Brain Alterations in Paedophilia: a Critical Review

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Progress in Neurobiology 122 (2014) 1–23

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Progress in Neurobiology

jo urnal homepage: www.elsevier.com/locate/pneurobio

Brain alterations in paedophilia: A critical review

a, a b

Sebastian Mohnke *, Sabine Mu¨ ller , Till Amelung ,

c d e

Tillmann H.C. Kru¨ ger , Jorge Ponseti , Boris Schiffer ,

f b a,

Martin Walter , Klaus M. Beier , Henrik Walter **

Charite´ – Universita¨tsmedizin Berlin, Department of Psychiatry and Psychotherapy, Charite´platz 1, 10117 Berlin, Germany

Charite´ – Universita¨tsmedizin Berlin, Institute of Sexology and Sexual Medicine, Luisenstr. 57, 10117 Berlin, Germany

Hannover Medical School, Department of Clinical Psychiatry, Social Psychiatry, and Psychotherapy, Carl-Neuberg-Str. 1, 30625 Hannover, Germany

University Medical Center Schleswig-Holstein, Section for Sexual Medicine, Arnold-Heller-Str. 3, 24105 Kiel, Germany

Division of Forensic Psychiatry, Department of Psychiatry, Psychotherapy and Preventive Medicine, LWL-University Hospital, Bochum, Germany

Otto-von-Guericke-University Magdeburg, Department of Psychiatry, Leipziger Str. 44, 39120 Magdeburg, Germany

A R T I C L E I N F O A B S T R A C T

Article history: Psychosocial and biological factors have been implicated in paedophilia, such as alterations in brain

Received 5 December 2013

structure and function. The purpose of this paper is to review the expanding body of literature on this

Received in revised form 25 July 2014

topic including brain abnormality case reports, as well as structural and functional neuroimaging

Accepted 31 July 2014

studies. Case studies of men who have committed sexual offences against children implicate frontal

Available online 10 August 2014

and temporal abnormalities that may be associated with impaired impulse inhibition. Structural

neuroimaging investigations show volume reductions in paedophilic men. Although the ﬁndings have

Keywords:

been heterogeneous, smaller amygdala volume has been replicated repeatedly. Functional neuroimaging

Child sexual abuse

investigations demonstrate an overlap between paedophiles and teleiophiles during sexual arousal

Sexual arousal

processing. While it is controversial among studies regarding group differences, reliable discrimination

Sexual offending

Brain pathology between paedophilic and teleiophilic men may be achieved using functional activation patterns.

Magnetic resonance imaging Nevertheless, the heterogeneous ﬁndings published so far suggest further research is necessary to

disentangle the neurobiological mechanisms of paedophilic preference. A number of methodological

confounds have been identiﬁed, which may account for the inconsistent results that could prove to be

beneﬁcial for future investigations.

Contents

1. Introduction ...... 2

1.1. Diagnosis ...... 2

1.2. Prevalence ...... 2

1.3. Paedophilia vs. sexual offending against children ...... 3

1.4. Aetiology ...... 4

1.5. The neurophenomenological model of sexual arousal ...... 4

1.6. Literature search ...... 4

Abbreviations: ICD-10, International Classiﬁcation of Diseases and Related Health Problems, 10th Revision, World Health Organization; DSM-5, Diagnostic and Statistical

Manual of Mental Disorders, 5th Edition, American Psychiatric Association; CSA, child sexual abuse; CSO, child sexual offender; NSO, non-sexual offender; MRI, magnetic

resonance imaging; fMRI, functional magnetic resonance imaging; PET, positron emission tomography; CT, computed tomography; VBM, voxel-based morphometry; ROI,

region of interest; FWE, familywise error; FDR, false discovery rate.

* Corresponding author at: Charite´ – Universita¨tsmedizin Berlin, Campus Mitte, Department of Psychiatry and Psychotherapy, Division of Mind and Brain Research,

Charite´platz 1, 10117 Berlin, Germany. Tel.: +49 30 450 517 223; fax: +49 30 450 517 906.

** Corresponding author at: Charite´ – Universita¨tsmedizin Berlin, Campus Mitte, Department of Psychiatry and Psychotherapy, Division of Mind and Brain Research,

Charite´platz 1, 10117 Berlin, Germany. Tel.: +49 30 450 517 141; fax: +49 30 450 517 906.

E-mail addresses: [email protected] (S. Mohnke), [email protected] (S. Mu¨ ller), [email protected] (T. Amelung),

[email protected] (Tillmann H.C. Kru¨ ger), [email protected] (J. Ponseti), [email protected] (B. Schiffer), [email protected]

(M. Walter), [email protected] (K.M. Beier), [email protected] (H. Walter).

http://dx.doi.org/10.1016/j.pneurobio.2014.07.005

2 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

2. Neurological case reports ...... 5

2.1. Brain tumours ...... 5

2.2. Different forms of dementias ...... 7

2.3. Parkinson’s disease ...... 7

2.4. Further neurological disorders ...... 8

3. Neuroimaging ...... 8

3.1. Structural neuroimaging...... 8

3.1.1. CT studies...... 8

3.1.2. MRI studies ...... 8

3.2. Functional neuroimaging ...... 12

3.2.1. PET studies...... 12

3.2.2. fMRI studies...... 12

3.3. Correlational analyses in neuroimaging studies ...... 18

4. Discussion ...... 19

Acknowledgements ...... 22

References ...... 22

1. Introduction et al., 2013), implying that the sexual interest in prepubertal

children would be distinguishable from the sexual interest in

1.1. Diagnosis pubertal children. Contrary to early propositions, and after an

extensive debate, the diagnosis of hebephilia was not included in

Paedophilia is commonly viewed as an adult sexual responsive- the DSM-5 (for a summary of this discussion see Blanchard, 2013).

ness towards immature (prepubescent) subjects. Research distin- In addition, the ICD-10 requires the presence of recurrent sexual

guishes it from teleiophilia as the sexual responsiveness to mature fantasies or urges towards children, and these elements are not

(postpubertal) subjects and hebephilia, the sexual responsiveness necessary according to the DSM-5. Following DSM-criteria sexual

to pubertal children (Beier et al., 2013; Blanchard et al., 2000). behaviour with prepubescent children that persists more than six

Paedophilia appears in both psychiatric diagnostic systems, the months would be sufﬁcient for the diagnosis of paedophilic

ICD-10 and the DSM-5, under disorders of sexual preference disorder, even in the absence of arousing fantasies or urges.

(paraphilia). Since the DSM-5, paedophilia is explicitly distin- The DSM-5 distinguishes between an exclusive and a non-

guished from paedophilic disorder, deﬁned via recurrent, intense exclusive type of paedophilia (whether the person can be sexually

sexually arousing fantasies, and sexual urges towards prepubes- aroused only by children or also by elder persons), a gender

cent children. The latter additionally requires either that these preference, and a limitation to incest. Also, the criteria within each

sexual urges lead to marked distress, interpersonal difﬁculty, or diagnostic system have been changed signiﬁcantly during its

that the individual has acted out on these sexual urges. Therefore, development (for DSM criteria, see Blanchard, 2010). Therefore,

by the redeﬁnition of the term paedophilia (i.e., sexual focus on the different deﬁnitions of paedophilia comprise different popula-

children without distress, interpersonal difﬁculty, and sexual acts tions that have a common intersecting-set but are not identical

involving children), the mere sexual preference for children has (see Fig. 1).

been depathologized. This makes sense from both a clinical and a The stability of paedophilia is also controversial. In general,

forensic perspective, since paedophilia which causes neither paedophilia has been seen as a lifelong individual trait (e.g., Seto,

suffering nor child harm requires no therapy or prosecution 2008, 2012). Cases in which paedophilic behaviours occurred after

(although preventive measures could be indicated, because the brain lesions have thus been discussed as behavioural manifesta-

preference may still constitute a risk factor for later offending; see tions of pre-existent latent paedophilic urges due to general

Section 1.3). impulse disinhibition. In contrast, there are some reports claiming

Both ICD-10 and DSM-5 require that the affected person’s successful therapeutic alteration of sexual preference and reduced

sexual urges/fantasies have been acted upon or cause marked reoffending in paedophilic child sexual offenders (CSO; Marshall

distress or interpersonal difﬁculty. Furthermore, both systems et al., 2005; Marshall, 2008). Additionally, a change in psycho-

specify that the affected person must be 16 years and at least ﬁve physiological reaction to child sexual stimuli has been recently

years older than the sexually desired children. In contrast to the demonstrated in some men (Mu¨ ller et al., 2014). Whether the

ICD-10, the DSM-5 further speciﬁes that individuals in late changes reported represent an ‘‘elimination’’ of paedophilia or

adolescence who are in ongoing sexual relationships with 12– rather a control of symptoms remains unclear. While the ﬁndings

13-year-olds do not ﬁt the criteria for paedophilia. Further remain anecdotal, they might still challenge the state of the art

disagreement between the diagnostic systems exists with regard view of paedophilia as a stable and unchangeable condition.

to the (body) age of the desired children: ICD-10 deﬁnes Neurobiological correlates may be particularly useful to disentan-

paedophilia (F65.4) as a sexual preference for children who are gle whether paedophilia is mutable by: ﬁrst, elucidating the

either prepubescent or in an early state of puberty, but might also aetiology of human sexual preference (see Section 1.4); and

be younger; in contrast, the DSM-5 deﬁnes paedophilia or second, uncovering the link between preference and behaviour

paedophilic disorder (302.2) by recurrent, intense sexually leading to the risk of potentially endangering others as suggested

arousing fantasies, sexual urges, or behaviours involving sexual by the hypothesis that paraphilic interest can become behaviou-

activity with prepubescent children (generally age 13 years or rally manifest following brain damage (see also Section 1.3).

younger), which have to persist over a period of at least six months.

Note that the sexual preference for pubertal children has been 1.2. Prevalence

termed hebephilia and was repeatedly described as a distinguish-

able phenomenon (Beier et al., 2013; Blanchard, 2010). Further- Due to the lack of epidemiological studies, the exact prevalence

more, a recent study using multiple taxometric analyses supports of paedophilia is unknown. However, in the Berlin Male Study,

the view of paedophilia as a separate diagnostic entity (Schmidt conducted on a population-based sample of men between 40 and

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 3

Fig. 1. The diagnosis of paedophilia/paedophilic disorder according to the ICD-10 and the DSM-5.

79 years, 367 participants volunteered to anonymously ﬁll out they cannot be used synonymously. Not all CSOs have

questionnaires on paraphilic arousal patterns. Of these men 9.5% paedophilia, just as not all paedophilic men necessarily commit

reported sexual fantasies involving children, 6% masturbated to child sexual abuse (CSA). Therefore, CSOs can be grouped in

these fantasies, and 3.8% admitted sexual contact with children those: (1) without a sexual preference for children that have

below 13 years of age (Ahlers et al., 2009). Of note, only two sexually abused children (e.g., sexually inexperienced adoles-

participants (0.5%) reported to be distressed by their excitability by cents seeking a surrogate; persons with antisocial personality

children. A population-based Finnish study on 3967 male twins disorders or perpetrators within general traumatizing family

between the ages of 21 and 43 years found a 12-month-prevalence constellations; Seto, 2008), and, (2) with a sexual preference for

of 0.3% (95% conﬁdence interval: [0.08–0.61%]) for sexual interest children (e.g., paedophilia and/or hebephilia). The proportion of

in children (judging from respective sexual fantasies or actions; paedophiles in CSOs is about 40–50% (Maletzky and Steinhauser,

Mokros et al., 2012; Alanko et al., 2013). Furthermore, 2.7% of the 2002; Seto and Lalumiere, 2001; Seto, 2008). Conversely, the

participants reported masturbation phantasies involving children proportion of paedophiles who sexually approach children

below the age of 16, and 0.3% had sexual contact with children of seems to be similarly high with about 43% (Seto et al., 2006).

that age group during the past 12 months. Taking together, the In that respect, it has to be kept in mind that a paedophilic

point prevalence for paedophilia could be estimated to be around inclination in an individual does not mean that the inclined

0.3–3.8% (Ahlers et al., 2009; Alanko et al., 2013). There are isolated person will necessarily act on his fantasies. On the other hand,

reports of paedophilia in women (Chow and Choy, 2002), although paedophilia is a major risk factor for committing sexual offences

it seems to be substantially more frequent in men (Denov, 2003). against children, particularly for sexual recidivism (Hanson and

Morton-Bourgon, 2005). The distinction between paedophilia

1.3. Paedophilia vs. sexual offending against children and CSA is important to consider, since most research has been

conducted on CSOs that have not always been reliably

The term paedophilia is often used interchangeably with sexual diagnosed. Results from studies on these populations may be

offending against children, although research clearly shows that additionally confounded by antisocial traits of the subjects and

4 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

the forensic settings. Very little is known about undiagnosed (Cantor et al., 2004; Joyal et al., 2014; Kru¨ ger and Schiffer,

paedophiles who have not sexually abused a child. 2011; Schiffer and Vonlaufen, 2011). Additionally, Blanchard et al.

(2002, 2003) detected an increased rate of head injuries with

1.4. Aetiology temporary unconsciousness in paedophilic sex offenders. Impor-

tantly, only the incidence of head injuries before the age of 13 was

The aetiology of paedophilia is uncertain, but seems to be elevated in paedophiles, which points to possibly damaging effects

multifactorial, comprising psychosocial and biological factors. on neuronal development.

