P300 event-related potential amplitude as an endophenotype of alcoholism--evidence from the collaborative study on the genetics of alcoholism

The Collaborative Study on the Genetics of Alcoholism: Overview

Alcohol use disorders (AUD) are commonly occurring, heritable and polygenic disorders with etiological origins in the brain and the environment. To outline the causes and consequences of alcohol-related milestones, including AUD, and their related psychiatric comorbidities, the Collaborative Study on the Genetics of Alcoholism (COGA) was launched in 1989 with a gene-brain-behavior framework. COGA is a family based, diverse (~25% self-identified African American, ~52% female) sample, including data on 17,878 individuals, ages 7-97 years, in 2246 families of which a proportion are densely affected for AUD. All participants responded to questionnaires (e.g., personality) and the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) which gathers information on psychiatric diagnoses, conditions and related behaviors (e.g., parental monitoring). In addition, 9871 individuals have brain function data from electroencephalogram (EEG) recordings while 12,009 individuals have been genotyped on genome-wide association study (GWAS) arrays. A series of functional genomics studies examine the specific cellular and molecular mechanisms underlying AUD. This overview provides the framework for the development of COGA as a scientific resource in the past three decades, with individual reviews providing in-depth descriptions of data on and discoveries from behavioral and clinical, brain function, genetic and functional genomics data. The value of COGA also resides in its data sharing policies, its efforts to communicate scientific findings to the broader community via a project website and its potential to nurture early career investigators and to generate independent research that has broadened the impact of gene-brain-behavior research into AUD.

Paternal alcohol exposure has task- and sex-dependent behavioral effect in offspring

BACKGROUND

Endophenotypes for alcohol use disorder are well known and may reflect paternal exposure effects passed down to offspring via epigenetic mechanisms. Previously, we showed that paternal alcohol exposure prior to conception attenuates the acquisition of operant alcohol self-administration. We now test whether paternal alcohol exposure alters their offsprings' behavioral responses to alcohol (endophenotypes) and global DNA methylation levels in reward-related brain regions.

METHODS

Adult male rats were exposed to alcohol vapors or air for 6 weeks and mated with alcohol-naïve females 8 weeks later. Adult male and female offspring of the alcohol- and control-sired litters were tested on three behaviors 30 m after gavage with water or alcohol (1.5 g/kg): open field, elevated plus maze, and accelerating rotarod. Global DNA methylation levels in sperm, nucleus accumbens, and prefrontal cortex were examined in male sires and in another group of offspring.

RESULTS

Alcohol-sired males showed less anxiety-like behavior in the elevated plus maze that was not affected by alcohol administration. By contrast, alcohol had anxiolytic effects in the open field in male offspring only with no paternal alcohol effect. Neither paternal alcohol exposure nor alcohol administration altered locomotor activity in either sex. Sex-specific effects of paternal alcohol exposure were seen in the rotarod test. Alcohol-sired male offspring showed blunted sensitivity to the alcohol's motor-impairing effects, whereas alcohol-sired female offspring showed enhanced sensitivity. Global DNA methylation was altered in the sperm of alcohol-exposed males, but no changes were seen in their offspring.

CONCLUSIONS

Paternal alcohol exposure prior to conception has sex- and task-dependent effects on unconditioned behaviors in their offspring.

Cognitive impairment in the co-occurrence of alcohol dependence and major depression: neuropsychological assessment and event-related potentials analyses

To evaluate the putative detrimental effect of Major Depressive Disorder (MDD) on the cognitive impairment associated with Alcohol Dependence (AD), we contrasted the neuropsychological profile and behavioral responses of AD subjects, MDD individuals, and in those with a co-occurring AD-MDD diagnosis (DD). Patients and healthy subjects completed a comprehensive neuropsychological battery and were recorded for P200, P300, and N450 event-related potentials during memory and Stroop tasks. AD subjects exhibited a generalized detrimental neuropsychological performance; in contrast, in MDD individuals, impairment was limited to discrete domains. Notably, the deficits were distinctive in DD cases. A P200 increased amplitude in MDD, a decrease in P300 amplitude in AD, and increased latency of P300 in DD patients were the overt electrophysiological abnormalities identified. Dual patients also exhibited a distinct pattern of behavioral responses, particularly apparent during high-demand cognitive tasks. Specific ERP adjustments were associated with the short-term fluoxetine treatment in DD and MDD subjects; the SSRI also improved altered baseline performance in learning and cognitive flexibility in DD subjects. In conclusion, the neuropsychological and behavioral alterations detected in the co-occurrence of AD-MDD did not seem to be merely the sum of the negative contributions of the independent disorders.

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Dual diagnosis (DD) patients exhibited a distinctive pattern of cognitive impairments compared to single diagnosis subjects.

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The ERP alterations identified were not shared among affected groups.

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Dual patients exhibited idiosyncratic behavioral responses.

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Impaired executive functions in DD subjects improved with SSRI medication.

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Neuropsychological and behavioral alterations are not explained as the sum of negative contributions of individual diagnosis.

Predictors of chronicity in alcohol use disorder: an evoked response potential study

INTRODUCTION

Evoked response potentials (ERP) can reliably map key neurocognitive processes which are putatively responsible for chronic alcohol use disorder (AUD). Aim of the present study was to study P300 auditory odd ball and N400 visual semantic incongruity paradigm mapping executive functions rubric as a potential biomarker predicting chronicity in AUDs. Methodology: 60 right handed 18 to 54 years age subjects were divided into chronic "CAD" and non chronic alcohol dependence "NAD" in addition to healthy control "HC" (N = 30). Subjects were assessed by Addiction Severity Index (ASI), P300 auditory odd ball paradigm in midline region and visual N400 semantic incongruity task in centro-parietal region in a cross sectional design. Results: All the three groups differed significantly for P300 and N400 amplitude in all the leads with maximum attenuation seen in CAD. On discriminant function analysis (DFA), P300 Pz and N 400 C2 amplitude values could accurately classified 78.3% subjects. Composite sensitivity and specificity of the two predictor variables differentiating CAD subjects from NAD were 79.31 and 77.41%. receiver operating characteristic curve generated an area under the curve of .758 and .847 i.e., "fair to good" ability to predict CAD from NAD. Conclusion: We conclude that specific ERP paradigm can be used as a state marker to map the cognitive deficits and as a biomarker to detect chronic AUDs.

