October 7, 2011 report
Can brain scans be used to detect pedophiles?
(PhysOrg.com) -- A new study published in the Archives of General Psychiatry describes how the use of functional Magnetic Resonance Imagery, or fMRI, is able to detect and diagnose pedophilia with greater accuracy than current options.
The researchers looked at the different brain responses of participants when they were shown photographs of naked children and adults. The participants included 32 healthy male volunteers and 24 acknowledged pedophiles. The pedophile group consisted of 13 homosexual pedophiles and 11 that were attracted to young girls. The healthy subjects consisted of 18 heterosexual men and 14 homosexual men.
The participants were placed in an MRI scanner and shown a series of 490 random pictures. Within these pictures were photos of both adults and children shown in full frontal views, facial pictures, or photos of the genitals only.
The researchers looked at the regions of the brain that were activated when participants were shown the photos and found the responses in the regions of sexual impulses and arousal were quite different between the four groups. The only group which did not show a distinct difference in the area of arousal was the heterosexual pedophiles however there brain did show a distinctly different response when shown the pictures of female children. The results, when plotted, show a distinct difference between the pedophile and the control group.
While this new test is the first time brain activity has been used to detect pedophiles, it is not clear exactly what the scans are measuring. While the pedophile group showed the same activity, it is unclear if the activity is related to sexual attraction or guilt because of what they have done.
Researchers are hoping this new test could be an important tool to courts in determining if treatment is working and if an individual is safe to return to society.
Context Accurately assessing sexual preference is important in the treatment of child sex offenders. Phallometry is the standard method to identify sexual preference; however, this measure has been criticized for its intrusiveness and limited reliability.
Objective To evaluate whether spatial response pattern to sexual stimuli as revealed by a change in the blood oxygen leveldependent signal facilitates the identification of pedophiles.
Design During functional magnetic resonance imaging, pedophilic and nonpedophilic participants were briefly exposed to same- and opposite-sex images of nude children and adults. We calculated differences in blood oxygen leveldependent signals to child and adult sexual stimuli for each participant. The corresponding contrast images were entered into a group analysis to calculate whole-brain difference maps between groups. We calculated an expression value that corresponded to the group result for each participant. These expression values were submitted to 2 different classification algorithms: Fisher linear discriminant analysis and -nearest neighbor analysis. This classification procedure was cross-validated using the leave-one-out method.
Setting Section of Sexual Medicine, Medical School, Christian Albrechts University of Kiel, Kiel, Germany.
Participants We recruited 24 participants with pedophilia who were sexually attracted to either prepubescent girls (n = 11) or prepubescent boys (n = 13) and 32 healthy male controls who were sexually attracted to either adult women (n = 18) or adult men (n = 14).
Main Outcome Measures Sensitivity and specificity scores of the 2 classification algorithms.
Results The highest classification accuracy was achieved by Fisher linear discriminant analysis, which showed a mean accuracy of 95% (100% specificity, 88% sensitivity).
Conclusions Functional brain response patterns to sexual stimuli contain sufficient information to identify pedophiles with high accuracy. The automatic classification of these patterns is a promising objective tool to clinically diagnose pedophilia.
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