The Neurobiology of Behavioral Impulsivity as Expressed in the Hyperactive-Impulsive and Combined Presentations of Attention-Deficit/ Hyperactivity Disorder

The article provided a mini review of the neuropathology of behavioral impulsivity as expressed in the hyperactive-impulsive and combined presentations of ADHD. The two most important neural circuits subserving behavior impulsivity are the mesolimbic and mesocortical dopamine circuits. A dysfunctional mesolimbic circuit is implicated in the generation of behavioral impulsivity and the mesocortical circuit is implicated in the failure to control behavioral impulsivity. Through complex interaction with various environmental risk factors, the impulsivity subserved by these circuits increases the risk for various antisocial disorders across development. Received: June 09, 2017; Accepted: June 20, 2017; Published: June 29, 2017 *Corresponding author: Robert Eme, Professor of Clinical Psychology, Illinois School of Professional Psychology at Argosy University at Schaumburg Campus, Schaumburg, Illinois, U.S.A, Tel: 847.969. 4943; fax: 847.969. 4998; E-mail: reme@argosy.edu manifestation of ADHD is important for understanding how it increases the risk for the development of antisocial behavior. Neurobiology of Behavioral Impulsivity Impulsivity is a multifaceted trait mediated by distinct psychological and neurobiological mechanisms [7]. 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 [5,7]. Dopamine is a monoamine neurotransmitter that is implicated in the neural processing of reward-related stimuli such as food, sex, including those associated with drugs of abuse [8,9]. Rewards defined scientifically act as positive reinforcers to induce learning, elicit movements towards a desired object, and elicit emotions such as pleasure and desire [10]. Dopamine (DA) projections are divided into four primary neural systems, two of which are relevant to behavioral impulsivity: the mesolimbic and mesocortical [5,8]. Several current comprehensive reviews concur in implicating impairments in both neural circuits and their interconnections to one another as well as other brain regions as the central neurobiological mechanisms in generating behavioral impulsivity [5,7,8,11,12,13,14,15]. These two circuits are linked to two different aspects of impulsivity: impulse generation and impulse control [12]. Mesolimbic Dopamine Circuit and Impulse Generation The subcortical mesolimbic DA projections ascend from the ventral tegmental area to the ventral striatum, including the nucleus accumbens and the ventral regions of the caudate nucleus and putamen [8]. Several lines of research indicate that this circuit is the brain’s most important reward system [5,8]. For example: a) stimulation of the mesolimbic structures in various ways is so highly reinforcing that animals trained Introduction The neuropsychiatric disorder of Attention-deficit/ hyperactivity Disorder (ADHD) is the diagnosis given to juveniles and adults who present with impairing symptoms of attention and/or impulsivity and hyperactivity [1]. Its importance is underscored by the fact that it is one of the most prevalent juvenile disorders as well as one of the most common reasons children with behavioral problems are referred to medical and mental health practitioners in the United States. Its causes are primarily genetic with other variables such as low birth weight, exposure to lead, etc. also contributing to its origin [2]. In addition, it substantially increases the risk for a kaleidoscope of long-term adverse outcomes [4]. Of all the adverse outcomes, the antisocial disorders of Oppositional Defiant Disorder, Conduct Disorder, Substance Use Disorder, and Antisocial Personality Disorder which disproportionately affect males are arguably the most serious because of the consequences they pose for the individual as well as society [5,6]. This increased risk of antisocial disorders is primarily driven by the behavioral impulsivity expressed early in life in the hyperactive-impulsive and combined presentations of ADHD [5]. Hence a basic grasp of the neurobiology of this