Liars

The brains of pathological liars have structural abnormalities that could make fibbing come naturally.

"Some people have an edge up on others in their ability to tell lies," says Adrian Raine, a psychologist at the University of Southern California in Los Angeles. "They are better wired for the complex computations involved in sophisticated lies."

He found that pathological liars have on average more white matter in their prefrontal cortex, the area of the brain that is active during lying, and less grey matter than people who are not serial fibbers. White matter enables quick, complex thinking while grey matter mediates inhibitions.

Raine says the combination of extra white matter and less grey matter could be giving people exactly the right mix of traits to make them into good liars. These are the first biological differences to be discovered between pathological liars and the general population.

Systematic manipulation

Other researchers have used brain imaging to show that the prefrontal cortex is more active when ordinary people tell lies. They are looking for ways to use this as an alternative to the polygraph test.

But pathological liars are a distinct group who systematically manipulate others, lie or use aliases for financial gain or personal pleasure, such as to get sickness benefits or to skip work. "It's almost like a livelihood," says Raine.

Until now no one has looked at the structure of the brains of this particular group, says psychologist Maureen O'Sullivan of the University of San Francisco in California, who specialises in lying and truthfulness.

Raine interviewed 108 volunteers from five temporary employment agencies in Los Angeles and set them standard psychopathic tests. This allowed him to identify 12 as pathological liars, 16 as people with a personality disorder but who did not exhibit pathological lying and 21 as controls, who were neither anti-social, nor liars.

White matter

Using magnetic resonance imaging (MRI), he scanned the brains of all three groups and found that liars had 26% more white matter compared with anti-social, non-liars, and 22% more than the controls. Liars also had 14% less grey matter than the controls.

Responsible for information transmission, white matter is composed of nerve fibres or "axons"