The conditioning hypothesis points to the relevance of ﬁrst sexual Recent research began to shed light on the manifestations of the

contact with same-aged peers during childhood (Marshall and presumed neurodevelopmental disruptions by exploring abnor-

Eccles, 1993). During these experiences, an association between malities in brain function and structure. The aim of this paper is to

formerly neutral stimuli like a prepubescent body schema and review the neuroimaging literature on paedophilic men to provide

unconditioned stimuli such as sexual gratiﬁcation would be an overview of published ﬁndings concerning abnormalities in

learned and result in the persistent sexual preference for brain anatomy and functional processing during visual sexual

respective sexual partners. This theory is contrary to the fact that stimulation. Historically, the ﬁrst clues on brain structures

most people have their ﬁrst sexual experiences during early implicated in paedophilic sexual arousal stem from several

puberty, but only a small percentage develops paedophilically neurological case reports describing paraphilia-like behaviour

motivated interest. Furthermore, some paedophilic men report that occurred with brain pathology. Therefore, we will start by

that they were aware of their sexual interest in children before summarizing the ﬁndings from these case studies.

their ﬁrst sexual contacts (Dandescu and Wolfe, 2003).

Experience of having been sexually abused: Several reports show 1.5. The neurophenomenological model of sexual arousal

concordantly that sexual offenders against children who have been

abused in childhood themselves, are more likely to develop A framework helpful to interpret the reviewed ﬁndings is the

paedophilic interest (e.g., Nunes et al., 2013). However, the neurophenomenological model of sexual arousal (Fig. 2; Redoute´

evidence for this relationship in non-offender groups is substan- et al., 2000; Stole´ru et al., 1999). This model attempts to explain the

tially weaker (Fromuth et al., 1991) and, only a small proportion of speciﬁc roles of different brain regions typically activated in

sexually abused children develop paedophilia. There is evidence healthy men during stimulation with sexually arousing stimuli

that this association might be moderated by further environmental (Ku¨ hn and Gallinat, 2011; Poeppl et al., 2014; Stole´ru et al., 2012).

factors (for instance, experiences of neglect in childhood, lack of It assigns sexual stimulation to intertwined psychological sub-

parental supervision, intrafamilial violence, poor parent-child processes: a cognitive component comprises the evaluation of

attachment; Marshall and Marshall, 2000; Salter et al., 2003), and stimuli as sexually incentive (mediated by activity of the right

certain characteristics of the experienced abuse (duration, timing, lateral orbitofrontal cortex and inferior temporal gyrus), the focus

use of violence, penetration, relationship to the perpetrator, having of attention on these stimuli (superior and inferior parietal lobule),

perpetrators of both sexes; Burton et al., 2002). The exact and the motor imagery of potential sexual behaviour (ventral

mechanism by which history of being sexually abused increases premotor area, supplementary motor area, inferior parietal lobule,

the likelihood of developing paedophilia is unknown. Theoretical- and cerebellum). The experience of the hedonic quality of sexual

ly, learning mechanisms (e.g., imitation) as well as the facilitation arousal is provided by an emotional component (somatosensory

of attitudes and beliefs supporting adult-child-sex are assumed cortex, amygdala, and posterior insula), while a motivational

(Seto, 2008). An alternative explanation for the facts that not all component would orientate behaviour towards the desired goal

sexually abused children and not all children who had sexual and enable the perception of sexual desire (anterior cingulate

contact with other children develop paedophilia is an interaction cortex, claustrum, posterior parietal cortex, hypothalamus, sub-

with biological factors, such as genetic predisposition. stantia nigra, and ventral striatum). A physiological component

Genetics: First clues regarding potential genetic inﬂuences on would control various somatic responses in order to prepare the

paedophilia came from a study by Gaffney et al. (1984). organism for sexual behaviour (anterior cingulate cortex, anterior

Retrospectively reviewing medical records they found that insula, putamen, and hypothalamus). Last, the model proposes

paedophilia was signiﬁcantly more prevalent in ﬁrst-degree different inhibitory processes, which include the prevention of

relatives of patients fulﬁlling DSM-III criteria for paedophilia than emergence of sexual arousal in unsuitable situations and cognitive

in families of patients with non-paedophilic paraphilias or appraisal to reduce the incentiveness of stimuli (medial and left

depression. While this investigation was limited by its small lateral orbitofrontal cortex, and lateral temporal cortex) as well as

sample size (n = 33 paedophilic patients, n = 21 non-paedophilic the control of executed sexual behaviour (caudate and caudal

paraphilic patients, n = 33 depressed patients) and did not rule out anterior cingulate cortex). When discussing the neural correlates

alternative explanations for the familial accumulation, a larger of paedophilia we will refer to this model, which might give further

recent study by Alanko et al. (2013) gives further support for the insights into the meaning of the observed abnormalities.

assumption of genetic underpinnings. In the population-based

Finnish sample, the amount of non-additive genetic variance that 1.6. Literature search

could be accounted for sexual interest in children and youth below

the age of 16 was 14.6%. However, this percentage also emphasizes An extensive literature search was conducted using the

the importance of environmental factors. electronic databases PubMed, ISI Web of Science, and PsycInfo

Neurodevelopmental perturbations: Further research on the in order to identify all relevant articles published until April 2014.

biological aetiology of paedophilia mostly builds on the assump- We used the following search terms in the title, abstract or

tion, which is based on a multitude of indirect evidence, that keywords: (‘‘pedophil*’’ or ‘‘child molest*’’ or ‘‘sexual abuse’’ or

paedophilia could result from neurodevelopmental abnormalities. ‘‘sexual offend*’’) and (‘‘imaging’’ or ‘‘magnetic resonance imaging’’

There are reports of neuropsychological deﬁcits including lower or ‘‘computed tomography’’ or ‘‘positron emission tomography’’ or

intelligence, impaired response inhibition, dampened attention, ‘‘brain’’). Additional papers were searched by checking the

reduced verbal and visuospatial learning abilities, slower proces- literature cited in the articles identiﬁed by the electronic database

sing speed, diminished task switching, and cognitive reasoning search. Studies were included if they provided original data on (a)

abilities as well as an increased rate of left-handedness brain damage associated with paedophilia or sexual offending

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 5

Fig. 2. The neurophenomenological model of sexual arousal.

Adapted from Stole´ru et al. (2012).

against prepubescent children, (b) structural neuroimaging in speciﬁed in one case (Regestein and Reich, 1978). Another patient

subjects diagnosed with paedophilia or who sexually offended suffered from a brainstem glioma additionally affecting the pons,

against prepubescent children or (c) functional neuroimaging ventral midbrain, thalamus, and hypothalamus, which affected

studies on sexual arousal processing in paedophiles or CSOs. Both both hemispheres, but was more pronounced in the left

case reports and studies comparing samples of paedophilic hemisphere (Miller et al., 1986). In addition to the abuse or

subjects or CSOs against controls were included. molestation of children, an increase of general sexual interest, the

preoccupation with sex or a disinhibition of sexual behaviour was

2. Neurological case reports common to all cases. Therefore, none of the abnormalities were

limited to CSA, but instead suggested general hypersexuality.

Before controlled imaging studies were available, the ﬁrst Furthermore, the abnormalities were not isolated to symptoms on

evidence implicating brain structures in paraphilia-like behaviours the sexual level; patients exhibited personality changes and

was provided by neurological case reports. These reports show that impulsivity (Burns and Swerdlow, 2003; Lesniak et al., 1972;

paedophilic behaviour can be provoked by a variety of diseases Regestein and Reich, 1978) or diminished ﬁnancial judgement

such as brain tumours, different forms of dementias, Parkinson’s (Miller et al., 1986). Three of these patients were tested

disease, Huntington’s disease, hippocampal sclerosis as well as neuropsychologically (the one not tested was described to have

encephalitis, and may also result from surgical treatment, e.g., normal intelligence; Miller et al., 1986) and demonstrated deﬁcits

temporal lobotomy or pallidotomy (see Table 1). In the following including reduced intelligence (Lesniak et al., 1972), reduced

section we will review the literature pertaining to these cases cognitive ﬂexibility and attention (Regestein and Reich, 1978), and

separately for the different diagnoses. We only consider reports disturbed memory recall, apraxia and agraphia (Burns and

about sexual behaviour or interest in prepubescent children. There Swerdlow, 2003). In light of this additional symptomatology it

are some papers in which sexual interest in pubertal children was appears unlikely that the tumours caused a speciﬁc change in

termed paedophile, which will not be discussed here. sexual preference. The variety of symptoms reported rather speak

in favour of the assumption that the neoplasms led to unspeciﬁc

2.1. Brain tumours disinhibition, which also affected sexual experience and behaviour,

thereby increasing the risk for sexual abusive behaviour. It is

There are reports of CSA emergent from brain neoplasms in four conceivable that such a disinhibition could result in acting out

married men (Table 1). In three cases these were located in the premorbid paedophile interest (Burns and Swerdlow, 2003;

right frontal lobe: medial paracentral (Lesniak et al., 1972), medial Mendez and Shapira, 2011). An elevated sexual drive alone could

orbitofrontal (Burns and Swerdlow, 2003), and not further potentially lead to behaviours involving minors of age even in the

6 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

Table 1

Summary of case reports of paedophilic behaviour occurring with neurological disorders.

Refs. Age Diagnosis/Localization Paedophilic symptoms Further symptoms Neuropsychological ﬁndings

Brain tumours

Lesniak et al. (1972) 56 Right-sided medial- Sexual intercourse with Sodomy, masochism, sadism, Reduced intelligence

paracentral glioma or minor daughter, bathing repeated sex proposals to

meningioma nude with children of both different woman, impulse

sexes, exposition of penis control problems, personality

in front of children and changes

encouragement to touch

it, urination into the face

of minor boy

Regestein and Reich (1978) 56 Right-sided frontal Multiple molestation of Increased sexual desire, more Reduced attention and

meningioma pre- and pubertal children frequent sexual intercourse cognitive ﬂexibility

of both sexes with wife, personality

changes, inability to sustain

erection, inability to learn

new music

Miller et al. (1986) 34 Brainstem glioma involving Multiple sexual advances Collection of pornography, Normal intelligence

the thalamus, hypothalamus, towards young children, difﬁculties with erection and

ventral midbrain and pons including prepubertal ejaculation, conversation

(more pronounced in left daughter ﬁlled with sexual innuendo,

hemisphere) Idiopathic showing pornographic

hydrocephalus, Weber‘s pictures to visitors at home,

syndrome, Benedikt‘s personality changes, poor

syndrome, hypothyroidism ﬁnancial judgement

Burns and Swerdlow (2003) 40 Right-sided orbitofrontal Interest in child Increased sexual desire Delayed recall, agraphia,

hemangiopericytoma pornography, advances (pornography, incl. child apraxia

towards prepubertal pornography), sexual

stepdaughter, denied advances towards female

previous attraction to medical staff and other

children patients, suicidal ideation,

balance problems, urinated

on himself being

unconcerned of it; severe headaches

Dementias

Mendez et al. (2000) 60 Frontotemporal dementia Molestation of Sexualized behaviour, Verbal stereotypies, mild

(hypometabolism in right prepubertal children, disinhibited and aggressive echolalia, diminished

inferior temporal region, exhibitionism behaviour, compulsive memory and executive

more subtle left) behaviour, decline in social functions

and personal awareness,

decreased judgement

Mendez and Shapira (2011) 67 Frontotemporal dementia Sexual advances towards Preoccupation with sexuality, Reduced verbal ﬂuency,

(frontal atrophy and daughters multiple daily sexual diminished memory and

hypoperfusion, more advances towards wife, executive functions

pronounced in right fondling of wife in public,

hemisphere) touching of women’s breasts

in magazines, decline in work

performance, disinhibited

behaviour, compulsive

behaviour

Mendez and Shapira (2011) 82 Vascular dementia following Molestation of Frequent masturbation, Deﬁcits in attention,

stroke (subcortical lacunes in stepdaughter talking about sex, sexualized verbal ﬂuency, working

left caudate head and right language, inappropriate memory, executive

globus pallidus, touching of others, functions and visuospatial

hypometabolism in right disinhibited behaviour construction

posterior cingulate cortex)

Rainero et al. (2011) 49 Frontotemporal dementia Sexual arousal and urges Mutation in PGRN verbal and Mild episodic memory

(bilateral frontal atrophy and towards 9-year-old- physical hetero-directed impairment

hypoperfusion) daughter aggressive behaviour, no

further disinhibition

Parkinson’s disease

Berger et al. (2003) 57 Unknown Repeated sexual Increased sexual urges, Below average

molestation of 10-year- problems with erections and intelligence

old boy and 6-year-old girl orgasms

Mendez and Shapira (2011) 59 No known abnormalities Interest in child Increased sexual urges, use of No abnormalities

pornography pornography (incl. child

pornography)

Mendez and Shapira (2011) 59 Pallidotomy, no further Molestation of 5-year-old Increased sexual urges No abnormalities

abnormalities granddaughter, (hiring strippers and

masturbation while prostitutes, use of

viewing photo of pornography, intrusive

granddaughter sexual thoughts, forced wife

to have sex with him several

times a day, propositions to

wife’s female friends)

