Executive Control Processes: Dimensions, Development and ADHD

Abstract: Deficits in higher order cognitive processes such as inhibitory control and working memory (WM), grouped under the term of executive function (EF), have been shown to constitute one important component of the complex neuropsychology of Attention Deficit Hyperactivity Disorder (ADHD). The aim of the present thesis was to examine EF in relation to ADHD, with primary focus on structure (i.e., dimensions) and developmental change. Rooted in the developmental and dimensional perspectives of ADHD, which propose that the disorder represents the extreme of or quantitative delays in traits that are present throughout the general population, four studies (I-IV) based on non-clinical and clinical samples of children at different developmental levels were conducted.Together, the results from Study I-IV suggest that inhibitory control and WM are important components of EF in typically developing children as well as in relation to ADHD symptoms. Of particular interest are the findings from Study II, III, and IV, showing that inhibitory control and WM seem to be of different importance depending on the child’s age. More specifically, the non-clinical and clinical studies suggest that inhibitory control and WM are important in predicting ADHD symptoms, with deficits in inhibitory control primarily being associated with ADHD symptoms for preschool and younger elementary school-aged children, whereas deficits in WM are associated with ADHD symptoms for older elementary school-aged children. In conclusion, the results of the present thesis are consistent with Barkley’s (1997) developmental prediction concerning the relation between EF and ADHD, which suggests that impaired inhibitory control is an early developmental precursor to or a factor that “sets the stage” for deficits in more complex EFs such as WM. The home taking message from the present thesis is that age matters not only in the behavioral, but also in the neuropsychological manifestation of ADHD. To our knowledge, these findings are among the first to show that age is an important factor that should be taken into account in future ADHD research, theory, and treatment.