Increased cardiac vagal tone in childhood-only, adolescent-only, and persistently antisocial teenagers: the mediating role of low heart rate.

BACKGROUND: Cardiac vagal tone is an indicator of parasympathetic nervous system functioning, and there is increasing interest in its relation to antisocial behavior. It is unclear however whether antisocial individuals are characterized by increased or decreased vagal tone, and whether increased vagal tone is the source of the low heart rate frequently reported in antisocial populations. METHODS: Participants consisted of four groups of community-dwelling adolescent boys aged 15.7 years: (1) controls, (2) childhood-only antisocial, (3) adolescent-only antisocial, and (4) persistently antisocial. Heart rate and vagal tone were assessed in three different conditions: rest, cognitive stressor, and social stressor. RESULTS: All three antisocial groups had both lower resting heart rates and increased vagal tone compared to the low antisocial controls across all three conditions. Low heart rate partially mediated the relationship between vagal tone and antisocial behavior. CONCLUSIONS: Results indicate that increased vagal tone and reduced heart rate are relatively broad risk factors for different developmental forms of antisocial behavior. Findings are the first to implicate vagal tone as an explanatory factor in understanding heart rate - antisocial behavior relationships. Future experimental work using non-invasive vagus nerve stimulation or heart rate variability biofeedback is needed to more systematically evaluate this conclusion.

Callous-unemotional traits, cognitive functioning, and externalizing problems in a propensity-matched sample from the ABCD study.

BACKGROUND: Many studies show that both callous-unemotional (CU) traits (e.g., low empathy, lack of guilt) and cognitive difficulties increase risk for externalizing psychopathology across development. However, other work suggests that some aggression (e.g., relational, proactive) may rely on intact cognitive function, which could vary based on the presence of CU traits. Moreover, no prior research has adequately accounted for common risk factors shared by CU traits, cognitive difficulties, and externalizing problems, which confounds conclusions that can be drawn about their purported relationships. The current study addressed these knowledge gaps by leveraging rigorous propensity matching methods to isolate associations between CU traits and different dimensions of cognitive function and externalizing problems. METHODS: Associations between CU traits, cognitive functioning, and externalizing outcomes were tested within dimensional (n = 11,868) and propensity-matched group-based (n = 1,224) models using data from the Adolescent Brain Cognitive Development Study®, with rigorous statistical control for shared sociodemographic risk factors. Cross-sectional outcomes were parent-reported symptoms of conduct disorder (CD), oppositional defiant disorder (ODD), and attention deficit hyperactivity disorder (ADHD). Longitudinal outcomes were child-reported overt and relational aggression. RESULTS: CU traits were uniquely related to more parent-reported CD, ODD, ADHD symptoms, as well as more child-reported aggressive behaviors. Effects of cognitive difficulties were domain specific and were not consistent across dimensional and propensity matched models. There was minimal evidence for divergent associations between CU traits and externalizing outcomes as a function of cognition (i.e., no moderation). CONCLUSIONS: Rigorous control for sociodemographic factors within propensity-matched models establish CU traits as a robust and unique risk factor for externalizing psychopathology, over and above difficulties with cognitive functioning.

P-Factor(s) for Youth Psychopathology Across Informants and Models in 24 Societies.

OBJECTIVE: Although the significance of the general factor of psychopathology (p) is being increasingly recognized, it remains unclear how to best operationalize and measure p. To test variations in the operationalizations of p and make practical recommendations for its assessment, we compared p-factor scores derived from four models. METHODS: We compared p scores derived from principal axis (Model 1), hierarchical factor (Model 2), and bifactor (Model 3) analyses, plus a Total Problem score (sum of unit-weighted ratings of all problem items; Model 4) for parent- and self-rated youth psychopathology from 24 societies. Separately for each sample, we fitted the models to parent-ratings on the Child Behavior Checklist for Ages 6-18 (CBCL/6-18) and self-ratings on the Youth Self-Report (YSR) for 25,643 11-18-year-olds. Separately for each sample, we computed correlations between p-scores obtained for each pair of models, cross-informant correlations between p-scores for each model, and Q-correlations between mean item x p-score correlations for each pair of models. RESULTS: Results were similar for all models, as indicated by correlations of .973-.994 between p-scores for Models 1-4, plus similar cross-informant correlations between CBCL/6-18 and YSR Model 1-4 p-scores. Item x p correlations had similar rank orders between Models 1-4, as indicated by Q correlations of .957-.993. CONCLUSIONS: The similar results obtained for Models 1-4 argue for using the simplest model - the unit-weighted Total Problem score - to measure p for clinical and research assessment of youth psychopathology. Practical methods for measuring p may advance the field toward transdiagnostic patterns of problems.