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 7

Table 1 (Continued )

Refs. Age Diagnosis/Localization Paedophilic symptoms Further symptoms Neuropsychological

ﬁndings

Further neurological disorders

Fairweather (1947) 24 (of 154) patients with Sexual molestation of Unknown Unknown

postencephalitic ‘‘little girls’’

parkinsonism

Mendez et al. (2000) 67 Hippocampal sclerosis Molestation of 5-year-old Sexual preoccupation, past Deﬁcits in working

(volume loss in mesial boy; son of patient drug abuse, advances memory

temporal lobes and reported to have been towards female physician

hypometabolism in right molested by him in

temporal lobe) childhood

Devinsky et al. (2010) 39 Epilepsy (symptoms started Use of child pornography Hypersexuality, coprophilia, Unknown

after resecting posterior more frequent masturbations

temporal parts) and sexual intercourse with

wife, increased use of

pornography (incl. child

pornography)

Mendez and Shapira (2011) 32 Huntington’s disease Inappropriate touching of Verbally and physically Deﬁcits in verbal ﬂuency

(bilateral atrophy of caudate 6-year-old girl aggressive, constricted affect, and executive functions

and putamen nuclei; moodiness, depression,

hypometabolism of striatum) irritability, disorganization

absence of paedophilic preference. It might foster an unselective 2011). As in most cases described above, CSA did not arise in an

search for sexual partners. The neurophenomenological model isolated manner, but in the context of marked hypersexuality. In

supports this interpretation since behavioural control functions one patient the symptomatology appeared after a right pallidoto-

are ascribed to the implicated medial frontal areas (Redoute´ et al., my, which he underwent after suffering from Parkinson’s disease

2000; Stole´ru et al., 1999). for 16 years (Mendez and Shapira, 2011). As for the other two

examined patients, neuroimaging did not reveal any structural

2.2. Different forms of dementias alterations (Mendez and Shapira, 2011). All of these cases were

medicated with dopamine agonists, and no further psychiatric or

There are three reports of frontotemporal dementia (Mendez neuropsychological abnormalities were reported. Despite a

and Shapira, 2011; Mendez et al., 2000; Rainero et al., 2011) and sexually satisfying relationship with his wife, the patient described

one of vascular dementia following stroke (Mendez and Shapira, by Berger et al. (2003) seems to have been aware of a pre-existing

2011) leading to sexual child molestation. Two men with paedophilic disposition. However, he never acted on it until his

frontotemporal dementia exhibited frontal hypoperfusion and wife refused sexual contact, which was mainly due to the patient’s

atrophies, while one had no structural abnormalities on the erectile and orgasmic dysfunctions. These symptoms developed at

magnetic resonance imaging (MRI) scan; however, positron the same time as an increased libido. Both followed dopaminergic

emission tomography (PET) revealed right anterior temporal medication and were even more pronounced after the patient

hypoperfusion that may have been extended into the orbitofrontal increased medication on his own authority. This supports the idea

cortex. Computed tomography (CT) of the patient with vascular that brain pathology can lead to paraphilia-like behaviour without

dementia showed subcortical lacunes in the left caudate head and changing an actual existing sexual preference. Instead, neural

the right globus pallidus while PET additionally revealed a alterations might have dampened inhibiting mechanisms, which

hypometabolism in the right posterior cingulate. Three of these allowed for the manifestation of aberrant sexual behaviour,

four men showed hypersexual behaviour not limited to children. especially in the absence of other possibilities to act on strongly

This provides further evidence that brain pathology led to increased sexual urges. While again underlining a possible role of

disinhibition rather than to a speciﬁc change in sexual age the pallidum, this also implies that anatomical abnormalities must

preference. Additionally, in all cases personality changes, as well as not be a necessary prerequisite for the exertion of CSA, pointing to

obsessive-compulsive, impulsive or hetero-directed aggressive the importance of changes on the functional level. This is further

behaviour were described. Furthermore, all patients also suffered supported by the fact that all patients received dopaminergic

from neuropsychological deﬁcits in executive functions, memory, medication, which implies a potential role of this transmitter

attention, verbal ﬂuency, visuospatial abilities or demonstrated system in evoking hypersexuality. A recent cross-sectional study

verbal stereotypies, and echolalia. These reports suggested that the on 3090 patients with Parkinson’s disease conﬁrmed effects of

temporal cortex, the basal ganglia, and the frontal regions, are dopaminergic drugs on impulse control disorders, including

involved in CSA via disinhibited sexual behaviour. A disinhibited compulsive sexual behaviour (Weintraub et al., 2010). A possible

sexual drive following lesions of the temporal lobes and the explanation is that some substances non-selectively bind to

amygdala is a well-known symptom of the Klu¨ ver–Bucy syndrome. dopamine D1 and D2 receptors mainly located in the dorsal

Klu¨ ver and Bucy (1939) concluded that the temporal cortex exerts striatum, and probably mediating motor effects, but also to D3

an inhibiting function on sexual behaviour. This is in line with the receptors abundant in the ventral striatum. The ventral striatum

neurophenomenological model (Redoute´ et al., 2000; Stole´ru et al., (which includes the pallidum) is well-known to be associated with

1999), which ascribes inhibiting and action control functions to the behavioural addiction and substance dependence (Potenza, 2013;

implicated structures. Schacht et al., 2013). Dopaminergic medication has repeatedly

been shown to alter activity of brain areas involved in reward and

2.3. Parkinson’s disease motivation (Kassubek et al., 2011). A functional magnetic

resonance imaging (fMRI) investigation suggests that such

CSA was also reported to occur in male patients suffering from dopamine-mediated effects might already occur in very early

Parkinson’s disease (Berger et al., 2003; Mendez and Shapira, stages of sexual arousal processing. Oei et al. (2012) presented

8 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

healthy males with sexual photographs, which were shown so fast, 3. Neuroimaging

that they could not be processed consciously. During this

subconscious processing, dopamine administration led to in- In this section we will review structural (Section 3.1) and

creased brain activation in brain regions associated with the functional neuroimaging studies (Section 3.2) on paedophilia. In

motivational component of sexual arousal (Redoute´ et al., 2000; addition to identifying brain areas associated with sexual arousal

Stole´ru et al., 1999), namely the nucleus accumbens and dorsal processing in paedophilia and analysing differences in brain

anterior cingulate. Since these regions are thought to regulate structure and function compared to a control group, numerous

behavioural drive towards a desired target (‘‘wanting’’; Berridge studies also reported correlations between brain volume or

and Robinson, 1998), dopaminergic medication could contribute to activity and parameters for paedophilic interest, offence char-

compulsive behaviour as a result of stimulating a ‘‘running start’’ of acteristics or psychopathology. These results are discussed in

this circuit. Section 3.3.

2.4. Further neurological disorders 3.1. Structural neuroimaging

There are isolated accounts of CSA in other disorders. Mendez 3.1.1. CT studies

and Shapira (2011) described a patient suffering from Huntington’s The ﬁrst studies on structural brain abnormalities in paedo-

disease, who had bilateral atrophy of the caudate and putamen philes employed CT. Graber et al. (1982) observed reduced brain

nuclei as well as striatal hypometabolism. In one instance this man density in three men who had molested children (judging from the

inappropriately touched a 6-year-old-girl. Amongst other symp- case reports at least two of these did not show exclusive

toms, he had impulse control problems, heightened irritability and paedophilic interest). This was also found by Hendricks et al.

aggression, and executive deﬁcits. Another patient suffering from (1988) who collected data from 12 men incarcerated because of

hippocampal sclerosis had bilateral mesial temporal volume molestation of children or adolescents (no diagnosed paedophiles),

reductions and right temporal hypometabolism (Mendez et al., 10 patients from radiology without cerebral abnormalities, and 16

2000). While also showing increased sexual interest and preoccu- healthy controls. The control group was inadequate since it

pation, this man was reported to have molested prepubescent and included women (three in the radiology patient group and two in

pubescent boys. Clues for a possible premorbid paedophilic the healthy control group), whereas all CSOs were male. Hucker

interest existed, particularly the patient’s son claimed to have et al. (1986) found enlargement of the left temporal and anterior

been molested by him as a child. Devinsky et al. (2010) reported a horns to be more common in paedophilic sex offenders (n = 41)

patient suffering from epilepsy, who began collecting child than in a non-sex offender control group (n = 14). Yet, these results

pornography following a second temporal lobotomy. Interestingly, were not replicated in subsequent CT studies (Langevin et al., 1989,

this activity as well as hypersexuality did not evolve until his 1988; Wright et al., 1990). However, Wright et al. (1990) noted

second temporal lobotomy during which more posterior temporal greater brain asymmetry in paedophiles, mostly with smaller left-

areas were resected. The ﬁrst surgical intervention, in which more hemispheric widths, which was mainly attributable to the

anterior temporal regions and the amygdala were removed, did not temporal lobe. While the results from these studies are hardly

entail the symptomatology. Finally, Fairweather (1947) noted that comparable, two of them implicate some temporal abnormalities.

in his sample of 154 postencephalitic male patients, 24 had These abnormalities seem to be unspeciﬁc, since they were not

committed sexual offences against ‘‘little girls’’. only present in paedophilic sex offenders (all CT studies were

In none of the above cited cases, brain pathology speciﬁcally carried out with forensic samples), but also in other sexually

led to paedophilia. Rather, in the majority of cases CSA occurred aggressive men (e.g., non-paedophilic incest offenders; Langevin

in the context of hypersexuality, broader changes in personality, et al., 1988). This further supports the notion that temporal

impulse control problems and/or neuropsychological deﬁcits. abnormalities might play a role in disinhibited behaviour. Besides

Thus, a change in sexual age preference caused by the involved the low spatial resolution, CT studies are limited to the analyses of

pathological processes may not be a sufﬁcient explanation for the frequencies of rater-classiﬁed structural pathology, thereby

full spectrum of symptoms observed. It is more likely that the possibly missing more subtle abnormalities. In addition, conclu-

abnormalities resulted in reduced behavioural control leading to sions about paedophilia from these reports are impossible because

paedophilia-like behaviour on the background of a premorbid the necessary distinction between paedophilic men and CSOs is

sexual interest in children or a lack of more preferred sexual missing.

partners. Brain damages described were located mainly frontal,

temporal or within the basal ganglia. According to the 3.1.2. MRI studies

neurophenomenological model (Redoute´ et al., 2000; Stole´ ru The ﬁrst study using MRI to study structural brain abnormali-

et al., 1999) these structures are implicated in inhibition and ties in a sample including paedophilic men was conducted in

appraisal processes, which ﬁts well with the interpretation made Austria. Eher et al. (2000) investigated a sample of 38 imprisoned

above. sexual offenders of which 15 had offended against minors and

Case reports naturally suffer from the shortcoming that they are eight met diagnostic criteria for paedophilia. Similar to previous CT

based on observations of single patients. In these studies studies, and unlike subsequent MRI studies (which used more

paedophilic preferences often have not been diagnosed thorough- quantitative methods, see below), a qualitative analysis approach

ly. These studies were the ﬁrst to uncover brain regions, which was chosen investigating narrative reports of neuroradiologists.

could provide evidence for why some patients act out abnormal These were coded for the presence of brain abnormalities and

sexual interests. It should be stressed that patients who acted on subsequently, respective frequencies were compared between

their urges were investigated, which could be the reason for the groups. In a total of 38 sexual offenders, 17 were found to have

detection of areas primarily implicated in control processes. In structural abnormalities: four cortical atrophy, one periventricular

order to identify brain regions involved in the sexual preference for lesions, six deep white matter lesions, one ventricular enlarge-

children, diagnosed paedophile patients would have to be directly ments, and ﬁve multiple lesions. Additionally, in offenders without

compared to non-paedophile control subjects. This has been anatomical abnormalities self-perceived aggressiveness was cor-

accomplished in several neuroimaging studies conducted within related with self-reported interpersonal problems, and social

the last years, which we will discuss in the following sections. anxiety. This association with aggressiveness was not found in the

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 9

Table 2

Summary of structural MRI studies.

Refs. Sample Sexual orientation Medication Method Main ﬁndings Signiﬁcance

Schiltz et al. (2007) 15 CSO, inpatient Exclusive-type None in at VBM/MM GM reductions in p < .05 corrected

15 community paedophilia in at least 13 CSOs paedophiles: for multiple

controls least 13 CSOs Amygdala R, comparisons

Gender orientation Hypothalamus L/R, within ROIs

unknown Innominate substance L/R,

Bed nucleus striae

terminalis L/R, Septal

region R

Enlargement of the

temporal horn R in

paedophiles

Schiffer et al. (2007) 18 CSO, inpatient Exclusive-type None VBM GM reductions in p < .05 FDR

24 community paedophilia paedophiles: corrected for whole

controls Attracted to males: Cerebellum L/R*, Inferior brain

9 paedophiles frontal gyrus L/R*, *Additionally

12 teleiophiles Cingulate gyrus L/R*, p < .05 FWE

Posterior cingulate gyrus corrected within

L*, Insula L/R*, Precuneus ROIs

L/R, Parahippocampal

gyrus L/R*, Superior

temporal gyrus L/R,

Middle temporal gyrus R,

Putamen L/R*

(Amygdala L/R in

unpublished re-analysis)

Cantor et al. (2008) 44 CSO, outpatient Unknown Unknown VBM/MM WM reductions in paedo- p < .05 FDR

(paedo- & and hebephiles: corrected for whole

hebephilic) Superior fronto-occipital brain

53 NSO, outpatient fasciculus L, Arcuate

fasciculus R

Cantor & Blanchard 19 paedophilic CSO, Unknown Unknown MM WM reductions in paedo- p < .05 uncorrected

(2012) outpatient and hebephiles in bilateral (2 models)

49 hebephilic CSO, temporal (p = .04) and

outpatient parietal lobes (p = .06)

47 NSO, outpatient

Poeppl et al. (2013) 9 CSO, inpatient Exclusivity of age None VBM GM reduction in p < .05 FWE

11 NSO, inpatient preference paedophiles: corrected within

unknown Amygdala R ROIs

Attracted to males:

7 paedophiles

0 teleiophiles

Annotations: MRI magnetic resonance imaging, CSO child sex offender, NSO non-sex offender, VBM voxel-based morphometry, MM manual morphometry, ROI region of

interest, L/R left/right, GM grey matter, WM white matter, FWE familywise error correction, FDR false discovery rate.

