Attention-deficit hyperactivity disorder
Attention-Deficit/Hyperactivity Disorder (ADHD) is characterized by persistent and chronic inattention and/or excessive motor restlessness and impulsivity. Inattentive symptoms include poor organizational skills, making careless errors, forgetfulness, trouble listening, and distractibility. Hyperactive/impulsive symptoms include restlessness, excessive talking, and interrupting. For the purpose of diagnosis, symptom manifestation should be developmentally inappropriate and exhibited in two or more settings (e.g., home and school). Much of the research in the past decade has focused on deficits associated with the disorder in regard to executive function, response inhibition, cognitive control, and motivational dysfunction in response to delayed reinforcers.
The manifestation of ADHD and its associated core problems vary with development. ADHD in the combined subtype is characterized in the preschool and prepubescent period by high rates of gross motor activity, difficulty sitting in one’s seat, academic difficulties, and peer-interaction problems. ADHD in adolescence is a period associated with high risk-taking behavior, and teenagers and young adults with ADHD are likely to have more traffic accidents, substance abuse, treatment for sexually transmitted diseases (Barkley et al., 2006), and earlier initiation of sexual activity and intercourse (Flory,
Pelham, et al., 2006). ADHD in adulthood is recognized as a period with less observable gross motor hyperactivity.
However, problems with sustaining attention and impulsive behavior continue to result in poor work performance, greater unemployment, higher divorce rates, and engagement in criminal behavior (Barkley, 2006).
According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR, 2000), there are three ADHD subtypes: predominantly inattentive, predominantly hyperactive-impulsive, and a combined subtype that is the most prevalent. Individuals diagnosed with the combined subtype exhibit both inattentive and hyperactive/impulsive symptoms to a significant degree. Individuals identified with the inattentive or hyperactive/impulsive diagnoses present with predominant inattention or hyperactive and impulsive symptoms, respectively. There is also recent interest in a subset of the ADHD, inattentive, which is characterized by slow or sluggish cognitive tempo (McBurnett et al., 2001). Children with this inattentive type of ADHD appear hypoactive and seem to be in a fog or daydreaming.
There is evidence to suggest that there are differences in the genetic profile and treatment response among the ADHD subtypes. Consistent, robust differences on a neuropsychological level among the ADHD subtypes are difficult to identify, however. Neuropsychological studies that have found differences have been contradictory in nature or apply primarily to a subset of the subjects. In general, however, it appears that children with the ADHD combined subtype perform poorly on planning, cognitive flexibility, and response inhibition tasks, whereas children with the ADHD inattentive subtype display difficulty using cues to guide their behavior and demonstrate slowed motor output, impaired vigilance, and altered arousal effects. ADHD is frequently comorbid with other disorders, most commonly with disruptive behavior disorders. From 42.7% to 56% of children meeting criteria for ADHD in community samples meet criteria for conduct disorder as well. It is the ADHD-type symptoms rather than the conduct disorder symptoms that are most likely to predict academic achievement, thus indicating that the attentional symptoms need to be addressed as robustly as the conduct problems in children who have both. Other frequently occurring comorbid disorders in childhood ADHD include learning disabilities and anxiety disorders. Children with ADHD are also more vulnerable than young people in