American Scientist

Are you really telling the truth? For decades scientists have sought reliable ways to detect deception, only to be outwitted by liars capable of deceiving their instruments. But current technology is providing novel ways to study deception—and furthering understanding of how the brain works.

Active deception results in perceptible changes in brain activity, say scientists who presented a study at the Society for Neuroscience meeting in San Diego, California, last November. Daniel Langleben, an assistant professor of psychiatry at the University of Pennsylvania School of Medicine, and his colleagues detected patterns of increased brain activity during functional magnetic resonance imaging (fMRI) in volunteers when they lied compared with when they told the truth.

In the study, volunteers were given a sealed envelope containing a playing card and a $20 bill and asked not to disclose the identity of the card they held. Investigators told the volunteers to deny having the card during a computerized interrogation, telling them they could keep the $20 if they successfully "convinced" the computer that they didn't have the card.

When the subjects were lying, the scientists found significantly increased activity in both the anterior cingulate cortex, a section of the brain that has been linked to monitoring of errors and attention, and the prefrontal and premotor cortices, areas involved in the initiation of voluntary movement. Functional magnetic resonance imaging measures brain activity by detecting changes in brain blood flow and metabolic rate. By using a scenario with "as little nonspecific activity as possible"—the subjects simply answered "No" to the computer's questions—it is possible to correlate a task with changes in brain activity, said Langleben.

What's most interesting (in terms of brain research) is the finding that deception appears to be the suppression of truth: Whereas the brain regions mentioned above were more active during lying than truth-telling, no regions were more active during truth-telling. Lying resulted in a strictly positive difference in activity, which suggests that truth is the baseline cognitive state and that "the first thing you need to do [to lie] is to not tell the truth," said Langleben.

The team, whose study is published in the February issue of NeuroImage, doesn't claim to have identified the signature of deception, but their findings open the door to a type of lie detection independent of the nonspecific physiological variables such as blood flow, pulse and skin conductance upon which the traditional—and controversial—polygraph test relies.

Although fMRI scanning is a potentially powerful method of lie detection, it certainly has its drawbacks. For one, it requires enormous resources, says James Levine, an endocrinologist at the Mayo Clinic and author of a January Nature paper that promises an alternative lie-detection method using thermal imaging technology. In the study, Levine and his colleagues asked volunteers to commit a mock crime—stab a mannequin and rob it of $20—and then claim innocence. Using high-definition thermal imaging of the face during interrogation, the scientists looked for a characteristic and instantaneous warming around the eyes, which they had previously documented following auditory startling and which they hypothesized might also accompany deception.

The thermal imaging system had success rates consistent with those of a traditional polygraph, correctly identifying 6 out of 8 of the lying individuals and 11 out of 12 of the truth-telling individuals. (The controls in this experiment had no knowledge of the plot to stab and rob the mannequins.)

Many people are vehemently opposed to the traditional polygraph because the same signs that indicate deception may also indicate anxiety, frustration, anger or any number of emotional states. George Maschke, co-founder of AntiPolygraph.org, said he believes Levine and his colleagues are likely to encounter the same problems presented by traditional polygraphy because their data depend on nonspecific physiological responses.

They are interpreting data "two times removed from the brain," said Langleben.

In his seminal work Beyond Good and Evil, philosopher Friedrich Nietzsche wrote, "The mouth may lie, all right, but the face it makes nonetheless tells the truth." With neither fMRI nor thermal imaging machines to guide him, Nietzsche nonetheless managed to come as close to the truth as scientists have more than a century later.—Rebecca Sloan Slotnick