Etiology of psychopathy: Theories about the role of childhood maltreatment

Speculating about the etiology of psychopathy, Cleckley [1] tended more towards an organic origin, although not necessarily hereditary: “If an inborn biologic defect exists and plays an important part in such a psychopath’s disorder, it is not necessary to assume that the defect is hereditary. Perhaps it may be the result of a subtle failure in maturation, an agenesis of unknown etiology” (p. 412). Checkley also showed appreciation for the work of Karpman [15] who maintained that psychogenic factors are responsible for the majority of cases of psychopathy. For a psychoanalyst like Karpman [16], ‘psychogenic’ largely referred to so-called oedipal conflicts, although he was also attuned to the relevance of parental maltreatment and rejection in the etiology of ‘secondary psychopathy’, as he termed it. This secondary psychopathy should be distinguished from primary psychopathy which, according to Karpman [16], was present in only a minority of cases (15%; p. 487) in which an inborn or constitutional defect caused the disorder.

Although most mental health problems are likely the result of complex interactions between ‘innate’ and ‘acquired’ components [17], over the past decades research into psychopathy has been dominated by a focus on its genetic and neurobiological underpinnings (e.g., [18–20]). Hare’s view that the disorder has a neurobiological and/or genetic origin and is therefore basically untreatable [21–23] had a notable impact on this. Recently, Frazier and colleagues [20] provided cogent criticism on this disbalance in the psychopathy research literature. They demonstrated that developmental research has consistently shown that children exposed to neglect, abuse, and other types of childhood maltreatment (CM) exhibit many of the same neurobiological abnormalities observed in adults with high scores on psychopathy [20]. A thorough review of this research literature is beyond the scope of the present paper. We will provide some recent examples from empirical studies that illustrate the complex nature of the association between CM and neurobiological functioning as it relates to the affective facet of psychopathy.

The affective facet of psychopathy has been shown to be related to a reduced psychophysiological response to negative emotional stimuli [24, 25] and suppression of neural activity and/or volume of the amygdalae [26–28], a limbic structure responsive to threatening stimuli. Interestingly, the effects of CM on amygdala responses may vary according to the type and timing of CM [29]: Amygdala responses to threatening stimuli were attenuated in adults reporting exposure to physical abuse between 3 and 6 years of age, but exacerbated in adults reporting exposure to emotional bullying at 13–15 years. The authors offer plausible explanations for these differential neuroplastic adaptations. Whereas a decreased fight-flight response may be adaptive for a child that is dependent on periodically physically abusive parents; for a teenager an increased fight-flight response may be more beneficial [30].

Recently, several scholars have returned to Karpman’s concept of secondary psychopathy [31] or acquired callousness [32], focusing on the experience of childhood psychological trauma. Earlier, Porter [33] had already provided an alternate causal pathway to the predominant view of a genetic predisposition to psychopathy of that time. He hypothesized that (secondary) psychopathy is the result of “‘de-activation’ or dissociation of a developing basic affective nature and conscience” (p. 183). This de-activation is viewed as a coping mechanism in response to traumatic interpersonal experiences. Porter [33] linked the affective blunting in psychopathy to the emotional numbing and feelings of detachment that are key diagnostic symptoms of Posttraumatic Stress Disorder (PTSD; [34]).

Other theoretical formulations, notably complex trauma [35] and Betrayal Trauma Theory (BTT; [36]) are also relevant in relation to the etiology of psychopathy. Complex trauma is defined as exposure to traumatic stressors at an age (e.g., early childhood) or in a context (e.g., prolonged torture or captivity) that compromises secure attachment with primary caregivers [37]. Complex trauma causes the organism to enter into “survival mode”, resulting in changes to many developing self-regulatory mechanisms [35], including: (a) attention and learning; (b) sensorimotor functions; (c) working (short-term processing), declarative (verbal) and narrative (autobiographical) memory; and (d) emotion regulation and social relatedness (attachment). BTT emphasizes the interpersonal context in which most early CM takes place, particularly intrafamilial abuse. Central to BTT is attachment theory, the notion that humans depend on others for physical survival and emotional responsiveness [38]. According to BTT, the degree to which the abuse represents a betrayal by the trusted and needed attachment figure mediates the way in which abuse-related information is processed and remembered [39]. Forgetting and misremembering of the abuse, as well as emotional dissociation, are hypothesized to be specifically linked to betrayal vs. other, nonbetrayal trauma [40].

