Scott R. Carlson

Etiologic Connections Among Substance Dependence, Antisocial Behavior, and Personality: Modeling the Externalizing Spectrum

A hierarchical biometric model is presented of the origins of comorbidity among substance dependence, antisocial behavior, and a disinhibited personality style. The model posits a spectrum of personality and psychopathology, united by an externalizing factor linked to each phenotype within the spectrum, as well as specific factors that account for distinctions among phenotypes within the spectrum. This model fit self-report and mother-report data from 1,048 male and female 17-year-old twins. The variance of the externalizing factor was mostly genetic, but both genetic and environmental factors accounted for distinctions among phenotypes within the spectrum. These results reconcile evidence for general and specific causal factors within the externalizing spectrum and offer the externalizing factor as a novel target for future research.

Behavioral disinhibition and the development of substance-use disorders: Findings from the Minnesota Twin Family Study

One variant of substance-use disorder is characterized by behavioral disinhibition. In this report, we martial evidence for a model for the development of this variant. We hypothesize that genetic liability for this variant is reflected in a spectrum of risk indicators linked to the inability or unwillingness to inhibit behavioral impulses. Included in this spectrum are personality traits suggesting low constraint, and externalizing psychopathology, including conduct, oppositional defiant, and attention-deficit disorder in children and antisocial personality disorder and behavior in adults. We further hypothesize that these individual differences in behavioral disinhibition are manifestations of underlying central nervous system processes associated with various psychophysiological anomalies, some of which may index genetic risk for substance abuse. Support for the model is derived from the analysis of findings from the Minnesota Twin Family Study, an epidemiological investigation of approximately 2,700 adolescent twins and their parents.

A twin study of self-reported psychopathic personality traits

Previous twin studies attempting to assess the origins of psychopathic personality traits have mainly focused on an overt behavioral conceptualization of the syndrome as defined by a history of chronic antisocial behaviors. This investigation instead focused on a personality-based approach which emphasizes maladaptive personality traits as central to the syndrome. Psychopathic traits were indexed by the Psychopathic Personality Inventory (PPI), a self-report measure designed to assess the personality domain of the disorder. Biometric parameters obtained from the responses of 353 male twins from the Minnesota Twin Registry revealed significant genetic influences, largely non-additive in nature. Although preliminary due to the modest sample size, the findings encourage a larger scale investigation with greater statistical power to evaluate competing models of genetic influence.

Disinhibited characteristics and binge drinking among university student drinkers

Binge drinking is a major problem at North American universities. Disinhibited traits have provided insight on other patterns of alcohol involvement, but less is known about how they relate to bingeing. Drinkers at a large urban university (n=293) completed the Barratt Impulsiveness Scale 11 (BIS-11), the Aggression Questionnaire, and the Thrill and Adventure Seeking and Boredom Susceptibility scales. Binge drinking was assessed using the NIAAA recommendation for standardizing binge frequency. Hierarchical regression was used to evaluate relationships between disinhibited traits and bingeing. BIS-11 Motor Impulsiveness, Thrill and Adventure Seeking and Boredom Susceptibility predicted bingeing. As about 15% of the variability in bingeing was due to disinhibition facets, they should be considered in future models of student vulnerability to bingeing.

Identifying a multivariate endophenotype for substance use disorders using psychophysiological measures

This investigation examined how reduced amplitude of the P300 event-related potential (elicited from a visual oddball task) can be used together with an electrodermal response modulation measure (indexing the ability to inhibit responsivity to a temporally predictable aversive stimulus) to identify adolescents at especially high risk to develop substance dependence. One hundred and twenty-nine 17-year-old boys were divided into groups characterized as low risk (high amplitude P300 and good electrodermal modulation), high risk (reduced amplitude P300 and poor modulation), or intermediate risk (a high or good score on one measure and a low or poor score on the other). P300 amplitude and electrodermal modulation were uncorrelated. High-risk boys had 4-6 times more alcohol dependence than intermediate or low-risk boys and 2-3 times more nicotine dependence. Performance on an antisaccade eye-tracking task in which participants directed their gaze in a direction opposite to target movement was related to electrodermal modulation but not P300 amplitude. The results from all three psychophysiological measures together suggest that the neural circuits affecting P300 amplitude and electrodermal response modulation are different and that poor electrodermal response modulation may reflect an inhibitory control deficit mediated by the frontal lobes.

