The (in)consistency of changes in brain macrostructure in male paedophiles: A combined T1-weighted and diffusion tensor imaging study
Graphical abstract
Introduction
Although the prevalence of child sexual abuse is declining somewhat, it is still estimated that 6.7% of children in the United States are being abused sexually (Finkelhor et al., 2010). As child sexual abuse leads to high tangible and intangible costs (Miller et al., 1996), it is a matter of great public concern. Approximately half of first-time child sex offenders are paedophilic men, i.e. men who experience intense and sustained sexual attraction to prepubescent children (Blanchard et al., 2001, Seto, 2007). This has motivated research into the aetiology of sexual attraction to pre-pubescent children. Some findings indicate a neurodevelopmental contribution to paedophilia as it has been associated with an increased likelihood of left-handedness, a lower intelligence quotient (IQ), a higher incidence of head injuries in childhood and deficits in executive functioning (Blanchard et al., 2002, Blanchard et al., 2007, Blanchard et al., 2003, Cantor et al., 2004, Schiffer and Vonlaufen, 2011). This has prompted four research groups to use structural magnetic resonance imaging (sMRI) of the brain to pinpoint regional changes in the macrostructure of paedophiles (Cantor et al., 2008, Poeppl et al., 2013, Schiffer et al., 2007, Schiltz et al., 2007). However, these studies have fallen short to reveal a consistent pattern of morphological brain anomalies in paedophiles. While each study reported regional reductions in grey or white matter, these changes were found in different brain areas with little overlap among studies (see Table 1). Schiffer et al. (2007) performed whole-brain voxel-based morphometry (VBM) to compare paedophiles and controls. In their study, paedophilia was associated with a decrease in grey matter density in several brain regions after false discovery rate correction for multiple comparisons, including clusters in the cerebellum, orbitofrontal and temporal cortex. The authors argue that paedophilia might be conceptualized as an obsessive-compulsive spectrum disorder as these disorders were shown to be associated with abnormalities in similar brain areas. Schiltz et al. (2007) predefined regions of interest (ROIs) and found regional reductions in grey matter in the right amygdala, hypothalamus (bilateral), substantia innominata (bilateral), right septal regions and bed nucleus striae terminalis (bilateral). They hypothesize that structural deficits in the right amygdala might interfere with sexual development in puberty. According to the authors this could obstruct the devalorisation of pre-existing sexual interest in children and result in a paedophilic preference combined with an adult sex drive. Poeppl et al. (2013) used whole-brain VBM and performed small volume correction (SVC) for those regions that had been identified in Schiffer et al.'s (2007) and Schiltz et al.'s (2007) studies, and were able to replicate a reduction in grey matter volume in the right amygdala. The authors thereby take their finding as a proof of the hypothesis outlined by Schiltz et al. (2007). Cantor et al. (2008) analysed structural brain scans in a sample of 44 paedophiles and hebephiles and 53 controls. Their sample was three to five times larger than the samples of the other sMRI studies, ranging between a full sample size of 20 and 42 participants. This study found no differences in regional grey matter in the paedophilic and hebephilic (i.e. sexually attracted to pubescent children) subjects. However, they observed decreased white matter volumes in the bilateral temporal and right parietal lobes as well as in the corpus callosum of paedophiles and hebephiles compared to teleiophiles. According to Cantor et al. (2008) their findings implicate that paedophilia results from a partial disconnection of brain areas crucial for recognising sexual stimuli. In summary, there is one replicated structural MRI finding: an amygdala volume reduction in paedophilic men (cf. Mohnke et al., 2014).
The otherwise divergent results can at least partially be attributed to methodological differences and limitations. In three out of the four sMRI studies, the experimental and comparison groups varied with respect to one or more of the following variables: sexual gender orientation, IQ, years of education, comorbidity, offending behaviour and incarceration-related stress. Furthermore, there were differences with respect to the non-paedophilic groups, which in some cases consisted of non-sexual offenders and in other cases of community controls. Concerning the reported white matter differences, it remains uncertain whether this finding can be replicated with the diffusion tensor imaging (DTI) technique, which provides more advanced features for white matter than VBM methods with T1-weighted images. Taken together, the mostly heterogeneous findings regarding regional changes in brain structure and the methodological issues give rise to questions concerning the existence of paedophilia-related changes in brain morphology which can be detected with the current sMRI resolution of approximately 1 or 2 mm.
