Assessment of sexual orientation using the hemodynamic brain response to visual sexual stimuli.
BACKGROUND
The assessment of sexual orientation is of importance to the diagnosis and treatment of sex offenders and paraphilic disorders. Phallometry is considered gold standard in objectifying sexual orientation, yet this measurement has been criticized because of its intrusiveness and limited reliability.


OBJECTIVE
To evaluate whether the spatial response pattern to sexual stimuli as revealed by a change in blood oxygen level-dependent (BOLD) signal can be used for individual classification of sexual orientation.


METHODS
We used a preexisting functional MRI (fMRI) data set that had been acquired in a nonclinical sample of 12 heterosexual men and 14 homosexual men. During fMRI, participants were briefly exposed to pictures of same-sex and opposite-sex genitals. Data analysis involved four steps: (i) differences in the BOLD response to female and male sexual stimuli were calculated for each subject; (ii) these contrast images were entered into a group analysis to calculate whole-brain difference maps between homosexual and heterosexual participants; (iii) a single expression value was computed for each subject expressing its correspondence to the group result; and (iv) based on these expression values, Fisher's linear discriminant analysis and the kappa-nearest neighbor classification method were used to predict the sexual orientation of each subject.


METHODS
Sensitivity and specificity of the two classification methods in predicting individual sexual orientation.


RESULTS
Both classification methods performed well in predicting individual sexual orientation with a mean accuracy of >85% (Fisher's linear discriminant analysis: 92% sensitivity, 85% specificity; kappa-nearest neighbor classification: 88% sensitivity, 92% specificity).


CONCLUSIONS
Despite the small sample size, the functional response patterns of the brain to sexual stimuli contained sufficient information to predict individual sexual orientation with high accuracy. These results suggest that fMRI-based classification methods hold promise for the diagnosis of paraphilic disorders (e.g., pedophilia).
Ponseti
Jorge
J
Section of Sexual Medicine, Kiel, Germany;. Electronic address: Ponseti@sexmed.uni-kiel.de.
Granert
Oliver
O
Department of Neurology, Kiel, Germany.
Jansen
Olav
O
Section of Neuroradiology, Kiel, Germany.
Wolff
Stephan
S
Department of Neurosurgery, Christian-Albrechts-University, Kiel, Germany.
Mehdorn
Hubertus
H
Department of Neurosurgery, Christian-Albrechts-University, Kiel, Germany.
Bosinski
Hartmut
H
Section of Sexual Medicine, Kiel, Germany.
Siebner
Hartwig
H
Danish Research Center for Magnetic Resonance Imaging, Hvidovre University Hospital, Hvidovre, Denmark.
D000328:Adult; D000886:Anthropometry; D001921:Brain / Q000033:anatomy & histology* / Q000098:blood supply*; D004882:Erotica; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D020010:Heterosexuality; D018451:Homosexuality, Male; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010262:Paraphilic Disorders / Q000175:diagnosis* / Q000523:psychology; D010413:Penis / Q000033:anatomy & histology; D010775:Photic Stimulation; D012725:Sexual Behavior; D011795:Surveys and Questionnaires