Feb. 2, 2006 -- When people are lying, their brains work harder than people who tell the truth.
Lying leaves telltale traces on brain scans, report Feroze Mohamed, PhD, and colleagues in Radiology.
So can brain scans pick liars out of a lineup? Not yet. "Being a scientist, I am cautiously optimistic that one day we'll reach that [point]," Mohamed tells WebMD.
Mohamed works at Temple University as an associate professor of radiology and associate director of Temple's Functional Brain Imaging Center.
Mohamed and colleagues studied lies, honesty, and the brain. They found that "there are indeed regions in the brain that are unique to deception and that are unique to truth telling," Mohamed says.
Mohamed's study was small. It included 11 people, six of whom were assigned to go into a test room and fire a starter pistol with blank bullets.
The researchers questioned participants about the mock shooting, saying the participants had been spotted in surveillance tapes. The shooters were instructed to lie about their involvement. The innocent participants were told to be honest.
Meanwhile, participants got brain scans during the questioning. The scans used functional magnetic resonance imaging (fMRI).
Mohamed says he and his colleagues wanted to create a real experience so that the guilty people wouldn't be lying about lying. Instead, they would have smelled the gunpowder and felt the gun in their hands, Mohamed says.
"I mean, someone gives me a gun and I'm nervous. I don't even have to shoot," he says. "So we thought that in order to induce simulated lying, you need to create as close to a real-life scenario as possible."
During lying, the brain scans showed 14 activated brain areas, compared with seven different activated brain areas when people are being honest.
Lying likely makes the brain work harder because people have to suppress the truth, concoct a lie, and keep their story straight, the researchers note.
Participants also took polygraph ("lie detector") tests. Those tests correctly flagged 92% of the liars but only 70% of the honestly innocent, write Mohamed and colleagues.
Were the brain scans a better test? "Unfortunately, I don't know the answer to that because my study was not based on individual analysis. It's based on a group analysis," Mohamed says.
"We need to collect more data and repeat the experiment on a lot more subjects. Only then will we be able to make such conclusions," he adds.
Little Fibs Different?
Mohamed's study focused on big lies. Are little lies easier on the brain?
"Possibly ... but we don't know the answer to that," Mohamed says. He says his "educated guess" is that "some lies probably take more energy of the brain to form ... than a small fib."
"We need to do more studies on different kinds of lying," Mohamed says. He points out that some people are better liars than others and that the brain may react differently when the stakes are high.
"Consequences are very different when somebody shot a gun and when somebody has stolen candy from a store," Mohamed says.
"Pathological liars ... you can look at their face and probably they'll be bluffing to you and you can't even figure it out," he says. "But I think the source is the brain for all these activities, and if you can go to the source, you might be able to detect things accurately."
It may be harder to bluff your way through a brain scan. Or as Mohamed sums up his theory, "You can't fool the brain."