According to the latest research pathological liars may have structural abnormalities in their brains.
In a new study Dr. Adrian Raine and Yaling Yang of the University of Southern California, and colleagues found that individuals who habitually lied and cheated had less gray matter and more white matter in their prefrontal cortex than normal people.
In the past studies have found that the prefrontal cortex shows heightened activity when normal people lie, and it is believed to be involved in both learning moral behavior and feeling remorse.
According to Raine, because gray matter consists of brain cells, while white matter forms the "wiring" or connections between these cells, pathological liars may have more capacity to lie and fewer moral restraints.
The study authors suggest these people have the equipment to lie, but they don't have the disinhibition that the rest of us have in telling the big ones.
In the study, the researchers used a series of psychological tests and interviews on a group of volunteers to identify 12 pathological liars, 16 people with antisocial personality disorder but no history of lying, and 21 normal people.
They then examined the brains of all study participants using magnetic resonance imaging.
Apparently the liars had 26 percent more white matter in their prefrontal cortex than people with antisocial personality disorder, and 22 percent more than normal people. But they had 14 percent less gray matter than normal individuals.
The researchers interestingly noted that autistic people, who are known to have difficulty lying, show a shift in gray-to-white matter ratio opposite to that seen among liars in the current study.
The authors say that although autism is a complex condition and cannot be taken as a model for lying, the results on autistic children, combined with the prior functional Magnetic Resonance Imaging (fMRI) findings on lying in normal controls, converge with current findings on adult liars suggesting that the prefrontal cortex is centrally involved in the capacity to lie.
They also note that while small children aren't good liars, by the age of 10, when a burst in white matter volume has occurred, they become much more proficient in telling lies.
The authors suggest that while the findings have no practical implications at present, if confirmed they could be useful in clinical diagnoses as to whether a person is pretending to be sick; in criminal justice settings, by helping police determine if a suspect is lying; and in pre-employment screening.
The study is published in the British Journal of Psychiatry, October 2005.