17 offenders with structural abnormalities. Eher et al. (2000) included in these studies. In four of the investigations voxel-based

speculated that the observed multi-locus alterations might lead to morphometry (VBM) was used for data analysis. Two studies

violent behaviour by interfering with social information proces- additionally employed traditional morphometry; one study used it

sing. Although the study’s ﬁndings were interesting, the reported exclusively. In the following sections we will review the results

results are unspeciﬁc and the localization of anatomical abnor- concerning group differences between paedophiles and teleio-

malities remains unclear. Furthermore, conclusions regarding the philes from these studies (see Fig. 3 for a summary of

paedophilic subgroup are impossible (although this was not the methodological details).

main aim of the investigation), because paedophilic CSOs were The ﬁrst published study by Schiltz et al. (2007) analysed MRI

analysed jointly with CSOs without paedophilia. Last, a control data of 15 paedophilic sex offenders recruited from a forensic

group was missing. clinic, and 15 community controls using VBM and manual

Further MRI studies appeared from 2007 onwards. These used morphometry. Six of the paedophile patients had committed

higher spatial resolution (Eher et al. (2000) employed a T2- offences exclusively against girls, three exclusively boys, and six

weighted spin-echo imaging sequence in axial plane with a slice against both sexes. Further sample characteristics were not

thickness of 5 mm at 0.5 Tesla, while subsequent studies utilized reported, but as Schiltz et al. (2007) analysed data from the same

T1-weighted 3-dimensional sequences with a maximum slice sample as Walter et al. (2007) (see Section 3.2.2.2 and Tables 2 and

thickness of 1.5 mm at 1.5 Tesla), more sophisticated quantitative 4), it can be concluded that at least 13 of the 15 patients were

analysis methods and focused investigation of well-deﬁned exclusively oriented towards children and did not receive

paedophilic samples (diagnosed by structured clinical procedures). medication (Walter, personal communication). The VBM results

To date, ﬁve such studies have been published (summarized in were restricted to four predeﬁned regions, known to be associated

Table 2), with three of them conducted with German samples and with the regulation of sexual function: (1) The left and (2) right

two stemming from Canada, with the latter two relying on the amygdala, (3) the bilateral septal region and the bed nucleus striae

same data set. Overall 61 paedophilic (and 49 hebephilic men; terminalis as well as the (4) hypothalamus and the substantia

Cantor and Blanchard, 2012) and 103 teleiophilic men were innominata. The authors employed a signiﬁcance level of p < .05,

10 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

Fig. 3. Relevant methodological speciﬁcs of MRI studies. See refs. (Ashburner and Friston, 2000; Genovese et al., 2002; Kriegeskorte et al., 2009).

corrected for multiple comparisons within these regions of interest handedness, and gender orientation. In both groups, 50% of

(ROIs). VBM and manual morphometry exhibited a reduction of participants were exclusively attracted to males, while the other

right amygdala volume accompanied by an enlargement of the 50% were exclusively attracted to females. The paedophilic

right temporal horn in paedophilic offenders. While manual patients were exclusively attracted to prepubescent children and

morphometry showed a similar effect for the left amygdala, this they were not medicated. The authors applied both whole brain

could not be conﬁrmed by VBM. VBM did reveal volume reductions (thresholded at p < .05, false discovery rate correction, FDR) as

in all other ROIs. Schiltz et al. (2007) suggested that neurodevelop- well as ROI analyses (p < .05, familywise error correction, FWE)

mental problems cause the abnormalities, proposing that a carried out if an a priori ROI was signiﬁcant at an uncorrected

dysfunction of the structures implicated might interfere with threshold of p < .001 and a cluster extent of k 100 voxels) to

sexual maturation. They further speculated that a devaluation of their data. Assuming a relation of paedophilia to obsessive-

infantile sexual interest, which would usually develop during compulsive spectrum disorders, Schiffer et al. (2007) predicted

puberty, might not occur (Freund and Kuban, 1993). associations within the frontrostriatal, limbic system, insulo-

The second study was published by Schiffer et al. (2007), opercular segments, and cerebellum. The whole brain analysis

applied VBM and compared 18 paedophilic inpatients with 24 yielded grey matter reductions in paedophilic patients in the

controls. The sample did not differ signiﬁcantly in age, bilateral orbitofrontal cortex, insula, ventral striatum (putamen),

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 11

cingulate, precuneus, parahippocampal gyrus, superior temporal ‘‘The larger region followed the superior fronto-occipital

gyrus, cerebellum, left posterior cingulate, and the right medial fasciculus; it ran along the dorsal border of the caudate

temporal gyrus. Of the 15 ROI analyses carried out additionally, nucleus, extending posteriorly toward the occipital pole and

only an effect in the left parahippocampal gyrus would remain extending anteriorly to terminate primarily in the middle

statistically signiﬁcant at p < .05 FWE if one applied Bonferroni frontal gyrus. The anterior extension appeared also to terminate

correction (for the 15 separate tests). Consistent with their in two other, weaker clusters, one in the frontal operculum and

hypothesis, the authors interpreted their results as evidence for one in the opercular part of the inferior frontal gyrus. [. . .] The

relatedness of paedophilia with the obsessive-compulsive second region occurred only in the right hemisphere, following

spectrum. In addition, in an unpublished post hoc analyses of the arcuate fasciculus from the parietal opercular region to the

the data, Schiffer (personal communication) conﬁrmed ROI- temporal opercula, wrapping around the posterior extension of

corrected (p < .05 FWE) volume reductions within the bilateral the Sylvian ﬁssure and descending to the inferior temporal and

amygdala, consistent with the results of Schiltz et al. (2007). fusiform gyri’’ (Cantor et al., 2008, p. 137).

The third German study in which data of paedophilic patients

were analysed with VBM was published by Poeppl and colleagues In addition, a phallometric paedophilia index score correlated

in 2013. They compared nine unmedicated paedophilic CSOs with with brain regions that largely overlapped with the areas revealed

11 non-sexual offenders (NSOs, who had mainly committed by the manual and voxel-based morphometry analyses (see also

property offences). Importantly, as both groups were recruited Section 3.3 and Tables 2 and 7). This study had some major

from forensic high security hospitals, the authors controlled for methodological strengths like the large sample, availability of

potential effects of forensic inpatient status. Seven of the phallometric data, stringent statistics, and the inclusion of a NSO

paedophilic patients were attracted to males but none of the control group. However, the results were limited by the possibility

controls, which limits interpretability of the results. Moreover, that hebephilic subjects might have been included in the data set; a

information regarding the exclusivity of paedophilic interest is limitation which led to a reanalysis by Cantor and Blanchard

lacking and the paedophilic group was signiﬁcantly older than the (2012).

NSOs. The authors applied whole brain analyses and small volume The reanalysis, based on phallometric data or self-report,

corrections for all regions in which Schiltz et al. (2007) and Schiffer classiﬁed subjects as paedophilic if there was evidence for sexual

et al. (2007) found grey matter reductions at a FWE corrected interest in children below 10 years of age, hebephilic for interest in

signiﬁcance level of p < .05. The only region for which Poeppl et al. children between 11 and 14 years and teleiophilic if both the

(2013) replicated grey matter reductions in was the right phallometric response as well as self-report conﬁrmed interest in

amygdala, although this ﬁnding would not reach the required men and women older than 17 years, and no sexual offences

signiﬁcance threshold if corrected for the number of ROI analyses, against minors were known. Accordingly, 19 subjects were

as the authors remark themselves. The authors concluded that an classiﬁed as paedophilic (as opposed to 44 in the original

anatomical reduction of amygdala volume may not directly cause analysis), 49 as hebephilic, and 47 as teleiophilic. There was no

paedophilia. Instead, in line with Schiltz et al. (2007), they differences in age or years of education between these groups. The

suggested that the observed abnormality might be evidence for a analyses were restricted to a manual morphometric examination

deﬁcient developmental differentiation of this structure. Further, of those regions for which signiﬁcant reductions were found

this aberrant differentiation could result in the non-initiation of a previously (Cantor et al., 2008), namely the white matter portions

devaluation process of infantile erotic interest. of bilateral temporal and parietal lobes. The analyses showed no

In addition to the three German studies described above, Cantor differences between paedophilic and hebephilic subjects for

et al. (2008) examined a Canadian sample of 44 CSOs who either temporal white matter but reduced volumes in both groups

conﬁrmed paedophilic interest in a diagnostic interview, showed a compared to teleiophilic men. Group differences for parietal

stronger phallometric response to photos of children compared to regions had a similar pattern, although these were only

adults or (when phallometry was not available or unusable) had marginally signiﬁcant (p = .06). Therefore, this reanalysis showed

committed at least one sexual offence against a child below the age comparable white matter abnormalities in paedophilia and

of 14. Hence, although the collection of phallometric data is a hebephilia, although the spatial resolution here was low. Cantor

strength of this study, the diagnostic heuristic leaves the et al. (2008) suggested that the observed white matter reductions

possibility that non-paedophilic offenders might have been could be indicative of diminished connectivity between regions

included here, since children below the age of 14 might very well involved in the processing of sexual arousal. However, connec-

have reached puberty and because there may be other reasons than tivity analyses (techniques to investigate the interaction of

paedophilia to molest children (see Section 1.3). In the offender different brain regions) or diffusion tensor imaging (DTI; An

group, 91% of men had molested girls and 32% had molested boys. MRI technique which allows inferences on white matter structure

No further information regarding sexual preference or medication by measuring the diffusion of molecules, especially water) would

were given. The control group consisted of 53 non-paedophilic be needed to support this conclusion.

NSOs, who did not differ from the patient sample in age, In summary, there is one structural MRI ﬁnding observed in

intelligence, years of education, and handedness. A major three of the four published samples. Schiltz et al. (2007), Schiffer

difference to the other studies is that subjects were not (personal communication), and Poeppl et al. (2013) all found

incarcerated but on probation or parole. In addition to VBM, the amygdala volume reductions, pointing to disturbances in emo-

authors manually parcellated 39 regions for which they tested tional processing of sexual arousal (Redoute´ et al., 2000; Stole´ru

group differences combined in four models (for cortical and et al., 1999). The fact that this ﬁnding was replicated twice is

subcortical grey matter, white matter, and cerebrospinal ﬂuid) to promising, still, it requires further conﬁrmation as the results were

circumvent multiple testing. Only whole brain analyses corrected obtained with multiple testing and at least in one case (Poeppl

for FDR were performed. With both techniques, no group et al., 2013) would not withhold statistical correction for these.

differences in CSF or grey matter were observable, which stands Aside from this, the available investigations led to rather

in contrast to the three German reports. Instead, manual heterogeneous results. While the three German studies conducted

morphometry pointed to temporal and parietal white matter with smaller samples found grey matter reductions in varying

deﬁciencies in the CSO group. Consistent with this, VBM showed brain structures (Poeppl et al., 2013; Schiffer et al., 2007; Schiltz

that especially two regions were involved here: et al., 2007), studies relying on one Canadian data set showed

12 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

white matter reductions exclusively (Cantor and Blanchard, 2012; fMRI studies on different psychological processes (response

Cantor et al., 2008). inhibition and face processing) in paedophilic men, which are

described in Section 3.2.2.3.

3.2. Functional neuroimaging

3.2.2.1. fMRI case reports on sexual arousal processing and neural

3.2.1. PET studies effects of LH-RH agonists. To date, four case reports providing data

There are two studies already mentioned (Graber et al., 1982; on sexual arousal processing in paedophilic CSOs have been

Hendricks et al., 1988) in which, additionally to CT scans, PET was published (Table 3). All of the ﬁndings summarized in the

employed to investigate alterations in brain activity in CSOs. following section have to be taken cautiously because the results

Results of both investigations showed reduced cerebral blood ﬂow were acquired from individual subjects that probably show

in the CSO groups. In the study by Hendricks et al. (1988) this substantial inter-individual variability in activation patterns.

difference was greater at anterior than posterior sites. In a further Furthermore, they differed in their gender orientation, exclusivity

PET investigation Cohen et al. (2002) compared seven CSOs of paedophilic preference, and medication status. Also, stimuli and

diagnosed with non-exclusive paedophilia (attracted to girls) who statistical analysis (such as contrasts and signiﬁcance levels)

underwent an outpatient treatment with seven healthy controls. varied across studies.

