Genes mediate the association between P3 amplitude and externalizing disorders

P300 amplitude reduction is associated with early-onset and late-onset pathological substance use in a prospectively studied cohort of 14-year-old adolescents

P3 amplitude reduction (P3AR) is associated with risk for adolescent-onset pathological substance use (PSU). In this longitudinal study, data from over 1,100 adolescent twins were used to examine P3AR in relation to early adolescent onset PSU (i.e., by age 14), late adolescent onset PSU (i.e., ages 14-18), misuse of different classes of substances (PSU-nicotine, PSU-alcohol, PSU-illicit), degree of PSU comorbidity, and gender differences. P3 amplitude was recorded at age 14 from two midline electrodes during a visual oddball paradigm. PSU was defined as meeting criteria for any symptom of a substance use disorder assessed using semistructured clinical interviews. P3AR was associated with degree of drug class comorbidity, early adolescent onset PSU for all three substance classes, and late adolescent onset PSU for alcohol and illicit PSU. Gender differences in P3AR were not statistically significant. These findings provide further evidence that P3AR indexes a nonspecific diathesis for adolescent-onset PSU.

Association between P3 event-related potential amplitude and externalizing disorders: a time-domain and time-frequency investigation of 29-year-old adults

This study determined whether time-domain P3 amplitude and time-frequency principal component (TF-PC) reductions are present in adulthood (age 29) when participants have largely passed through the age of heaviest substance misuse. Participants were assessed from age 17 through 29 for lifetime externalizing (EXT) disorders. EEG comparisons from three topographic regions were examined for P3 amplitude and TF-PCs at delta and theta frequency ranges. Significant P3 amplitude reductions were found in those with EXT for both regional and site-Pz analyses, with stronger effects observed the greater the EXT comorbidity. Reductions were also observed in all eight TF-PCs extracted, with a delta component yielding frontal effects not apparent in the time domain. Overall, results suggest that these brain measures continue, at age 29, to provide effective indices of EXT that potentially tap a neural substrate related to behavioral disinhibition.

Evidence for a Heritable Brain Basis to Deviance-Promoting Deficits in Self-Control

PURPOSE

Classic criminological theories emphasize the role of impaired self-control in behavioral deviancy. Reduced amplitude of the P300 brain response is reliably observed in individuals with antisocial and substance-related problems, suggesting it may serve as a neurophysiological indicator of deficiencies in self-control that confer liability to deviancy.

METHODS

The current study evaluated the role of self-control capacity - operationalized by scores on a scale measure of trait disinhibition - in mediating the relationship between P300 brain response and behavioral deviancy in a sample of adult twins (N=419) assessed for symptoms of antisocial/addictive disorders and P300 brain response.

RESULTS

As predicted, greater disorder symptoms and higher trait disinhibition scores each predicted smaller P300 amplitude, and trait disinhibition mediated observed relations between antisocial/addictive disorders and P300 response. Further, twin modeling analyses revealed that trait disinhibition scores and disorder symptoms reflected a common genetic liability, and this genetic liability largely accounted for the observed phenotypic relationship between antisocial-addictive problems and P300 brain response.

CONCLUSIONS

These results provide further evidence that heritable weaknesses in self-control capacity confer liability to antisocial/addictive outcomes and that P300 brain response indexes this dispositional liability.

Dissociation between affective sharing and emotion understanding in juvenile psychopaths

Empathy dysfunction is one of the core characteristics of youth with callous-unemotional (CU) traits. How such a dysfunction is associated with abnormal neural processing, however, remains to be determined. This study combined assessment of Hare Psychopathy Checklist Youth Version, pressure pain threshold, and event-related brain potentials elicited by the perception of people in pain in 15 young offenders with low CU traits (LCU), 13 with high CU traits (HCU), and 15 typically developing controls. Compared to the controls, LCU and HCU had higher pain thresholds. Although only the central late positive potential (LPP) was reduced in LCU, both the frontal N120 and central LPP were diminished in HCU. When exposed to situations in which someone was harmed by another, HCU retained the LPP, and this response was significantly correlated with their psychopathic traits and pain thresholds. Both groups had no deficit in sensorimotor resonance as assessed by mu suppression. These results demonstrate that youth with HCU exhibit atypical neural dynamics of pain empathy processing in the early stage of affective arousal, which is coupled with their relative insensitivity to actual pain. Their capacity to understand intentionality, however, was not affected. Such uncoupling between affective arousal and emotion understanding may contribute to instigating aggressive behaviors in juvenile psychopaths.

The association between p3 amplitude at age 11 and criminal offending at age 23

Reduced P3 amplitude to targets is an information-processing deficit associated with adult antisocial behavior and may reflect dysfunction of the temporal-parietal junction. This study aims to examine whether this deficit precedes criminal offending. From a birth cohort of 1,795 children, 73 individuals who become criminal offenders at age 23 and 123 noncriminal individuals were assessed on P3 amplitude. The two groups did not differ on gender, ethnicity, and social adversity. P3 amplitude was measured over the temporal-parietal junction during a visual continuous performance task at age 11, together with antisocial behavior. Criminal convictions were assessed at age 23. Reduced P3 amplitude at age 11 was associated with increased antisocial behavior at age 11. Criminal offenders showed significantly reduced P3 amplitudes to target stimuli compared to controls. Findings remained significant after controlling for antisocial behavior and hyperactivity at age 11 and alcoholism at age 23. P3 deficits at age 11 are associated with adult crime at age 23, suggesting that reduced P3 may be an early neurobiological marker for cognitive and affective processes subserved by the temporal-parietal junction that place a child at risk for adult crime.

