| This work elaborates a theoretical framework integrating psychometric and neurobiological approaches to personality and applies it to understanding cognitive ability and externalizing behavior (a broad category including impulsivity, aggression, hyperactivity, and antisocial behavior). In Chapter 1, a hierarchical model of personality is described, based on the Big Five and their higher-order factors, or metatraits, which I label Stability (Neuroticism reversed, Agreeableness, and Conscientiousness) and Plasticity (Extraversion and Openness/Intellect). Evidence for the existence of the metatraits is provided through multi-trait, multi-method confirmatory factor analysis, using Big Five ratings of 490 participants by four informants, and the metatraits are hypothesized to be related to the neurotransmitters serotonin and dopamine. In Chapter 2, a more detailed model is proposed for the neurobiological sources of Openness/Intellect and its relation to general cognitive ability (g). A battery of seven tasks assessing the functions of dorsolateral prefrontal cortex and associated with g is shown to predict Openness/Intellect but no other Big Five trait, in a sample of 175 participants. In Chapter 3, Stability, Plasticity, and g are used to locate externalizing behavior within a taxonomy of personality traits. The results from a study of 139 male adolescents provide evidence that impulsivity is an emergent trait resulting from the combination of low Stability and high Plasticity, and that externalizing behavior more generally is associated with the same combination of metatraits plus low g. Additionally, in the context of the literature on neurobiological correlates of impulsivity and externalizing behavior, these findings support the hypothesis that Stability and Plasticity are associated with serotonin and dopamine, respectively. Finally, Chapter 4 uses molecular genetic analysis to investigate the neurobiological source of the negative correlation between cognitive ability and externalizing behavior. In three male samples with high mean levels of externalizing behavior, variation in the dopamine D4 receptor gene is shown to moderate the association between cognitive ability and externalizing behavior. This work thus provides evidence, at multiple levels of analysis, for the utility of an integrated psychobiological approach to personality. |
