Pathological liars' brains are different from normal people's. The fibbers had up to 26 per cent more white matter than the honest folk, a study has found, suggesting that it is the white matter that allows people to deceive, and that pathological liars may not always be in complete control of their porkies.

The findings, published in the British Journal of Psychiatry, are in line with similar research into autism. Autistic people have more grey matter than non-autistic people, and generally find it much harder to lie.

Grey matter processes information, while white matter merely transmits it. having more white matter might make it easier to lie, the University of Southern California researchers suggest. But this is unlikely to be the full story, and the team says it expects to find more physical differences, the BBC reports.

The researchers studied three groups: a group of 12 men and women with a history of deceitful and manipulative behaviour, a control group of 21 "normal" people, and a third group of 16 people with anti-social personality disorder.

All participants underwent structural magnetic resonance imaging (MRI) brain scans so that researchers could assess how much grey vs. white matter each group had.

The liars had between 22 and 26 per cent more white matter than either of the other groups. The researchers say the difference could not be accounted for by variations in age, ethnicity, IQ, head injury or substance misuse.

Dr Cosmo Hallstrom, a consultant psychiatrist in London, told the BBC: "The issue is always how much of our behaviour is under voluntary control and how much is innate. The finding of brain abnormalities lends weight to the idea that a strong component of such difficulties may well be beyond voluntary control at least in part."

The research team says more work is needed to find out at what stage in the brain's development these differences appear. ®