Using the brain P300 response to identify novel phenotypes reflecting genetic vulnerability for adolescent substance misuse

Examining associations between genetic and neural risk for externalizing behaviors in adolescence and early adulthood

BACKGROUND

Researchers have identified genetic and neural risk factors for externalizing behaviors. However, it has not yet been determined if genetic liability is conferred in part through associations with more proximal neurophysiological risk markers.

METHODS

Participants from the Collaborative Study on the Genetics of Alcoholism, a large, family-based study of alcohol use disorders were genotyped and polygenic scores for externalizing (EXT PGS) were calculated. Associations with target P3 amplitude from a visual oddball task (P3) and broad endorsement of externalizing behaviors (indexed via self-report of alcohol and cannabis use, and antisocial behavior) were assessed in participants of European (EA; N = 2851) and African ancestry (AA; N = 1402). Analyses were also stratified by age (adolescents, age 12-17 and young adults, age 18-32).

RESULTS

The EXT PGS was significantly associated with higher levels of externalizing behaviors among EA adolescents and young adults as well as AA young adults. P3 was inversely associated with externalizing behaviors among EA young adults. EXT PGS was not significantly associated with P3 amplitude and therefore, there was no evidence that P3 amplitude indirectly accounted for the association between EXT PGS and externalizing behaviors.

CONCLUSIONS

Both the EXT PGS and P3 amplitude were significantly associated with externalizing behaviors among EA young adults. However, these associations with externalizing behaviors appear to be independent of each other, suggesting that they may index different facets of externalizing.

Signal in the noise: Altered brain activation among adolescent alcohol users detected via the analysis of intra-individual variability1

RATIONALE

Unlike its average level, the variability in brain activation over time or trials can capture subtle and brief disruptions likely to occur among participants with low-to-moderate levels of substance use or misuse.

OBJECTIVE

The present study used this intra-individual variability measurement approach to detect neural processing differences associated with light-to-moderate use of alcohol among 14-19-year-old adolescents.

METHOD

A total of 128 participants reporting any level of alcohol use during the previous 6 months and 87 participants reporting no use during this period completed intake questionnaires and interviews as well as an assessment of P300 electroencephalographic responses to novel stimuli recorded during two separate tasks.

RESULTS

In addition to differing in recent alcohol use, the groups differed in nicotine and cannabis use, risk-taking behavior and conduct disorder symptoms, and P300 amplitude inter-trial variability (ITV) across both tasks. Across all participants, P300 ITV was positively correlated with a family history of depression but not with a family history of alcohol dependence. There were no group differences in P300 amplitude averaged across trials.

CONCLUSIONS

Recent reports attributing brain volume or brain function differences to an effect of light-to-moderate alcohol use should be viewed with great caution. In the present analysis of brain function differences among substance-using adolescents, the group differences were small, complicated by many factors coinciding with or preceding alcohol use, and not reflected in a stable central tendency.

Interaction of sex and cannabis in adult in vivo brain imaging studies: A systematic review

Cannabis has been shown to cause structural and functional neurocognitive changes in heavy users. Cannabis use initiation aligns with brain development trajectories; therefore, it is imperative that the potential neurological implications of cannabis use are understood. Males and females reach neurodevelopmental milestones at different rates making it necessary to consider biological sex in all cannabis and brain-based research. Through use of a systamatic review in accordance with PRISMA guidelines, we aimed to understand the interaction between biological sex and cannabis use on brain-based markers. In total, 18 articles containing a sex-based analysis of cannabis users were identified. While the majority of studies (n = 11) reported no sex by cannabis use interactions on brain-based markers, those that reported findings (n = 8) suggest females may be more susceptible to cannabis’ neurotoxic effects. Unfortunately, a large portion of the literature was excluded due to no sex-based analysis. In addition, studies that reported no sex differences often contained a reduced number of females which may result in some studies being underpowered for sex-based analyses, making it difficult to draw firm conclusions. Suggestions to improve cannabis and sex-based reseach are proposed.

