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Can Brain Scans Detect Pedophiles?

80beatsBy Veronique GreenwoodOctober 6, 2011 12:45 AM


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What's the News: A new study suggests that watching brain activity when subjects are shown images of naked children can identify which are pedophiles. But what does this really mean in practical terms? How the Heck:

  • 24 self-identified pedophiles, from a clinic that offers anonymous treatment, and 32 male controls were shown pictures of naked men, women, and children. Blogger Neuroskeptic, who brought this study to the web's attention, notes in an aside that getting that past a university ethics board is quite a coup.

  • Using fMRI, the researchers recorded their brains' responses and found that by comparing an individual's brain to the average of the pedophiles and the average of the controls, they could assign them to the correct group more than 90% of the time. Their handling of the statistics avoids the most obvious pitfalls: they used an analyses technique called leave-one-out cross-validation to avoid comparing a given scan to an average that includes it, a common error in neuro studies.

  • When they plotted how the neural scans lined up along the age and sex axes (see image above), the pedophile and control scans formed two clear, separate clusters.

What's the Context:

  • First, a caveat: the team wasn't looking for any specific brain activity, and who knows what exactly the pedophiles were thinking when they saw the images of children. It could be sexual attraction, or it could be any number other things, like shame, which seems like a strong candidate, given that these people were in treatment for their pedophilia. Pedophiles who aren't in treatment, or pedophiles who've never acted on their feelings, might not be so easily clustered with these subjects. The point is that the only thing shown here is that this group of pedophiles' brains behaved differently than those of controls.

  • But moving along to the philosophy, ever since science brought the revelation that our brains are what make us who we are---rather than something like a soul, for example---there's been the question of to what extent we can be judged on the basis of our biology. This study, raising as it does the idea that your brain betrays you, and that certain brain profiles could be linked with crimes, recalls a piece neuroscientist David Eagleman wrote for The Atlantic recently:

If you are a carrier of a particular set of genes, the probability that you will commit a violent crime is four times as high as it would be if you lacked those genes. You’re three times as likely to commit robbery, five times as likely to commit aggravated assault, eight times as likely to be arrested for murder, and 13 times as likely to be arrested for a sexual offense. The overwhelming majority of prisoners carry these genes; 98.1 percent of death-row inmates do...As regards that dangerous set of genes, you’ve probably heard of them. They are summarized as the Y chromosome. If you’re a carrier, we call you a male.

The Future Holds: Realistically, we can't judge people on their biological red flags---whether it's brain scans or genetics---without entering a Minority Report-style future. That's because being attracted to children isn't a crime. Acting on it is. Generally, a brain scan is not required to find out whether the crime has happened---there are other, more reliable forms of evidence, like porn downloads. Given that, it's unlikely that you'll be seeing regular scanning for pedophilic tendencies anytime soon. And for that, we should be grateful. Reference: Ponseti, J., Granert, O., Jansen, O., Wolff, S., Beier, K., Neutze, J., Deuschl, G., Mehdorn, H., Siebner, H., & Bosinski, H. (2011). Assessment of Pedophilia Using Hemodynamic Brain Response to Sexual Stimuli. Archives of General Psychiatry DOI: 10.1001/archgenpsychiatry.2011.130

[via Neuroskeptic


Image courtesy of Archives of General Psychiatry, Ponseti, et al., via Neuroskeptic

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