Reconceptualizing antisocial deviance in neurobehavioral terms

We propose that neuroscientific understanding of antisocial behavior can be advanced by focusing programmatic efforts on neurobehavioral trait constructs, that is, individual difference constructs with direct referents in neurobiology as well as behavior. As specific examples, we highlight inhibitory control and defensive reactivity as two such constructs with clear relevance for understanding antisocial behavior in the context of development. Variations in inhibitory control are theorized to reflect individual differences in the functioning of brain systems that operate to guide and inhibit behavior and regulate emotional response in the service of nonimmediate goals. Variations in defensive reactivity are posited to reflect individual differences in the sensitivity of the brain's aversive motivational (fear) system. We describe how these constructs have been conceptualized in the adult and child literatures and review work pertaining to traditional psychometric (rating and behaviorally based) assessment of these constructs and their known physiological correlates at differing ages as well as evidence linking these constructs to antisocial behavior problems in children and adults. We outline a psychoneurometric approach, which entails systematic development of neurobiological measures of target trait constructs through reference to psychological phenotypes, as a paradigm for linking clinical disorders to neurobiological systems. We provide a concrete illustration of this approach in the domain of externalizing proneness and discuss its broader implications for research on conduct disorder, antisocial personality, and psychopathy.

The role of conduct disorder in the association between ADHD and alcohol use (disorder). Results from the Netherlands Mental Health Survey and Incidence Study-2

BACKGROUND

Much is unclear about the association between attention-deficit/hyperactivity disorder (ADHD) and alcohol use (disorder). Research on this subject is hindered by the role of conduct disorder (CD). We investigate whether (1) childhood ADHD is associated with higher prevalence and earlier onset of alcohol initiation, regular alcohol use and alcohol use disorder (AUD) (2) CD mediates or modifies this association.

METHODS

Data were derived from the baseline assessment of the Netherlands Mental Health Survey and Incidence Study-2, a general population study. ADHD and CD were assessed among respondents aged 18-44 (n=3309). ADHD, CD, and alcohol use (disorder) were assessed using the Composite International Diagnostic Interview 3.0.

RESULTS

Lifetime prevalence was 2.9% for ADHD, 5.6% for CD, 94.3% for alcohol initiation, 85.7% for regular alcohol use and 19.0% for AUD; mean ages of onset were 6.7, 11.5, 14.8, 16.7 and 19.2 years, respectively. After correction for gender and age, ADHD was associated with a higher prevalence of all three stages of alcohol use, but not with earlier onset of these stages. The association between ADHD and prevalence of AUD was fully explained by a mediating role of CD. CD did not modify the associations between ADHD and prevalence and onset of alcohol use (disorder).

CONCLUSIONS

The mediating role of CD in the association between ADHD and AUD suggests a developmental pathway from ADHD to CD and subsequent AUD. Early interventions in children with ADHD may prevent CD and subsequent onset of AUD.

Examining electrodermal hyporeactivity as a marker of externalizing psychopathology: a twin study

Literature suggests that reduced electrodermal reactivity (EDR) is related to externalizing problems. However, the genetic and environmental etiology of this association is unknown. Using a standard habituation paradigm, we measured responses to 15 loud tones in four cohorts of adolescent twins (N = 2,129). We quantified EDR as the average size of elicited responses (amplitude) and by counting the number of skin conductance responses (frequency). Externalizing liability was indexed through a general factor underlying substance-related problems and antisocial behavior. Response frequency, but not mean amplitude, was inversely associated with externalizing liability in each twin cohort. Biometric modeling revealed that most of the overlap between response frequency and externalizing liability was due to genetic influences common to both phenotypes. It is argued that neurological mechanisms involved in habituation may shed light on the etiology of psychopathology.

Is the continuity of externalizing psychopathology the same in adolescents and middle-aged adults? A test of the externalizing spectrum's developmental coherence

Externalizing psychopathology (EXT) is a framework for understanding diagnostic comorbidity and etiology of antisocial and substance-use behaviors. EXT indicates continuity in adulthood but the structure of adolescent EXT is less clear. This report examines whether adolescent EXT is trait-like, as has been found with adults, or categorical. We use tests of measurement invariance to determine how diagnostic indicators of EXT differ in adolescents compared to adults. The EXT measures employed were DSM-IIIR diagnoses of adult antisocial behavior, conduct disorder, and alcohol, marijuana, and drug dependence. Latent trait, latent class, and hybrid models were fit to two separate data sets: 2,769 seventeen-year-old adolescents and 2,619 adults from the Minnesota Twin Family Study. The best model in both samples was a single-trait LT model. Parameters from the adolescent and adult models were equivalent for all disorders except alcohol dependence. It appears that EXT in adolescence can be accurately represented by a single-trait model, and the measurement properties of EXT are similar during these time periods with the exception of alcohol dependence.

Developmental Endophenotypes: Indexing Genetic Risk for Substance Abuse with the P300 Brain Event-Related Potential

Although substance use disorders are heritable, their complexity has made identifying genes underlying their development challenging. Endophenotypes, biologically informed quantitative measures that index genetic risk for a disorder, are being recognized for their potential to assist the search for disorder relevant genes. After outlining criteria for an endophenotype that includes developmental considerations, we review how the brain P300 response serves as an index of genetic risk for substance abuse and related externalizing disorders. The P300 response is highly heritable and associated broadly with characteristics of externalizing disorder, including childhood disruptive disorders, antisociality, and precocious expression of deviant behavior. This association appears to be mediated by shared genetic influences. Prospective studies confirm that reduced P300 amplitude present in youth prior to significant exposure to addictive substances is associated with the subsequent development of substance use disorders. Despite pronounced change in mean level over the course of development, P300 amplitude shows strong rank order stability with repeated assessment through young adulthood. In addition, P300 developmental trajectories based on multiple assessments show very high heritability and may be especially informative as measures of genetic risk. Collectively, these findings provide strong support that P300 amplitude and its change through development reflect genetic vulnerability to substance abuse and related externalizing psychopathology.

