Brain scans studied for use in diagnosing pedophilia

A new study suggests that brain scans can reveal pedophilia and detect the sexual orientation of possble offenders. (Don Carstens / Brand X/Corbis)

For years, pedophiles have been diagnosed either after they have committed sexual offenses or after they have agreed to submit to an intrusive and imperfectly reliable test that measures penile changes as a subject looks at pictures of nude children. A new study suggests that a pedophile's different brain responses to photos of unclothed children and adults can detect pedophilia with greater accuracy.
The technique used also appears able to detect whether the individual's pedophilic urges are hetero- or homosexual -- a distinction that may call for different approaches to treatment.
Published "online first" on Monday in the Archives of General Psychiatry, the study describes the use of functional Magnetic Resonance Imagery (fMRI) to map distinct patterns of brain activation in 24 acknowledged pedophiles and 32 healthy male volunteers of similar age and intelligence levels. Among the acknowledged pedophiles were 11 who were attracted to prepubescent girls and 13 who were homosexually pedophilic. The healthy volunteer group was made up of 18 men attracted to adult women and 14 men attracted to adult men.
While lying in the MRI scanner, which detects increased blood flow to specific regions of the brain in response to stimuli, each man was shown the same random sequence of 490 pictures. Scattered among neutral photographs were 280 photos of children and adults, both male and female, shown for just a second. For each category of person -- adult male, adult female, female child, male child -- separate pictures depicted a whole-body frontal view, genitals only, or face only.
The patterns of activation in several regions of the brain where sexual impulses and arousal are processed were quite distinct across the four groups. Only one group -- heterosexual pedophiles -- failed to show a significantly distinct pattern of arousal when shown pictures of adult women and female children. But their brains responded to pictures of female children in ways that made them easily distinguishable from the heterosexual control group.
The researchers, from Kiel and Berlin in Germany and Hvidovre, Denmark, said this is a first-ever effort to use "neurofunctional pattern classification" to assess pedophilia. Compared to the existing test of phallometry -- the measurement of penile changes in response to various pictures, the use of fMRI seems to be slightly less sensitive -- meaning it may not detect all pedophiles.  But it appears to be much more specific than phallometry, meaning it is less likely than phallometry to identify people as pedophilic who are not.
An accurate gauge of pedophilia could be an important tool in detecting whether court-ordered treatment is working, and whether a convicted pedophile can be safely released into society. It might also identify those who need the most intensive treatment: Among single-victim offenders, the phallometry test suggests that only about half have the sustained sexual attraction to children that classifies them as pedophilic.