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There's No Denying It

Brain scans show a difference between truth and deception

THURSDAY, Dec. 6, 2001 (HealthDayNews) -- You know the old saying, "You can't lie to yourself"? Now, brain scans show that adage is all too true.

In findings that could put the lie detector machine out of business, a new study has found brain scans can detect when someone is lying.

Researchers used functional magnetic resonance imaging (fMRI) to track the brain activity of 18 college student volunteers who were given a version of the Guilty Knowledge Test, a method of interrogation frequently used by law enforcement officials.

The students were given an envelope containing the five of clubs playing card. They were told to hide it in their pockets and to deny they had it when asked.

The students then were placed in a fMRI scanner and "interrogated" by a computer that showed them a series of playing cards accompanied by the question: "Do you have this card?"

When the students lied, the areas of the brain that play a role in paying attention and controlling error were much more active than when the students told the truth. The brain sections include the anterior cingulate gyrus, located deep in the brain towards the top of the head, and parts of the prefrontal and premotor cortexes, both located in the very front of the brain.

"It requires more brain activity to lie than to tell the truth," says lead study author Dr. Daniel Langleben, assistant professor of psychiatry at the University of Pennsylvania. ''Truth is the default position of the brain. It's harder to lie than to tell the truth because the first thing we need to do to lie is to suppress something."

The study was presented at the recent national meeting of the Society for Neuroscience in San Diego.

So what does this mean for the future of catching criminals?

Langleben says more testing is needed, but brain scans could eventually become the "gold standard" to refine other methods now used to determine truth and deception.

The most commonly used lie-detecting device now is the polygraph, an instrument that uses electrodes to measure physiological changes associated with nervousness, such as increased respiration, heart rate and perspiration. Presumably, people who are lying are more nervous than those telling the truth.

But the polygraph is very controversial. Critics say it's not reliable and that people can easily learn to fool the system.

Researchers around the world are experimenting with newer technologies to develop more accurate lie-detection methods, including analyzing movements of eye muscles and "brain fingerprinting," a method that measures brain waves called P300. These brain waves are triggered when someone sees something familiar.

Emanuel Donchin, professor of psychology at the University of South Florida, in Tampa, says looking for clues about lying by examining brain scans or brain waves is fraught with problems.

In the experiment using fMRI scans, the researcher found the students' brains reacted differently to the five of clubs than to the other cards. But the study did not prove that the difference in brain activity was the result of lying.

The brain could be reacting to the previous knowledge that the card had been singled out, Donchin says.

"Lies are not being detected. What is being detected is an emotional response to an item," Donchin says.

And he cites a real world example. In the Guilty Knowledge Test, suspects are asked about their knowledge of some aspect of a crime known only to the guilty person and the police.

Say a wallet was stolen and hidden under an aquarium. The police ask the suspect a series of questions about the location of the wallet. (Is the wallet in the cabinet? on the table?)

When the police ask if the wallet is under the aquarium, the suspect's brain might respond differently to that question. But this could be because the suspect forgot to feed his fish, or because, when he was a child, he got into big trouble for knocking over an aquarium.

"If you respond differentially, you know the item has special significance, but you don't know that the person is lying," Donchin says.

What To Do

To read more about polygraphs, check Howstuffworks or, which is critical of polygraphs.

You can read more about P300 at BrainWave Science. And here's a pinup of the cingulate gyrus.

SOURCES: Interviews with Daniel Langleben, M.D., assistant professor of psychiatry, University of Pennsylvania, Philadelphia; Emanuel Donchin, Ph.D., professor of psychology, University of South Florida, Tampa; Nov. 13, 2001, national meeting of the Society for Neuroscience, San Diego, Calif.
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