The P300 event-related brain potential as a neurobiological endophenotype for substance use disorders: a meta-analytic investigation

Endophenotypes are intermediate phenotypes on the putative causal pathway from genotype to phenotype and can aid in discovering the genetic etiology of a disorder. There are currently very few suitable endophenotypes available for substance use disorders (SUD). The amplitude of the P300 event-related brain potential is a possible candidate. The present study determined whether the P300 amplitude fulfils two fundamental criteria for an endophenotype: (1) an association with the disorder (disease marker), and (2) presence in unaffected biological relatives of those who have the disorder (vulnerability marker). For this purpose, two separate meta-analyses were performed. Meta-analysis 1 investigated the P300 amplitude in relation to SUD in 39 studies and Meta-analysis 2 investigated P300 amplitude in relation to a family history (FH+) of SUD in 35 studies. The findings indicate that a reduced P300 amplitude is significantly associated with SUD (d=0.51) and, though to a lesser extent, with a FH+ of SUD (d=0.28). As a disease maker, the association between reduced P300 amplitude and SUD is significantly larger for participants that were exclusively recruited from treatment facilities (d=0.67) than by other methods (i.e., community samples and family studies; d=0.45 and 0.32, respectively), and larger for abstinent SUD patients (d=0.71) than for current substance users (d=0.37). Furthermore, in contrast to FH+ males, a P300 amplitude reduction seems not to be present in FH+ females (d=-0.07). Taken together, these results suggest that P300 amplitude reduction can be both a useful disease and vulnerability marker and is a promising neurobiological endophenotype for SUD, though only in males. Implications and future directions are discussed.

All about the Money - External Performance Monitoring is Affected by Monetary, but Not by Socially Conveyed Feedback Cues in More Antisocial Individuals

This study investigated the relationship between feedback processing and antisocial personality traits measured by the PSSI questionnaire (Kuhl and Kazén, 1997) in a healthy undergraduate sample. While event-related potentials [feedback related negativity (FRN), P300] were recorded, participants encountered expected and unexpected feedback during a gambling task. As recent findings suggest learning problems and deficiencies during feedback processing in clinical populations of antisocial individuals, we performed two experiments with different healthy participants in which feedback about monetary gains or losses consisted either of social-emotional (facial emotion displays) or non-social cues (numerical stimuli). Since the FRN and P300 are both sensitive to different aspects of feedback processing we hypothesized that they might help to differentiate between individuals scoring high and low on an antisocial trait measure. In line with previous evidence FRN amplitudes were enhanced after negative and after unexpected feedback stimuli. Crucially, participants scoring high on antisocial traits displayed larger FRN amplitudes than those scoring low only in response to expected and unexpected negative numerical feedback, but not in response to social-emotional feedback - irrespective of expectancy. P300 amplitudes were not modulated by antisocial traits at all, but by subjective reward probabilities. The present findings indicate that individuals scoring high on antisociality attribute higher motivational salience to monetary compared to emotional-social feedback which is reflected in FRN amplitude enhancement. Contrary to recent findings, however, no processing deficiencies concerning social-emotional feedback stimuli were apparent in those individuals. This indicates that stimulus salience is an important aspect in learning and feedback processes in individuals with antisocial traits which has potential implications for therapeutic interventions in clinical populations.

Is the P3 amplitude reduction seen in externalizing psychopathology attributable to stimulus sequence effects?

P3 amplitude reduction (P3-AR) is associated with biological vulnerability to a spectrum of externalizing (EXT) disorders, such as conduct disorder, antisocial behavior, and substance use disorders. P3 amplitude, however, can be affected by the context within which it is measured, for example, by the position of the target in the sequence of stimuli during an oddball task. We hypothesized that EXT-related P3-AR may be due to attention or working memory deficits in EXT that would weaken these stimulus sequence effects. Using a community-based sample of adolescent males, we examined the relationship between P3 and EXT as a function of the number of standards preceding the target. Higher EXT was associated with significantly smaller P3 amplitude, regardless of the number of standards preceding the target. These results suggest that P3-AR in EXT does not vary as a function of stimulus sequence, further supporting P3-AR as an endophenotype for EXT disorders.

Personality correlates of the common and unique variance across conduct disorder and substance misuse symptoms in adolescence

Externalising behaviours such as substance misuse (SM) and conduct disorder (CD) symptoms highly co-occur in adolescence. While disinhibited personality traits have been consistently linked to externalising behaviours there is evidence that these traits may relate differentially to SM and CD. The current study aimed to assess whether this was the case, after examining the nature of the relationship between SM and CD symptoms in an adolescent sample (N = 392), using structural equation modelling. Similar to those found in adults (Krueger et al. Journal of Abnormal Psychology 116: 645-666, 2007), results showed that CD and SM symptoms were organized hierarchically, with symptoms explaining a single broad, coherent construct of externalising behaviour, but also explaining specific factors of SM and CD that vary independently from the general externalising factor. Furthermore, disinhibited personality traits related differentially to these factors, with results showing that, even controlling for inhibited personality traits, impulsivity was associated with CD and the common variance shared by CD and SM, while sensation seeking was specifically associated with SM only. Hopelessness was also associated with the common variance shared by SM and CD. Results confirm impulsivity, hopelessness and sensation seeking as key correlates of externalising behaviour problems in adolescence, identifying them as clear targets for intervention and prevention strategies.

