Trait Impulsivity and the Externalizing Spectrum

Abstract

This article reviews evidence that trait impulsivity-expressed early in life as the hyperactive-impulsive and combined presentations of attention-deficit/hyperactivity disorder (ADHD)-is a bottom-up, subcortically mediated vulnerability to all externalizing disorders. This vulnerability arises from deficient mesolimbic dopamine responding, which imbues psychological states (irritability, discontentment) that motivate excessive approach behavior (hyperactivity, impulsivity). Through complex interactions with (a) aversive motivational states that arise from largely independent subcortical systems, (b) emotion regulatory mechanisms that arise from top-down, cortical modulation of subcortical neural function, and (c) environmental risk factors that shape and maintain emotion dysregulation, trait impulsivity confers vulnerability to increasingly severe externalizing behaviors across development. This perspective highlights the importance of identifying transdiagnostic neural vulnerabilities to psychopathology; dovetails with the hierarchical, latent structure of psychopathology; and suggests that progression along the externalizing spectrum is an ontogenic process whereby a common, multifactorially inherited trait interacts with endogenous and exogenous influences to yield increasingly intractable externalizing behaviors across development.

How Serious is ADHD?

“…These genetic factors have been linked multiple structural (e.g., smaller volume) and functional (e.g., underactivation, impaired connectivity) brain abnormalities in individuals with ADHD which compromise the functioning of neural circuits related to attention, inhibitory control, reward motivation, and emotional regulation and which in turn can be linked to ADHD symptoms and consequent impairments in major life activities [3,7,9,15,16,17]. However, although the evidence for these linkages is robust, the research is correlational and therefore cannot be interpreted as causal on the sole basis of the linkage [16].…”

“…Among the various disorders, the strongest link is with sequential development of disorders in the externalizing spectrum, i.e., Oppositional Defiant Disorder, Conduct Disorder, Substance Use Disorder, and Antisocial Personality Disorder [8,15,22]. This developmental cascade in turn increases the risk for juvenile delinquency and adult criminality such that a systematic review and meta-analysis of 11 prospective studies (N=15,442) found that childhood ADHD was significantly associated with increased risk for juvenile arrests (RR: 2.2, 95%, CI: 1.3-3.5),convictions (RR: 3.3, 95%, CI: 2.1-5.2), and incarcerations (RR: 2.9, 95%, CI: 1.9-4.3) [23].…”

“…Namely, ADHD was a strong predictor for the development of the argumentative/defiant symptoms of ODD. This progression from ADHD to ODD is best explained by the ADHD symptoms of behavioral and emotional impulsivity which greatly increase the risk for coercive, oppositional interchanges with significant others in the child's life [15,26,27]. Indeed, it is estimated that a typical child with ADHD has an astonishing half a million of these negative interchanges each year [28].…”

“…Behavioral impulsivity is characterized by: a) decisions based on a preference for smaller, immediate rewards over larger, delayed rewards, and b) a tendency to make rapid decisions without forethought, adequate consideration of the evidence [15]. Current comprehensive reviews concur in implicating impairments in the mesolimbic and mesocortical dopamine (DA) neural circuits and their interconnections to one another as well as other brain regions as the central neurobiological mechanisms in generating behavioral impulsivity [9,15,29].…”

“…Several lines of research indicate that this circuit is the brain's most important reward system [15,30]. Subsequently, extensive neuroimaging research has found reduced mesolimbic activity during the anticipation of reward in individuals with ADHD [15,30].…”