Omega-3 supplementation reduces aggressive behavior: A meta-analytic review of randomized controlled trials.

There is increasing interest in the use of omega-3 supplements to reduce aggressive behavior. This meta-analysis summarizes findings from 28 RCTs (randomized controlled trials) on omega-3 supplementation to reduce aggression, yielding 35 independent samples with a total of 3,918 participants. Three analyses were conducted where the unit of analysis was independent samples, independent studies, and independent laboratories. Significant effect sizes were observed for all three analyses (g = .16, .20, .28 respectively), averaging .22, in the direction of omega-3 supplementation reducing aggression. There was no evidence of publication bias, and sensitivity analyses confirmed findings. Moderator analyses were largely non-significant, indicating that beneficial effects are obtained across age, gender, recruitment sample, diagnoses, treatment duration, and dosage. Omega-3 also reduced both reactive and proactive forms of aggression, particularly with respect to self-reports (g = .27 and .20 respectively). It is concluded that there is now sufficient evidence to begin to implement omega-3 supplementation to reduce aggression in children and adults - irrespective of whether the setting is the community, the clinic, or the criminal justice system.

High resting heart rate protects against the intergenerational transmission of antisocial behavior: a birth cohort study.

Although social influences have been identified that protect against the intergenerational transmission of antisocial behavior, there has been no prior research on biological protective factors. This study examines whether high resting heart rate may be one such factor. Resting heart rate was measured in 405 children of parents from a birth cohort, together with antisocial behavior in both the parent and the child. Children who were not antisocial, but had a parent high on antisocial behavior, had higher resting heart rates than all three other parent-child antisocial behavior groupings. Results withstood control for age, gender, ethnicity, body mass index, and psychosocial adversity. Robustness checks confirmed these results. Findings are the first to identify a biological protective factor against the intergenerational transmission of childhood antisocial behavior.

Blood lead levels mediate the relationship between social adversity and child externalizing behavior.

BACKGROUND/AIMS: The association between social adversity and externalizing behavioral problems in children is well-documented. What is much less researched are biological mechanisms that may mediate such relationships. This study examines the hypothesis that low blood lead mediates the relationship between social adversity and child externalizing behavior problems. METHODS: In this cross-sectional study, participants were 131 children aged 11-12 years (mean = 11.90) from Philadelphia, US. A venous fasting blood sample was taken and analyzed for blood lead levels. A social adversity index was calculated based on 10 total indicators derived from a psychosocial interview of the parent and official neighborhood data, while child behavior outcomes (internalizing and externalizing behavior) were assessed using both parent-report and child self-report. RESULTS: The mean blood lead level was 2.20 µg/dL. Both relatively higher blood lead levels and higher social adversity scores were associated with higher levels of parent-reported and child self-reported externalizing behaviors. Additionally, blood lead mediated the relationship between social adversity and child-reported externalizing behavior (Indirect effect: B = 0.03, 95% CI: 0.004, 0.09) and partially mediated the relationship between social adversity and parent-reported externalizing behavior (Indirect Effect: B = 0.03, 95% CI: 0.01, 0.07). CONCLUSION: To our knowledge, this study is the first to suggest that blood lead levels play a mediating role in the relationship between externalizing behavior problems and social adversity. Findings have potentially important implications for public health and environmental regulation as well as understanding biological mechanisms that link social inequality with health outcomes, especially in youth from low-income, urban areas.

Lower dietary intake of magnesium is associated with more callous-unemotional traits in children.