Electrophysiological markers of genetic risk for attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder with complex genetic aetiology. The identification of candidate intermediate phenotypes may facilitate the detection of susceptibility genes and neurobiological mechanisms underlying the disorder. Electroencephalography (EEG) is an ideal neuroscientific approach, providing a direct measurement of neural activity that demonstrates reliability, developmental stability and high heritability. This systematic review evaluates the utility of a subset of electrophysiological measures as potential intermediate phenotypes for ADHD: quantitative EEG indices of arousal and intraindividual variability, and functional investigations of attention, inhibition and performance monitoring using the event-related potential (ERP) technique. Each measure demonstrates consistent and meaningful associations with ADHD, a degree of genetic overlap with ADHD and potential links to specific genetic variants. Investigations of the genetic and environmental contributions to EEG/ERP and shared genetic overlap with ADHD might enhance molecular genetic studies and provide novel insights into aetiology. Such research will aid in the precise characterisation of the clinical deficits seen in ADHD and guide the development of novel intervention and prevention strategies for those at risk.

Clarifying relations between dispositional aggression and brain potential response: overlapping and distinct contributions of impulsivity and stress reactivity

Impulsive-aggressive individuals exhibit deficits in amplitude of the P3 brain potential response, however, it remains unclear how separable dispositional traits account for this association. The current study sought to clarify the basis of this association by examining contributions of trait impulsiveness and stress reactivity to the observed relationship between dispositional aggression and amplitude of the P3 brain potential response in a visual novelty-oddball procedure. A significant negative association was found between aggressiveness and amplitude of P3 response to both target and novel stimuli over frontal-central scalp sites. Impulsivity showed a parallel inverse relationship with P3 amplitude, attributable to its overlap with dispositional aggression. In contrast, stress reactivity did not exhibit a zero-order association with P3 amplitude, but modestly predicted P3 in a positive direction after accounting for its overlap with aggression. Results are discussed in terms of their implications for individual difference variables and brain processes underlying impulsive-aggressive behavior.

P3a amplitude predicts successful treatment program completion in substance-dependent individuals

This study examined P3a amplitude as a direct predictor of treatment success for substance dependence. Participants were 35 adults (27 men, 8 women) undergoing treatment for substance dependence at an urban residential treatment facility between October 2005 and July 2007. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) criteria were used to confirm substance dependence. P3a amplitude was significantly smaller for those who dropped out of treatment. Discriminant function analysis confirmed that P3a amplitude was a robust predictor of treatment completion, more sensitive than other measures including substance abuse severity. Implications for the interpretation of P3a amplitude as an index of executive function are discussed.

Operationalizing proneness to externalizing psychopathology as a multivariate psychophysiological phenotype

The externalizing dimension is viewed as a broad dispositional factor underlying risk for numerous disinhibitory disorders. Prior work has documented deficits in event-related brain potential (ERP) responses in individuals prone to externalizing problems. Here, we constructed a direct physiological index of externalizing vulnerability from three ERP indicators and evaluated its validity in relation to criterion measures in two distinct domains: psychometric and physiological. The index was derived from three ERP measures that covaried in their relations with externalizing proneness-the error-related negativity and two variants of the P3. Scores on this ERP composite predicted psychometric criterion variables and accounted for externalizing-related variance in P3 response from a separate task. These findings illustrate how a diagnostic construct can be operationalized as a composite (multivariate) psychophysiological variable (phenotype).

Psychometric and genetic architecture of substance use disorder and behavioral disinhibition measures for gene association studies

Using large twin, family, and adoption studies conducted at the Minnesota Center for Twin and Family Research, we describe our efforts to develop measures of substance use disorder (SUD) related phenotypes for targets in genome wide association analyses. Beginning with a diverse set of relatively narrow facet-level measures, we identified 5 constructs of intermediate complexity: nicotine, alcohol consumption, alcohol dependence, illicit drug, and behavioral disinhibition. The 5 constructs were moderately correlated (mean r = .57) reflecting a general externalizing liability to substance abuse and antisocial behavior. Analyses of the twin and adoption data revealed that this general externalizing liability accounted for much of the genetic risk in each of the intermediate-level constructs, though each also exhibited significant unique genetic and environmental risk. Additional analyses revealed substantial effects for age and sex, significant shared environmental effects, and that the mechanism of these shared environmental effects operates via siblings rather than parents. Our results provide a foundation for genome wide association analyses to detect risk alleles for SUDs as well as novel insights into genetic and environmental risk for SUDs.

Gender differences in the relationship of internalizing and externalizing psychopathology to alcohol dependence: likelihood, expression and course

OBJECTIVE

To determine whether internalizing and externalizing psychopathology were differentially associated with alcohol dependence in men and women.

METHODS

Four categories of lifetime psychopathology were examined: neither internalizing nor externalizing (NINE), internalizing only (IO), externalizing only (EO) and both internalizing and externalizing (BIE). Multivariate models assessed gender differences in the adjusted associations of these categories with the odds of lifetime alcohol dependence in a representative sample of 43,093 U.S. adults 18 and older and with clinical course and expression in a subsample of 4781 lifetime alcoholics.

RESULTS

The excess odds of lifetime alcohol dependence associated with IO, EO and BIE were significantly greater for women than men, OR=2.6, 8.8 and 10.7 versus 1.9, 4.0 and 6.5, respectively. Regardless of gender, the ORs were significantly higher for EO than IO and for BIE than EO. Gender differences in the expression and course of alcoholism were most pronounced for the categories of NINE and IO, with men having greater consumption, dependence severity and treatment but less familial alcoholism. Gender variation in the association of psychopathology with the expression and course of alcoholism was most evident in the BIE category, where the associations were stronger for women. Lifetime externalizing psychopathology was associated with an increased likelihood of treatment utilization, especially among women.