Electrophysiological indexes for impaired response inhibition and salience attribution in substance (stimulants and depressants) use disorders: A meta-analysis

The impairment of inhibitory control and reward system is the core feature underlying substance use disorder (SUD). Previous studies suggested that it can be regarded as impaired response inhibition and salience attribution syndrome (iRISA). The neural substrates of the two deficit functions were widely investigated in neuroimaging studies, and the impaired prefrontal cortex, limbic-orbitofrontal network, and fronto-insular-parietal network were observed. Previous Event-related potential (ERP) studies were also conducted to explore EEG indexes related to abnormal brain function. In the current meta-analysis, we aimed to explore the consistency of ERP indexes that can reflect the two aberrant processes: P300/slow potential (SP) for salience attribution and Error-related negativity (ERN)/Nogo-N200/Nogo-P300 for inhibitory control and conflict monitoring. Subgroup analyses for drug type and drug use conditions were also conducted. According to the 60 research studies, we found significantly enhanced drug-cue-induced P300 amplitude and attenuated Nogo-N200 amplitude in SUD individuals relative to Healthy control (HC), which supports the dual model. Moreover, the drug-cue-induced P300 displayed time-dependence recovery, suggesting a potential index for treatment evaluation. In conclusion, drug-cue-induced P300 and Nogo-N200 demonstrated high consistency, and the drug-cue-induced P300 can be used to track the changes of functional recovery for SUD. The integration of the two ERP components could be regarded as a potential biomarker for SUD, which may provide a new insight for clinical treatment and investigation.

Heritability and molecular-genetic basis of the P3 event-related brain potential: a genome-wide association study

P3 amplitude is a candidate endophenotype for disinhibitory psychopathology, psychosis, and other disorders. The present study is a comprehensive analysis of the behavioral- and molecular-genetic basis of P3 amplitude and a P3 genetic factor score in a large community sample (N = 4,211) of adolescent twins and their parents, genotyped for 527,829 single nucleotide polymorphisms (SNPs). Biometric models indicated that as much as 65% of the variance in each measure was due to additive genes. All SNPs in aggregate accounted for approximately 40% to 50% of the heritable variance. However, analyses of individual SNPs did not yield any significant associations. Analyses of individual genes did not confirm previous associations between P3 amplitude and candidate genes but did yield a novel association with myelin expression factor 2 (MYEF2). Main effects of individual variants may be too small to be detected by GWAS without larger samples.

Longitudinal stability and predictive utility of the visual P3 response in adults with externalizing psychopathology

We determined whether time-domain P3 amplitude and time-frequency principal component (TF-PC) reductions could serve as stable and predictive developmental endophenotypes of externalizing psychopathology. Participants from the Minnesota Twin Family Study were assessed at age 17 and again at age 29 for lifetime externalizing (EXT) disorders. Comparisons of P3 amplitude and TF-PCs at delta and theta frequencies were made between EXT and unaffected comparison subjects. P3 amplitude and all five extracted TF-PCs were significantly reduced in those presenting lifetime EXT disorders at both ages 17 and 29 and showed substantial 12-year rank-order stability. P3 amplitude and delta TF-PCs measured at age 17 also predicted subsequent development of EXT by age 29, with every 1-microvolt decrease in age 17 amplitude associated with an approximately 5% increase in risk for an EXT diagnosis by age 29. Overall, results from this study further confirm that these P3-derived brain measures maintain their potential as putative EXT endophenotypes through the third decade of life.

The Power of Theory, Research Design, and Transdisciplinary Integration in Moving Psychopathology Forward

While the past few decades have seen much work in psychopathology research that has yielded provocative insights, relatively little progress has been made in understanding the etiology of mental disorders. We contend that this is due to an overreliance on statistics and technology with insufficient attention to adequacy of experimental design, a lack of integration of data across various domains of research, and testing of theoretical models using relatively weak study designs. We provide a conceptual discussion of these issues and follow with a concrete demonstration of our proposed solution. Using two different disorders - depression and substance use - as examples, we illustrate how we can evaluate competing theories regarding their etiology by integrating information from various domains including latent variable models, neurobiology, and quasi-experimental data such as twin and adoption studies, rather than relying on any single methodology alone. More broadly, we discuss the extent to which such integrative thinking allows for inferences about the etiology of mental disorders, rather than focusing on descriptive correlates alone. Greater scientific insight will require stringent tests of competing theories and a deeper conceptual understanding of the advantages and pitfalls of methodologies and criteria we use in our studies.

