Here is an interesting story in the Economist.
“IN THE late 1990s a previously blameless American began collecting child pornography and propositioning children. On the day before he was due to be sentenced to prison for his crimes, he had his brain scanned. He had a tumour. When it had been removed, his paedophilic tendencies went away. When it started growing back, they returned. When the regrowth was removed, they vanished again. Who then was the child abuser?”