CONCLUSIONS

Findings highlight the need to increase alcoholism screening, prevention and intervention among women with psychopathology, especially externalizing. The greater numbers of internalizing than externalizing alcoholics emphasize the need to treat symptoms of depression and anxiety in alcohol treatment settings.

Measuring addiction propensity and severity: the need for a new instrument

Drug addiction research requires but lacks a valid and reliable way to measure both the risk (propensity) to develop addiction and the severity of manifest addiction. This paper argues for a new measurement approach and instrument to quantify propensity to and severity of addiction, based on the testable assumption that these constructs can be mapped onto the same dimension of liability to addiction. The case for this new direction becomes clear from a critical review of empirical data and the current instrumentation. The many assessment instruments in use today have proven utility, reliability, and validity, but they are of limited use for evaluating individual differences in propensity and severity. The conceptual and methodological shortcomings of instruments currently used in research and clinical practice can be overcome through the use of new technologies to develop a reliable, valid, and standardized assessment instrument(s) to measure and distinguish individual variations in expression of the underlying latent trait(s) that comprises propensity to and severity of drug addiction. Such instrumentation would enhance our capacity for drug addiction research on linkages and interactions among familial, genetic, psychosocial, and neurobiological factors associated with variations in propensity and severity. It would lead to new opportunities in substance abuse prevention, treatment, and services research, as well as in interventions and implementation science for drug addiction.

Dysfunctional reward processing in male alcoholics: an ERP study during a gambling task

OBJECTIVE

A dysfunctional neural reward system has been shown to be associated with alcoholism. The current study aims to examine reward processing in male alcoholics by using event-related potentials (ERPs) as well as behavioral measures of impulsivity and risk-taking.

METHODS

Outcome-related negativity (ORN/N2) and positivity (ORP/P3) derived from a single outcome gambling task were analyzed using a mixed model procedure. Current density was compared across groups and outcomes using standardized low resolution electromagnetic tomography (sLORETA). Behavioral scores were also compared across groups. Correlations of ERP factors with behavioral and impulsivity factors were also analyzed.

RESULTS

Alcoholics showed significantly lower amplitude than controls during all outcome conditions for the ORP component and decreased amplitude during the loss conditions for the ORN component. Within conditions, gain produced higher amplitudes than loss conditions. Topographically, both groups had an anterior focus during loss conditions and posterior maxima during gain conditions, especially for the ORN component. Decreased ORP current density at cingulate gyrus and less negative ORN current density at sensory and motor areas characterized the alcoholics. Alcoholics had higher levels of impulsivity and risk-taking features than controls.

CONCLUSIONS

Deficient outcome/reward processing and increased impulsivity and risk-taking observed in alcoholics may be at least partly due to reward deficiency and/or dysfunctional reward circuitry in the brain, suggesting that alcoholism can be considered as part of the cluster of the reward deficiency syndrome (RDS).

The genetic epidemiology of personality disorders

Genetic epidemiologic studies indicate that all ten personality disorders (PDs) classified on the DSM-IV axis II are modestly to moderately heritable. Shared environmental and nonadditive genetic factors are of minor or no importance. No sex differences have been identified. Multivariate studies suggest that the extensive comorbidity between the PDs can be explained by three common genetic and environmental risk factors. The genetic factors do not reflect the DSM-IV cluster structure, but rather: i) broad vulnerability to PD pathology or negative emotionality; ii) high impulsivity/low agreeableness; and iii) introversion. Common genetic and environmental liability factors contribute to comorbidity between pairs or clusters of axis I and axis II disorders. Molecular genetic studies of PDs, mostly candidate gene association studies, indicate that genes linked to neurotransmitter pathways, especially in the serotonergic and dopaminergic systems, are involved. Future studies, using newer methods like genome-wide association, might take advantage of the use of endophenotypes.

Brain electrophysiological endophenotypes for externalizing psychopathology: a multivariate approach

Abnormalities in electrophysiological measures of stimulus-evoked brain activity (including the P3 event-related potential (ERP) and its associated delta and theta time-frequency (TF) components), and intrinsic, resting state brain activity (including EEG in the beta frequency band) have each been associated with biological vulnerability to a variety of externalizing (EXT) spectrum disorders, such as substance use disorders, conduct disorder, and antisocial behavior. While each of these individual measures has shown promise as an endophenotype for one or more aspects of EXT, we proposed that the power to identify EXT-related genes may be enhanced by using these measures collectively. Thus, we sought to explore a multivariate approach to identifying electrophysiological endophenotypes related to EXT, using measures identified in the literature as promising individual endophenotypes for EXT. Using data from our large twin sample (634 MZ and 335 DZ, male and female same-sex pairs), and fitting multivariate biometric Cholesky models, we found that these measures (1) were heritable, (2) showed significant phenotypic and genetic correlation with a general vulnerability to EXT (which is itself highly heritable), (3) showed modest phenotypic and genetic correlation with each other, and (4) were sensitive to genetic effects that differed as a function of gender. These relationships suggest that these endophenotypes are likely tapping into neurophysiological processes and genes that are both common across them and unique to each-all of which are relevant to a biological vulnerability to EXT psychopathology.