The Role of Nicotine in Schizophrenia

Schizophrenia is associated with by severe disruptions in thought, cognition, emotion, and behavior. Patients show a marked increase in rates of smoking and nicotine dependence relative to nonaffected individuals, a finding commonly ascribed to the potential ameliorative effects of nicotine on symptom severity and cognitive impairment. Indeed, many studies have demonstrated improvement in patients following the administration of nicotine. Such findings have led to an increased emphasis on the development of therapeutic agents to target the nicotinic system as well as increasing the impetus to understand the genetic basis for nicotinic dysfunction in schizophrenia. The goal of this review article is to provide a critical summary of evidence for the role of the nicotinic system in schizophrenia. The first part will review the role of nicotine in normalization of primary dysfunctions and endophenotypical changes found in schizophrenia. The second part will provide a summary of genetic evidence linking polymorphisms in nicotinic receptor genes to smoking and schizophrenia. The third part will summarize attempts to treat schizophrenia using agents specifically targeting nicotinic and nicotinic receptor subtypes. Although currently available antipsychotic treatments are generally able to manage some aspects of schizophrenia (e.g., positive symptoms) they fail to address several other critically effected aspects of the disease. As such, the search for novel mechanisms to treat this disease is necessary.

Does electroencephalogram phase variability account for reduced P3 brain potential in externalizing disorders?

OBJECTIVE

Amplitude deficits of the P3 event-related potential (ERP) are associated with externalizing psychopathology but little is known about the nature of underlying brain electrical activity that accounts for this amplitude reduction. We sought to understand if group differences in task-induced phase-locking in electroencephalographic (EEG) delta and theta frequencies may account for P3-externalizing associations.

METHODS

Adult males (N=410) completed a visual oddball task and frontal and parietal P3-related delta- and theta-band phase-invariant evoked energy and inter-trial phase-locking measures were investigated with respect to the externalizing spectrum, including substance dependence, adult antisociality, and childhood disruptive disorders. We hypothesized that P3-related phase-locking is weaker in externalizing-diagnosed individuals and this might mediate prior findings of reduced evoked P3 energy.

RESULTS

Reductions in both evoked energy and phase-locking, in both frequency bands, at both scalp sites, were associated with greater odds of externalizing diagnoses. Generally, adding phase-locking to evoked energy came with better prediction model fit. Moreover, reduced theta-band phase-locking partially mediated the effects of within-frequency evoked energy on externalizing prediction.

CONCLUSIONS

Inter-trial phase-locking underlying P3 appears to be an important distinction between externalizing and control subjects.

SIGNIFICANCE

This cross-trial phase-variability for externalizing-diagnosed individuals might reflect deficient top-down "tuning" by neuromodulatory systems.

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.

Genetic influences on composite neural activations supporting visual target identification

Behavior genetic studies of brain activity associated with complex cognitive operations may further elucidate the genetic and physiological underpinnings of basic and complex neural processing. In the present project, monozygotic (N=51 pairs) and dizygotic (N=48 pairs) twins performed a visual oddball task with dense-array EEG. Using spatial PCA, two principal components each were retained for targets and standards; wavelets were used to obtain time-frequency maps of eigenvalue-weighted event-related oscillations for each individual. Distribution of inter-trial phase coherence (ITC) and single trial power (STP) over time indicated that the early principal component was primarily associated with ITC while the later component was associated with a mixture of ITC and STP. Spatial PCA on point-by-point broad sense heritability matrices revealed data-derived frequency bands similar to those well established in EEG literature. Biometric models of eigenvalue-weighted time-frequency data suggest a link between physiology of oscillatory brain activity and patterns of genetic influence.