Establishing norms for error-related brain activity during the arrow Flanker task among young adults

Psychological assessments typically rely on self-report and behavioral measures. Augmenting these with neurophysiological measures of the construct in question may increase the accuracy and predictive power of these assessments. Moreover, thinking about neurophysiological measures from an assessment perspective may facilitate under-utilized research approaches (e.g., brain-based recruitment of participants). However, the lack of normative data for most neurophysiological measures has prevented the comparison of individual responses to the general population, precluding these approaches. The current work examines the distributions of two event-related potentials (ERPs) commonly used in individual differences research: the error-related negativity (ERN) and error positivity (Pe). Across three lab sites, 800 unselected participants between the ages of 18 and 30 performed the arrow version of a Flanker task while EEG was recorded. Percentile scores and distributions for ERPs on error trials, correct trials, and the difference (ΔERN, ΔPe; error minus correct) at Fz, Cz and Pz are reported. The 25th, 50th, and 75th percentile values for the ΔERN at Cz were -2.37 ​μV, -5.41 ​μV, and -8.65 ​μV, respectively. The same values for ΔPe at Cz were 7.51 ​μV, 11.18 ​μV, and 15.55 ​μV. Females displayed significantly larger ΔPe magnitudes and smaller ΔERN magnitudes than males. Additionally, normative data for behavioral performance (accuracy, post-error slowing, and reaction time) on the Flanker task is reported. Results provide a means by which ERN and Pe amplitudes of young adults elicited by the arrow Flanker task can be benchmarked, facilitating the classification of neural responses as 'large,' 'medium,' or 'small'. The ability to classify responses in this manner is a necessary step towards expanded use of these measures in assessment and research settings. These norms may not apply to ERPs elicited by other tasks, and future work should establish similar norms using other tasks.

Density and Dichotomous Family History Measures of Alcohol Use Disorder as Predictors of Behavioral and Neural Phenotypes: A Comparative Study Across Gender and Race/Ethnicity

BACKGROUND

Family history (FH) is an important risk factor for the development of alcohol use disorder (AUD). A variety of dichotomous and density measures of FH have been used to predict alcohol outcomes; yet, a systematic comparison of these FH measures is lacking. We compared 4 density and 4 commonly used dichotomous FH measures and examined variations by gender and race/ethnicity in their associations with age of onset of regular drinking, parietal P3 amplitude to visual target, and likelihood of developing AUD.

METHODS

Data from the Collaborative Study on the Genetics of Alcoholism (COGA) were utilized to compute the density and dichotomous measures. Only subjects and their family members with DSM-5 AUD diagnostic information obtained through direct interviews using the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) were included in the study. Area under receiver operating characteristic curves were used to compare the diagnostic accuracy of FH measures at classifying DSM-5 AUD diagnosis. Logistic and linear regression models were used to examine associations of FH measures with alcohol outcomes.

RESULTS

Density measures had greater diagnostic accuracy at classifying AUD diagnosis, whereas dichotomous measures presented diagnostic accuracy closer to random chance. Both dichotomous and density measures were significantly associated with likelihood of AUD, early onset of regular drinking, and low parietal P3 amplitude, but density measures presented consistently more robust associations. Further, variations in these associations were observed such that among males (vs. females) and Whites (vs. Blacks), associations of alcohol outcomes with density (vs. dichotomous) measures were greater in magnitude.

CONCLUSIONS

Density (vs. dichotomous) measures seem to present more robust associations with alcohol outcomes. However, associations of dichotomous and density FH measures with different alcohol outcomes (behavioral vs. neural) varied across gender and race/ethnicity. These findings have great applicability for alcohol research examining FH of AUD.

Smaller Feedback-Related Negativity (FRN) Reflects the Risky Decision-Making Deficits of Methamphetamine Dependent Individuals

Methamphetamine (MA) chronic users show risky decision-making deficits. However, the neural mechanisms underlying these deficits remain unclear. A case-control study was conducted to understand how MA users and healthy controls differ in electrophysiological responses associated with series decision-making. Electroencephalography of 31 MA users and 27 healthy controls was recorded when they performed the Balloon Analogue Risk Task involving risky decision-making with uncertain gain or loss. Feedback-related negativity (FRN) was measured and their association with their risky decision-making and impulsivity were examined. Compared to healthy controls, MA users showed smaller peak FRN amplitudes in fronto-central electrodes (F _{(1, 56)} =4.559, p=0.037), and the attenuated peak FRN amplitudes correlated with more risk-taking behavior (r=0.48, p=0.012). Besides, MA users exhibited later FRN (F _{(1, 56)} = 7.561, p=0.008) and earlier P300 (F _{(1, 56)} = 3.582, p = 0.041) compared to healthy controls in fronto-central electrodes, which were correlated with higher score of impulsivity. These findings provided further evidence that MA users showed insensitivity to negative feedback in risky decision-making. FRN might be a promising biomarker of dependence.

Sustained dysfunctional information processing in patients with Internet gaming disorder: 6-month follow-up ERP study

Internet gaming disorder (IGD), defined as an inability to control Internet-based game play, leads to serious impairment in psychological and social functioning, but few studies have identified the neurophysiological characteristics of patients with IGD. The aim of this study was to determine neurophysiological markers of P300 components associated with changes in symptoms after outpatient management with pharmacotherapy in patients with IGD. The present prospective longitudinal study included 18 patients with IGD and 29 healthy controls. The patients with IGD completed a 6-month outpatient management program including selective serotonin reuptake inhibitor-based pharmacotherapy. Event-related potentials (ERPs) were acquired during the auditory oddball task. ERPs of the patients with IGD were recorded before and after treatment. Between-group differences and the pre-to-post treatment differences in P300 components were investigated using repeated-measures analysis of variance. The primary treatment outcome was a change in score on Young Internet Addiction Test between before and after treatment. At baseline assessments, the IGD group showed significantly reduced P300 amplitudes and delayed latencies at the midline centro-parietal site compared with those in the healthy controls. No significant changes in the P300 indices were observed between pre and post-treatment in the patients with IGD after 6 months of treatment, even though the patients with IGD exhibited significant improvements in their IGD symptoms. Furthermore, no significant difference in ERPs was observed between responders and nonresponders to a 6-month treatment in patients with IGD. These results suggest that reduced P300 amplitudes and delayed latencies are candidate endophenotypes in the pathophysiology of IGD.