The enrichment study of the Minnesota twin family study: increasing the yield of twin families at high risk for externalizing psychopathology

The Enrichment Study (ES) was designed to extend the Minnesota Twin Family Study (MTFS) by oversampling 11-year-old twins at especially high risk for substance use disorders by virtue of having a childhood disruptive disorder. The sample was ascertained from Minnesota birth records. To identify high-risk twins, we conducted telephone screening interviews for parent-reported symptoms of attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD) as well as indications of academic disengagement. Twins who exceeded a predetermined threshold were invited to participate. To facilitate comparison with the previously ascertained MTFS participants, a random sample of 11-year-old twins was also recruited. As part of the ES study, 499 twin pairs, and their parents, visited the University of Minnesota, where each participant completed a clinical interview, psychophysiological evaluation, and thorough assessment of environmental risk. We were highly successful in recruiting at-risk twins; 52% of the screened male twins and 41% of the screened females met criteria for a diagnosis of ADHD, CD, or oppositional defiant disorder (ODD). At the pair level, 63% of the screened pairs had at least one member with a childhood disruptive disorder. This article provides an overview of the study design and includes a review of recent findings using this sample of twins.

Externalizing disorders: cluster 5 of the proposed meta-structure for DSM-V and ICD-11

BACKGROUND

The extant major psychiatric classifications DSM-IV and ICD-10 are purportedly atheoretical and largely descriptive. Although this achieves good reliability, the validity of a medical diagnosis is greatly enhanced by an understanding of the etiology. In an attempt to group mental disorders on the basis of etiology, five clusters have been proposed. We consider the validity of the fifth cluster, externalizing disorders, within this proposal.

METHOD

We reviewed the literature in relation to 11 validating criteria proposed by the Study Group of the DSM-V Task Force, in terms of the extent to which these criteria support the idea of a coherent externalizing spectrum of disorders.

RESULTS

This cluster distinguishes itself by the central role of disinhibitory personality in mental disorders spread throughout sections of the current classifications, including substance dependence, antisocial personality disorder and conduct disorder. Shared biomarkers, co-morbidity and course offer additional evidence for a valid cluster of externalizing disorders.

CONCLUSION

Externalizing disorders meet many of the salient criteria proposed by the Study Group of the DSM-V Task Force to suggest a classification cluster.

Childhood risk factors for young adult substance dependence outcome in offspring from multiplex alcohol dependence families: a prospective study

BACKGROUND

Age of onset to begin drinking is a known risk factor for alcohol dependence. Factors have been identified that contribute to age of onset to begin regular drinking. These include reduced P300, increased postural sway, and personality variation. A longitudinal study spanning childhood to young adulthood provided the opportunity to determine if these same factors would predict the presence and onset of substance use disorders (SUD).

METHODS

Multiplex families were identified through two or more alcohol-dependent brothers. Offspring from these multiplex or control families (n = 133) were followed annually during childhood. Using childhood predictors previously identified as risk factors for age of onset to begin drinking, SUD outcome by young adulthood was modeled.

RESULTS

Familial risk status was a significant predictor of young adult SUD outcome as a main effect and as an interaction with P300 amplitude recorded before the age of 13. In adolescence (age 15), increased postural sway and familial risk predicted the SUD outcome by age 22. Analysis comparing the presence of one or both risk factors showed that those above the median for sway and below the median for P300 amplitude had substantially increased odds of developing SUD (odds ratio = 8.08 [confidence interval = 1.52-42.83]).

CONCLUSIONS

Our findings indicate that among the factors predicting age of onset to begin regular drinking, P300 predicts SUD outcome across an 11-year span. The present findings provide the longest follow-up to date demonstrating that neurobiological factors in childhood are among the most salient predictors of young adult SUD outcome.

Event-related potentials in clinical research: guidelines for eliciting, recording, and quantifying mismatch negativity, P300, and N400

This paper describes recommended methods for the use of event-related brain potentials (ERPs) in clinical research and reviews applications to a variety of psychiatric and neurological disorders. Techniques are presented for eliciting, recording, and quantifying three major cognitive components with confirmed clinical utility: mismatch negativity (MMN), P300, and N400. Also highlighted are applications of each of the components as methods of investigating central nervous system pathology. The guidelines are intended to assist investigators who use ERPs in clinical research, in an effort to provide clear and concise recommendations and thereby to standardize methodology and facilitate comparability of data across laboratories.

Relationship between the P3 event-related potential, its associated time-frequency components, and externalizing psychopathology

P3 amplitude reduction (P3-AR) is associated with biological vulnerability to a spectrum of externalizing disorders, such as ADHD, conduct disorder, and substance use disorders. P3, however, is generally characterized as a broad activation involving multiple neurophysiological processes. One approach to separating P3-related processes is time-frequency (TF) analysis. The current study used a novel PCA-based TF analysis method to investigate relationships between P3, its associated TF components, and externalizing in a community-based sample of adolescent males. Results showed that 1) alone, P3 and each TF-PCA derived component could successfully discriminate diagnostic groups from controls, and 2) delta components in specific time ranges accounted for variance beyond that accounted for by P3. One delta component was associated with all diagnostic groups, suggesting it may represent a more parsimonious endophenotype for externalizing than P3-AR.

The heritability of P300 amplitude in 18-year-olds is robust to adolescent alcohol use

P3 amplitude reduction (P3AR) is associated with adolescent alcohol use (AAU) and highly heritable, suggesting that P3AR may index a genetic predisposition (e.g., an endophenotype) for AAU. However, because P3AR and AAU covary naturally in the population, these observations are also consistent with P3AR reflecting neurotoxic effects of AAU on the developing adolescent brain. In this report, we describe the use of recent advancements in biometric modeling to examine changes in the genetic and environmental contributions to variability in P3 amplitude related to cumulative AAU by late adolescence in a large community-based twin sample. We found that the genetic and environmental contributions to variability in P3 amplitude were unaffected by AAU. This suggests that P3AR indexes risk for alcoholism independent of any deleterious effect of AAU on adolescent brain development.

Rank-based inverse normal transformations are increasingly used, but are they merited?

