Behavioural performance in the Go/NoGo task was compared with caregiver and teacher reports of inattention and hyperactivity–impulsivity in 1,151 children (N = 557 boys; N = 594 girls) age 9–10 years old. Errors of commission (NoGo errors) were significantly correlated with symptom counts of hyperactivity–impulsivity, while errors of omission (Go errors) were significantly correlated with symptom counts for inattention in both caregiver and teacher reports. Cross-correlations were also evident, however, such that errors of commission were related to inattention symptoms, and errors of omission were related to hyperactivity–impulsivity. Moreover, hyperactivity–impulsivity and inattention symptoms were highly intercorrelated in both caregiver (r = .52) and teacher reports (r = .70), while errors of commission and omission were virtually uncorrelated in the Go/NoGo task (r = .06). The results highlight the difficulty in disentangling hyperactivity–impulsivity and inattention in questionnaires, and suggest that these constructs may be more clearly distinguished in laboratory measures such as the Go/NoGo task.

Genetic and environmental influences on childhood antisocial and aggressive behavior (ASB) during childhood were examined in 9-to 10-year-old twins, using a multi-informant approach. The sample (605 families of twins or triplets) was socioeconomically and ethnically diverse, representative of the culturally diverse urban population in Southern California. Measures of ASB included symptom counts for conduct disorder, ratings of aggression, delinquency, and psychopathic traits obtained through child self-reports, teacher, and caregiver ratings. Multivariate analysis revealed a common ASB factor across informants that was strongly heritable (heritability was .96), highlighting the importance of a broad, general measure obtained from multiple sources as a plausible construct for future investigations of specific genetic mechanisms in ASB. The best fitting multivariate model required informant-specific genetic, environmental, and rater effects for variation in observed ASB measures. The results suggest that parent, children, and teachers have only a partly "shared view" and that the additional factors that influence the "rater-specific" view of the child's antisocial behavior vary for different informants. This is the first study to demonstrate strong heritable effects on ASB in ethnically and economically diverse samples. Keywords antisocial behavior; aggression; genes; environment Why do some children grow up to be prosocial, law-abiding individuals, whereas others engage in patterns of disruptive, defiant, and delinquent behavior, even falling into the criminal justice system well before reaching adulthood? A plethora of studies have investigated the etiology of such individual differences, with abundant evidence demonstrating the importance of both social circumstances and biological risk factors in antisocial behavior across the life span (Baker, 1999;Raine, 1993Raine, ,2002Raine, Brennan, Farrington, & Mednick, 1997;Stoff, Breiling, & Maser, 1997). Among these risk factors, genetic and environmental influences have been of considerable interest and are likely to play a key role in our understanding of aggression and other antisocial behaviors and, thus, our ability to avert them.

This study investigated the relationship of skin conductance response (SCR) to a child psychopathy measure. Blunted electrodermal activity is a theoretically important characteristic of psychopathy, but has not been fully explored in preadolescents or females. We tested the hypothesis that reduced SCR magnitude is associated with psychopathic-like traits in boys and girls. Participants were drawn from an ethnically diverse community sample of 9-10 year old twins. Given the fact that members of each twin pair were rated by the same individual (i.e., their caregiver) on the Child Psychopathy Scale, we examined individual differences at the within-family level. Skin conductance data were collected during a passive auditory task consisting of 75-dB tones as well as miscellaneous sounds (e.g., baby cries, bird noises, and speech-like stimuli). Reduced SCR magnitude (hyporeactivity) was only characteristic of boys with higher psychopathy scores. More specifically, electrodermal hyporeactivity was linked to the interpersonal facet of psychopathy, suggesting that it is a biological marker of a manipulative and deceitful orientation in males. No association was found between SCRs and psychopathic traits in girls, indicating the importance of sex specific etiologies of psychopathy in childhood.

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The genetic and environmental basis of a well-replicated association between antisocial behavior (ASB) and resting heart rate was investigated in a longitudinal twin study, based on two measurements between the ages of 9 and 14 years. ASB was defined as a broad continuum of externalizing behavior problems, assessed at each occasion through a composite measure based on parent ratings of trait aggression, delinquent behaviors, and psychopathic traits in their children. Parent ratings of ASB significantly decreased across age from childhood to early adolescence, although latent growth models indicated significant variation and twin similarity in the growth patterns, which were explained almost entirely by genetic influences. Resting heart rate at age 9–10 years old was inversely related to levels of ASB but not change patterns of ASB across age or occasions. Biometrical analyses indicated significant genetic influences on heart rate during childhood, as well as ASB throughout development from age 9 to 14. Both level and slope variation were significantly influenced by genetic factors. Of importance, the low resting heart rate and ASB association was significantly and entirely explained by their genetic covariation, although the heritable component of heart rate explained only a small portion (1–4%) of the substantial genetic variance in ASB. Although the effect size is small, children with low resting heart rate appear to be genetically predisposed toward externalizing behavior problems as early as age 9 years old.

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 count-down 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 unsignaled 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.

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The Southern California Twin Register was initiated in 1984 at the University of Southern California, and continues to grow. This article provides an update of the register since it was described in the 2002 special issue of this journal. The register has expanded considerably in the past 4 years, primarily as a result of recent access to Los Angeles County birth records and voter registration databases. Currently, this register contains nearly 5000 twin pairs, the majority of whom are school age. The potential for further expansion in adult twins using voter registration records is also described. Using the Los Angeles County voter registration database, we can identify a large group of individuals with a high probability of having a twin who also resides in Los Angeles County. In addition to describing the expansion of register, this article provides an overview of an ongoing investigation of 605 twin pairs who are participating in a longitudinal study of behavioral problems during childhood and adolescence. Characteristics of the twins and their families are presented, indicating baseline rates of conduct problems, depression and anxiety disorders, and attention-deficit/hyperactivity disorder diagnoses which are comparable to non-twins in this age range.