One-year developmental stability and covariance among oddball, novelty, go/no-go, and flanker event-related potentials in adolescence: A monozygotic twin study

ERP measures may index genetic risk for psychopathology before disorder onset in adolescence, but little is known about their developmental rank-order stability during this period of significant brain maturation. We studied ERP stability in 48 pairs of identical twins (age 14-16 years) tested 1 year apart. Trial-averaged voltage waveforms were extracted from electroencephalographic recordings from oddball/novelty, go/no-go, and flanker tasks, and 16 amplitude measures were examined. Members of twin pairs were highly similar, whether based on ERP amplitude measures (intraclass correlation [ICC] median = .64, range = .44-.86) or three factor scores (all ICCs ≥ .69) derived from them. Stability was high overall, with 69% of the 16 individual measures generating stability coefficients exceeding .70 and all factor scores showing stability above .75. Measures from 10 difference waveforms calculated from paired conditions within tasks were also examined, and were associated with lower twin similarity (ICC median = .52, .38-.64) and developmental stability (only 30% exceeding .70). In a supplemental analysis, we found significant developmental stability for error-related negativity (range = .45-.55) and positivity (.56-.70) measures when average waveforms were based on one or more trials, and that these values were equivalent to those derived from averages using the current field recommendation, which requires six or more trials. Overall, we conclude that the studied brain measures are largely stable over 1 year of mid- to late adolescence, likely reflecting familial etiologic influences on brain functions pertaining to cognitive control and salience recognition.

Dysfunctional information processing during an auditory event-related potential task in individuals with Internet gaming disorder

Internet gaming disorder (IGD) leading to serious impairments in cognitive, psychological and social functions has gradually been increasing. However, very few studies conducted to date have addressed issues related to the event-related potential (ERP) patterns in IGD. Identifying the neurobiological characteristics of IGD is important to elucidate the pathophysiology of this condition. P300 is a useful ERP component for investigating electrophysiological features of the brain. The aims of the present study were to investigate differences between patients with IGD and healthy controls (HCs), with regard to the P300 component of the ERP during an auditory oddball task, and to examine the relationship of this component to the severity of IGD symptoms in identifying the relevant neurophysiological features of IGD. Twenty-six patients diagnosed with IGD and 23 age-, sex-, education- and intelligence quotient-matched HCs participated in this study. During an auditory oddball task, participants had to respond to the rare, deviant tones presented in a sequence of frequent, standard tones. The IGD group exhibited a significant reduction in response to deviant tones compared with the HC group in the P300 amplitudes at the midline centro-parietal electrode regions. We also found a negative correlation between the severity of IGD and P300 amplitudes. The reduced amplitude of the P300 component in an auditory oddball task may reflect dysfunction in auditory information processing and cognitive capabilities in IGD. These findings suggest that reduced P300 amplitudes may be candidate neurobiological marker for IGD.

Electrophysiological Endophenotypes for Schizophrenia

Endophenotypes are quantitative, heritable traits that may help to elucidate the pathophysiologic mechanisms underlying complex disease syndromes, such as schizophrenia. They can be assessed at numerous levels of analysis; here, we review electrophysiological endophenotypes that have shown promise in helping us understand schizophrenia from a more mechanistic point of view. For each endophenotype, we describe typical experimental procedures, reliability, heritability, and reported gene and neurobiological associations. We discuss recent findings regarding the genetic architecture of specific electrophysiological endophenotypes, as well as converging evidence from EEG studies implicating disrupted balance of glutamatergic signaling and GABAergic inhibition in the pathophysiology of schizophrenia. We conclude that refining the measurement of electrophysiological endophenotypes, expanding genetic association studies, and integrating data sets are important next steps for understanding the mechanisms that connect identified genetic risk loci for schizophrenia to the disease phenotype.

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.

Drinking beyond a lifetime: New and emerging insights into paternal alcohol exposure on subsequent generations

Alcohol-use disorder (AUD) is prevalent and associated with substantial socioeconomic costs. While heritability estimates of AUD are ∼50%, identifying specific gene variants associated with risk for AUD has proven challenging despite considerable investment. Emerging research into heritability of complex diseases has implicated transmission of epigenetic variants in the development of behavioral phenotypes, including drug preference and drug-induced behavior. Several recent rodent studies have specifically focused on paternal transmission of epigenetic variants, which is especially relevant because sires are not present for offspring rearing and changes to offspring phenotype are assumed to result from modifications to the sperm epigenome. While considerable interest in paternal transmission of epigenetic variants has emerged recently, paternal alcohol exposures have been studied for 30+ years with interesting behavioral and physiologic effects noted on offspring. However, only recently, with improvements in technology to identify epigenetic modifications in germ cells, has it been possible to identify mechanisms by which paternal ethanol exposure alters offspring behavior. This review presents an overview of epigenetic inheritance in the context of paternal ethanol exposure and suggests future studies to identify specific effects of paternal ethanol exposure on offspring behavior and response to ethanol.

Blunted feedback processing during risk-taking in adolescents with features of problematic Internet use

While the conceptualization of problematic Internet use (PIU) as a "behavioral addiction" resembling substance-use disorders is debated, the neurobiological underpinnings of PIU remain understudied. This study examined whether adolescents displaying features of PIU (at-risk PIU; ARPIU) are more impulsive and exhibit blunted responding in the neural mechanisms underlying feedback processing and outcome evaluation during risk-taking. Event-related potentials (ERPs) elicited by positive (i.e. reward) and negative (i.e. loss) feedback were recorded during performance on a modified version of the Balloon Analogue Risk Task (BART) among ARPIU (n=39) and non-ARPIU subjects (n=27). Compared to non-ARPIU, ARPIU adolescents displayed higher levels of urgency and lack of perseverance on the UPPS Impulsive Behavior Scale. Although no between-group difference in BART performance was observed, ERPs demonstrated overall decreased sensitivity to feedback in ARPIU compared to non-ARPIU adolescents, as indexed by blunted feedback-related negativity (FRN) and P300 amplitudes to both negative and positive feedback. The present study provides evidence for feedback processing during risk-taking as a neural correlate of ARPIU. Given recent concerns regarding the growing prevalence of PIU as a health concern, future work should examine the extent to which feedback processing may represent a risk factor for PIU, a consequence of PIU, or possibly both.

