ADHD is the most common neuropsychiatric disorder in childhood, affecting an estimated 3-8% of children. The core behavioral symptoms of this disorder (inattention, impulsivity and hyperactivity) cause impairment in family and social relationships and in school performance. The impact of ADHD is amplified further through its comorbidity with a number of psychiatric and neurodevelopmental disorders, including learning disabilities and Tourette syndrome. Although the causes of ADHD are unknown, recent research clearly identifies ADHD as a neurobiological disorder. Because ADHD presents in a variety of ways, it is unlikely to have a single cause. Despite the possibility of multiple origins, the cardinal symptoms of ADHD may emanate from closely related disturbances in cerebral function. Once these dysfunctions are understood, they can serve as biomarkers that help to guide diagnosis and can be used as “intermediate” indicators in studies of genetic and environmental causes and mechanisms of compensation, treatment, and recovery.
There is strong evidence to suggest that impaired response control is a core defining neurologic feature of ADHD. Studies from a number of laboratories, including our own, reveals that children with ADHD show impaired performance on a wide range of measures assessing response selection and inhibition, and that these impairments in response control contribute to the excessive impulsive, hyperactive, and distractible behavior that defines ADHD. In the current study we are using a combination of structural and functional imaging approaches to further our understanding of the neurologic basis of ADHD-associated impairments in response control. The knowledge gained will help identify meaningful intermediate biomarkers of ADHD that can be applied to studies examining potential genetic and environmental causes.
Our ongoing studies will also contribute to the development of novel treatment interventions. To this end, we are currently examining the impact of a range of behavioral adjustments on the ability of children with ADHD to engage effective response control, These include the use of reward as well as increasing the variability of stimulus presentation by “jittering” the timing of stimuli. We have thus far observed a positive impact and we are now moving to develop “real world” interventions based on these findings.