BACKGROUND: Although researchers increasingly recognize the role of nutrition in mental health, little research has examined specific micronutrient intake in relation to antisocial behavior and callous-unemotional (CU) traits in children. Vitamin B6 and magnesium are involved in neurochemical processes implicated in modulating antisocial behavior and CU traits. The current study examined dietary intakes of magnesium and vitamin B6 in relation to antisocial behavior and CU traits. METHOD: : We enrolled 11-12 year old children (n = 446, mean age = 11.9 years) participating in the Healthy Brains and Behavior Study. Magnesium and vitamin B6 dietary intake were assessed with three 24-hour dietary recall interviews in children. CU traits and antisocial behavior were assessed by caregiver-reported questionnaires. We controlled for age, sex, race, total energy intake, body mass index, social adversity, ADHD or learning disability diagnosis, and internalizing behavior in all regression analyses. RESULTS: Children with lower magnesium intake had higher levels of CU traits, controlling for covariates (ß = -0.18, B = -0.0066, SE = 0.0027, p < 0.05). Vitamin B6 intake was not significantly associated with CU traits (ß = 0.061, B = 0.19, SE = 0.20, p > 0.05). Neither magnesium (ß = 0.014, B = 0.0020, SE = 0.0093, p > 0.05) nor vitamin B6 (ß = 0.025, B = 0.33, SE = 0.70, p > 0.05) were significantly associated with antisocial behavior. CONCLUSIONS: Findings suggest that low dietary intake of magnesium may play a role in the etiology of CU traits but not general antisocial behavior. More studies are needed to determine if magnesium supplementation or diets higher in magnesium could improve CU traits in children.

Pursuing the developmental aims of the triarchic model of psychopathy: Creation and validation of triarchic scales for use in the USC: RFAB longitudinal twin project.

The triarchic model was advanced as an integrative, trait-based framework for investigating psychopathy using different assessment methods and across developmental periods. Recent research has shown that the triarchic traits of boldness, meanness, and disinhibition can be operationalized effectively in youth, but longitudinal research is needed to realize the model's potential to advance developmental understanding of psychopathy. We report on the creation and validation of scale measures of the triarchic traits using questionnaire items available in the University of Southern California Risk Factors for Antisocial Behavior (RFAB) project, a large-scale longitudinal study of the development of antisocial behavior that includes measures from multiple modalities (self-report, informant rating, clinical-diagnostic, task-behavioral, physiological). Using a construct-rating and psychometric refinement approach, we developed triarchic scales that showed acceptable reliability, expected intercorrelations, and good temporal stability. The scales showed theory-consistent relations with external criteria including measures of psychopathy, internalizing/externalizing psychopathology, antisocial behavior, and substance use. Findings demonstrate the viability of measuring triarchic traits in the RFAB sample, extend the known nomological network of these traits into the developmental realm, and provide a foundation for follow-up studies examining the etiology of psychopathic traits and their relations with multimodal measures of cognitive-affective function and proneness to clinical problems.

The Cognitive, Affective and Somatic Empathy Scales for Adults.

The Cognitive, Affective and Somatic Empathy Scales (CASES) assess three forms of empathy, each with subscales for positive and negative empathy. The present study extends this child instrument to adults and examines its factor structure and construct validity. A secondary aim is to investigate the under-researched area of positive empathy. Community samples totaling 2,604 adults completed the CASES for adults, together with scales assessing construct validity. Confirmatory factor analysis supported the three-factor cognitive-affective-somatic model and a two-factor positive-negative empathy model. Findings were replicated in a second independent sample. Internal reliabilities ranged from .80 to .92. Individuals with higher psychopathy and stimulation-seeking scores were less impaired in their empathic reactions to positive relative to negative valence events, suggesting that they are relatively capable of responding emotionally to rewarding events. Somatic empathy was most strongly associated with pleasure in affective touch and with female > male gender differences. While proactive aggression was associated with reduced cognitive and affective empathy, reactive aggression was associated with increased empathy. Findings provide initial support for the utility of CASES for assessing different forms of empathy and suggest that the balance between positive and negative empathy could provide new insights into psychological traits.

Developmental Trajectories of Delinquent and Aggressive Behavior: Evidence for Differential Heritability.

The developmental course of antisocial behavior is often described in terms of qualitatively distinct trajectories. However, the genetic etiology of various trajectories is not well understood. We examined heterogeneity in the development of delinquent and aggressive behavior in 1532 twin youth using four waves of data collection, spanning ages 9-10 to 16-18. A latent class growth analysis was used to uncover relevant subgroups. For delinquent behavior, three latent classes emerged: Non-Delinquent, Low-Level Delinquent, and Persistent Delinquent. Liability for persistent delinquency had a substantial genetic origin (heritability = 67%), whereas genetic influences were negligible for lower-risk subgroups. Three classes of aggressive behavior were identified: Non-Aggressive, Moderate, and High. Moderate heritability spanned the entire continuum of risk for aggressive behavior. Thus, there are differences between aggressive behavior and non-aggressive delinquency with respect to heterogeneity of etiology. We conclude that persistent delinquency represents an etiologically distinct class of rule-breaking with strong genetic roots.