In summary, there appears to be an increased interest in theoretical models that assign an etiological role to early CM in the development of psychopathy. Several theorists proposed models in which early maltreatment experiences, particularly those with primary caregivers, produce a blunted or dissociative response to stress, as a key factor in the affective deficits observed in psychopathy (e.g., [31, 32, 41]), whereas previously, the so-called ‘affective core’ of psychopathy was viewed as largely innate [23]. CM has also been linked to the type of externalizing symptoms represented by Factor 2 of psychopathy (e.g., [42]). If it can be demonstrated that environmental factors, such as CM, play a role in the development of psychopathy, these factors could be targeted for preventive efforts and treatment interventions.

Empirical studies about the role of childhood maltreatment in psychopathy

Research on the relationship between CM and psychopathology, including psychopathy, is mired by a number of methodological difficulties. Ideally, CM would be measured prospectively and objectively, before the onset of psychopathy. However, in studies of adults, CM is mostly measured through retrospective self-report, which can be biased in the form of memory errors of both omission and commission [43–45]. Other research designs use official Child Protection Services records, but these are likely to underestimate the true prevalence of maltreatment [43]. As best-evidence practice, CM would be established through triangulation, using official records, collateral informants, and self-report, but this type of rigor is still quite rare.

The first studies that explored the hypothesized link between CM and psychopathy were case studies conducted in the 1940s (e.g., [16, 46]). Weiler and Widom [47] performed one of the first prospective studies that used the PCL-R in a large sample of young adults (n = 652) and compared them with a control group, matched for demographics and criminal history (n = 489). The abused and neglected group was composed of substantiated cases of childhood physical and sexual abuse and/or neglect processed in the county juvenile or adult criminal court and the subjects were 11 years or younger at the time of receiving maltreatment. Abused/neglected individuals had statistically significantly higher PCL-R total scores than matched controls, regardless of gender or ethnicity. Lang et al. [48] attempted to replicate the Weiler and Widom study with a Swedish sample, comprised of 192 boys aged 11–14 years accused of property crimes and 95 boys, matched for age, family type (separated or not), social group and neighborhood. Child abuse and neglect was determined at age 11–14 by means of triangulation, using school and social work records, parent and child interviews and self-report. The sample was followed up at age 32–40. Mean PCL-R scores of the high victimization group were statistically significantly higher than those of the low victimization group. Notably, neither of these studies examined associations between the four PCL-R facets and CM.

Another early study into the association between CM and PCL psychopathy used a purely retrospective design in a Scottish prison sample [49]. Fifty psychopaths (Mean PCL-R = 29) and 55 nonpsychopaths (Mean PCL-R = 13) were administered the Childhood Experience of Care and Abuse interview (CECA; [50]). The CECA asks about specific experiences and events occurring in childhood as opposed to subjective feelings. The authors found statistically significantly higher scores in the psychopathic group compared to the nonpsychopathic group on parental discipline, parental antipathy, parental neglect, parental control, and psychological abuse. No differences were found for physical and sexual abuse. Using multiple regression analysis, Marshall and Cooke [49] found that victimization within the family statistically significantly predicted PCL-R Factor 1 scores, whereas societal adversity (school experience, school performance, institutional stay) was the main predictor of PCL-R Factor 2 scores. This was one of the first studies that showed a specific effect for childhood family trauma on the Affective-Interpersonal factor. However, a study that used a relatively similar design (a sample of 615 male American offenders, retrospective reports of child abuse/neglect and PCL-R rated psychopathy) did not replicate this finding [51]. Using the Cooke and Michie [10] 13-item model, these authors found a statistically significant association of CM with the behavioral lifestyle factor, but not with the affective and the interpersonal factors [51].

The present study

Given the current theoretical models and prior empirical research on the link between CM and psychopathy, we deemed it appropriate to conduct a meta-analysis of this literature. We chose to include both Hare PCL-derived scales and self-report instruments, which have been used most prominently in the field. We believed this would on the one hand cast the widest net in terms of allowing us to include a large number of studies, and on the other hand give us the possibility to gain insight into the link between the four facets of psychopathy and CM. We opted to include all types of CM, but did not include other indicators of childhood adversity, such as socioeconomic adversity or community violence, although we acknowledge that these may act as risk factors for antisocial and psychopathic behavior [57].