They used narrative scenarios about sexual contact between a man In three of the four fMRI case studies intra-subject contrasts

and either (a) a prepubescent girl, (b) a 30-year-old woman or (c) were performed comparing the neural processing of preferred

words from the dictionary being read out loud. During the last (nude children or children dressed in swimsuits) against non-

condition they observed diminished glucose metabolism in preferred stimuli (dressed children or nude adults). There is some

paedophiles within the right inferior temporal gyrus and ventral overlap in activation of occipital areas, the right prefrontal cortex,

superior frontal gyrus. In addition to no group differences during anterior cingulate cortex, and superior temporal gyrus (Table 3).

the condition of interest, observed effects were detected via ROI Activation of all of these areas have also been observed by group

analyses, of which a total of 120 were conducted. The authors studies on paedophilic men (see Section 3.2.2.2 and Table 5).

discuss that no effects survived correction for multiple compar- However, only two of these three studies can be compared directly

isons. Hence, although the results of Cohen et al. (2002) pointed to (which is further complicated by imprecise coordinates given in

regions previously mentioned in case reports, these ﬁrst results one study; Dreßing et al., 2001). The ﬁndings reported by Schiffer

remained inconclusive and interpretability suffers from methodo- et al. (2009) were obtained from a patient who was on antilibidinal

logical ﬂaws like small sample sizes, unclear diagnoses and/or medication for three months (while the others were not).

imprecise localizations. Narrowing comparisons to the two remaining studies (Dreßing

et al., 2001; Habermeyer et al., 2012) decreases concordant

3.2.2. fMRI studies activation to the fusiform gyrus. This is likely due to high inter-

There are seven fMRI investigations and four single case reports subject variability in brain activity because there is large overlap

(three of these primarily studied neural effects of antilibidinal for intra-group contrasts across respective studies (see Section

medication) on sexual arousal processing in paedophilia. A total of 3.2.2.2).

87 paedophilic and 100 teleiophilic men have been examined. Because of the small number of subjects included, most authors

Eight of these investigations were performed in Germany, two in of case reports abstained from making direct comparisons between

Switzerland, and one was conducted in France. Voxel-wise them with the exception of Moulier et al. (2012). After masking out

analyses over the whole brain were conducted in 10 of the 11 activation observed in the control subject from the same contrast

studies. In the remaining study analyses were constricted to the as analysed in the paedophilic patient (male children in

amygdala. swimsuits > female children in swimsuits), the patient showed

In all of these studies erotic pictures were presented in order to additional activity within the left calcarine ﬁssure, left anterior

compare their neural processing in paedophilic men and non- insula, caudal anterior cingulate, and left cerebellar vermis. These

paedophilic control groups. Erotic pictures typically were photo- ﬁndings show little agreement with results from inter-group

graphs of children or adults, either nude or dressed in bathing suits contrasts (Table 6), although, results of overall group comparisons

or underwear. These were compared to control conditions during in general are quite inconsistent (see Section 3.2.2.2).

which either fully dressed people, people of a non-preferred age or Finally, the main focus of three of the fMRI case reports was to

neutral stimuli were shown. Some fMRI paradigms included investigate effects of pharmacological treatment with a long-

control tasks, like pressing a button whenever a certain stimulus acting luteinizing hormone-releasing hormone agonist (LH-RH,

appeared on screen to ensure attention of subjects. Further leuprolide acetate) on neural activation in paedophilia. LH-RH

information on the employed paradigms can be found in Table 4. agonists were shown to suppress deviant sexual urges and

Studies typically investigated the following questions: arousability (Ro¨sler and Witztum, 1998). The report by Schiffer

et al. (2009) only allows indirect comparisons of the activity found

(1) On the intra-group level: Which regions are activated during in the medicated patient with those seen in their previous

visual sexual stimulation? unmedicated sample (Schiffer et al., 2008b) at best, since he was

(2) On the inter-group level: Are there differences in brain activity scanned only once while medicated. The lack of recruitment of a

between paedophiles and control subjects during stimulation number of areas involved in emotional, motivational, and

with child and/or adult stimuli? autonomic aspects of sexual arousal (e.g., thalamus, amygdala,

(3) On the inter-group level: Are there differences in brain activity insula, substantia nigra, hippocampus, and the rostral anterior

between paedophiles and control subjects when only proces- cingulate), which the authors observed in their sample of

sing of the respective arousing stimuli is taken into account unmedicated paedophilic CSOs (Schiffer et al., 2008b), suggested

(children in paedophiles and adults in teleiophiles)? that LH-RH agonists might primarily suppress subcortical brain

activity. Two longitudinal studies on LH-RH effects on neural

In the following sections, we will ﬁrst review the publications activation used longitudinal designs, scanning the patient before

on sexual arousal processing in single cases using fMRI (Section and some months after the onset of treatment. Partially conﬁrming

3.2.2.1), before we will turn to studies providing group statistics on the hypothesis by Schiffer et al. (2009), Moulier et al. (2012) found

that matter (Section 3.2.2.2). In addition, there are two further that after ﬁve months of leuprolide acetate treatment, activity was

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 13

Table 3

Summary of fMRI case reports.

Refs. Subjects Treatment/Design Paradigm/Stimuli Main ﬁndings

Dreßing et al. (2001) Patient: Treatment unknown Passive viewing of women in Stronger recruitment of the visual

Paedophilia, bathing suits or underwear, boys in cortex, brain stem R, ACC, PFC R, basal

attracted to boys Cross-sectional bathing suits or underwear, control ganglia R, OFC R during boys in bathing

CSO pictures without subjects or objects suits only in paedophilic patient

Age: 33 years of same colour intensity and Fus L was stronger recruited during

Controls (n = 2): complexity; presented in boys in bathing suits in paedophilic

Teleiophilia, alternating blocks (19.2s/block) patient; in controls during photographs

attracted to women of women

Stronger recruitment of medial

temporal and left frontal areas in

controls, but not in patient

Only qualitative comparison of intra-

subject/group contrasts; signiﬁcance

level unknown

Schiffer et al. (2009) Patient: Trenantone Passive viewing of 7 photographs of Nude girls > dressed girls: IFG L, ACC

Paedophilia, (leuprolide acetate) nude girls and 7 of nude women L, STG L, Cuneus R, MOG bil.

attracted to girls 11.25 mg/3 months presented alternating with 7 images Nude girls > nude women: DLPFC R,

Exclusive-type of dressed girls and 7 of dressed STL L, SPL bil., MOG bil.

CSO Cross-sectional women (38.5 s/image) No effects for the contrasts dressed vs.

Age: 38.4 years undressed women and dressed girls vs.

dressed women

No control Signiﬁcance level unknown

Moulier et al. (2012) Patient: Leuprorelin Passive viewing of photographs of Boys swimsuits > girls swimsuits

Paedophilia, (leuprolide acetate) boys in swimsuits, girls in (masked by this contrast in the control

attracted to boys 3.75 mg/4 weeks swimsuits, dressed girls, women in subject): calcarine ﬁssure L (p < .001,

CSO Mianserin swimsuits, dressed women; corrected), AI L (p < .05, corrected),

Age: 46 years 30 mg/day presented in separate 35 s runs, each caudal ACC (p < .001, corrected),

Supportive 3 times cerebellar vermis L (p < .01, corrected)

Control: psychotherapy All activations disappeared on

Teleiophilia, Same order of stimulus categories at treatment ((T1 boys swimsuits > girls

attracted to women second treatment, but different set swimsuits) > (T2 boys swimsuits > girls

Age: 47 years Longitudinal (pre- vs. of photographs to maintain degree swimsuits)); no signiﬁcant changes in

on treatment, 5 of novelty control subject

months) Multiple comparison correction

method unknown; ROI analyses in

some comparisons

Habermeyer et al. Paedophilia, Lucrin Passive viewing of 10 photographs Boys bathing suits > boys dressed:

(2012) attracted to boys (leuprolide acetate) of boys and 10 of men in bathing Amy R, Fus R, STG

Non-exclusive 11.25 mg/3 months suits presented alternating with 10 Men bathing suits > men dressed:

type images of dressed boys and 10 of Amy/PHc R, STG bil., Pre R, MFG R,

CSO Longitudinal (pre- vs. dressed men (38.5 s/image); MedFG L, occipital R

Age: 43 years on treatment, 10 Adopted from Schiffer et al. (2008b, Conjunction ((Boys bathing

months) 2009) suits > boys dressed) & (Men bathing

No control suits > men dressed)): Amy/PHc R

Same picture set pre- and on Nude boys vs. nude men: Lin L

treatment Pre- > On Treatment: Amy R, SFG R,

MedFG L, MFG L, Pre R, STG bil.

Signiﬁcance level: p < .005

uncorrected (voxel-level), p < .05

corrected using Montecarlo

simulations (cluster-level)

Annotations: n sub-sample size, CSO child sex offender, s seconds, mg milligramme, L left, R right, ACC anterior cingulate cortex, PFC prefrontal cortex, OFC orbitofrontal cortex,

Fus fusiform gyrus, IFG inferior frontal gyrus, STG superior temporal gyrus, MOG middle occipital gyrus, DLPFC dorsolateral prefrontal cortex, STL superior temporal lobule,

SPL superior parietal lobule, AI anterior insula, Amy amygdala, PHc parahippocampal gyrus, Pre precentral gyrus, MFG middle frontal gyrus, MedFG medial frontal gyrus, Lin

lingual gyrus, SFG superior frontal gyrus, ROI region of interest.

signiﬁcantly diminished in those areas, which were initially paedophilic patients hold the promise to reveal more insightful

activated more strongly in the patient than in the control (insula, data. These will be reviewed in the following section.

rostral ACC, calcarine ﬁssure, cerebellar vermis). In contrast,

Habermeyer et al. (2012) did not replicate any of the regions 3.2.2.2. fMRI studies on sexual arousal processing in samples of

named by Moulier et al. (2012) in their patient after 10 months of paedophilic men. We will now mainly focus on comparability of

treatment. Moreover, except for declining activity within the those six (of seven) group fMRI studies reporting similar contrasts

amygdala, and the adjacent parahippocampal gyrus over time, from whole brain analyses. But ﬁrst we will brieﬂy outline the

their results mainly pointed to pharmacological effects in frontal main results of one remaining investigation focusing on amygdala

and temporal cortical regions. activity. Sartorius et al. (2008) investigated 10 paedophilic CSOs

Comparability of the results are limited by above mentioned attracted to boys from a forensic inpatient setting, and 10 controls

differences in methodological approaches, and by the fact that attracted to women. Sexual age preference information was not

single cases were analysed in which activation patterns cannot be provided and subjects were unmedicated. Restricting their

readily generalized. Studies investigating larger groups of analyses to the bilateral amygdala, they found signiﬁcantly

14 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

stronger activity in paedophilic subjects compared to the controls NSOs as control group, while all other reports included community

during the presentation of child stimuli, but no group effects controls. At least in ﬁve of these studies, patients were free of any

during adult stimuli. Within-group comparisons showed that medication or did not take antilibidinal drugs. Characteristics of

amygdala activity was lower during child compared to adult sexual orientation like exclusivity or gender orientation were

stimuli in controls while the opposite pattern was true for controlled for by some, but not all studies. Please refer to Table 4

paedophiles. This study provides further evidence for amygdala for details.

abnormalities, but it neglects potential further effects since whole 3.2.2.2.1. Intra-group contrasts. Data regarding intra-group con-

brain analyses were not reported. Further, it suffers from small trasts are available from three studies (Poeppl et al., 2011; Schiffer

sample size, lack of differentiation between gender preferences, et al., 2008a, 2008b), in which the sexually preferred images were

and missing adequate control for exclusivity of paedophilic contrasted with respective control stimuli (which were different

preference. across studies; Table 4). As can be seen from Table 5, results

Six studies were comparable in sample size and methodology. congruently show activations within comparable regions in

Four investigated forensic inpatient samples and two studied paedophiles and teleiophiles that are distributed over all

patients from outpatient prevention and therapy programmes. The components of the neurophenomenological model (Redoute´

number of included patients ranged from 8 to 24 (Table 4). Note, et al., 2000; Stole´ru et al., 1999). A recent preliminary meta-

that the sample investigated by Ponseti et al. (2012) was the only analysis (Polisois-Keating and Joyal, 2013) conﬁrms this picture

one including men who admitted their sexual attraction to demonstrating robust activations in both groups within the

children by themselves and who were not forced to intervention fusiform gyrus, occipital cortex, cerebellum, anterior cingulate

by legal authorities. Poeppl et al. (2011) were the only ones to use cortex, and substantia nigra. In paedophilic men, a greater number

Table 4

Description of functional MRI studies.