The utility of P300 as a schizophrenia endophenotype and predictive biomarker: clinical and socio-demographic modulators in COGS-2

Reduced auditory P300 amplitude is a robust schizophrenia deficit exhibiting the qualities of a viable genetic endophenotype. These include heritability, test-retest reliability, and trait-like stability. Recent evidence suggests that P300 may also serve as a predictive biomarker for transition to psychosis during the schizophrenia prodrome. Historically, the utility of the P300 has been limited by its clinical nonspecificity, cross-site measurement variability, and required EEG expertise. The Consortium on the Genetics of Schizophrenia (COGS-2) study provided an opportunity to examine the consistency of the measure across multiple sites with varying degrees of EEG experience, and to identify important modulating factors that contribute to measurement variability. Auditory P300 was acquired from 649 controls and 587 patients at 5 sites. An overall patient deficit was observed with effect size 0.62. Each site independently observed a significant patient deficit, but site differences also existed. In patients, site differences reflected clinical differences in positive symptomatology and functional capacity. In controls, site differences reflected differences in racial stratification, smoking and substance use history. These factors differentially suppressed the P300 response, but only in control subjects. This led to an attenuated patient-control difference among smokers and among African Americans with history of substance use. These findings indicate that the P300 can be adequately assessed quantitatively, across sites, without substantial EEG expertise. Measurements are suitable for both genetic endophenotype analyses and studies of psychosis risk and conversion. However, careful attention must be given to selection of appropriate comparison samples to avoid misleading false negative results.

Endophenotypes for Alcohol Use Disorder: An Update on the Field

The endophenotype concept was first proposed as a strategy to use (purportedly) genetically simpler phenotypes in gene identification studies for psychiatric disorders, and is distinct from the closely related concept of intermediate phenotypes. In the area of alcohol use disorder (AUD) research, two candidate endophenotypes have produced replicable genetic associations: level of response to alcohol and neurophysiology markers (e.g., event-related oscillations and event-related potentials). Additional candidate endophenotypes from the cognitive, sensory, and neuroimaging literatures show promise, although more evidence is needed to fully evaluate their potential utility. Translational approaches to AUD endophenotypes have helped characterize the underlying neurobiology and genetics of AUD endophenotypes and identified relevant pharmacological interventions. Future research that capitalizes on the polygenic nature of endophenotypes and emphasizes endophenotypes that may change across development will enhance the usefulness of this concept to understand the genetically-influenced pathways toward AUD.

Family history of alcohol use disorders and neuromaturation: a functional connectivity study with adolescents

BACKGROUND

A positive family history (FHP) of alcohol use disorders (AUD) is linked to increased risk for personal AUD, but the mechanisms behind this risk are unclear. Previous research suggests that a subtle neurodevelopmental lag in FHP adolescents may contribute to risk for future AUD.

METHODS

Functional magnetic resonance imaging (fMRI) response to a spatial working memory (SWM) task was examined for markers of neuromaturational delay in 85 youth with and without FHP. It was hypothesized that FHP adolescents (n = 24, ages 12-14 years), as compared to matched FHN youth (n = 26, ages 12-14 years), would show less similarity to brain connectivity observed in older adolescents (n = 35, ages 16-20 years) and that statistical comparison of SWM functional connectivity models would differentiate FHN and FHP youth. Structural equation modeling tested the fit of brain response connectivity between FH groups and against the older-adolescent model.

RESULTS

Patterns of connectivity were more similar between older adolescent and FHN than FHP adolescents; FHP youth demonstrated higher association between right posterior and left frontal brain regions than FHN and older adolescent youth. Comparison of FH groups indicated a significant difference on the pathway from the right superior parietal lobule to the left middle frontal gyrus.

CONCLUSIONS

These findings provide additional support for the notion of a neuromaturational lag in FHP youth. Protracted neuromaturation may be a mechanism by which FH increases risk for alcohol dependence, and this less mature neural connectivity pattern may provide a novel endophenotype for identifying youth at risk for drinking problems.

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.

Single-subject classification of schizophrenia using event-related potentials obtained during auditory and visual oddball paradigms

In the search for the biomarkers of schizophrenia, event-related potential (ERP) deficits obtained by applying the classic oddball paradigm are among the most consistent findings. However, the single-subject classification rate based on these parameters remains to be determined. Here, we present a data-driven approach by applying machine learning classifiers to relevant oddball ERPs. Twenty-four schizophrenic patients and 24 matched healthy controls finished auditory and visual oddball tasks while high-density electrophysiological recordings were applied. The N1 component in response to standards and target as well as the P3 component following targets were submitted to different machine learning algorithms and the resulting ERP features were submitted to further correlation analyses. We obtained a classification accuracy of 72.4 % using only two ERP components. Latencies of parietal N1 components to visual standard stimuli at electrode positions Pz and P1 were sufficient for classification. Further analysis revealed a high correlation of these features in controls and an intermediate correlation in schizophrenia patients. These data exemplarily show how automated inference may be applied to classify a pathological state in single subjects without prior knowledge of their diagnoses and illustrate the potential of machine learning algorithms for the identification of potential biomarkers. Moreover, this approach assesses the discriminative accuracy of one of the most consistent findings in schizophrenia research by means of single-subject classification.

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.

Efficiency of responding to unexpected information varies with sex, age, and pubertal development in early adolescence

Entry into adolescence is marked by dramatic changes resulting from a dynamic interplay among biological and psychosocial processes. Despite the complexity, development is often indexed only by age in event-related potential (ERP) studies. To broaden this approach, we address the effects of gender and pubertal development, along with age, in adolescents using a psychophysiological probe of decision making, the P300 component. Overall, girls exhibited shorter P300 latencies and smaller P300 amplitudes compared to boys, suggesting more efficient information processing. In both genders, P300 latency and amplitude also diminished as age and pubertal status increased, again suggesting increasing efficiency of information processing with development. Our findings highlight the necessity of considering more than age when examining cognitive functioning in adolescents and, in particular, the necessity of considering gender whenever developmental issues are addressed.

Confirmation of prior evidence of genetic susceptibility to alcoholism in a genome-wide association study of comorbid alcoholism and bipolar disorder

OBJECTIVES

Alcoholism and affective disorders are both strongly comorbid and heritable. We have investigated the genetic comorbidity between bipolar affective disorder and alcoholism.

METHODS

A genome-wide allelic association study of 506 patients from the University College London bipolar disorder case-control sample and 510 ancestrally matched supernormal controls. One hundred forty-three of the bipolar patients fulfilled the Research Diagnostic Criteria diagnosis of alcoholism. A total of 372 193 single nucleotide polymorphisms (SNPs) were genotyped. Genes previously shown to be associated with alcoholism and addiction phenotypes were then tested for association in the bipolar alcoholic sample using gene-wise permutation tests of all SNPs genotyped within a 50-kb region flanking each gene.