By conducting a meta-analysis of the existing research base, we aimed to find answers to the following questions:

1. 1. Is there a statistically significant association between any type of CM and psychopathy in general and as defined by its two factors and four facets?
2. 2. Do different types of CM (neglect vs. physical vs. sexual vs. emotional abuse) have similar associations with psychopathy and its factors and facets?

We were also interested in conducting several moderator analyses:

1. 3. Does gender (male vs. female) impact the link between psychopathy and CM?
2. 4. Does the psychopathy measure used (PCL-scale vs. other psychopathy measure) impact the link between psychopathy and CM?
3. 5. Does the type of publication (peer reviewed journal articles vs. grey literature) impact the link between psychopathy and CM?
4. 6. Does study design (prospective vs. retrospective) impact the link between psychopathy and CM?
5. 7. Does sample type (clinical/correctional vs. community) impact the link between psychopathy and CM?

Because there is currently no comprehensive theoretical framework on the relationships between specific types of CM and the different psychopathic traits, our meta-analysis is mostly exploratory. However, we did formulate a few specific hypotheses, which we believed could be supported by the current literature.

H1: Factor 1 is related to CM in general, and emotional abuse/neglect in specific, based on the ‘deactivation’ hypothesis (e.g., [33]) and prior research (e.g., [58]) showing that emotional abuse by attachment figures in childhood is likely mediated by neurocognitive adaptations that result in ‘blunted’ affective responsiveness to threat [33, 58]. Thus, we predict that childhood emotional abuse will relate most strongly to Factor 1 (including both the affective and the interpersonal facets).

H2: Factor 2 is related to CM in general, and physical abuse in specific, based on a large body of prior research (e.g., [42, 59]) that demonstrated that anger, impulsivity, and antisocial acting out are related to childhood physical abuse by attachment figures, likely mediated by neurocognitive changes that result in increased stress reactivity. We predict that childhood physical abuse will relate most strongly to Factor 2 (including both the lifestyle and the antisocial facets).

Protocol and open data

This meta-analysis was pre-registered on March 26, 2018, under the PROSPERO platform, an international prospective register of systematic reviews. The registration can be found on their webpage (https://www.crd.york.ac.uk/PROSPERO/) with the ID: CRD42018091678. Furthermore, the raw data are accessible under the Open Science Framework (OSF; https://osf.io/2kqcw/).

Inclusion criteria

Our variables of interest were psychopathy, measured by means of self-report or clinical judgment, and CM as defined by the World Health Organization (WHO):

Child maltreatment is the abuse and neglect that occurs to children under 18 years of age. It includes all types of physical and/or emotional ill-treatment, sexual abuse, neglect, negligence and commercial or other exploitation, which results in actual or potential harm to the child’s health, survival, development or dignity in the context of a relationship of responsibility, trust or power. Exposure to intimate partner violence is also sometimes included as a form of child maltreatment [60].

The following criteria were used to include studies: (1) peer-reviewed articles, grey literature, book chapters/books and dissertations; (2) prospective and retrospective studies; (3) studies reported in the English language. Studies needed to include: (1) community, clinical, or correctional samples of children or adults (male and female) in which both CM and psychopathy were measured; (2) CM: physical abuse, emotional abuse, sexual abuse, and neglect, measured by means of self-report and/or official reports; (3) psychopathy measured by means of self-report or clinician rated scales.

Exclusion criteria

We excluded: (1) single-case studies, conference abstracts without primary study data, book reviews; (2) papers not written in English; (3) studies which focused on childhood adversities outside the family or primary caretaking environment, such as war trauma or community violence; (4) studies on other types of childhood adversity, such as loss of a parent or serious accidental injury, or traumatic experiences after age 18; and (5) studies without an objective measure of psychopathy.

Unlike initially specified in our PROSPERO registration, studies that focused solely on callous-unemotional (CU) traits were excluded from the current review. This decision was made as the number of located articles investigating psychopathy exceeded our expectation so that the inclusion of CU traits would only add heterogeneity to the synthesis of effect sizes.

