lie about having one of the cards, and be honest about the other.
The scientists say that, by analysing brain activity, they were able to develop a mathematical formula that could detect lies from truth which was 99% accurate.
Daniel Langleben, who led the research, had previously said fMRI was a research tool, and could not be used to spot people lying in criminal or terrorist investigations.
But he said this latest study had changed his mind because it looked at results from an individual lie, rather than looking at generic brain activity when people were being dishonest.
He told Nature: "We can't say whether this person will one day use a bomb.
"But we can use fMRI to find concealed information. We can ask: 'is X involved in terrorist organisation Y?'."
Rugen Gur, one of the team who worked on the study: "Now we can tell when the individual lies on a specific question. This is a major step forward."
He added: "A lie is always more complicated than the truth.
"You think a bit more, and fMRI picks that up."
But Jennifer Vendemia, an expert in lie detection research at the University of South Carolina, said laboratory experiments did not match real-life situations. "There is nothing you can do in the lab that would mimic job loss, the death penalty or public humiliation."
Dr Paul Seager, a psychologist who has focussed on how people behave when they lie, agreed.
He told the BBC News website:" You cannot generalise from lab studies to real life.
"Getting somebody to lie when there's really no consequence doesn't cut the mustard compared with a situation where the consequences could be being sent to prison."
And he said nothing had so far been shown to be 99% effective in detecting liars - and the claims for fMRI scanning needed to be replicated in other studies by other researchers.