Refs. Sample Sexual orientation Medication Paradigm/Stimuli

Walter et al. (2007) 13 CSO, inpatient Exclusive-type paedophilia None 256 erotic (nude adults only), emotional

14 community controls Gender orientation unknown and neutral photographs shown randomly

(5 s/image); expectancy period (4–6 s)

before 50% of runs; button press required at

appearance of each picture

Sartorius et al. (2008) 10 CSO, inpatient Exclusivity of age preference unknown None 500 stimuli, consisting of images of boys,

10 community controls Paedophiles attracted to boys girls, men and women (wearing swimsuits

Teleiophiles attracted to women or underwear; 15/category; 1 s/photo), 48

target stimuli, 392 neutral non-target

stimuli shown randomly

odd-ball task: button press of foreﬁnger

required on targets, button press of middle

ﬁnger required on other stimuli

Schiffer et al. (2008a) 11 CSO, inpatient Exclusive-type paedophilia None Passive viewing of 7 photographs of nude

10 community controls All subjects attracted to males boys and 7 of nude men presented

alternating with 7 images of dressed boys

and 7 of dressed men (38.5 s/image)

Schiffer et al. (2008b) 8 CSO, inpatient Exclusive-type paedophilia none Passive viewing of 7 photographs of nude

12 community controls All subjects attracted to females girls and 7 of nude women presented

alternating with 7 images of dressed girls

and 7 of dressed women (38.5 s/image)

Poeppl et al. (2011) 9 CSO, inpatient Exclusivity of age preference unknown None 144 pictures of nude males and females

11 NSO, inpatient Attracted to males: from Tanner stages 1, 3 and 5 and 24

8 paedophiles neutral stimuli (scrambled images of nude

0 teleiophiles people) shown randomly (4 s/image)

Choice reaction time task: A dot appeared

at 12 possible positions with each picture

requiring to press a button corresponding

to the position as quick as possible.

Ponseti et al. (2012) 24 outpatient (12 CSO) 17 Exclusive-type paedophilia No antilibidinal 490 pictures from 14 categories (consisting

32 community controls Attracted to males: medication of 35 images each): nude adults and

13 paedophiles children in whole-body frontal views,

14 teleiophiles genitals only, or face only (face pictures not

used for analyses), nonsexual pictures

evoking high or low arousal presented in a

pseudorandomized order (1 s/image)

odd-ball task: button press required on

target stimulus (presented 20 times)

Habermeyer et al. 8 outpatient (3 CSO) Exclusive-type paedophilia Unknown Passive viewing of 50 pictures from 5

(2013a,b) 8 community controls All subjects attracted to females categories (consisting of 10 images each):

boys, girls, men and women in bathing

clothes as well as control stimuli (objects)

presented for 0.75 s each; Instruction:

Attentive viewing in preparation of post-

scan recognition task

Annotations: MRI magnetic resonance imaging, CSO child sex offender, NSO non-sex offender, s seconds.

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 15

Table 5

Summary of ﬁndings from intra-group contrasts in fMRI studies.

Sexually arousing > Control stimuli Preferred > Non-preferred age

Paedophiles Teleiophiles Paedophiles Teleiophiles

Schiffer et al. Schiffer et al. Poeppl et al. Schiffer et al. Schiffer et al. Schiffer et al. Schiffer et al. Poeppl et al. Schiffer et al. Poeppl et al. (2008a)a,c (2008b)a,c (2011)b,c (2008a)a,c (2008b)a,c (2008a)c (2008b)c (2011)d (2008b)c (2011)d

SFG R

MFG L/R R R R L R L/R

IFG R L/R R L/R R L/R L

Pre R L/R

Par R

SMA L L

Ins R L/R R L/R

STG L/R R L/R X L/R

MTG L/R L/R L X L/R

ITG L/R R R X

e,f

Fus R L R L/R L/R L/R L R

SPL R R R R R

IPL L L

Pos R R L/R L

Pcu R R R R L/R L R L

PHc L/R L L/R L R L e

SOG R R

e,f

MOG L(R L/R L/R L/R L/R X L/R L/R L

IOG L/R R L/R L L/R L

Cun L R L

Cal R

Lin L

e,f

ACC L/R L/R L

MCC L

PCC L/R

HC L L/R L R

Amy R R L/R R

Cau R R L/R R L

Tha L L/R L R

e,f

SN L/R L R

Put R L/R

GP R R Cere,f R

MB R

Annotations: SFG superior frontal gyrus, MFG middle frontal gyrus, IFG inferior frontal gyrus, Pre precentral gyrus, Par paracentral lobule, SMA supplementary motor area, Ins

insula, STG superior temporal gyrus, MTG middle temporal gyrus, ITG inferior temporal gyrus, Fus fusiform gyrus, SPL superior parietal lobule, IPL inferior parietal lobule, Pos

postcentral gyrus, Pcu precuneus, PHc parahippocampal gyrus, SOG superior occipital gyrus, MOG middle occipital gyrus, IOG inferior occipital gyrus, Cun cuneus, Cal

calcarine gyrus, Lin lingual gyrus, ACC anterior cingulate cortex, MCC middle cingulate cortex, PCC posterior cingulate cortex, HC hippocampus, Amy Amygdala, Cau caudate,

Tha thalamus, SN substantia nigra, Put putamen, GB globus pallidus, Cer cerebellum, MB midbrain, L/R left/right, X region implicated, but hemisphere not speciﬁed.

Contrast: nude children/adults > dressed children/adults.

Contrast: nude children > scrambled pictures of children.

p < .05 corrected for multiple comparisons using False Discovery Rate (FDR).

p < .001 uncorrected.

Meta-analytic support for teleiophiles.

Meta-analytic support for paedophiles by Polisois-Keating and Joyal (2013).

of signiﬁcantly activated regions were observed with additional In addition, there are three studies examining group

clusters in the middle frontal gyrus, superior parietal lobule, differences during stimulation with the respective preferred

hippocampus, and the insula. In teleiophilic men, amygdala photos (that is: paedophiles[child > control stimuli] < > teleio-

activity was observed, which was not detectable in paedophiles. teleiophiles[adult > control stimuli]; Poeppl et al., 2011; Schiffer

These regions correspond well with results of meta-analyses on et al., 2008a, 2008b). The ﬁndings between studies are inconsis-

cue-induced sexual arousal and the components of the neurophe- tent, with the only congruency being that two of three studies

nomenological model (Ku¨ hn and Gallinat, 2011; Poeppl et al., found no stronger activation in teleiophiles compared to paedo-

2014). philes (Table 6). In the remaining study stronger activation in

3.2.2.2.2. Inter-group contrasts. There are inconsistencies regarding frontal regions and the cingulate was observed in teleiophiles

the different brain structures implicated when groups are (Schiffer et al., 2008b). Investigating brain activity stronger in

compared for either child or adult stimuli (Table 6). Only the paedophiles compared to controls, Schiffer et al. (2008a, 2008b)

right medial frontal gyrus (Poeppl et al., 2011; Schiffer et al., found (incongruent) effects in frontal regions, while Poeppl et al.

2008a), hippocampus, and thalamus (Poeppl et al., 2011; Schiffer (2011) observed increased recruitment of posterior areas (Table 6).

et al., 2008b) were repeatedly found to be more strongly activated The meta-analysis by Polisois-Keating and Joyal (2013) showed no

in paedophiles compared to teleiophiles for the child stimuli. signiﬁcant differences between groups for these contrasts (at a

Comparing activations between groups for the adult stimuli led to FDR-corrected signiﬁcance level of p < .05 and a cluster threshold

a variety of different regions implicated across studies, with only of k 200 voxels).

the right insula and right cuneus replicated as more activated in Ponseti et al. (2012) used similar contrasts for the deﬁnition of

teleiophiles (see Table 6; Poeppl et al., 2011; Schiffer et al., 2008b; the group-discriminative pattern for subsequent pattern analyses

Walter et al., 2007). (see below). Divided by the sex of the presented stimuli they 16

Table 6 Summary of ﬁndings from inter-group contrasts in fMRI studies.

Child stimuli Adult stimuli Preferred stimuli Child > Adult Adult > Child

Paedo > Teleio Teleio > Paedo Paedo > Teleio Teleio > Paedo Paedo > Teleio Teleio > Paedo

Schiffer Schiffer Poeppl Walter Schiffer Schiffer Poeppl Schiffer Schiffer Poeppl Schiffer Schiffer Poeppl Habermeyer Ponseti Ponseti et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. et al. a,f a,f b,h c,i a,f a,f b,h a,f a,f b,h a,f a,f b,h d,g e,h f,h (2008a) (2008b) (2011) (2007) (2008a) (2008b) (2011) (2008a) (2008b) (2011) (2008a) (2008b) (2011) (2013a,b) (2012) (2012) MFG R R L L NO EFFECTS R NO EFFECTS MiFG R IFG R R L/R R

Pre L/R S.

Par L Mohnke Ins R R L/R L STG L/R

MTG R R R et

ITG R L/R al.

Fus L/R R L L L/R Progress SPL L/R IPL L

Pos R in

Ang R Neurobiology Pcu L PHc MOG LL

Lin L L/R 122 Cun R R

ACC L/R R L/R L (2014) MCC L R L/R

PCC R L 1–23 HC L/R R R Amy L Cau R L/R Tha R L LL Hyp L Cer R L/R R MB R

Annotations: MFG medial frontal gyrus, IFG inferior frontal gyrus, Pre precentral gyrus, Par paracentral lobule, Ins insula, STG superior temporal gyrus, MTG middle temporal gyrus, ITG inferior temporal gyrus, Fus fusiform gyrus, SPL superior parietal lobule, IPL inferior parietal lobule, Pos postcentral gyrus, Ang angular gyrus, Pcu precuneus, PHc parahippocampal gyrus, MOG middle occipital gyrus, Cun cuneus, Lin lingual gyrus, ACC anterior cingulate cortex, a MCCContrast: middle cingulate nude children/adults cortex, PCC posterior> dressed cingulate children/adults. cortex, HC hippocampus, Amy Amygdala, Cau caudate, Tha thalamus, Hyp hypothalamus, Cer cerebellum, MB midbrain, L/R left/right. b Contrast: nude children > scrambled pictures of children. c Contrast: sexually arousing pictures of adults > emotional pictures. d Contrast: nude men/genitals > nude boys/genitals. Contrast: girls > woman in bathing suits. e Contrast: nude women/genitals > nude girls/genitals. f p < .05 corrected for multiple comparisons using False Discovery Rate (FDR). g p < .05 corrected for multiple comparisons using cluster-level correction based on Monte Carlo simulations. h p < .001 uncorrected. i p < .005 uncorrected.

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 17

exclusively investigated hyperactivation of controls viewing adult investigations on differing psychological processes. In a sample

stimuli compared to paedophiles viewing child stimuli and overlapping with the one in which Habermeyer et al. (2013a)

observed widespread effects located mainly in posterior and studied sexual arousal processing, the same group (Habermeyer

subcortical structures (Table 6). Employing yet another analysis et al., 2013b) employed a go-/no-go task in order to investigate

strategy Habermeyer et al. (2013a) observed a signiﬁcant 3-way- response inhibition. The task consisted of two alternating

interaction of group and the within-subject factors age and gender conditions: In the ‘‘go’’ condition subjects were required to press

(of presented stimuli) within the right lateral middle frontal gyrus. a button whenever a letter was presented on the screen (here only

Paedophiles showed hyperactivation of the right lateral middle ‘M’s were presented). In the ‘‘no-go’’ condition ‘M’s and ‘W’s were

frontal gyrus exclusively during presentation of erotic girl stimuli, presented in a pseudorandom order with the task being to press

while controls showed hypoactivation across all experimental the button only in response to ‘M’s, but not to ‘W’s. A total of 11

conditions. More results from between-group contrasts were not paedophiles were recruited from an outpatient cognitive beha-

reported from this study. vioural therapy group. These men did not admit their sexual

In summary, the available fMRI studies reviewed here show attraction towards children before getting into contact with the

much stronger consistencies when focusing on similarities legal system because of sexual offences against children that

between teleiophiles and paedophiles, but led to very different involved direct physical contact (n = 5) or the use of child

results for group differences. These incongruencies aggravate clear pornography (n = 6). They were compared to eight healthy

conclusions and complicate, if not prohibit, classiﬁcation according controls, not differing signiﬁcantly in age and intelligence. Three

to the neurophenomenological model. The heterogeneous results of the paedophiles were attracted to boys, while none of the

suggest that the methodological approaches may have been controls were attracted to men. Behaviourally, the paedophilic

inappropriate. In contrast, results of ﬁrst discriminative analysis CSOs showed longer reaction times in the no-go condition and less

strategies look more promising. Walter (2008; Walter et al., 2010) accurate discrimination of stimuli (‘W’ and ‘M’) than controls.

used a stepwise discriminant analysis based on functional regions However, there was no higher rate of commission errors (the

in which group differences during either cognitive anticipation or failure to suppress an inappropriate response) in paedophiles.

passive viewing of erotic stimuli were observed (Walter et al., These results was interpreted as being more indicative of