RESULTS

Several central nervous system genes showed significant (P<0.05) gene-wise evidence of association with bipolar alcoholism. The genes implicated, which replicated genes previously shown to be associated with alcoholism were: cadherin 11, collagen type 11 α2, neuromedin U receptor 2, exportin7, and semaphorin-associated protein 5A. The SNPs most strongly implicated in bipolar alcoholism, but, which did not meet conventional genome-wide significance criteria were the insulin-like growth factor-binding protein 7, carboxypeptidase O, cerebellin 2, and the cadherin 12 genes.

CONCLUSION

We have confirmed the role of some genes previously shown to be associated with alcoholism in the comorbid bipolar alcoholism subgroup. In this subgroup, bipolar disorder may lower the threshold for the phenotypic expression of these alcoholism susceptibility genes. We also show that some genes may independently increase susceptibility to affective disorder and alcoholism.

A roadmap for the development and validation of event-related potential biomarkers in schizophrenia research

New efforts to develop treatments for cognitive dysfunction in mental illnesses would benefit enormously from biomarkers that provide sensitive and reliable measures of the neural events underlying cognition. Here, we evaluate the promise of event-related potentials (ERPs) as biomarkers of cognitive dysfunction in schizophrenia. We conclude that ERPs have several desirable properties: (1) they provide a direct measure of electrical activity during neurotransmission; (2) their high temporal resolutions make it possible to measure neural synchrony and oscillations; (3) they are relatively inexpensive and convenient to record; (4) animal models are readily available for several ERP components; (5) decades of research has established the sensitivity and reliability of ERP measures in psychiatric illnesses; and 6) feasibility of large N (>500) multisite studies has been demonstrated for key measures. Consequently, ERPs may be useful for identifying endophenotypes and defining treatment targets, for evaluating new compounds in animals and in humans, and for identifying individuals who are good candidates for early interventions or for specific treatments. However, several challenges must be overcome before ERPs gain widespread use as biomarkers in schizophrenia research, and we make several recommendations for the research that is necessary to develop and validate ERP-based biomarkers that can have a real impact on treatment development.

Independent contributions of cortical gray matter, aging, sex and alcoholism to K-complex amplitude evoked during sleep

STUDY OBJECTIVES

The amplitude of the N550 component derived from the averaged evoked K-complex decreases with normal aging and with alcoholism. The study was designed to determine whether these declines are related to the extent of cortical or subcortical shrinkage.

SETTING

Research sleep laboratory and MR imaging facility

PARTICIPANTS

26 abstinent long-term alcoholic men, 14 abstinent long-term alcoholic women, 18 control men, and 22 control women.

MEASUREMENTS AND RESULTS

MRI data collected at 3T were analyzed from alcoholic and control men and women previously reported to have significantly different evoked delta activity during sleep. Segmented and parcellated MRI data collected at 3T were compared between these groups and evaluated for correlation with evoked K-complex amplitude measured at FP1, Fz, FCz, Cz, CPz, and Pz. Cortical gray matter and regional subcortical tissue volumes entered as predictors into stepwise multiple regression identified cortical gray matter as a unique significant predictor of evoked K-complex at all sites. Age added independent variance at 5 of the 6 sites, while alcoholism and sex added independent variance at frontal sites only.

CONCLUSIONS

These data support recent intracranial studies showing cortical generation of K-complexes by indicating that cortical, but not subcortical volume contributes to K-complex amplitude. Establishing the extent of the relation between cortical volume and K-complex amplitude provides a mechanistic understanding of sleep compromise clinically relevant to normal aging, alcoholism, and likely other conditions affecting cortical volume and integrity.

Reduced resource optimization in male alcoholics: N400 in a lexical decision paradigm

BACKGROUND

Event Related Potential (ERP) studies have highlighted some measures, notably P3 amplitude, that are associated with both state and trait deficits in alcoholism, while studies examining N400 amplitude in alcoholism are few. The present study aims to examine differences in the N400 component, an electrophysiological correlate of semantic priming, in event-related potentials from a lexical decision task in 87 alcohol dependent subjects and 57 community controls.

METHODS

 Each subject was presented with 300 stimuli sequentially in a quasi-randomized design, where 150 stimuli were words and 150 were non-words. The subjects made a lexical decision indicating the word/non-word status with a button press. Among the words, 50 words (primed) were always preceded by their antonyms (prime, n=50), whereas the remaining 50 words were unrelated. N400 amplitude and latency measures were compiled from ERPs to the primed and unprimed words. Corresponding reaction time (RT) and response characteristics were also analyzed.

RESULTS

Control subjects revealed a significant attenuation of the N400 response to the primed word when compared to the unprimed word. Significantly less attenuation was observed in alcohol dependent subjects. No significant group differences were seen for latency and behavioral measures. All subjects had slower RT for unprimed words compared to primed words; however significantly less RT savings between the unprimed and primed condition was noted for alcoholics.

CONCLUSIONS

 These results suggest a reduced flexibility in the cognitive networks and a lack of resource optimization in alcoholics. The reduced attenuation of N400 during the primed condition in the alcohol dependent subjects may reflect an inability to engage similar neuronal substrates associated with semantic relatedness as seen in the controls. As diminished N400 attenuation during priming is observed in both alcoholics and high risk subjects, it may be a marker of risk and a good endophenotype for alcoholism.

Specificity of P3 event-related potential reactivity to alcohol cues in individuals low in alcohol sensitivity

Recent research using event-related potentials (ERPs) has shown that individuals low in alcohol sensitivity show increased P3 reactivity to alcohol cues (Bartholow, Henry, & Lust, 2007). The current research sought to test the specificity of this effect by including other arousing cues in addition to alcohol, and by controlling for individual differences in trait impulsivity. Forty-seven participants varying in self-reported alcohol sensitivity completed a visual oddball task including neutral, arousing (erotic and adventure-related), and beverage-related images while ERPs were recorded. Low-sensitivity participants showed increased P3 reactivity to alcohol cues relative to their high-sensitivity peers. However, P3 amplitude elicited by all other targets did not differ as a function of alcohol sensitivity levels. Differences in impulsivity and recent alcohol consumption did not account for sensitivity group differences in alcohol cue reactivity. These results point to the specific motivational salience of alcohol cues to individuals at risk for alcohol problems because of low alcohol sensitivity and suggest that P3 reactivity to alcohol cues could be a new endophenotype for alcohol use disorder risk.