A meta-analysis on shared and distinct neural correlates of the decision-making underlying altruistic and retaliatory punishment.

Individuals who violate social norms will most likely face social punishment sanctions. Those sanctions are based on different motivation aspects, depending on the context. Altruistic punishment occurs if punishment aims to re-establish the social norms even at cost for the punisher. Retaliatory punishment is driven by anger or spite and aims to harm the other. While neuroimaging research highlighted the neural networks supporting decision-making in both types of punishment in isolation, it remains unclear whether they rely on the same or distinct neural systems. We ran an activation likelihood estimation meta-analysis on functional magnetic resonance imaging data on 24 altruistic and 19 retaliatory punishment studies to investigate the neural correlates of decision-making underlying social punishment and whether altruistic and retaliatory punishments share similar brain networks. Social punishment reliably activated the bilateral insula, inferior frontal gyrus, midcingulate cortex (MCC), and superior and medial frontal gyri. This network largely overlapped with activation clusters found for altruistic punishment. However, retaliatory punishment revealed only one cluster in a posterior part of the MCC, which was not recruited in altruistic punishment. Our results support previous models on social punishment and highlight differential involvement of the MCC in altruistic and retaliatory punishments, reflecting the underlying different motivations.

Vitamin D sufficiency attenuates the effect of early social adversity on child antisocial behavior.

BACKGROUND: Vitamin D insufficiency and child antisocial behavior are public health concerns. It is unknown whether vitamin D plays a role in antisocial outcomes. This study examines whether higher levels of vitamin D can act as a protective factor against antisocial behavior for children who are exposed to early social adversity. METHODS: In a community sample of 300 children aged 11-12 years (151 females, 149 males), serum concentrations of 25-hydroxyvitamin D [25(OH)D] were assessed alongside early social adversity, and both parent and child-reported antisocial behavior. RESULTS: Vitamin D moderated the association between early social adversity and multiple antisocial outcomes. Higher social adversity was associated with greater antisocial behavior among vitamin D-insufficient [25(OH)D < 30 ng/mL], but not vitamin D-sufficient children [25(OH)D ⩾ 30 ng/mL], after adjusting for other variables. Results from child reports of antisocial behavior were replicated with parent reports, providing support for the robustness of the findings. At serum 25(OH)D concentrations above 27.16-30.69 ng/mL (close to 30 ng/mL, the recommended optimal vitamin D level for pediatric populations), the effect of social adversity on antisocial behavior outcomes was nullified. CONCLUSIONS: To our knowledge, this study is the first to document that a nutritional factor, vitamin D, can potentially confer resilience to antisocial behavior. Our findings in a pediatric population suggest a possible role of vitamin D supplementation in interventions to reduce antisocial behavior, which may be further investigated in future randomized controlled trials.

Omega-3 supplementation, child antisocial behavior, and psychopathic personality: a randomized, double-blind, placebo-controlled, stratified, parallel group trial.

While some RCTs have observed efficacy for omega-3 supplementation in reducing antisocial behavior, the role of psychopathic personality and gender in moderating treatment outcome has not been examined. This study examines whether omega-3 supplementation reduces antisocial behavior, and whether any treatment effects are a function of gender and psychopathy. Three hundred and twenty-four schoolchildren with a mean age of 11.9 years were randomized into 3 groups: omega-3 (N = 108), placebo (N = 110), and no-treatment controls (N = 106). Parent and child reports of child antisocial and aggressive behavior and psychopathic-like personality were collected at 0 months (baseline), 6 months (end of treatment), and 12 months (6 months post-treatment). A group × time × gender interaction (p = .016) indicated that only females in the omega-3 group showed a significant reduction in antisocial behavior 6 months post-treatment compared to baseline (d = .35), whereas the females in the two control groups showed no change over time. A group x time x psychopathy interaction (p < .006) was also observed, with psychopathic personality levels moderating treatment outcome. Children in the omega-3 group with high (but not low) psychopathic-like personality showed significant improvements in child-reported antisocial behavior at the end of treatment (d = .19) Results suggest that omega-3 supplementation may be helpful in reducing childhood antisocial and aggressive behavior in females, and those with psychopathic-like personalities.

