Pedophiles have significantly different brains than people without the condition, indicates new research, suggesting pedophilia may have physical causes.

Pedophiles have considerably less brain white matter than people not sexually attracted to children, says the research released Wednesday from the Toronto-based Centre for Addiction and Mental Health.

It was published online earlier this week in the Journal of Psychiatric Research.

White matter, found in both the parietal and temporal lobes of the brain, contains nerve fibres.

Researchers used MRIs to scan the brains of 127 sexual and non-sexual offenders. The sexual offenders were recruited from the Kurt Freund Laboratory of the Centre for Addiction and Mental Health.

Patients who had committed one or more sexual offenses against children aged 14 years or younger but not against young adults aged 17 and older were allowed to participate. Non-sexual offenders were recruited from provincial and federal parole and probation offices in the Toronto area.

Of the 65 sexual offenders, researchers classified 44 as pedophilic based on their offences with children 14 and under.

They discovered that in the brains of men who were sexually attracted to children, the frontal parts that govern a person's reponses to sexual stimuli had less white matter.

The researchers theorize pedophilia is the result of a "partial disconnection within that network.

"The most straightforward explanation of the present result is that low white matter volumes increase the risk of developing pedophilia," they write. "Regardless of whether white matter deficiencies produce pedophilia or a susceptibility to it, the present results suggest the need to pursue what causes the white matter deficiencies."

They add that white matter abnormalities have already been implicated in other psychiatric illnesses, including bipolar disorder, obsessive-compulsive disorder and schizophrenia.