Single-nucleotide polymorphisms in corticotropin releasing hormone receptor 1 gene (CRHR1) are associated with quantitative trait of event-related potential and alcohol dependence

BACKGROUND

Endophenotypes reflect more proximal effects of genes than diagnostic categories, hence providing a more powerful strategy in searching for genes involved in complex psychiatric disorders. There is strong evidence suggesting the P3 amplitude of the event-related potential (ERP) as an endophenotype for the risk of alcoholism and other disinhibitory disorders. Recent studies demonstrated a crucial role of corticotropin releasing hormone receptor 1 (CRHR1) in the environmental stress response and ethanol self-administration in animal models. The aim of the present study was to test the potential associations between single-nucleotide polymorphisms (SNPs) in the CRHR1 gene and the quantitative trait, P3 amplitude during the processing of visual target signals in an oddball paradigm, as well as alcohol dependence diagnosis.

METHODS

We analyzed a sample from the Collaborative Study on the Genetics of Alcoholism (COGA) comprising 1049 Caucasian subjects from 209 families (including 472 alcohol-dependent individuals). Quantitative transmission disequilibrium test (QTDT) and family-based association test (FBAT) were used to test the association, and false discovery rate (FDR) was applied to correct for multiple comparisons.

RESULTS

Significant associations (p < 0.05) were found between the P3 amplitude and alcohol dependence with multiple SNPs in the CRHR1 gene.

CONCLUSIONS

Our results suggest that CRHR1 may be involved in modulating the P3 component of the ERP during information processing and in vulnerability to alcoholism. These findings underscore the utility of electrophysiology and the endophenotype approach in the genetic study of psychiatric disorders.

Eating disorder symptoms and alcohol use among adolescents in substance abuse treatment

OBJECTIVE

To examine the relationship of eating disorder (ED) symptoms with the severity of alcohol use among adolescents in treatment for alcohol and other substance use disorders (AOSUDs).

METHOD

A sample consisted of 177 adolescents who participated in outpatient AOSUD treatment programs in Connecticut. Chi square tests, one-way ANOVAs and Pearson's correlation coefficients were used to describe the prevalence and correlates of any eating disorders, and the related symptoms. Multivariate regression was used to test the associations between ED symptoms and alcohol consumption.

RESULTS

26.4% of the participants had at least one ED symptom, with the highest number of symptoms occurring in females. The number of ED symptoms was associated with increases in the number of times that they became intoxicated in the year before entering treatment, the number of alcohol-related social problems, and the number of alcohol-related physical symptoms after taking into consideration the effects of age and gender.

CONCLUSIONS

The prevalence of symptoms of EDs is high in adolescents with AOSUDs, with the number of ED symptoms correlating with increased alcohol consumption. Further studies on the course and treatment of adolescents with AOSUDs and symptoms of EDs are warranted.

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.

Association of single nucleotide polymorphisms in a glutamate receptor gene (GRM8) with theta power of event-related oscillations and alcohol dependence

Evidence suggests the P3 amplitude of the event-related potential and its underlying superimposed event-related oscillations (EROs), primarily in the theta (4-5 Hz) and delta (1-3 Hz) frequencies, as endophenotypes for the risk of alcoholism and other disinhibitory disorders. Major neurochemical substrates contributing to theta and delta rhythms and P3 involve strong GABAergic, cholinergic and glutamatergic system interactions. The aim of this study was to test the potential associations between single nucleotide polymorphisms (SNPs) in glutamate receptor genes and ERO quantitative traits. GRM8 was selected because it maps at chromosome 7q31.3-q32.1 under the peak region where we previously identified significant linkage (peak LOD = 3.5) using a genome-wide linkage scan of the same phenotype (event-related theta band for the target visual stimuli). Neural activities recorded from scalp electrodes during a visual oddball task in which rare target elicited P3s were analyzed in a subset of the Collaborative Study on the Genetics of Alcoholism (COGA) sample comprising 1,049 Caucasian subjects from 209 families (with 472 DSM-IV alcohol dependent individuals). The family-based association test (FBAT) detected significant association (P < 0.05) with multiple SNPs in the GRM8 gene and event-related theta power to target visual stimuli, and also with alcohol dependence, even after correction for multiple comparisons by false discovery rate (FDR). Our results suggest that variation in GRM8 may be involved in modulating event-related theta oscillations during information processing and also in vulnerability to alcoholism. These findings underscore the utility of electrophysiology and the endophenotype approach in the genetic study of psychiatric disorders.

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.

Review. Genetics of addictions: strategies for addressing heterogeneity and polygenicity of substance use disorders

Addictions are common psychiatric disorders that exert high cost to the individual and to society. Addictions are a result of the interplay of multiple genetic and environmental factors. They are characterized by phenotypic and genetic heterogeneity as well as polygenicity, implying a contribution of different neurobiological mechanisms to the clinical diagnosis. Therefore, treatments for most substance use disorders are often only partially effective, with a substantial proportion of patients failing to respond. To address heterogeneity and polygenicity, strategies have been developed to identify more homogeneous subgroups of patients and to characterize genes contributing to their phenotype. These include genetic linkage and association studies as well as functional genetic analysis using endophenotypes and animal behavioural experimentation. Applying these strategies in a translational context aims at improving therapeutic response by the identification of subgroups of addiction patients for individualized, targeted treatment strategies. This article aims to discuss strategies addressing heterogeneity and polygenicity of substance use disorders by presenting results of recent research on genetic and environmental components of addiction. It will also introduce the European IMAGEN study that aims to integrate methodical approaches discussed in order to identify the genetic and neurobiological basis of behavioural traits relevant to the development of addictions.

Eye movement dysfunction in first-degree relatives of patients with schizophrenia: a meta-analytic evaluation of candidate endophenotypes

Several forms of eye movement dysfunction (EMD) are regarded as promising candidate endophenotypes of schizophrenia. Discrepancies in individual study results have led to inconsistent conclusions regarding particular aspects of EMD in relatives of schizophrenia patients. To quantitatively evaluate and compare the candidacy of smooth pursuit, saccade and fixation deficits in first-degree biological relatives, we conducted a set of meta-analytic investigations. Among 18 measures of EMD, memory-guided saccade accuracy and error rate, global smooth pursuit dysfunction, intrusive saccades during fixation, antisaccade error rate and smooth pursuit closed-loop gain emerged as best differentiating relatives from controls (standardized mean differences ranged from .46 to .66), with no significant differences among these measures. Anticipatory saccades, but no other smooth pursuit component measures were also increased in relatives. Visually-guided reflexive saccades were largely normal. Moderator analyses examining design characteristics revealed few variables affecting the magnitude of the meta-analytically observed effects. Moderate effect sizes of relatives v. controls in selective aspects of EMD supports their endophenotype potential. Future work should focus on facilitating endophenotype utility through attention to heterogeneity of EMD performance, relationships among forms of EMD, and application in molecular genetics studies.

