Some of the definitions and descriptions of attention-deficit/hyperactivity disorder (ADHD) have been changed or refined as a result of all that we have learned in recent years from neuroscience, brain imaging, and clinical studies, and likely will continue to do so in the future. Until recently, ADHD was classified as a neurobehavioral disorder, characterized by the three core symptoms of inattention, impulsivity, and sometimes hyperactivity.
It is now recognized that ADHD is a far more complex disorder, involving impairment in a whole range of abilities related to self-regulation and executive functioning (Lists 1.2, 1.4). This more recent understanding of ADHD is reflected in some of the following descriptions, as shared by leading ADHD authorities Russell A. Barkley, Thomas E. Brown, Sam Goldstein, and others. Some of the following descriptions are from Children and Adults with Attention-Deficit/Hyperactivity Disorder (CHADD)), as well as the National Institute of Mental Health (NIMH), and other expert sources.