2007; see Table 4). This showed that groups (n = 13 unmedicated inattention, rather than impulsivity. In line with this, there were

paedophilic CSOs, n = 13 teleiophilic controls) could be separated no group differences in the activation of brain areas typically

by neural activity within the dorsal anterior cingulate during the involved in response inhibition (anterior insula, anterior and

expectancy period, and hypothalamic activation during stimulus dorsolateral prefrontal cortices, supplementary motor area, and

consummation. However, these results were obtained using a parietal cortices; Wager et al., 2005), but in regions belonging to

small size and validation in an independent data set would be the brain’s default mode network (Whitﬁeld-Gabrieli and Ford,

essential. Additionally, the ﬁndings are limited by the a priori 2012). A signiﬁcant interaction effect (group condition) showed

selection of regions included in the model. Ponseti et al. (2012) that paedophiles (compared to controls) exhibited less deactiva-

used whole-brain fMRI pattern classiﬁcation in a sample of 24 tion of the precuneus and the angular gyrus during the ‘no-go’

paedophilic men and 32 community controls (Table 4). In this condition compared to the ‘go’ condition. In addition, activity

study paedophilic and teleiophilic sexual orientations were within these regions was signiﬁcantly correlated with reaction

discriminable with a speciﬁcity of 100% and sensitivity of 88%. times during ‘no-go’. Since the default mode network is usually

This investigation employed a paradigm (presentation of photos of activated when the brain is at rest, and is implicated in processes

full frontal nudes as well as genitals only from adults and children such as self-reﬂection and mentalizing (thinking about mental

of both sexes for 1 s) comparable to those used in other studies. The states of others; Whitﬁeld-Gabrieli and Ford, 2012), the authors

classiﬁcation was based on the calculation of group differences in interpreted that the paedophilic men might have been more

activation patterns, computed similarly as in other studies, but went occupied with these processes (e.g., they might have thought about

a step further. As its purpose was the examination of the their socially unwanted sexual preference, because it was

discriminative power of such a design, individual statistics (for currently scientiﬁcally investigated) rather than focussing their

boys < men and girls < women) were then projected on these group attention on the cognitively more demanding ‘no-go’ condition.

differences to obtain individual expression values representing the In a subsequent study Ponseti et al. (2014) studied neural face

degree to which the activation pattern of a single subject matched processing in the sample in which they performed their

the group’s brain response. These values were subsequently used for classiﬁcation analyses based on visual sexual stimuli (Ponseti

classiﬁcation algorithms. Importantly, Ponseti et al. (2012) cross- et al., 2012; see Table 4). The authors presented photographs of

validated their results to estimate the model’s ability to classify faces of women, men, girls, and boys as well as further arousing

unknown data. Using the leave-one-out method, the model was pictures. In order to investigate the neural processing of faces of

repeatedly recalculated leaving out one subject at a time. Group the preferred age they contrasted pictures of the preferred type

statistics from the respective remaining sample (n = 55) were used with those of the preferred sex, but not of the preferred age (e.g., for

to calculate the expression value for the left out subject, which was paedophiles attracted to boys: boys’ faces vs. men’s faces) for each

then submitted to classiﬁcation. This procedure was repeated for group of participants (teleiophiles/paedophiles attracted to males/

each individual subject, so that it had to be performed 56 times. females). Subsequently, they conducted a conjunction analysis on

However, validation in a completely independent data set would these contrasts in order to identify brain regions that teleiophiles

still be desirable and the validity of the ﬁndings is somewhat recruited more strongly during adult faces compared to child faces

constricted by the fact that signiﬁcance values were not reported for and that paedophiles activated more strongly in response to child

the group classiﬁcation. Still, the high accuracy achieved points to faces compared to adult faces. During viewing faces of the

the presence of functional differences between paedophilic and preferred age, paedophiles and teleiophiles activated a network

teleiophilic men, and supports the utility of fMRI research in this of face- and sex-sensitive areas comprising the inferior occipital

population. However, it challenges ‘‘classical’’ analysis strategies, gyrus, fusiform gyrus, caudate, putamen, sulcus calcarinus, and

which only focus on group differences. ventrolateral prefrontal cortex. Therefore, in both groups the same

network was activated in response to respective sexually preferred

3.2.2.3. fMRI studies on further psychological processes. In addition faces. This agrees with the observation that paedophilic and

to the studies reviewed above, there were two more fMRI teleiophilic men activate largely comparable brain areas during

18 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

sexual arousal processing (see Section 3.2.2.2). However, it was not variables such as: indexes for sexual arousal or paedophilic

reported whether there were any group differences during face interest, offence characteristics (e.g., the number of sexual offence

processing. types, incestuous child abuse, age of victims), or psychopathology

(obsessiveness and depression). The number of different param-

3.3. Correlational analyses in neuroimaging studies eters complicates comparisons of the published ﬁndings (Table 7).

Nevertheless there are results of interest across studies.

Most neuroimaging studies also investigated correlations Walter et al. (2007) and Schiffer et al. (2008b) both found

between brain structure/activity in paedophilia and a variety of negative associations between the Multiphasic Sex Inventory (MSI)

Table 7

Signiﬁcant correlative ﬁndings from MRI studies.

Refs. Measure Brain area Test statistic

Structural MRI studies

Schiltz et al. (2007) SVR-20 ‘‘Multiple sexual offence types’’ Amygdala R r = .69

MSI ‘‘Incestuous child abuse’’ Amygdala R r = .58

Schiffer et al. (2007) MMPI-2 ‘‘Obsessiveness’’ Negative correlations

IFG L T = 7.00

SFG R T = 5.44

Putamen L T = 5.37

Putamen R T = 4.73

Cerebellum T = 5.30

MMPI-2 ‘‘Depression’’ Negative correlations

MFG R T = 6.10

MFG L T = 5.06

RG T = 5.39

b c

Cantor et al. (2008) Phallometric paedophilia index White matter:

Temporal Lobe R/L r = .31/.25

Parietal Lobe R/L r = .32/.33

Corpus callosum r = .19

CSF:

Lateral ventricle R/L r = .19/.22

Poeppl et al. (2013) SSPI Insula/Parietal operculum r = 45

DLPFC L (IFG) r = .64

Age of victims OFC R (RG) r = .98

Angular L r = .70

Angular R r = .93

Functional MRI studies

Walter et al. (2007) MSI ‘‘Sexual abuse of children’’ Negative correlations

(contrast: sexual > emotional arousal) DLPFC R (Precentral) Z = 3.61

DLPFC R (MFG/SFG) Z = 3.30

DLPFC L (SFG) Z = 3.24

occipital L Z = 3.57

Schiffer et al. (2008a) Sexual arousal ratings Paedophiles:

(contrast: nude > dessed boys) SFG R r = .68

MiFG L r = .72

ACC R/L r = .84/.83

STG R/L r = .76/.80

MTG R r = .86

Teleiophiles:

Fusiform R r = .68

(contrast: nude > dressed men) Fusiform L r = .87

Schiffer et al. (2008b) Sexual arousal ratings Paedophiles:

(contrast: nude > dessed girls) FPPFC R (MFG) r = .67

Fusiform L r = .62

ITG R r = .75

Teleiophiles:

Putamen R r = .62

(contrast: nude > dessed women) Paedophiles:

Fusiform R r = .56

Teleiophiles:

OFC R r = .76

Fusiform R r = .55

Pcu L r = .58

IPL L r = .61

MSI ‘‘Sexual abuse of children’’ ACC L r = .65

(contrast nude > dressed girls) Caudate R r = .59

Thalamus L r = .55

Fusiform L r = .51

OFC L (IFG/MFG) r = .64/r = .55

DLPFC L (SFG) r = .67

DLPFC R (SFG) r = .45

FPPPFC (SFG) r = .49

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 19

Table 7 (Continued )

Refs. Measure Brain area Test statistic

a d

Poeppl et al. (2011) Paedophilic preference index Positive correlations

(contrast: Tanner 1 > Tanner 5) MiFG L T = 9.37

Putamen L T = 6.82

Post-/Precentral L T = 6.81

Negative correlations

Corpus callosum L/R T = 23.94

MTG L T = 10.41

Corpus callosum R T = 9.38

STG L T = 9.03

MTG R T = 8.62

Pcu/SOG R T = 7.84

Angular L T = 7.08

Calcarine/PCC R T = 6.91

Dentate R T = 6.76

PCC/Pcu R T = 6.75

Correlations observed in paedophile subjects only.

Correlations observed in a combined analyses with paedophile and teleiophile subjects.

Phallometric paedophilia index was calculated by subtracting phallometric responses to adult stimuli from those to child stimuli.

Paedophilic preference index was calculated by subtracting mean response latencies for adult stimuli (Tanner 5) from those for prepubescent stimuli (Tanner 1), SVR-20

sexual violence risk scale-20 (Boer et al., 1997), MSI ‘Multiphasic sex inventory’ (Deegener, 1996), MMPI-2 Minnesota multiphasic personality inventory (Hathaway et al.,

2001), SSPI Screening scale of paedophilic interest (Seto and Lalumiere, 2001), IFG inferior frontal gyrus, MiFG middle frontal gyrus, SFG superior frontal gyrus, RG rectal gyrus,

DLPFC dorsolateral prefrontal cortex, OFC orbitofrontal cortex, ACC anterior cingulate cortex, FPPFC frontopolar prefrontal cortex, MFG medial frontal gyrus, STG superior

temporal gyrus, MTG middle temporal gyrus, ITG inferior temporal gyrus, Pcu Precuneus, SOG Superior occipital gyrus, PCC posterior cingulate cortex, L left, R right.

subscale ‘‘Sexual abuse of children’’ (Deegener, 1996) and bilateral paedophilia. Although neurological case reports frequently point-

dorsolateral prefrontal cortex activity during sexual arousal ed to pathology of the frontal lobes, temporal lobes, and the basal

processing. In both papers it was assumed that the dorsolateral ganglia, these regions seem to be associated with diminished

prefrontal cortex modulates vegetative-autonomic components of behavioural control that may apply to hypersexuality rather than

arousal processing (Beauregard et al., 2001). This allows for the paedophilic sexual preference itself. These abnormalities were

speculation that sexual offending could be promoted by decreased observed in CSOs and although CSA did not occur as a speciﬁc

recruitment of the dorsolateral prefrontal cortex that may entail consequence, it was observable in the context of overall increased

insufﬁcient regulation of physical states. sexualized behaviour and reduced impulse control. Hence, these

Schiffer et al. (2008a, 2008b) reported the repeated involve- ﬁndings may be more closely associated with sexual offending,

ment of the fusiform gyrus, despite inconsistent correlations probably provoked by a more general disinhibition rather than

between sexual arousal ratings and brain activation between paraphilic interest, per se (see also Mendez and Shapira, 2011).

paedophiles (attracted to boys or girls) and teleiophiles (attracted Moreover, the case studies are selective reports, therefore may be

to men or women). The fusiform gyrus is implicated in the neural inherently biased. This line of research neglects unpublished

processing of sexual arousal (Ku¨ hn and Gallinat, 2011; Poeppl ﬁndings as well as further abnormalities that may have remained

et al., 2014; Polisois-Keating and Joyal, 2013; Stole´ru et al., 2012) undetected due to patients not being systematically investigated.

and has been consistently observed in intra-group contrasts in Furthermore, these studies suffer from the lack of distinction

fMRI studies on paedophilia (see Table 5). It is assumed to be between CSO and paedophilia and often subjects were not properly

involved in processing motivationally relevant stimuli, including diagnosed. Nevertheless, they provide preliminary evidence on

erotic images and is therefore counted in the ‘‘appraisal’’ structural brain abnormalities underlying inappropriate sexual

component of the neurophenomenological model (Redoute´ behaviour, which is of relevance in paedophilic motivated sexual

et al., 2000; Stole´ru et al., 1999). behaviour.

One structural and one functional MRI study employed Structural neuroimaging studies employing either CT or MRI,

paedophilia index scores (operationalized either by the difference generally conducted on diagnosed forensic samples, also led to

in phallometric responses; Cantor et al., 2008; or reaction times; inconsistent results. Nevertheless, the volume reduction of the

Poeppl et al., 2011; during stimulation with child vs. adult stimuli; amygdala in paedophilic CSOs was observed in three independent

Table 7) for correlational analyses. Both studies coincide in ﬁnding VBM studies (Poeppl et al., 2013; Schiltz et al., 2007; Schiffer,

negative associations between activity or structure of the corpus personal communication); thus, it is an interesting and promising

callosum and bilateral temporal white matter and the score for result. Some issues remain that should be addressed in future

paedophilic interest. There is also weaker overlap between both replications of the amygdala association. First, the results were

studies in associations with parietal white matter areas. These obtained using numerous separate ROI analyses and, at least in the

observations support the conclusions made by Cantor et al. (2008) investigation of Poeppl et al. (2013), would not survive correction

in which neural abnormalities might rather be manifested in for the number of small volume corrections. Still, the results from

alterations of connectivity of areas involved in sexual arousal the three studies consistently demonstrated a large effect size

processing than with circumscribed grey matter aberrances. (Cohen’s d = 1.22–1.51 ); however, each study was in a limited

Further study is necessary to elucidate the exact roles of brain sample size, therefore it is possible that the effects are inﬂated.

connectivity and the functional signiﬁcance of the dorsolateral Hence, future analyses should include a well-powered sample to

prefrontal cortex and fusiform gyrus in this context. replicate the result and conﬁrm the true effect size. In addition, it is

doubtable, whether the ﬁnding of reduced amygdala volume

4. Discussion represents an abnormality speciﬁc to paedophilia. The amygdala

has frequently been implicated in sexual arousal processing.