Attentional deficits in cocaine-dependent patients: converging behavioral and electrophysiological evidence

Although there are several reports of patients with cocaine dependence displaying cognitive deficits, the nature of their information processing deficits is not well characterized. In the present study, the attentional performance of cocaine-dependent patients (n=14) was examined and compared with that of healthy control individuals (n=15). Attention was assessed using an auditory oddball event-related task as well as the Continuous Performance Test (CPT, Identical Pairs version). The cocaine-dependent group displayed P300 amplitude reduction compared to controls. The group difference in P300 response latency did not reach significance. On the CPT, the cocaine-dependent patients displayed significantly poorer discriminability and greater errors of commission than the controls. There was a positive correlation between performance on the oddball event-related task and performance on the CPT. This investigation provides converging behavioral and electrophysiological evidence of attentional deficits in cocaine-dependent patients.

Effects of family history of alcohol use disorders on spatial working memory BOLD response in adolescents

BACKGROUND

A positive family history (FH) of alcohol use disorders (AUD) has been linked to increased risk for the development of AUD, and neurocognitive factors have been postulated as important underlying mechanisms of familial alcoholism transmission.

METHODS

We used functional magnetic resonance imaging (fMRI) during a spatial working memory (SWM) and vigilance paradigm to investigate potential neurodevelopmental differences linked to familial density of AUD in 72 adolescents aged 12 to 14 years.

RESULTS

Youth with denser family histories of AUD showed less activation during a simple vigilance condition relative to SWM in cingulate and medial frontal gyri (beta = 0.28, p = 0.03), and a trend for more relative activity during rest (beta = -0.25, p = 0.07) in this cluster.

CONCLUSIONS

Youth with greater familial densities of AUD may be less successful at modulating activity of the default network, potentially indicating a greater propensity for task-independent thought or reduced inhibition of task-irrelevant processing. Failure to moderate activation of the default network may have implications for cognitive efficiency and goal directed behavior in youth with dense FH. Further, aberrant activation in cingulate regions may be linked to genetic variation in GABA receptor units, suggesting a useful endophenotype for risk associated with alcohol dependence.

The effects of HIV on P300 are moderated by familial risk for substance dependence: implications for a theory of brain reserve

BACKGROUND

The goal of the study was to test the validity of additive versus synergistic versus underadditive versions of brain reserve theory within the context of HIV/AIDS. In addition, it tested the convergent validity of 2 operational definitions of premorbid reserve: verbal IQ (VIQ) and a family history (FH) of substance abuse or dependence.

METHODS

Seventy HIV-1 seronegative and 115 HIV-1 seropositive male and female volunteers were assigned to 4 subgroups defined by the crossing of a VIQ score < versus > or = 90 with the presence versus absence of a paternal history of alcohol, cocaine, or opiate abuse or dependence. The principal dependent measure was the P300 event related brain potential elicited during the Stroop color-word interference task.

RESULTS

The principal finding was an underadditive effect of FH plus HIV/AIDS on P300 area over the frontal region: FH reduced frontal scalp P300 to such a degree that the additional effects of HIV/AIDS were blunted. The alternate operational definition of brain reserve, VIQ, had no effect on P300 and did not alter the effects of HIV/AIDS.

CONCLUSIONS

Familial risk for substance dependence and low VIQ compromise different aspects of brain structure and/or function and therefore differ in their relationship to HIV/AIDS and P300. Genetic differences associated with familial risk may reduce brain reserve to such a degree that the neurophysiological effects of HIV/AIDS can no longer be measured.

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.

Rates of ethanol metabolism decrease in sons of alcoholics following a priming dose of ethanol

Rapid changes in rates of ethanol metabolism in response to acute ethanol administration have been observed in animals and humans. To examine whether this phenomenon might vary by risk for alcoholism, 23 young men with a positive family history of alcoholism (family history positive [FHP]) were compared to 15 young men without a family history of alcoholism (family history negative [FHN]). Rates of ethanol metabolism were measured in all subjects first after an initial ethanol dose (0.85 g/kg) and then, several hours later, a second dose (0.3 g/kg), and the two rates were compared. The two groups of subjects were similar in their histories of ethanol consumption. FHP subjects demonstrated faster initial rates of ethanol metabolism, 148+/-36 mg/kg/h, compared to FHN subjects, 124+/-18 mg/kg/h, P=.01. However, FHN subjects increased their rate of metabolism by 10+/-27% compared to a decrease of -15+/-24% in FHP subjects, P=.007. Fifty-two percent of the FHP and none of the FHN subjects exhibited a decline in metabolic rate of 20% or more, P=.0008. Since a significant proportion of FHP subjects exhibited a decrease in the second rate of ethanol metabolism, these preliminary data might help to partly explain why FHP individuals differ in their sensitivity to ethanol and are more likely to develop alcohol dependence.

Neurophysiological endophenotypes of schizophrenia: the viability of selected candidate measures

In an effort to reveal susceptibility genes, schizophrenia research has turned to the endophenotype strategy. Endophenotypes are characteristics that reflect the actions of genes predisposing an individual to a disorder, even in the absence of diagnosable pathology. Individual endophenotypes are presumably determined by fewer genes than the more complex phenotype of schizophrenia and would, therefore, reduce the complexity of genetic analyses. Unfortunately, despite there being rational criteria to define a viable endophenotype, the term is sometimes applied indiscriminately to characteristics that are deviant in affected individuals. Schizophrenia patients exhibit deficits in several neurophysiological measures of information processing that have been proposed as candidate endophenotypes. Successful processing of sensory inputs requires the ability to inhibit intrinsic responses to redundant stimuli and, reciprocally, to facilitate responses to less frequent salient stimuli. There is evidence to suggest that both these processes are "impaired" in schizophrenia. Measures of inhibitory failure include prepulse inhibition of the startle reflex, P50 auditory evoked potential suppression, and antisaccade eye movements. Measures of impaired deviance detection include mismatch negativity and the P300 event-related potential. The purpose of this review is to systematically evaluate the endophenotype candidacy of these key neurophysiological abilities. For each candidate, we describe typical experimental procedures, the current understanding of the underlying neurobiology, the nature of the abnormality in schizophrenia, the reliability, stability and heritability of the measure, and any reported gene associations. We conclude with a discussion of the few studies thus far that have employed a multivariate approach with these candidates.

