Pedophilia is a psychiatric disorder of high public concern characterized by intense, sexually arousing urges and behaviours that focus on sexual activity with a prepubescent child.1
According to the estimates of the German authorities, the incidence of child sexual abuse in Germany is as high as 550 cases daily (200 000 annually), though only every 20th case is recorded. For the United States, the estimates are as high as 500 000 annually.2
With regard to pedophilia, numerous studies have discussed associations between behavioural disinhibition, frontal abnormalities and impaired cognitive executive functioning.3–6
Although recent data from neuropsychological, sexual history, plethysmography and neuroimaging investigations suggest that pedophilia is linked to early neurodevelopmental perturbations,4,7
the neurobiological basis of the disorder is still unidentified.
Human sexual arousal is a multidimensional experience comprising physiological and psychological processes. Modern imaging techniques allow the in vivo observation of brain activation correlated with sensory or cognitive processing and emotional states.8
using functional magnetic resonance imaging (fMRI) or positron emission tomography (PET) and remote sexual stimuli such as visual erotica have shown increased neural activity in several areas, including the inferior right frontal cortex, the inferior temporal cortex, the left anterior cingulate cortex and the right insula, possibly representing a distributed network.
Moreover, imaging studies have revealed hypoactive frontal lobes in patients with impulsive personality disorders and in violent psychiatric inpatients.20–22
Additionally, in the etiology of psychopathic, antisocial and violent behaviour in general, imaging data implicate brain differences in the prefrontal cortex, hippocampus, parahippocampal gyrus, angular gyrus, cingulate gyrus, basal ganglia and amygdala.23
Although critically reviewed recently,24
some studies suggest frontotemporal dysfunctions in pedophilia,4,7,25,26
indicating that a wide range of psychiatric disorders (i.e., obsessive–compulsive [OC] spectrum disorders) may share a neural substrate characterized by inadequate urges and poorly inhibited repetitive thoughts or cognitions or behaviours.27,28
However, some older studies on frontal lobe functioning in pedophilia failed to find such an association and instead suggested a more general neuropathology (for a detailed discussion see Blanchard et al24
), although these results were mainly derived from computertomographic investigations, which do not provide sufficient spatial resolution. Additional research using modern imaging techniques such as PET or fMRI is therefore needed to examine these hypotheses further.
Although a difference of opinion exists concerning which illnesses should be included in the category of OC spectrum disorders, the symptom domain (i.e., the presence of obsessions or repetitive behaviours, or both) is the usual starting point for determining whether a given disorder is a spectrum candidate. Apart from obsessive–compulsive disorder, OC symptoms can be found in several disorders, including Tourette syndrome, body dismorphic disorder, hypochondriasis and trichotillomania; it is often hypothesized that these disorders belong to the OC spectrum. However, the eating disorders, autism, pathological gambling, kleptomania, depersonalization disorder, sexual compulsions and paraphilias are sometimes also included in the OC spectrum.29
Not only are all these disorders highly comorbid, they also share phenomenological similarities and biological correlates and may therefore resemble alternative phenotypic expressions of a related genetic background.30
This hypothesis is in line with the concept that a genetically driven state of reward deficiency is a common denominator in the delineated spectrum.31,32
From a neuronal point of view, the cortico-striato-thalamo-cortical network initially described by Alexander and colleagues33
seems to be of specific importance. This network is closely associated with the dopaminergic innervations of the frontal lobes corresponding to the reward system and is related to the pathophysiology of OC spectrum disorders.5,34
However, empirical evidence of a causal relation between abnormal brain functioning and pedophilia has remained elusive. An imaging study using PET demonstrated that there is persistently decreased glucose metabolism in the right inferior temporal and superior ventral frontal gyrus.7
An fMRI case study of 1 homosexual pedophile suggested abnormalities in the fusiform gyrus and the right orbitofrontal cortex during visual sexual stimulation.35
Our own recent morphometric study using structural MRI found decreased grey matter volume in the ventral striatum, also affecting the nucleus accumbens, the orbitofrontal cortex and the cerebellum in pedophiles.36
These findings may underline an association between frontostriatal morphometric abnormalities and pedophilia and may support the hypothesis that there is a shared etiopathological mechanism in OC spectrum disorders. However, apart from 2 anecdotal case reports25,26
that also suggest temporal and orbitofrontal disturbances, no data obtained from fMRI techniques have been reported on characteristics of brain function in pedophilia. Moreover, it is completely unknown whether neuronal activation patterns during visual sexual stimulation depend on the normative deviance of the respective sexual interest.
Therefore, using the fMRI technique and photographs of nude boys and men as well as control stimuli (dressed boys and men), we compared the neuronal responses of pedophiles who were exclusively attracted to male children with those of healthy homosexual control subjects. From the preliminary data described above, we hypothesized that, in pedophiles, there would be alterations in the activation pattern in the frontostriatal system and closely related structures such as the thalamus.