Psychopathic traits and physiological responses to aversive stimuli in children aged 9-11 years

Atypical eletrodermal and cardiovascular response patterns in psychopathic individuals are thought to be biological indicators of fearless and disinhibition. This study investigated the relationship between psychopathic traits and these autonomic response patterns using a countdown task in 843 children (aged 9-10 years). Heart rate (HR) and non-specific skin conductance responses (NS-SCRs) were recorded while participants anticipated and reacted to 105 dB signaled or un-signaled white-noise bursts. Using multilevel regression models, both larger HR acceleration and fewer NS-SCR were found to be significantly associated with psychopathic traits during anticipation of signaled white-noise bursts. However, two divergent patterns appeared for HR and SCR: (1) larger HR acceleration was specific to the callousness-disinhibition factor of psychopathic traits while reduced NS-SCR was only associated with the manipulative-deceitfulness factor; (2) the negative association between the manipulative-deceitfulness factor and NS-SCR was only found in boys but not in girls. These findings replicated what has been found in psychopathic adults, suggesting that autonomic deficits present in children at risk may predispose them to later psychopathy. The divergent findings across psychopathic facets and sexes raised the possibility of different etiologies underlying psychopathy, which may in turn suggest multiple treatment strategies for boys and girls.

Minnesota Center for Twin and Family Research

The Minnesota Center for Twin and Family Research (MCTFR) houses a collection of longitudinal, community-based twin-family and adoptee-family projects that focus on the mental health outcomes of adolescent youth with a special focus on the development of substance use and related behavior disorders. The Minnesota Twin Family Study includes epidemiological investigations of 11- and 17-year-old twins, an examination of 11-year-old twins selected for being at high risk for having a childhood disruptive behavior disorder, and a supplemental registry of young adult twins age 18 years and older who are not enrolled in these longitudinal studies. Also, part of the MCTFR is the Sibling Interaction and Behavior Study, a complementary prospective investigation of adolescent sibling pairs in families with adoptive and biological offspring. MCTFR participants from these various projects are assessed in person and through multiple informants to provide comprehensive coverage of psychological adjustment, mental health, and psychosocial risk/protective factors. Measurement of EEG and autonomic nervous system reactivity is also part of the assessment battery for twin families. This article provides an overview of study design and includes a review of recent MCTFR findings.

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.

A longitudinal twin study of effects of adolescent alcohol abuse on the neurophysiology of attention and orienting

BACKGROUND

Long-term functional brain effects of adolescent alcohol abuse remain uncertain, partially because of difficulties in distinguishing inherited deficits from neuronal effects of ethanol and by confounds associated with alcohol abuse, especially nicotine exposure. We conducted a longitudinal twin study to determine neurocognitive effects of adolescent alcohol abuse, as measured with the auditory event-related potential (ERP) component P3, a putative marker of genetic vulnerability to alcoholism.

METHODS

Twin pairs (N=177; 150 selected for intrapair concordance/discordance for alcohol-related problems at age 18½) were recruited from ongoing studies of twins born 1975-1979 in Finland. Alcohol and tobacco use were assessed with questionnaires at ages 16, 17, 18½, and ~25, and by a structured psychiatric interview concurrent with the ERP testing at mean age 25.8. During ERP recordings, subjects were instructed to detect target tones within a train of frequent "standards" and to ignore occasional "novel" sounds. To distinguish familial factors from ethanol effects, ERP and self-reported alcohol use measures were incorporated into hierarchical multiple regression (HMR) analysis, and intrapair differences in ERP were associated with intra-pair differences in alcohol variables.

RESULTS

Novel-sound P3 amplitude correlated negatively with self-reported alcohol use in both between- and within-family analyses. No similar effect was observed for target-tone P3. HMR results suggest that twins' similarity for novel-sound P3 amplitude is modulated by their alcohol use, and this effect of alcohol use is influenced by genetic factors.

CONCLUSIONS

Our results, from a large sample of twins selected from a population-based registry for pairwise concordance/discordance for alcohol problems at 18½, demonstrate that adolescent alcohol abuse is associated with subtle neurophysiological changes in attention and orienting. The changes are reflected in decreased novel-sound P3 amplitude and may be modified by genetic factors.

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.

