The second conclusion that might be drawn from the foregoing discussion is that the HI and combined types are more reflective of a deficit in behavioral or response inhibition than of inattention. There is substantial support for this conclusion in the extant literature and it is increasing with each new study of response inhibition in ADHD (Barkley, in press; Pennington and Ozonoff). The importance of such a change in perspective on ADHD cannot be overemphasized.

Research in developmental psychology and neuropsychology have shown behavioral inhibition to be critical to the effective performance of several cognitive abilities considered executive functions because they are related to self-regulation. Not surprisingly, then, researchers in ADHD have begun to view ADHD as a disorder of self-regulation (Douglas) or executive function (Denckla), although both terms are vague when employed in this regard.

Nevertheless, the trend to a broader conceptualization of ADHD seems necessary given the variety of studies that either demonstrate or at least hint that ADHD children have deficits in working memory and sense of time; the cross-temporal organization of behavior; the internalization of speech and rule-governed behavior; the self-regulation of emotion and motivation; and the execution of complex, novel behavioral sequences (Barkley, in press). All of these are deemed executive functions and all seem to permit control of behavior by internally represented information.

Far more research is needed on these cognitive functions to cement their association with ADHD. However, the extant research offers the exciting possibility that ADHD is actually a developmental disorder of self-regulation, arising from a deficit in behavioral inhibition that in turn causes a deficiency in behavior regulation by internally represented information or events. If so, the hyperactivity and "inattention" (poor persistence/distractibility) seen in ADHD children and adults may simply be the most obvious (and most superficial) signs of a deeper, more pervasive, more socially significant disorder than has heretofore been imagined.

Clinical Implications

What are the clinical implications of such a shift in conceptualizing the nature of ADHD, should it transpire? Too many exist to list here, but several important ones deserve mention. First, ADHD would be viewed as a disorder of "doing what you know, not knowing what to do," of the "when" of behavior, not the "how," and of performance, not skill. If ADHD involves deficient inhibition that disrupts the regulation of behavior by internally represented information, it attacks the capacity to put intelligence into action. Clinically, this means that training ADHD patients in skills presumed to correct or compensate for their deficits should be deemphasized in most cases as it would be predicted not to work. Perhaps this accounts for the failure of cognitive therapies and other skills-training approaches to generalize outside the training context or to be maintained over time.

Instead, great emphasis would be placed on helping ADHD individuals do what they know; that is, to perform the skills already in their repertoire at the points of performance where such skills are useful to execute. Useful treatments, therefore, would be those that are in place at these points of performance in natural settings to help prompt use of the skill when it is needed and to reinforce its occurrence so as to maintain it (Ingersoll and Goldstein). From this perspective, weekly, clinic-based therapy hours, whether group or individual in nature, would be considered to be of little value for those with ADHD. Instead, working with parents and teachers to set up behavioral performance programs in natural settings would be more heavily emphasized. The role of mental health professionals shifts from that of direct therapist to the ADHD client to that of consultant to natural caregivers trained to carry out the treatment program in the client's natural social environment.

A second implication is that the behavioral inhibitory deficit is not wholly correctable through training or other psychosocial treatment methods. It is not likely to fall within the realm of volition or self-control but precedes such self-regulation and even permits it to occur. If so, training a child with ADHD to be less impulsive may be misguided, as we can now appreciate that ADHD disrupts the very neuropsychological mechanism that permits the training to serve as an internal template that effectively executes the associated responses at the right time. Time, timing, internally guided response execution and its persistence become far more important targets for treatments than does knowledge or skill.

Stimulant Medications

A further implication of such a conceptual shift is that stimulant medications, on the rise over the past decade, may be far more justifiable as a primary or central form of treatment for ADHD than was previously thought.

Until recently, many practitioners were trained or advised to consider behavioral and psychosocial treatments first before leaping too quickly for the prescription pad to dash off a recommendation for stimulants. Those who did so, even if justifiable by virtue of an absence of such alternative (and expensive) therapies in their geographic regions, may have suffered great pangs of conscience that the now almost proverbial "multimodal" treatments were not applied in such cases. Reconceptualizing ADHD as a developmental disorder of self-regulation (read prefrontal lobes) related to defective motor inhibition for which stimulants have repeatedly proven the most effective management methods challenges this older clinical wisdom.