Many complex traits studied in genetics have markedly non-normal distributions. This often implies that the assumption of normally distributed residuals has been violated. Recently, inverse normal transformations (INTs) have gained popularity among genetics researchers and are implemented as an option in several software packages. Despite this increasing use, we are unaware of extensive simulations or mathematical proofs showing that INTs have desirable statistical properties in the context of genetic studies. We show that INTs do not necessarily maintain proper Type 1 error control and can also reduce statistical power in some circumstances. Many alternatives to INTs exist. Therefore, we contend that there is a lack of justification for performing parametric statistical procedures on INTs with the exceptions of simple designs with moderate to large sample sizes, which makes permutation testing computationally infeasible and where maximum likelihood testing is used. Rigorous research evaluating the utility of INTs seems warranted.

Deviant P300 amplitude development in males is associated with paternal externalizing psychopathology

Boys at risk for alcoholism show deviant P300 amplitude development. Genetic influences on P300, however, are related to a range of externalizing disorders. This study examined whether P300 development from adolescence to early adulthood differed between groups varying in severity of paternal externalizing. Parietal P300 was assessed during the "rotated heads" task on up to 3 times between the ages of 17 and 24 years. Participants were divided into 3 paternal externalizing groups: (a) severe (father has adult antisocial behavior), (b) intermediate (father has alcohol dependence but not a more severe disorder), and (c) low (father has no externalizing disorders or substance treatment and is not extreme in alcohol use). Mixed models were used to evaluate linear change in amplitude. P300 decreased with age. The severe-risk group had smaller P300 initially and changed less with time than did the low-risk group. The intermediate-risk group did not differ significantly from the low-risk group, but differed marginally from the severe-risk males. Externalizing and early-onset substance disorders in the sons were associated with smaller initial values of P300. Measures of deviant P300 development may be vulnerability markers for externalizing psychopathology.

On the nature of nicotine addiction: a taxometric analysis

Taxometric procedures were used to determine whether nicotine addiction is best conceptualized as a dimensional or a categorical (i.e., taxonic) phenomenon. Using data from the 2003 National Survey on Drug Use and Health (NSDUH; N = 12,467), results from MAMBAC, MAXEIG, and LMODE taxometric analyses provided strong evidence that nicotine addiction has a taxonic latent structure. Members of the addiction taxon, which constituted approximately 48% of those who reported smoking in the past 30 days, consumed a higher number of cigarettes per day, had stronger craving, higher levels of nicotine tolerance, more inflexible smoking patterns, and shorter latencies to smoking their first cigarette on waking compared with nontaxon members. These findings of a distinct addiction taxonic structure were replicated using a 2002 NSDUH sample (N = 12,224). Finally, the predictive validity of the taxon variable was compared with a continuous indicator sum. The taxon accounted for most of the predictive variance in the indicator sum, but the latter generally showed significant predictive power even after controlling for the former. Thus, these smoking variables may have both a categorical and a dimensional structure.

Psychophysiological correlates of aggression and violence: an integrative review

This paper reviews existing psychophysiological studies of aggression and violent behaviour including research employing autonomic, electrocortical and neuroimaging measures. Robust physiological correlates of persistent aggressive behaviour evident in this literature include low baseline heart rate, enhanced autonomic reactivity to stressful or aversive stimuli, enhanced EEG slow wave activity, reduced P300 brain potential response and indications from structural and functional neuroimaging studies of dysfunction in frontocortical and limbic brain regions that mediate emotional processing and regulation. The findings are interpreted within a conceptual framework that draws on two integrative models in the literature. The first is a recently developed hierarchical model of impulse control (externalizing) problems, in which various disinhibitory syndromes including aggressive and addictive behaviours of different kinds are seen as arising from common as well as distinctive aetiologic factors. This model represents an approach to organizing these various interrelated phenotypes and investigating their common and distinctive aetiologic substrates. The other is a neurobiological model that posits impairments in affective regulatory circuits in the brain as a key mechanism for impulsive aggressive behaviour. This model provides a perspective for integrating findings from studies employing different measures that have implicated varying brain structures and physiological systems in violent and aggressive behaviour.

Parental smoking and adolescent problem behavior: an adoption study of general and specific effects

OBJECTIVE

It is essential to understand the effect of parental smoking on offspring tobacco use. In biologically related families, parents who smoke may transmit a nonspecific genetic risk for offspring disinhibited behavior, including tobacco use. Studying adoptive families allows one to control for genetic confounding when examining the environmental effect of exposure to parental smoking. The purpose of this study was to examine the genetic and environmental contributions to the risk represented by exposure to parental smoking and to assess the specificity of that risk.

METHODS

Adolescents adopted in infancy were systematically ascertained from records of three private Minnesota adoption agencies; nonadopted adolescents were ascertained from Minnesota birth records. Adolescents and their rearing parents participated in all assessments in person. The main outcome measures were self-reports of behavioral deviance, substance use, and personality, as well as DSM-IV clinical assessments of childhood disruptive disorders.

RESULTS

The data from adoptive families suggest that exposure to parental smoking represents an environmental risk for substance use in adolescent offspring. In biologically related families, the effect of exposure to parental smoking is larger and more diverse, including substance use, disruptive behavior disorders, delinquency, deviant peer affiliations, aggressive attitudes, and preference for risk taking.

CONCLUSIONS

This study provides evidence for an environmentally mediated pathway by which parental smoking increases risk specifically for substance use in adolescent offspring. The data are also consistent with a genetically mediated pathway by which nonadoptive parents who smoke may also transmit a nonspecific genetic risk to their offspring for disinhibited behavior.