Cerebellar lingula size and experiential risk factors associated with high levels of alcohol and drug use in young adults

Previous studies have reported cerebellar abnormalities or static ataxia associated with risk for chronic use of alcohol and drugs. Adverse childhood experience is another strong risk factor for later substance abuse. We therefore sought to ascertain the relationship between morphological phenotypes of the lingula (lobule I) of the anterior cerebellar vermis, and exposure to emotional (EM) versus physical (PM) maltreatment, on the degree of ongoing alcohol or drug use. The study design consisted of a cross-sectional in vivo neuroimaging study, utilizing retrospective assessment of maltreatment history and self-reports of alcohol and substance use. Study participants were 153 subjects (54 M/99F, 21.9 +/- 2.2 years) selected for imaging from a database of 1,402 community participants 18-25 years of age, who completed a detailed online screening instrument and met rigorous inclusion/exclusion criteria. Subjects were exposed to only physical abuse or harsh corporal punishment (HCP; PM group, n = 37) and parental verbal abuse and/or witnessing domestic violence (EM group, n = 58) or had no history of maltreatment or axis I disorders (n = 58). The main outcome measures consisted of the gray matter volume of lobule I as measured by manual tracing, number and type of alcoholic beverages consumed during a drinking session, number of sessions per month, and monthly drug use, along with family history of drug and alcohol abuse. Lingula thickness was not attenuated by alcohol use or maltreatment history. However, increased lingula thickness was associated with greater consumption of drugs and hard liquor, particularly in physically maltreated subjects who consumed 2.5- and 2.7-fold more alcohol and used drugs 6.1- and 7.8-fold more frequently than controls or EM subjects, respectively. In conclusion, physical maltreatment was observed to interact with cerebellar morphology resulting in a strong association with alcohol and substance use. Lingula thickness may represent a novel, experientially sensitive, phenotypic risk factor for enhanced alcohol and drug use that perhaps modulates sensitivity to these agents.

Cannabis with high δ9-THC contents affects perception and visual selective attention acutely: an event-related potential study

OBJECTIVE

Cannabis intake has been reported to affect cognitive functions such as selective attention. This study addressed the effects of exposure to cannabis with up to 69.4mg Delta(9)-tetrahydrocannabinol (THC) on Event-Related Potentials (ERPs) recorded during a visual selective attention task.

METHODS

Twenty-four participants smoked cannabis cigarettes with four doses of THC on four test days in a randomized, double blind, placebo-controlled, crossover study. Two hours after THC exposure the participants performed a visual selective attention task and concomitant ERPs were recorded.

RESULTS

Accuracy decreased linearly and reaction times increased linearly with THC dose. However, performance measures and most of the ERP components related specifically to selective attention did not show significant dose effects. Only in relatively light cannabis users the Occipital Selection Negativity decreased linearly with dose. Furthermore, ERP components reflecting perceptual processing, as well as the P300 component, decreased in amplitude after THC exposure. Only the former effect showed a linear dose-response relation.

CONCLUSIONS

The decrements in performance and ERP amplitudes induced by exposure to cannabis with high THC content resulted from a non-selective decrease in attentional or processing resources.

SIGNIFICANCE

Performance requiring attentional resources, such as vehicle control, may be compromised several hours after smoking cannabis cigarettes containing high doses of THC, as presently available in Europe and Northern America.

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.

A cognitive model for the intergenerational transference of alcohol use behavior

A family history of alcoholism has shown to be one of the greatest consistent risk factors in the intergenerational transference of alcohol problems. Whereas a large number of studies have attempted to identify the processes responsible for this interfamilial transfer, the mechanisms remain unclear. Family, twin and adoption studies, and environmental theories have resulted in a number of unanswered questions regarding the extent that these factors influence the transmission of alcohol behavior. Recently, cognitive theories have suggested that the observation of parental drinking habits contributes to the child's beliefs and expectations of alcohol's effects. A hypothesised cognitive model will be proposed suggesting that the mechanism for the transference of particular drinking styles from parent to offspring may be further explained by the transference of alcohol cognitions, in particular, alcohol expectancies and drinking refusal self-efficacy. This review focuses on research of bio/psycho/social factors that perpetuate alcohol misuse across generations, and will delineate the proposed cognitive mechanisms for the interfamilial transference of alcohol problems and discuss the implications of the proposed model.