The heterogeneous results summarized in this review make it Stole´ru et al. (2012) reported that it was implicated in 35% of fMRI

difﬁcult to draw any deﬁnitive conclusions on neural correlates of studies on male sexual arousal and it plays a likely role in

20 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

emotional appraisal and encoding of reward value. In line with this, and motivational processes as suggested by the neurophenome-

Schiltz et al. (2007) and Poeppl et al. (2013) concluded that smaller nological model (Redoute´ et al., 2000; Stole´ru et al., 1999). Similar

amygdala volume might indicate a lack of devaluation of infantile to the group’s VBM study (Schiffer et al., 2007), they assumed that

sexual interest, which would represent a neurodevelopmental dysfunction of appraisal processes mediated by this region could

abnormality. Further support for this comes from Schiltz et al. be associated with disturbed stimulus control as seen in (sexual)

(2007). It was reported that amygdala volume was negatively compulsive behaviour. Indeed, similar results were obtained by

correlated with exclusive paedophilic offences and incestuous CSA Poeppl et al. (2011) as well, but still, it was not consistently

(Table 7). Additionally, a recent meta-analysis shows that although supported by subsequent studies (see Table 6). Habermeyer et al.

direct comparisons did not yield signiﬁcant differences in (2013a) for example found stronger right orbitofrontal involve-

amygdala activity between paedophiles and teleiophiles, activa- ment only in paedophilic men while these were watching erotic

tion observable in teleiophiles during sexual arousal processing girl stimuli, interpreting very similarly as Schiffer et al. (2007), that

was not detectable in paedophiles (Polisois-Keating and Joyal, this area was involved in evaluating reinforcers, which would

2013). However, amygdala volume alterations could be apparent entail emotional and behavioural regulation. However, besides

for other reasons. For example, Pardini et al. (2013) reported an investigating samples from unequal settings (in- vs. outpatient),

association between lower amygdala volume and aggression, the orbitofrontal regions observed in these two studies were not

violence, and psychopathic traits. Instead of affecting sexual exactly congruent and the effects pointed into different directions,

preference, the structural alteration could be linked to factors so that these results could represent differing processes.

underlying psychopathy such as: aggression, impulsivity, lack of Other replicated ﬁndings from imaging studies include

empathy, and emotional unconcern (Anderson and Kiehl, 2012; hyperactivation of the cuneus in teleiophiles during photographs

Kiehl, 2006). Furthermore, diminished amygdala volume could of adults (Table 6). This region is not usually found during sexual

also be a correlate of more general affective symptoms comorbid arousal, but likely implicated in visual processing or inhibitory

with paedophilia, like depressed mood or anxiety. Thus, in control (Haldane et al., 2008). Insula activation was more

summary, there is considerable empirical support for structural consistently observed in studies on male sexual arousal. This

amygdala alterations in paedophilic CSOs, which have been region was found to be more strongly recruited by teleiophilic than

observed in three out of ﬁve studies (three out of four data sets). paedophilic men during presentation of adult stimuli (Walter et al.,

Nevertheless, further research on larger samples using stringent 2007; Poeppl et al., 2011). The insula may play various roles in

statistical methods are needed to verify this result and to elucidate sexual arousal including interoceptive awareness of bodily

the exact role of the amygdala in this context. processes, the mediation of autonomic responses (including penile

The fMRI studies deﬁnitively show that there may be more erection) as well as determination of the affective tone of sexual

similarities than differences between paedophiles and teleiophiles arousal (Stole´ru et al., 2012). Two studies found stronger

in the functional recruitment of brain areas during visual hippocampal and thalamic activity in paedophiles upon presenta-

stimulation with sexually preferred images (Polisois-Keating and tion of child images (Schiffer et al., 2008a; Poeppl et al., 2011)

Joyal, 2013; Seto, 2008; Schiffer et al., 2008b). Across studies, the pointing to roles in general emotional arousal and reward-

intra-group contrasts showed comparable activity of the sexual dependent action selection (Stole´ru et al., 2012). However, as

arousal network in both groups, corresponding to all components the same regions were also found to be more active in teleiophiles

of the neurophenomenological model of sexual arousal (Redoute´ in other studies using different contrasts, these results should be

et al., 2000; Stole´ru et al., 1999). In contrast, group differences interpreted with caution.

varied between studies, although the number of investigations The variability of these results might stem from a number of

providing data for comparable contrasts so far is admittedly low, as factors, such as: inclusion of differing paedophilic and control

different paradigms and analysis strategies were used. It is populations, insufﬁcient statistical power, divergent operationa-

noteworthy that Schiffer et al. (2008a, 2008b) and Habermeyer lization, analysis procedures, and differences in the fMRI para-

et al. (2013a) were the only ones to use correction for multiple digms. These varied in a number of factors like the stimuli used

comparisons over the whole brain in their between-group analyses (nude vs. partly dressed, inclusion of child photographies), number

and they still yielded inconsistent results. Hence, although of runs, instructions given, the inclusion of a task ensuring

statistical stringency is of course desirable, more concordant attention, and/or the duration of stimulus presentation, which

results may have not been reported because of this level of varied between 0.75 s and 38.5 s (Table 4). In their review on brain

signiﬁcance being too strict given the small sample sizes. imaging of sexual behaviour Georgiadis and Kringelbach (2012)

Given the aforementioned limitations, only cautious interpre- pointed out that there are well dissociable networks associated

tation can be derived. For instance, in face of several subcortical with short vs. long stimulus presentation times. They argued that a

and dorsolateral prefrontal minor activations in paedophiles, ‘‘sexual interest network’’, activated by brieﬂy presented stimuli,

Walter et al. (2007) speculated that a lack of sexual interest in could primarily be implicated in the evaluation of salience and

adults might stem from difﬁculties in recruiting regions responsi- hedonic value. In contrast, the ‘‘sexual arousal network’’, proces-

ble for vegetative-autonomic responses, potentially resulting from sing further physiological components of heightened arousal like

insufﬁcient dorsolateral prefrontal control. However, other reports penile tumescence or cardiovascular activity, was observable after

did not support dampened subcortical activity and some found more prolonged stimulus durations. Furthermore, longer presen-

even higher subcortical recruitment when child stimuli were tation times likely result in less distinct and more complex

employed (Poeppl et al., 2011; Sartorius et al., 2008; Schiffer et al., processes measured as other mind states like emotion regulation

2008b). Since Walter et al. (2007) exclusively used adult stimuli or self-referential processing might coincide with sexual arousal

the minor activations might stem from the fact that paedophiles (Georgiadis and Kringelbach, 2012; Habermeyer et al., 2013a). All

were less aroused by these photos (although they reported of the mentioned factors could have led to quite different arousal

otherwise, see below). Schiffer et al. (2008b) concluded from levels across studies, which limits comparability.

stronger orbitofrontal and general frontal involvement seen in Interpretability of some ﬁndings is further complicated by

teleiophiles that these regions might underlie altered evaluative behavioural ratings of stimuli. Walter et al. (2007) did not ﬁnd

group differences in the sexual arousal and emotional intensity

1 ratings for the adult stimuli between groups and Schiffer et al.

Values were calculated based on Z-values reported by both studies using the

pffiffiffiffi

formula: d ¼ ð2z= NÞ (Cohen, 1992). (2008b) found no signiﬁcant differences between exclusive-type

S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23 21

paedophiles’ rating of girls and women stimuli. On the one hand (Knight, 1988), or the degree of admittance to child sexual

this could point to response biases in terms of social desirability attraction (Grossman and Cavanaugh, 1990). However, these

or unreliable responses from forensic samples. On the other hand classiﬁcations remain controversial as to their utility to predict

this could also mean that the stimulus material employed in re-offence risk, which is a central outcome parameter of

these studies was insufﬁcient to produce the aspired group therapeutic approaches (Kingston et al., 2007). With the turn

differences. of the millennium, forensic research has shifted attention to

The inconsistencies in functional imaging studies contrast improve the prediction of re-offence risk using ‘‘actuarial’’ risk

discriminative analyses, showing that paedophiles and teleiophiles assessment tools or structured clinical judgement, which

very accurately can be separated based on activation patterns integrate and weigh the proposed classiﬁcations. These tools

(Ponseti et al., 2012; Walter et al., 2010). In spite of the described have shown good accuracy and thereby support the validity of

disagreement in other studies, these results speak in favour of the the classiﬁcation into subgroups (Tully et al., 2013). Hence, it

usefulness of fMRI to investigate paedophilia and point to the would be interesting to investigate whether neurobiological

possibility that abnormalities should not be looked for on the level correlates can be deﬁned that might validate the proposed

of isolated brain areas, but would be better characterized on a differentiations.

network level. Furthermore, correlative analyses yielded some Control for pharmacological treatment: There are some inves-

interesting ﬁrst clues on the role of the DLPFC in arousal regulation, tigations, which did not provide information on pharmacological

implying a relevance in CSO rather than in paedophilic preference treatment. Needless to say, this could inﬂuence brain activity and

per se (compare Walter et al., 2007) and suggested the importance in the long term brain structure. As paedophilic patients often

to study brain connectivity in paedophiles in face of replicated receive anti-androgenic or psychopharmacological medication,

associations of paedophilic preference with white matter structure this is an important factor to mention and to account for.

and function (Cantor et al., 2008; Cantor and Blanchard, 2012; Validation of stimulus sets: There are clues from some functional

Poeppl et al., 2011). imaging studies that the employed stimulus material was not

Concluding from the literature reviewed above we would like to sufﬁcient to show behavioural effects on excitability or reaction

point out some methodological suggestions for future studies: times (see above). Hence, it should be validated before being

used in the scanner to enable more reliable conclusions.

Larger sample sizes: Most studies published so far have included Deliberate about presentation times: Short as opposed to longer

very small samples. These investigations therefore lack sufﬁcient stimulus durations lead to differences in brain activity as various

statistical power to ﬁnd potential effects. It is of course difﬁcult processes play a role at different temporal stages of sexual

to collect larger samples of paedophiles, especially from a non- arousal. Early evaluative processes, which are more speciﬁcally

forensic context, but still, this profoundly hampers more measurable with brief presentation times, are followed by

sophisticated analyses. physiological processes and further cognitive elaboration, which

Differentiation between paedophiles who have and those who become more relevant with prolonged stimulation. Consequent-

have not committed sexual abuse: Most published studies were ly, depending on the process of interest, different presentation

conducted in forensic contexts and therefore included paedo- times might be appropriate.

philic CSOs. In contrast, little is known about paedophilic non- Focus on brain networks: Studies using traditional fMRI analysis

offenders. Conceivably, these groups could differ in quite a few methods led to very heterogeneous results while a study

important aspects like personality characteristics (e.g., antisocial focusing on brain activity patterns show high accuracy in its

tendencies), empathic abilities, and/or impulse control (Hanson attempt to differentiate between paedophiles and teleiophiles

and Morton-Bourgon, 2005). These variables in turn could be based on these patterns (Ponseti et al., 2012). Also, there is

confounded with differences seen in comparison to teleiophiles. suggestive evidence that abnormalities may particularly pertain

Control for the recruitment setting: The forensic context or the to the coupling of relevant brain areas (Cantor et al., 2008; Cantor

in- vs. out-patient status of patients should be accounted for, as and Blanchard, 2012; Poeppl et al., 2011). Therefore, it appears

this could also be associated with a range of potentially promising to turn to further analysis methods, which not only

confounded variables like factors mentioned above or reactive focus on mere activation differences but allow for the

psychopathological characteristics. Some studies already col- investigation of network characteristics and connectivity.

lected respective control groups and this practice should Exploration of correlations with real world behaviour: It is

certainly be maintained whenever possible. known that forensic populations tend to be not very accurate in

Control for aspects of sexual orientation: Important character- reporting their preferences or behavioural tendencies. It would

istics like gender orientation or the exclusivity of paedophilic be of high interest to investigate the prospective validity of

preference should be controlled for more thoroughly. This has neuroimaging measures to predict behaviour. This might be of

important implications for the reactivity to the employed particular relevance in the context of subjects with paedophilia

stimulus material in functional imaging studies as there might that have not yet offended as well as in samples that are on

be little differences in excitability and brain activity to stimuli of parole or ready to be released.

different age groups in non-exclusive paedophilic men. In the

sample of Ponseti et al. (2012) for example, 5 of 11 men attracted Taken together, the present evidence from brain lesion and

to girls as opposed to 2 of 13 men attracted to boys were neuroimaging studies in paedophilia is still in its infancy. Case

diagnosed with the non-exclusive type. Consequently, the reports point to the relevance of a number of regions, which are

authors observed more extended brain activation for the more likely to be implicated in behavioural control than in sexual

boys < men contrast as opposed to the girls < women contrast. preference. Furthermore, controlled neuroimaging studies show a

While it cannot be stated safely that this is due to the more heterogeneous picture and do not allow any ﬁrm conclusions to be

prevalent responsiveness to adults in the group attracted to drawn about the neurobiological mechanisms underlying paedo-

females, this remains a likely explanation. philic preference and behaviour. In fact, this is not very surprising

Control for differentiations given by forensic research: Sub- taking into account the small number of studies, the small sample

groups of paedophilia have been proposed based on clinical sizes, and the difﬁculty of performing such studies. However, even

presentation as given by the degree of ﬁxation to child sexual in the face of these complicating factors the existing reports have

attraction (Cohen and Galynker, 2002), mode of sexual offending shown some very encouraging results like a twofold replication of

22 S. Mohnke et al. / Progress in Neurobiology 122 (2014) 1–23

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