Literature search

Consistent with the Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines (PRISMA; [61]), a systematic literature search of papers published between January 1990 and January 2021 was conducted. The year 1990 was chosen because the first validation study of Hare’s revised version of the Psychopathy Checklist (PCL-R; [62]) was published in 1990. The first search was conducted in February 2018 on PsycINFO, PubMed, and Web of Science and subsequently updated in January 2021. The following keywords were used: (trauma* OR complex trauma* OR childhood trauma* OR abus* OR adverse childhood experience+ OR neglect OR maltreatment OR betrayal trauma) AND (psychopath+ OR psychopathic OR psychopathy OR callous unemotional trait+ OR CU trait+ OR CU-trait+ OR ODD OR CD OR conduct disorder+ OR oppositional defiant disorder+ OR PCL* OR antisocial OR dissocial).

To identify all potential and ongoing research, the project was uploaded to ResearchGate (https://www.researchgate.net/project/The-link-between-childhood-trauma-and-psychopathy-A-systematic-review). Additionally, researchers who had previously conducted research on psychopathy were contacted via email. Covidence software (www.covidence.org) was utilized to aid the process of the systematic review management and collaboration.

Study selection

The screening process was conducted in two stages. At each stage, two members of the research team independently assessed whether a publication should be included or excluded for further analysis. A consensus was reached if both assessors agreed on the inclusion or exclusion of the publication. Conflicts were resolved by the first author (CdR). Initially, studies were screened for eligibility by examining their title and abstract. Subsequently, eligible studies were assessed via full text screening. A number of dissertations and grey literature that could not be accessed from open sources were retrieved by contacting the University library in which the dissertation was defended or by contacting the authors through LinkedIn or other social media.

Data collection

The following information was retrieved from all studies that met the aforementioned inclusion criteria: type of publication; sample type; sample mean age and standard deviation; sample sex distribution; country of study; total sample size; CM measure; and psychopathy measure. On occasion, not all of the above data could be obtained from the text. In such instances, the corresponding author of the paper was contacted for necessary information. Data extraction per study was always carried out by a pair of authors who had to be in agreement. Effect size extraction was conducted by the second author (MB).

Summary measure

The Pearson product-moment correlation coefficient r was chosen as the effect size index because most studies reported correlational data to quantify the association between CM and psychopathy. If possible, coefficients were extracted directly from zero-order correlation matrices. Missing effect sizes were acquired either by contacting the corresponding authors or by estimating their magnitude from statistical information provided in the paper, such as t-statistics or d values [63]. For three studies [64–66], correlation coefficients had to be imputed from standardized regression coefficients using the equation r = .98β + .05λ, where λ equals 0 when β is negative and 1 when β is positive [67].

Given that each paper could report more than one effect size, the following approach was used to ensure independence among effect sizes [68]: (1) if a study reported data on two distinct samples (e.g., for men and women), the effect sizes were considered independent rather than combined into a composite effect size; (2) in cases where an author published multiple manuscripts, but used samples that were clearly drawn from the same population, only the study with the largest sample was included; (3) if applicable, separate effect sizes for general maltreatment, physical abuse, emotional abuse, sexual abuse, and physical and emotional neglect were derived from the same paper; (4) similarly, effect sizes for psychopathy total scores as well as for psychopathy factors and facets were extracted; and (5) composite effect sizes for psychopathy were calculated following the recommendations of Borenstein et al. [68] when multiple psychopathy measures were used or when estimates were only reported for psychopathy factors.

In an attempt to address the attenuation of correlation coefficients caused by measurement error [69], additional corrected effect sizes and variances were computed. The required reliability estimates were retrieved from the included articles, or if the information was lacking, they were imputed using the Mice package in R by averaging the results of five imputed data sets [70].

Meta-analysis

Because the distribution of correlation coefficients tends to be skewed in studies with a small sample size [71], the raw effect sizes were first transformed into Fisher’s z. All analyses were carried out using the transformed values, but were subsequently transformed back to correlation coefficients for presentation of the results. In addition, as studies were expected to vary fundamentally, random-effects models were chosen to calculate the average summary effect sizes [68]. The between-study variance τ² was estimated with restricted maximum likelihood method (REML) and used to assign weights to each study by the inverse of total variance: . Simulations have shown that REML tends to be less biased than other popular methods [72]. While τ² reflects the variance of true effects in absolute terms, I² was examined to quantify the relative amount of true heterogeneity among the total variability across studies. By convention, I² values of 25%, 50%, and 75% respectively indicate low, moderate, and high levels of inconsistency in a meta-analysis [73].

