12:51 20 August 2007
NewScientist.com news service
Roxanne Khamsi
Paedophiles may have reduced concentrations of nerve cells in key areas of the brain compared to normal people, according to a study published by German researchers.
The study could have significant legal implications, experts say, because it hints at a direct link between brain development and criminal behaviour.
The causes of paedophilia are not understood and even diagnosing the condition is controversial (see Sex offenders: Throwing away the key).
Boris Schiffer and colleagues of the University of Duisburg-Essen in Germany studied 18 convicted paedophiles with a history of repeatedly abusing children younger than 14.
Schiffer scanned their brains using magnetic resonance imaging and compared the scans to those of normal men of matching ages. The scans revealed that the paedophiles had less "grey matter" ? tissue with a high concentration of nerve cells ? in several areas of the brain.
Decreased grey matter
The men in Schiffer's study had an average IQ of about 90, which is not considered abnormally low, compared to an average of 100 for the control group.
Even accounting for an expected decrease in grey matter due to lower IQ scores, Schiffer's group found that the paedophiles had about 2 to 4% less grey matter in the orbitofrontal cortex ? an area of the brain that plays an important role in high-level decision making and reasoning.
They also had 5 to 7% less grey matter in a region called the putamen, which is implicated in a wide range of brain functions such as movement and learning.
Schiffer stresses that a causal relationship is far from clear. But he notes that similar differences have been found in people who suffer other forms of compulsive behaviour, and points out that the development of the orbitofrontal cortex is thought to play a crucial role in moderating addictive behaviour.
James Cantor at the Centre for Addiction and Mental Health in Toronto, Canada, who studies the causes of paedophilia, says the new study may provide important new clues about the role of brain development in paedophilia.
Legal concerns
Russell Swerdlow at the University of Virginia in Charlottesville, Virginia, adds that other evidence supports a link between impairments to the orbitofrontal cortex and paedophilia. One of his own patients developed paedophilic tendencies after suffering a tumour in this part of his brain. Each time the tumour recurred, the man's paedophilic compulsion also returned.
But other evidence presents a more complex picture. In April 2007, another team, led by Kolja Schiltz, at Otto-von-Guericke University, also in Germany, published a study of the brain scans of paedophiles who confessed to being attracted to both children and adults.
The researchers found no defects in the brain regions identified by Schiffer's group although less grey matter was detected in some other areas (Archives of General Psychiatry, vol 64, p 737).
Research in this area could have significant legal implications for cases involving paedophiles, says Deborah Denno at the Fordham University of Law in New York. She predicts that brain scans could be used in future trials, even though scientists do not always know whether such scans are reliable or meaningful.
"I do have concerns, and I have to say that my concerns have been heightened," she says. Denno notes that a scan revealing an abnormal cyst was used to obtain a plea bargain in a murder case in 1992.
Journal reference: Journal of Psychiatric Research (DOI: 10.1016/j.jpsychires.2006.06.003)
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