Visual P300s in long-term abstinent chronic alcoholics

BACKGROUND

Evidence of reduced P3b amplitudes in chronic alcoholics and individuals at risk for developing alcoholism suggest that the P3b may be an endophenotypic marker for alcoholism. If this is the case, then long-term abstinent alcoholics (LTAAs) should exhibit reduced P3b amplitudes. Thus far, P3b studies on chronic alcoholics have focused primarily on samples with relatively short-term abstinence (less than 15 months). This study examines the amplitude and latency of the P3b and P3a event-related brain electrical components in LTAAs compared with normal controls (NCs) and whether these measures are related to alcohol use and other subject variables.

METHODS

Electroencephalographs (EEGs) were recorded on 48 LTAAs (mean abstinence=6.7 years) compared with 48 age-matched and gender-matched NCs during a visual P300 experiment consisting of standard, target, and rare nontarget conditions. This paradigm elicited the P3b (target condition) and the P3a (rare nontarget condition) components.

RESULTS

Long-term abstinent alcoholics had reduced P3b amplitudes and increased P3b latencies in comparison with NCs. Long-term abstinent alcoholics also exhibited delayed P3a components, but no P3a amplitude reductions. Alcohol use variables, a family history of alcohol problems, and the duration of alcohol abstinence were not associated with any amplitude or latency variables.

CONCLUSIONS

Even after very prolonged abstinence, reduced P3b amplitudes are present in chronic alcoholics and are not associated with any family history or alcohol use variables. These results provide equivocal support for reduced P3b amplitude being an endophenotypic marker for alcoholism, but are also consistent with P3b being affected by a threshold of alcohol abuse, with the effect not resolving over long periods of abstinence.

Tobacco Use, Alcohol Dependence, and Cognitive Performance

Chronic alcohol abuse has long been associated with a mild, generalized pattern of cognitive decrements. However, it is important to note that problem drinking rarely occurs in isolation from abuse of other drugs. For people dependent upon alcohol, tobacco is one of the mostly commonly coabused substances. Recent research suggests that individuals with alcohol dependency may gravitate toward tobacco use, in part, because of the positive effects of nicotine on aspects of cognitive performance that may be compromised as a consequence of chronic alcohol misuse. In this article, the author focuses on the effects of nicotine on behavioral and electrophysiological indexes of cognitive performance, and the impact of these effects on alcohol-related cognitive decrements. The author discusses implications of these findings in the context of treatment and recovery of people with alcoholism.

Alcoholism: the dissection for endophenotypes

Alcohol dependence (alcoholism) is a complex disorder attributed to the interaction of genetic and environmental factors that form a collage of "disease" predisposition, which is not identical for every alcohol-dependent individual. There is considerable evidence to demonstrate that genetic predisposition accounts for roughly half the risk in the development of alcohol dependence. Both family and population studies have identified a number of genomic regions with suggestive links to alcoholism, yet there have been relatively few definitive findings with regard to genetic determinants of alcoholism. This ambiguity can be attributed to a multitude of complications of studying complex mental disorders, such as clinical heterogeneity, polygenic determinants, reduced penetrance, and epistatic effects. Complex mental disorders are clinical manifestations described by combinations of various signs and symptoms. One approach to overcoming the ambiguity in studying the association between genetic risk factors and disease is to dissect the complex, heterogeneous disorder by using intermediate phenotypes--or endophenotypes--to generate more homogeneous diagnostic groupings than an all-encompassing definition, such as the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV)-derived term "alcohol dependence" or the commonly used term "alcoholism." The advantage of using endophenotypes is that the number of influential factors that contribute to these characteristics should be fewer and more easily identified than the number of factors affecting the heterogeneous entity of alcohol dependence (alcoholism). A variety of alcohol-related characteristics have been investigated in epidemiological, clinical, and basic research as potential endophenotypes of alcohol dependence. These include phenotypes related to alcohol metabolism, physiological and endocrine measures, neural imaging, electrophysiology, personality, drinking behavior, and responses to alcohol and alcohol-derived cues. This review summarizes the current literature, focused on human data, of promising endophenotypes for dissecting alcoholism.

Alcoholism is a disinhibitory disorder: neurophysiological evidence from a Go/No-Go task

Response inhibition is considered a core dimension in alcoholism and its co-existing disorders. The major objective of this study is to compare the magnitude and spatial distribution of ERP components during response activation and inhibition in alcoholics (N = 30) and normal controls (N = 30) using a visual Go/No-Go task. The results indicate that alcoholics manifest a decreased P3(00) amplitude during Go as well as No-Go conditions. The difference between Go and No-Go processing was more evident in controls than in alcoholics. The topography of current source density in alcoholics during the P3 response was found to be very different from that of normals, suggesting that alcoholics perhaps activated inappropriate brain circuitry during cognitive processing. The significantly reduced No-Go P3 along with the relatively less anteriorized CSD topography during No-Go condition suggests poor inhibitory control in alcoholics. It is proposed that the No-Go P3, the electrophysiological signature of response inhibition, can be considered as an endophenotypic marker in alcoholism.

A genome wide search for alcoholism susceptibility genes

Alcoholism is currently one of the most serious public health problems in the US. Lifetime prevalence rates are relatively high with one in five men and one in 12 women meeting criteria for this condition. Identification of genetic loci conferring an increased susceptibility to developing alcohol dependence could strengthen prevention efforts by informing individuals of their risk before abusive drinking ensues. Families identified through a double proband methodology have provided an exceptional opportunity for gene-finding because of the increased recurrence risks seen in these sibships. A total of 360 markers for 22 autosomes were spaced at an average distance of 9.4 cM and genotyping performed for 330 members of these multiplex families. Extensive clinical data, personality variation, and event-related potential characteristics were available for reducing heterogeneity and detecting robust linkage signals. Multipoint linkage analysis using different analytic strategies give strong support for loci on chromosomes 1, 2, 6, 7, 10, 12, 14, 16, and 17.