Five separate meta-analyses were performed, for general maltreatment, physical abuse, emotional abuse, sexual abuse, and neglect. Moreover, a priori specified moderator analyses were conducted to determine whether the association between CM and psychopathy differed by (1) proportion of women in the sample; (2) type of sample (clinical/correctional vs. community sample); (3) psychopathy measure (PCL-scale vs. other psychopathy measure); and (4) type of publication (journal article vs. grey literature). Mixed-effect meta-regression models were fitted with categorical moderators included as dummy variables and the proportion of women as a continuous variable (ranging from 0 to 100%).

Given the multifaceted structure of psychopathy [74], additional subgroup analyses were carried out to examine whether the summary effect sizes vary across psychopathy factors and facets (i.e., affective, interpersonal, lifestyle, and antisocial). That is, each factor/facet was included as a subgroup and tested for between-group differences (H₀: r_factor1 = r_factor2 and H₀: r_affective = r_{interpersonal} = r_lifestyle = r_antisocial; [75]). Statistically significant differences between psychopathy facets were then further investigated with post-hoc analyses contrasting r_affective vs. r_lifestyle; r_affective vs. r_antisocial; r_{interpersonal} vs. r_lifestyle; r_{interpersonal} vs. r_antisocial. Because most studies reported effect sizes for the two factors and/or four facets, three-level random effects models were used. Multi-level meta-analyses allow for dependencies among effect sizes by breaking τ² down into the variance within samples (σ²_level2) and the variance between samples (σ²_level3; [76]).

To test the robustness of the results, included studies were assessed for influential effect sizes by the inspection of multiple influence measures (DIFFITS, Cook’s distance, covariance ratio) generated by the leave-one-out method [77]. Subsequent sensitivity analyses were performed to determine whether the deletion of such influential cases would alter the overall findings of this meta-analysis. If not, the results can be considered robust [77]. All analyses were performed with the metafor package [78] in the latest version of R 4.0.3 [79].

Publication bias

As with any meta-analysis, publication bias poses a risk to the interpretability of the pooled effect size [80]. Therefore, its presence and impact were examined in three ways. First, funnel plots were created and inspected visually for asymmetry. An asymmetrical distribution of studies across the mean effect size may suggest publication bias [81]. Second, Egger’s linear regression method was used to test for a linear relationship between the effect size and its standard error, which provides a less subjective measure of asymmetry in a funnel plot [82]. Third, Duval and Tweedie’s Trim and Fill method was applied to estimate an unbiased summary effect size by imputing missing effect sizes [83]. This approach allows one to quantify the impact of reporting bias on the observed result [84].

Descriptive results

Fig 1 provides a visual outline of the study selection process. Our literature search generated 28,368 papers. Subsequently, 5,920 duplicates were removed. The remaining 22,448 papers entered the title and abstract screening stage, in which 22,208 were excluded in accordance with the inclusion and exclusion criteria specified in the Method section. A total of 240 papers entered the full text screening stage, in which 193 were excluded. The reasons for exclusion were the following: The association between primary variables of interest was not explored (n = 124), full text not available (n = 31), not a primary study (n = 23), contains duplicate data (n = 9), insufficient statistical information to calculate effect size (n = 4), full text not in English (n = 1), and single case study (n = 1). The final sample included in the meta-analysis comprised 55 independent samples and a total of 389 effect sizes originating from 47 papers.

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Fig 1. PRISMA flowchart showing the study selection process.

https://doi.org/10.1371/journal.pone.0272704.g001

Meta-analytical results

Statistically significant positive associations were found between all five types of CM and the total psychopathy score. The pooled effect size for sexual abuse was smaller than for the other four types of maltreatment, but still statistically significant. Heterogeneity between studies was moderate to high. After excluding influential studies, effect sizes increased slightly and heterogeneity decreased considerably. The results are presented in Table 1. Corresponding figures, such as forest plots (S1–S5 Figs) and funnel plots (S6 Fig) can be found in our supporting material. In addition, we tested a multi-level model in which all effect sizes were included simultaneously (instead of five separate meta-analyses). Because this model yielded similar results, these are reported only in the S2 Table.