These considerations motivated this sMRI study in which we have tried to overcome some limitations of previous studies. We included the second largest – maybe even the largest – outpatient sample of paedophilic men that has been studied so far. Although Cantor et al. (2008) had about twice as much paedophilic men at their disposal, it is unclear how many of these 44 men were paedophilic (and not hebephilic) and how many of them had a history of offences against children. As Cantor et al. (2008) state that the primary source of referrals to their outpatient facility is parole and probation officers, one can assume that it must have been the majority. In contrast to this, approximately half of the men of our experimental group were recruited from the prevention project “Dunkelfeld”, which offers anonymous treatment for self-identified paedophiles who are not under actual judiciary supervision (Beier et al., 2009). We recruited a control group matched for sexual gender orientation, handedness, age and IQ. We conducted whole-brain analyses based on our high-resolution T1-weighted structural and diffusion MRI data. The only brain region for which we had an a priori assumption was the right amygdala, where two out of the four previous studies have reported reduced grey matter in paedophiles as compared to teleiophiles.
Section snippets
Participants
We scanned 24 male paedophiles from two outpatient facilities. Thirteen of these participants were part of the prevention project “Dunkelfeld” (Beier et al., 2009). The remaining 11 paedophiles were treated in our outpatient department. Ten paedophiles had been sentenced earlier in life (mostly for possessing child pornography), with three having served a prison sentence. Twelve paedophiles had a history of hands-on offences against children. Participants and recruitment procedure are described
Voxel-based morphometry
VBM analysis revealed no significant differences in cerebral grey or white matter between paedophiles and teleiophiles after FWE correction. This was also the case when comparing heterosexual and homosexual teleiophiles and paedophiles separately (i.e. comparing the HeTe group with the HePe group and the HoTe group with the HoPe group). The only exception was a cluster in the right inferior parietal lobe close to the intraparietal sulcus, where the HoTe group showed a significant reduction in
Discussion
Apart from the right inferior parietal lobe, there were no consistent differences in brain structure between our paedophilic and teleiophilic groups. While our analysis revealed a relative increase in regional grey matter in homophilic paedophiles compared to homophilic teleiophiles in some parts of the right inferior parietal lobe, no such differences were reported in three previous studies (Poeppl et al., 2013, Schiffer et al., 2007, Schiltz et al., 2007; for an overview of sMRI studies
Author contribution
Hannah Gerwinn and Alexander Pohl have contributed equally to this work. They were involved in data analysis and prepared and wrote the manuscript (mainly the introduction, the results and the discussion section).
Jorge Ponseti was involved in the study design, data collection, and the planning and revision of the manuscript.
Oliver Granert was involved in data analysis and wrote parts of the material and methods section of the manuscript.
Thilo van Eimeren was involved in study design and the
Funding sources
The funding sources named in the acknowledgement section had no involvement in study design; in the collection, analysis and interpretation of data; in the writing of the report; or in the decision to submit the article for publication.
Conflicts of interest
H.R.S. has received honoraria as a speaker from Lundbeck A/S, Valby, Denmark, Biogen Idec, Denmark A/S, Genzyme, Denmark and MerckSerono, Denmark, honoraria as an editor from Elsevier Publishers, Amsterdam, the Netherlands and Springer Publishing, Stuttgart, Germany, and travel support from MagVenture, Denmark. The other authors declare that they have no conflicts of interest.
G.D. has received lecture fees from UCB, Medtronic and Desitin and has been serving as a consultant for Medtronic,
Acknowledgements
MRI measurement was performed in the MRI unit sponsored by the Federal Ministry of Education and Research. A Federal Ministry of Education and Research grant to NeMUP-Nord (grant no. 01KR1205D) sponsored the research conducted by J.P., H.G. and A.P.
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Both authors contributed equally to this work.
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Present address: Department of Neurology and Psychiatry, Köln University, Medical School, Kerpener Str. 62, 50937, Köln, Germany.