The cognitive, affective, and somatic empathy scales (CASES): Cross-cultural replication and specificity to different forms of aggression and victimization.

A psychometrically sound measure of empathy that captures its multifaceted nature is critical in furthering research on empathy. The only instrument that assesses three domains of empathy together with positive and negative valence empathy is the newly developed 30-item cognitive, affective, and somatic empathy scales (CASES). The current study examines the cross-culture generalizability of CASES in Hong Kong and explores links between empathy and different forms of aggression and peer victimization. A sample of 4,676 Hong Kong youth (62% male) completed CASES, alongside measures of reactive/proactive aggression and multidimensional peer victimization. A subsample of youth (n = 2,321-2,464) and their parents completed additional instruments for testing the validity of CASES. We replicated most of the concurrent, convergent, and discriminant validity findings in the original development of CASES. Proactive aggression was most strongly linked to affective empathy, whereas reactive aggression was most strongly linked to somatic empathy. Differential associations were revealed between subscales of CASES and forms of peer victimization. Findings provide cross-cultural generalizability for a brief self-report instrument that captures the multifaceted nature of empathy. The multifaceted nature of empathy is further supported by differential associations with forms of aggression and victimization.

The relationship between resting heart rate and aggression in males is racially variant.

Although resting heart rate is thought to be a generalizable risk factor for aggression, very little research has examined whether this relationship varies by race. We addressed this limitation using longitudinal data from the Pittsburgh Youth Study. Current data are from 197 men who participated in a teenage biosocial study (mean age = 15.7 years) and adult follow-up study (mean age = 32.1 years). Teenage resting heart rate interacted with race to predict teenage and adult aggression. The relationship between heart rate and aggression was significant in White, but not in Black males. To our knowledge, this is the first study to find that the relationship between resting heart rate and aggression is racially variant, suggesting that resting heart rate may not be a generalizable biomarker for conduct problems. At an intervention-level, findings could contribute to the development of more accurate risk assessment tools that take into account racial variance in risk factors.

The utility of the Psychopathy Checklist-Revised (PCL-R) facet and item scores in predicting violent recidivism.

There is relatively limited research on psychopathy in non-Caucasian ethnic groups and even less on the utility of the Psychopathy Checklist-Revised (PCL-R) that focuses on PCL-R facet and item scores in predicting violent recidivism. In this study, we assessed the utility of the PCL-R in prospectively predicting violent versus nonviolent recidivism during an 11-year follow-up window. A high-risk sample of 451 incarcerated Korean male offenders was assessed on the PCL-R at baseline. A total of 445 were reconvicted after release (353 violent and 92 nonviolent recidivists). Psychopathy facet scores were higher in violent compared to nonviolent recidivists. Facet 2 (affective) showed the strongest effect size (Cohen's d = 0.53; Percentage change in odds = 22.6%) in predicting violent recidivism. Analyses of the four items constituting the affective facet indicated that callous/lack of empathy (Percentage change in odds = 134.4%) and failure to accept responsibility (Percentage change in odds = 94.5%) were the strongest predictors of violent recidivism. Findings are to our knowledge the first to document the utility of the PCL-R in distinguishing violent from nonviolent recidivism and highlight the role of affective impairment (particularly lack of empathy) in violent recidivism.

An Item Response Theory Analysis and Further Validation of the Reactive-Proactive Aggression Questionnaire (RPQ): The Serbian Adaptation of the RPQ.

The aim of this study was to further explore the psychometric properties of the Serbian adaptation of the Reactive-Proactive Aggression Questionnaire (RPQ) using item response theory to gain insight into measurement precision (information) and differential item functioning (DIF) across sexes. The sample consisted of 1,268 community-dwelling adults. Results confirmed a 2-factor structure and showed good reliabilities. Information of the reactive aggression scale covered a wider range of traits, but in the case of proactive aggression, it was limited in above-average and average levels of traits. Additionally, the impact of DIF on total scores was negligible. Furthermore, latent profile analysis showed that a clear proactive aggression profile could not be isolated, indicating that proactive aggression cooccurs with reactive aggression. However, both scales evidenced differential correlates. Reactive aggression was positively associated with anger and hostility and was negatively associated with agreeableness and forgiveness, whereas proactive aggression was positively related to indirect aggression and negatively to honesty-humility and emotionality. Taken together, although information for the proactive aggression scale is problematic, results overall support the 2-factor model of the RPQ and unbiased scale scores across sexes, and add further to the validity and cross-cultural generalizability of this scale.