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Table 1. Meta-analytical results of the association between childhood maltreatment and psychopathy.

https://doi.org/10.1371/journal.pone.0272704.t001

Correction for attenuation

Fitting the meta-analytical models with correlation coefficients corrected for attenuation produced only negligibly larger pooled effect sizes, with r_c = .24 (95% CI [.19, .28]), r_c = .22 (95% CI [.18, .26]), r_c = .17 (95% CI [.11, .23]), r_c = .11 (95% CI [.07, .15]), and r_c = .26 (95% CI [.19, .33]) for general maltreatment, physical abuse, emotional abuse, sexual abuse, and neglect, respectively.

Moderator analyses

The proportion of women in a sample, the type of psychopathy measure used (i.e., PCL-scale vs. other), and the type of publication (i.e., peer-reviewed journal article vs. grey literature) did not statistically significantly moderate the association between CM and psychopathy. The type of sample (i.e., clinical/correctional vs. community), on the other hand, revealed evidence for moderation (Q(1) = 6.50, p = .0108). Clinical and correctional samples showed smaller, but still statistically significant, positive associations between general maltreatment and psychopathy (Clinical/Correctional: r = .17 [.12, .21]) compared to community samples (Community: r = .26 [.20, .31]). The moderator analysis for prospective vs. retrospective studies of CM could not be carried out due to a lack of prospective studies.

Analyses for the four facets and two factors of psychopathy

Analyses on the facets and factors of psychopathy were conducted on a limited set of studies (facets: k between 9 and 11; factors: k between 2 and 7). For the psychopathy facets, the three-level random effects models revealed different patterns for the different types of CM (Table 2). General maltreatment, physical abuse, and neglect showed statistically significant associations with all four facets, although of different magnitudes. Emotional abuse and sexual abuse were statistically significantly correlated with some, but not with all of the four psychopathy facets. Statistically significant between-group differences across facets were found for general maltreatment, physical abuse, and emotional abuse. Subsequent post-hoc analyses indicated a stronger relationship between CM and the lifestyle and antisocial facets compared to the affective and interpersonal facets. These findings are presented in Table 2.

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Table 2. Between-group differences among psychopathy facets by each type of childhood maltreatment.

https://doi.org/10.1371/journal.pone.0272704.t002

Similar results were found for the two psychopathy factors. All types of CM showed larger effect sizes for Factor 2 than for Factor 1. However, given the low power due to the limited number of studies, differences between the two factors were statistically significant only for general maltreatment and sexual abuse (Table 3).

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Table 3. Between-group differences among psychopathy factors by each type of childhood maltreatment.

https://doi.org/10.1371/journal.pone.0272704.t003

Publication bias

The visual inspection of funnel plots provided no indication of asymmetry (S6 Fig). This was corroborated by statistically nonsignificant Egger’s regression tests for all types of CM. Furthermore, Duval and Tweedie’s Trim and Fill method imputed missing studies for physical abuse (k = 1), sexual abuse (k = 6), and neglect (k = 2) (S6 Fig), resulting in slightly larger unbiased pooled effect sizes: r_unbiased = .19 (95% CI [.15, .22]), r_unbiased = .12 (95% CI [.08, .17]), and r_unbiased = .23 (95% CI [.17, .28]), respectively. Overall, these results speak against the presence of publication bias.

Implications for theory and clinical practice

The present meta-analysis provides support for a moderate link between psychopathy and childhood physical abuse, emotional abuse, and neglect, as well as overall CM. The link between psychopathy and childhood sexual abuse is small. These associations are stronger for the lifestyle and antisocial facets than for the affective and interpersonal facets of psychopathy, but nearly all associations are statistically significant. Our findings are in line with theories of the impact of complex trauma [35] and BTT [36] on the development of serious personality pathology, although most previous theorizing and empirical research have focused on Borderline Personality Disorder (for a review, see [117]) and not psychopathy. An exception to this is a recent study by Yalch and Levendosky [118] who found that exposure to trauma high in betrayal was the only predictor of the vulnerable and grandiose dimensions of pathological narcissism in a college student sample, after controlling for other forms of (nonbetrayal) trauma exposure. The authors suggest “that not only does exposure to high betrayal trauma inflict a psychological wound (narcissistic vulnerability), but also that it influences the means by which people defend against that wound (narcissistic grandiosity)” [118]. Narcissistic grandiosity resembles the interpersonal facet of psychopathy.