Substance dependence and externalizing psychopathology in adolescent boys with small, average, or large P300 event‐related potential amplitude

To determine if the P300 component of the event-related potential indexes risk for substance use and related disorders, we presented a community sample of 377 16-18-year-old males a visual oddball task and selected 31 subjects with the smallest and 31 subjects with the largest P300 amplitudes. An additional 31 subjects whose amplitudes fell in the middle of the amplitude distribution were assigned to the average group. The small and average amplitude groups were more likely to have alcohol dependence and more symptoms of alcohol dependence than the large amplitude subjects. The small amplitude group had more symptoms of illicit drug dependence than the other groups. There was also a significantly larger proportion of subjects with externalizing disorders in the small amplitude group than in the large P300 group. These findings suggest that P300 amplitude may index a spectrum of risk for disinhibited psychopathology.

Individual differences in electrodermal responsivity to predictable aversive stimuli and substance dependence

To determine if the inability to take advantage of the predictability of an aversive stimulus to diminish its psychological impact reflects a deficit in inhibitory control related to the development of substance dependence, we recorded skin conductance responses (SCRs), heart rate (HR), and anticipatory electrodermal nonspecific fluctuations (NSFs) from 175 16-18-year-old boys when a white noise blast was either unpredictable or temporally predictable. Compared with boys who had moderately reduced or augmented SCRs to predictable blasts (moderate and poor modulators, respectively), boys whose SCRs were greatly reduced (good modulators) had fewer symptoms of alcohol and nicotine dependence and more anticipatory NSFs. HR appeared to index an active coping response for good and moderate modulators. The autonomic response pattern evident for good modulators may index an inhibitory control mechanism protecting them from developing substance dependence.

Visual P3 amplitude and self-reported psychopathic personality traits: Frontal reduction is associated with self-centered impulsivity

Past studies have examined P3 amplitude as an index of cognitive function related to psychopathy with mixed results. Psychopathy is a heterogeneous set of dissociable traits, and no previous study has examined relationships between P3 and specific traits. A Two Process Theory (TPT) of psychopathy has recently been advanced predicting that P3 reductions are related to only one dimension. We evaluated the relationship between P3 and the two factors of the Psychopathic Personality Inventory (PPI) in 96 undergraduates who performed a visual task. One factor of the PPI, Self-Centered Impulsivity, is related to the dimension of the TPT predicted to underlie P3 reduction. Frontal amplitude reduction was uniquely and inversely related to this trait. The other PPI factor, Fearless Dominance, was associated with faster reaction times. Future work on psychopathic personality and P3 should evaluate whether relationships are unique to one personality dimension.

Emotional modulation of the startle reflex in twins: preliminary findings

This study investigated twin similarity in general startle reflex reactivity and emotional modulation. Seventeen monozygotic (MZ) and 12 dizygotic (DZ) male twin pairs received startling acoustic stimuli while viewing emotionally positive, negative and neutral slides. Electromyographic (EMG) responses were recorded from the orbicularis oculi. Members of MZ twin pairs had similar response amplitudes under all three valence conditions. In addition, modulation scores for the positive and negative conditions, representing the percent change in response amplitude between the affective and the neutral conditions, also showed significant similarity within MZ twin pairs. Overall, members of DZ twin pairs were not found to be significantly similar of any of the measures. These preliminary findings suggest that emotional modulation of the startle reflex shows familial resemblance within MZ pairs. Given the lack of resemblance between DZ twins, it is tentatively suggested that affective modulation may be under partial genetic control.

P300 amplitude, externalizing psychopathology, and earlier- versus later-onset substance-use disorder.

P300 amplitude predicts substance use or disorder by age 21. Earlier- versus later-onset substance disorders may reflect different levels of an externalizing psychopathology dimension. P300 in adolescence may not be as strongly related to later-onset substance problems as it is to earlier-onset ones. In the present study, visual P300 amplitude was measured at age 17 in a community-representative sample of young men. Substance and externalizing disorders were assessed at approximately ages 17, 20, and 24. Earlier-onset (by age 20) substance disorder was associated with higher rates of externalizing disorders than were later-onset problems. P300 amplitude was reduced in subjects with earlier-onset substance disorders, relative to later-onset and disorder-free subjects. Amplitude was also reduced in subjects with an externalizing disorder but no substance disorder. Earlier-onset subjects had reduced P300, even in the absence of an externalizing disorder. The results could not be attributed to a concurrent disorder or to recent substance use at the time of the P300 recording. The findings are consistent with P300 indexing an externalizing spectrum. Earlier-onset substance disorders are more strongly related to P300 and externalizing than are later-onset problems.