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.

The P300 as a possible endophenotype for schizophrenia and bipolar disorder: Evidence from twin and patient studies

It has been proposed that psychophysiological abnormalities in schizophrenia, such as decreased amplitude of the evoked potential component P300, may be genetically influenced. Studies of heritability of the P300 have used different and typically more complex tasks than those used in clinical studies of schizophrenia. Here we present data on P300 parameters on the same set of auditory and visual tasks in samples of twins, and patients with schizophrenia or bipolar disorder to examine the P300 as a possible endophenotype. Evidence from the twin study indicated that the auditory, but not visual, P300 amplitude is genetically influenced at centro-parietal sites. Similarly, auditory and to a lesser extent visual P300 amplitude were decreased in schizophrenia and bipolar disorder. Results indicate that the auditory P300 may serve as an endophenotype for schizophrenia. However, given that schizophrenia and bipolar disorder patients could not be distinguished on these measures at midline sites, it appears that the P300 may be a marker for functional psychosis in general rather than being specific to schizophrenia.

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.

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.

Auditory event-related potentials (P3) and cognitive performance in recreational ecstasy polydrug users: evidence from a 12-month longitudinal study

RATIONALE

There is important preclinical evidence of the long-lasting neurotoxic and selective effects of ecstasy (MDMA) on serotonin systems in nonhuman primates. In humans, long-term recreational use of ecstasy has been mainly associated with memory impairment.

OBJECTIVE

The first aim of our study was to evaluate the cognitive and electrophysiological long-term alterations associated with lifetime ecstasy use within a sample of ecstasy polydrug users along a 1-year follow-up. Our second aim was to explore the relationship between specific cognitive functions and P300 (P3) event-related potentials (ERPs) in ecstasy users.

MATERIALS AND METHODS

We conducted auditory P3 latency and amplitude and administered a battery of cognitive tests to three groups of subjects: 14 current ecstasy polydrug users, 13 current cannabis users, and 22 controls free of illicit drugs in two evaluations during 1 year.

RESULTS

We found significant differences between ecstasy users and controls on cognitive measures of word fluency, processing speed, and memory recognition after 1-year follow-up. We found no significant differences between ecstasy and cannabis users or cannabis users and controls on cognitive tests. Lifetime ecstasy use was associated with poorer memory recognition. No group differences were shown on P3 latency or amplitude. Significant correlations emerged between P3 latency and cannabis lifetime use (higher cannabis use was related to faster latency, showing a paradoxical effect) but not with ecstasy exposure.

CONCLUSIONS

Our findings provide evidence of mild long-term cognitive deficits among ecstasy polydrug users. Both ecstasy use and the dynamic interaction between ecstasy and cannabis effects may account for these deficits. No significant P3 alterations were found in ecstasy users.

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.

Addictions biology: haplotype-based analysis for 130 candidate genes on a single array

AIMS

To develop a panel of markers able to extract full haplotype information for candidate genes in alcoholism, other addictions and disorders of mood and anxiety.

METHODS

A total of 130 genes were haplotype tagged and genotyped in 7 case/control populations and 51 reference populations using Illumina GoldenGate SNP genotyping technology, determining haplotype coverage. We also constructed and determined the efficacy of a panel of 186 ancestry informative markers.

RESULTS

An average of 1465 loci were genotyped at an average completion rate of 91.3%, with an average call rate of 98.3% and replication rate of 99.7%. Completion and call rates were lowered by the performance of two datasets, highlighting the importance of the DNA quality in high throughput assays. A comparison of haplotypes captured by the Addictions Array tagging SNPs and commercially available whole-genome arrays from Illumina and Affymetrix shows comparable performance of the tag SNPs to the best whole-genome array in all populations for which data are available.

CONCLUSIONS

Arrays of haplotype-tagged candidate genes, such as this addictions-focused array, represent a cost-effective approach to generate high-quality SNP genotyping data useful for the haplotype-based analysis of panels of genes such as these 130 genes of interest to alcohol and addictions researchers. The inclusion of the 186 ancestry informative markers allows for the detection and correction for admixture and further enhances the utility of the array.