During the past decade, researchers have become increasingly aware of the importance of CM as a risk factor for psychopathology generally (for recent reviews, see for example: [30, 119]). The notion that CM causes phenotypic alterations to the developing brain [120, 121], which are subsequently impacted by further epigenetic and developmental changes, is starting to impact psychiatric nosology [30]. In recent years, new diagnostic classifications, such as developmental trauma disorder [122] and complex PTSD [123, 124] have been developed. Teicher [30] is highly optimistic that revising the DSM to acknowledge the critical role of CM “would be a quantum step forward in the development of an etiologically informed classification system” (p. 5). The current psychiatric classification system focuses entirely on symptoms without regard to etiology, pathophysiology, or theory, which results in pathophysiologically heterogeneous disorders with similar clinical presentations being considered as unitary disorders. At the very least, the statistically significant association between CM and psychopathology should prompt mental health professionals to include trauma-informed assessment and treatment in their standards of (forensic) clinical practice [125, 126].

Recently, McCrory and colleagues [127] reviewed the existing functional neuroimaging research of children and adolescents exposed to maltreatment across four neurocognitive domains: threat processing, reward processing, emotion regulation, and executive control. They discussed these findings within the context of their “theory of latent vulnerability”, which conceptualizes the link between childhood maltreatment and risk of mental disorder across development [128]. According to this theory, maltreatment results in measurable alterations in several neurobiological systems that reflect adaptation to early abusive environments. In principle, these adaptations are often beneficial within the early adverse environment, but they are thought to incur long term disadvantages as they may mean that the individual is poorly equipped to adapt to more normative environments. Studies on processing of threatening stimuli show increased as well as decreased neural responsiveness in maltreated samples, particularly in the amygdala, thought to reflect hypervigilance and avoidance, respectively. Studies on reward processing report diminished neural responsiveness to anticipation and rewards, especially in the striatum. Research on emotion regulation reports increased activation of the anterior cingulate cortex (ACC) during active emotion regulation, possibly reflecting greater effortful processing. Finally, studies of executive control, although limited in number, report increased dorsal ACC activity during error monitoring and inhibition. All of these neurobiological systems have also been implicated in the development of psychopathic traits [129]. Future research into the neurobiological underpinnings of psychopathic traits should include assessment of childhood maltreatment, preferably using prospective and objective measures of maltreatment, such as records from child protection services, to avoid a premature conclusion on the ‘innateness’ of certain psychopathic traits [20].

The view that at least some of the signature features of psychopathy can be seen as responses to complex or betrayal trauma, that is, repeated incidents of maltreatment over an extended period of time (i.e., months or years) which includes emotional abuse, physical abuse, neglect, and/or witnessing family violence within the caregiver system, provides further direction for preventive and therapeutic efforts. Therapeutic interventions that focus on early childhood trauma can provide a test of the causal role of trauma, if it could be shown that processing of traumatic experiences leads to meaningful reductions in psychopathic traits.

Several trauma-focused treatment interventions for psychopathy have been developed: Dialectical Behavior Therapy for psychopathy [130] and Schema Therapy (ST) for forensic patients with personality disorders, including psychopathy [131]. Controlled effectiveness studies of these therapy models have not yet been published, but a single case study documented the process of individual ST in a Dutch forensic patient with psychopathic traits [132]. This patient had been a victim of extreme physical and emotional abuse as a child and the therapist used different ST techniques (e.g., limited reparenting, experiential techniques) to alter the patient’s maladaptive schema modes. The case study also showed the patient’s PCL-R total score changed from 27 at baseline to 14 after four years of intensive ST. Remarkably, the Affective facet showed the largest change: from 7 to 1; the Interpersonal facet decreased from 4 to 1. This finding, although just an N = 1 result, challenges the notion that affective and interpersonal features of psychopathy are immutable ([133]; see [134] for further argumentation).