Genetics of personality disorders

This review of the literature on genetic contributions to the etiology of personality disorders broadly follows the DSM classification, and begins by evaluating the current evidence for genetic influences on the DSM axis II disorders. One of the most exciting directions in psychiatric genetics is the rapidly developing field of molecular genetic studies aiming to identify specific genes correlated with psychiatric phenotypes. Personality disorders, like most other psychiatric diagnostic categories, are etiologically complex, which implies that they are influenced by several genes and several environmental factors. The interplay between genes and the environment is a field that is receiving increasing attention and is addressed both in relation to quantitative and molecular methods.

The effects of childhood disruptive disorder comorbidity on P3 event-related brain potentials in preadolescents with ADHD

The present study examined the degree to which the P300 component of the visual brain event-related potential and associated task performance deficits often observed in children with attention-deficit hyperactivity disorder (ADHD) are attributable to comorbid childhood disruptive disorders using a community sample of 11-year olds from the Minnesota Twin Family Study. Subjects were divided into "ADHD-pure" (ADHD without oppositional defiant disorder, ODD, or conduct disorder, CD), "ADHD-comorbid" (ADHD with ODD or CD), and comparison (no childhood disruptive disorder) groups using DSM-III-R diagnoses. Results showed that ADHD-comorbid but not ADHD-pure subjects displayed significant P3 amplitude reduction and poorer task performance compared to controls. No group effects for P3 latency or reaction time were seen. Although ADHD-comorbid children had marginally more ADHD symptoms compared to ADHD-pure children, this did not account for their reduced P3, suggesting that the observed neurobehavioral deficits reflected the effects of co-occurring childhood disruptive disorders.

The genetics of alcohol and other drug dependence

Alcohol dependence and dependence on other drugs frequently co-occur, and strong evidence suggests that both disorders are, at least in part, influenced by genetic factors. Indeed, studies using twins suggest that the overlap between dependence on alcohol and on other drugs largely results from shared genetic factors. This common genetic liability, which also extends to antisocial behavior, has been conceptualized as a general predisposition toward a variety of forms of psychopathology characterized by disinhibited behavior (i.e., externalizing psychopathology). Accordingly, many of the genetic factors affecting risk for dependence on alcohol or other drugs appear to act through a general externalizing factor; however, other genetic factors appear to be specific to a certain disorder. In recent years, researchers have identified numerous genes as affecting risk for dependence on alcohol and other drugs. These include genes involved in alcohol metabolism as well as in the transmission of nerve cell signals and modulation of nerve cell activity (i.e., γ-aminobutyric acid [GABA] and acetylcholinergic neurotransmission and the endogenous opioid and cannabinoid systems).

Updating P300: an integrative theory of P3a and P3b

The empirical and theoretical development of the P300 event-related brain potential (ERP) is reviewed by considering factors that contribute to its amplitude, latency, and general characteristics. The neuropsychological origins of the P3a and P3b subcomponents are detailed, and how target/standard discrimination difficulty modulates scalp topography is discussed. The neural loci of P3a and P3b generation are outlined, and a cognitive model is proffered: P3a originates from stimulus-driven frontal attention mechanisms during task processing, whereas P3b originates from temporal-parietal activity associated with attention and appears related to subsequent memory processing. Neurotransmitter actions associating P3a to frontal/dopaminergic and P3b to parietal/norepinephrine pathways are highlighted. Neuroinhibition is suggested as an overarching theoretical mechanism for P300, which is elicited when stimulus detection engages memory operations.

Updating P300: an integrative theory of P3a and P3b

The empirical and theoretical development of the P300 event-related brain potential (ERP) is reviewed by considering factors that contribute to its amplitude, latency, and general characteristics. The neuropsychological origins of the P3a and P3b subcomponents are detailed, and how target/standard discrimination difficulty modulates scalp topography is discussed. The neural loci of P3a and P3b generation are outlined, and a cognitive model is proffered: P3a originates from stimulus-driven frontal attention mechanisms during task processing, whereas P3b originates from temporal-parietal activity associated with attention and appears related to subsequent memory processing. Neurotransmitter actions associating P3a to frontal/dopaminergic and P3b to parietal/norepinephrine pathways are highlighted. Neuroinhibition is suggested as an overarching theoretical mechanism for P300, which is elicited when stimulus detection engages memory operations.

Updating P300: an integrative theory of P3a and P3b

The empirical and theoretical development of the P300 event-related brain potential (ERP) is reviewed by considering factors that contribute to its amplitude, latency, and general characteristics. The neuropsychological origins of the P3a and P3b subcomponents are detailed, and how target/standard discrimination difficulty modulates scalp topography is discussed. The neural loci of P3a and P3b generation are outlined, and a cognitive model is proffered: P3a originates from stimulus-driven frontal attention mechanisms during task processing, whereas P3b originates from temporal-parietal activity associated with attention and appears related to subsequent memory processing. Neurotransmitter actions associating P3a to frontal/dopaminergic and P3b to parietal/norepinephrine pathways are highlighted. Neuroinhibition is suggested as an overarching theoretical mechanism for P300, which is elicited when stimulus detection engages memory operations.

Association between P3 event-related brain potential amplitude and adolescent problem behavior

This study examined P3 event-related brain potential amplitude and the age of onset of adolescent problem behaviors associated with the development of externalizing psychopathology. Five hundred and one male and 627 female 17-year-old twins reported whether and when they had initiated tobacco, alcohol, or illicit drug use, had police contact, or had sexual intercourse. P3 amplitude was recorded using a visual oddball task. Each of these behaviors was associated with reduced P3 amplitude. When these five behaviors were used to create a composite early problem behavior scale reflecting onset prior to age 15, higher scores were associated with smaller P3 amplitudes. P3 amplitude reduction has been associated with genetic risk for alcoholism and other externalizing disorders associated with disinhibited behavior. Our results suggest that reduced P3 may also be associated with early expression of behaviors that predict the development of these disorders.