Stimulation of the Prefrontal Cortex Reduces Intentions to Commit Aggression: A Randomized, Double-Blind, Placebo-Controlled, Stratified, Parallel-Group Trial.

Although prefrontal brain impairments are one of the best-replicated brain imaging findings in relation to aggression, little is known about the causal role of this brain region. This study tests whether stimulating the dorsolateral prefrontal cortex using transcranial direct current stimulation (tDCS) reduces the likelihood of engaging in aggressive acts, and the mechanism underlying this relationship. In a double-blind, stratified, placebo-controlled, parallel-group, randomized trial, 81 human adults (36 males, 45 females) were randomly assigned to an active (N = 39) or placebo (N = 42) condition, and then followed up 1 d after the experiment session. Intentions to commit aggressive acts and behavioral aggression were assessed using hypothetical vignettes and a behavioral task, respectively. The secondary outcome was the perception of the moral wrongfulness of the aggressive acts. Compared with the sham controls, participants who received anodal stimulation reported being less likely to commit physical and sexual assault (p < 0.01). They also judged aggressive acts as more morally wrong (p < 0.05). Perceptions of greater moral wrongfulness regarding the aggressive acts accounted for 31% of the total effect of tDCS on intentions to commit aggression. Results provide experimental evidence that increasing activity in the prefrontal cortex can reduce intentions to commit aggression and enhance perceptions of the moral wrongfulness of the aggressive acts. Findings shed light on the biological underpinnings of aggression and theoretically have the potential to inform future interventions for aggression and violence.SIGNIFICANCE STATEMENT Aggressive behaviors pose significant public health risks. Understanding the etiology of aggression is paramount to violence reduction. Investigations of the neural basis of aggression have largely supported correlational, rather than causal, interpretations, and the mediating processes underlying the prefrontal-aggression relationship remain to be well elucidated. Through a double-blind, stratified, placebo-controlled, parallel-group, randomized trial, this study tested whether upregulation of the prefrontal cortex reduces the likelihood of engaging in aggression. Results provide experimental evidence that increasing prefrontal cortical activity can reduce intent to commit aggressive acts. They also shed light on moral judgment as one mechanism that may link prefrontal deficits to aggression and, in theory, have the potential to inform future approaches toward reducing aggression.

Neurocriminology: implications for the punishment, prediction and prevention of criminal behaviour.

Criminal behaviour and violence are increasingly viewed as worldwide public health problems. A growing body of knowledge shows that criminal behaviour has a neurobiological basis, and this has intensified judicial interest in the potential application of neuroscience to criminal law. It also gives rise to important questions. What are the implications of such application for predicting future criminal behaviour and protecting society? Can it be used to prevent violence? And what are the implications for the way offenders are punished?

Genetic and environmental influences on disinhibition, boldness, and meanness as assessed by the triarchic psychopathy measure in 19-20-year-old twins.

BACKGROUND: The Triarchic Psychopathy Measure (TriPM) provides Disinhibition, Boldness, and Meanness scales for assessing the three trait domains of the triarchic model. Here we examined the genetic and environmental etiology of these three domains, including evaluation of potential sex differences. METHODS: A total of 1016 men and women ages 19-20 years were drawn from the University of Southern California Risk Factors for Antisocial Behavior twin study. RESULTS: Scores for the three TriPM scales were correlated to differing degrees, with the strongest phenotypic correlation between Disinhibition and Meanness. No sex differences were found in the genetic and environmental influences underlying these three domains, suggesting that the same genes and life experiences contribute to these traits in young men and women. For TriPM Disinhibition and Boldness, genetic factors explained about half or less of the variance, with the rest of the variance being explained by non-shared environmental factors. For TriPM Meanness, on the other hand, genetic, shared environmental, and non-shared environmental factors accounted for the variance. The phenotypic correlation between Disinhibition and Meanness was explained in part by common genes (26%), with the remainder attributable about equally to common shared (39%), and non-shared environmental influences (35%). CONCLUSIONS: These findings contribute to our understanding of psychopathic personality traits by demonstrating the importance of heritable factors for disinhibition and boldness facets of psychopathy, and the importance of shared environmental influences for the meanness facet.