While previous research has shown that there is heightened activity in the prefrontal cortex – the area of the brain that enables most people to feel remorse or learn moral behavior – when normal people lie, this is the first study to provide evidence of structural differences in that area among pathological liars.

The research – led by Yaling Yang and Adrian Raine, both of the USC College of Letters, Arts and Sciences – is published in the October issue of the British Journal of Psychiatry.

The subjects were taken from a sample of 108 volunteers pulled from Los Angeles’ temporary employment pool. A series of psychological tests and interviews placed 12 in the category of people who had a history of repeated lying (11 men, one woman); 16 who exhibited signs of antisocial personality disorder but not pathological lying (15 men, one woman); and 21 who were normal controls (15 men, six women).

“We looked for things like inconsistencies in their stories about occupation, education, crimes and family background,” said Raine, a psychology professor at USC and co-author of the study.

Why not add the category — politician?

“Pathological liars can’t always tell truth from falsehood and contradict themselves in an interview. They are manipulative and they admit they prey on people. They are very brazen in terms of their manner, but very cool when talking about this.”

Aside from having histories of conning others or using aliases, the habitual liars also admitted to malingering, or telling falsehoods to obtain sickness benefits, Raine said.

After they were categorized, the researchers used Magnetic Resonance Imaging to explore structural brain differences between the groups. The liars had significantly more “white matter” and slightly less “gray matter” than those they were measured against, Raine said.

More white matter – the wiring in the brain – may provide liars with the tools necessary to master the complex art of deceit, Raine said.

“Lying takes a lot of effort,” he said.

But in normal people, it’s the gray matter – or the brain cells connected by the white matter – that helps keep the impulse to lie in check.

Pathological liars have a surplus of white matter, the study found, and a deficit of gray matter. That means they have more tools to lie coupled with fewer moral restraints than normal people, Raine said.

The researchers stopped short of asserting that these structural differences account for all lying.

“This is one of the components,” Raine said.

So, uh — when are they going to test Congress?