Neurobehavioral Diseases

Disorders of Excessive Motor Activity and Thought: Attention Deficit Hyperactivity Disorder

Attention deficit hyperactivity disorder (ADHD) is a debilitating psychiatric disorder manifested by paucity in the attention span and/or inappropriate hyperactivity and impulsivity. The DSM-IV distinguishes three forms of this disorder: exclusive disruption of attention span (ADHD, predominantly inattentive type); exclusive involvement of hyper-activity and impulsivity span (ADHD, predominantly hyperactive-impulsive type); or both (ADHD, combined type), with all symptoms being present in at least two situations (e.g., school, play, or home) and for longer than six months. Hallmarks of inattention include [Page 312]difficulty to attend to a task or to sustain attention for a longer period of time, forgetful behavior, and easy distraction. Hyperactivity is manifested by fidgetiness, excessive talking, and restlessness, while symptoms of impulsivity might range from tendency to interrupt conversations and difficulty in awaiting turn to acting without thinking about subsequent consequences.

Even though several theories have been contemplated for a potential explanation of this disorder, much still remains unknown. The possible genetic component of ADHD can be explained from twin studies and studies with siblings, which show a greater concordance of ADHD in monozygotic twins than in dizygotic twins and a higher risk in siblings of ADHD children to develop the disorder as compared to the general population. Apart from genes, the faulty development of the different brain areas during the pre- and perinatal period under the influence of various detrimental factors, such as hypoxia, toxic, and metabolic damage to the developing brain, have been also discussed. Recently, findings about functional differences in brain area activation patterns with the help of modern brain imaging techniques show a decreased activation of the frontal lobes (a structure responsible for inhibitory control of lower, more voluntarily acting systems) of the brain in children with ADHD, thus suggesting a reason for possible behavioral disinhibition.

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