QTLs identified for P3 amplitude in a non-clinical sample: importance of neurodevelopmental and neurotransmitter genes

BACKGROUND

The P3(00) event-related potential is an index of processing capacity (P3 amplitude) and stimulus evaluation (P3 latency) as well as a phenotypic marker of various forms of psychopathology where P3 abnormalities have been reported.

METHODS

A genome-wide linkage scan of 400-761 autosomal markers, at an average spacing of 5-10 centimorgans (cM), was completed in 647 twins/siblings (306 families mostly comprising dizygotic twins), mean age 16.3, range 15.4-20.1 years, for whom P3 amplitude and latency data were available.

RESULTS

Significant linkage for P3 amplitude was observed on chromosome 7q for the central recording site (logarithm-of-odds [LOD] = 3.88, p = .00002) and in the same region for both frontal (LOD = 2.19, p = .0015) and parietal (LOD = 1.67, p = .0053) sites, with multivariate analysis also identifying linkage in this region (LOD = 2.14, p = .0017). Suggestive linkage was also identified on 6p (LOD(max) = 2.49) and 12q (LOD(max) = 2.24), with other promising regions identified on 9q (LOD(max) = 2.14) and 10p (LOD(max) = 2.18). Less striking were the results for P3 latency; LOD > 1.5 were found on chromosomes 1q, 9q, 10q, 12q, and 19p.

CONCLUSIONS

This is a first step in the identification of genes for normal variation in the P3. Loci identified here for P3 amplitude suggest the possible importance of neurodevelopmental genes in addition to those influencing neurotransmitters, fitting with the evidence that P3 amplitude is sensitive to diverse types of brain abnormalities.

Polymorphisms of the dopamine D4 receptor gene (DRD4 VNTR) and cannabinoid CB1 receptor gene (CNR1) are not strongly related to cue-reactivity after alcohol exposure

Polymorphisms in the D4 dopamine receptor gene (DRD4) and the CB1 cannabinoid receptor gene (CNR1) have been associated with a differential response to alcohol after consumption. The goal of the present study was to investigate whether heavy drinkers with these polymorphisms would respond with enhanced cue-reactivity after alcohol exposure. Eighty-eight male heavy drinkers were genotyped for the DRD4 variable number of tandem repeats (VNTR) [either DRD4 long (L) or short (S)] and the CNR1 rs2023239 polymorphism (either CT/CC or TT). Participants were exposed to water and beer in 3-minute trials. Dependent variables of main interest were subjective craving for alcohol, subjective arousal and salivary reactivity. Overall, no strong evidence was found for stronger cue-reactivity (= outcome difference between beer and water trial) in the DRD4 L and CNR1 C allele groups. The DRD4 VNTR polymorphism tended to moderate salivary reactivity such that DRD4 L participants showed a larger beverage effect than the DRD4 S participants. Unexpectedly, the DRD4 L participants reported, on average, less craving for alcohol and more subjective arousal during cue exposure, compared with the DRD4 S participants. As weekly alcohol consumption increased, the CNR1 C allele group tended to report more craving for alcohol during the alcohol exposure than the T allele group. The DRD4 and CNR1 polymorphisms do not appear to strongly moderate cue-reactivity after alcohol cue exposure, in male heavy drinkers.

Heritability of P300 amplitude development from adolescence to adulthood

Early adulthood is a period of late brain development corresponding to the age of onset for psychopathology associated with P300 amplitude reductions. Although amplitude from a single occasion is heritable, little is known about genetic influences on change during this period. This is the first study of P300 change to combine latent growth and twin models. P300 at Pz was measured up to three times at approximately ages 17, 20, and 23 in monozygotic and dizygotic male twins using a visual task. P300 decreased with age. Correlations indexing the stability of amplitude over time were high (median r=.72) and almost 90% of the stable variance (i.e., the model intercept) was attributable to genetic influences. The rate of decrease was heritable, and the genes influencing intercept may be the same ones influencing change. Finally, intercept was more heritable than amplitude at any single time point. Intercept may be a more useful aid in the search for genes associated with relevant psychopathology than single measures of P300. Over a broader age range growth indices may be useful "developmental" endophenotypes.