Limitations

The findings of this systematic and meta-analytic review should be considered in light of a number of limitations. First and foremost, correlational analyses, such as those conducted in this meta-analysis, cannot be used to prove causality. Shadish, Cook, and Campbell [135] summarized John Stuart Mill’s three criteria for inferring causality: “A causal relationship exists if (1) the cause preceded the effect, (2) the cause was related to the effect, and (3) we can find no plausible alternative explanation for the effect other than the cause” (p. 6). Thus, the clearest evidence for a causal relationship comes from experimental rather than correlational research. From a strictly methodological standpoint, none of the studies included in our meta-analysis, not even those that used prospective measures of CM, such as child protection data, fulfill all of the three criteria. Potentially confounding variables were not included in most studies. A majority of the studies used a cross-sectional design in which psychopathic offenders retrospectively reported more childhood abuse than nonpsychopathic offenders. We cannot rule out the alternative hypothesis, that psychopathy caused CM because there is a possibility that psychopathic traits may have caused these individuals to retrospectively report higher rates of CM. The latter effect is generally referred to as ‘recall bias’ [136]. It occurs when the accuracy and inaccuracy in reporting prior experiences vary as a function of present (physical or psychological) health conditions. “One process believed to underlie the differential reporting accuracy is ‘effort after meaning,’ where unhealthy individuals exert more effort to search for disease explanation and assign more meaning to past events” [136]. Thus, people with psychopathic traits could attribute their problems in life to CM.

Second, the operationalization of CM varied greatly from study to study. In addition to different assessment measures, researchers also used diverse definitions of different types of CM. It would greatly benefit this field of study if scholars would agree on the operational definitions of the different types of CM. Perhaps, the definition of CM by the World Health Organization [137] could serve as a starting point. The 1999 WHO Consultation Group on Child Abuse Prevention distinguish four types of CM: physical abuse, emotional (or psychological) abuse, neglect, and sexual abuse. Recently, exposure to domestic violence has also been recognized as a separate form of CM by the WHO [137]. Additionally, the context of CM should be clearly operationalized in future studies because present day theories [e.g., 35] clearly distinguish between the psychological consequences of (chronic) maltreatment by primary caregivers versus other maltreatment of children (e.g., a single incident of sexual abuse by a stranger).

Third, although we managed to retrieve studies from six continents, samples from Western countries were clearly overrepresented in our meta-analysis. This has very likely impacted the findings, because the two variables we studied, psychopathy and CM, are not impervious to ethnic and cultural factors. A recent review of cultural and ethnic variations in psychopathy [138] concluded that there is evidence for ethnic differences in total psychopathy and facet scores, for instance, between African American and European American prisoners, as well as differential responding in laboratory tasks of emotional and cognitive processing between these groups. Thus, ethnic differences may exist in the way psychopathy manifests itself and its underlying mechanisms, possibly including its etiology. Furthermore, what is considered CM varies according to socially accepted norms, which are heavily influenced by culture. Certain parenting styles, such as corporal punishment, are viewed as inappropriate in some cultures, but are accepted and even promoted in others [139, 140]. Additionally, opinions about what constitutes child abuse have been found to differ amongst cultures (e.g., [141–143]). How cultural and ethnic factors shape the relationship between CM and psychopathic traits warrants further study.

Fourth, it should be noted that our results on the psychopathy factors and facets are limited to psychopathic traits as defined by Hare’s PCL-scales. Analyses on other psychopathy models could not be conducted due to a paucity of studies. Future research needs to examine how more novel models of psychopathy, such as the triarchic model, relate to CM [144–146].

Finally, some of our summary effect sizes, while statistically significant, are small in magnitude (i.e., sexual abuse). Small effects are to be expected for complex psychological constructs such as psychopathy and are not necessarily a limitation of this meta-analysis [95]. However, the issue of how to estimate the value of effect sizes is long debated, and scholars such as Robert Rosenthal [147] have convincingly argued that although the effect size is mathematically determined by characteristics of the study design and results, the interpretation of its real-life implications would depend upon the context (e.g., [148]) and the nature of the dependent variable. If childhood maltreatment is related to the development of psychopathic traits, even to a small extent, this is highly relevant information. The real-world implications of our findings are that prevention of childhood maltreatment could lead to a reduction of psychopathic traits, which in turn would lead to a reduction in antisocial and violent behavior in society at large.