Categorical and dimensional investigations of dynamic functional connectivity and behavior during response inhibition in children with and without ADHD

Attention-deficit/hyperactivity disorder (ADHD) is the most common neurodevelopmental disorder of childhood, affecting approximately 5-10% of children worldwide. ADHD is characterized by developmentally inappropriate levels of inattention, hyperactivity, and impulsivity, but there is much heterogeneity in the ADHD phenotype. Further, children with and without clinical ADHD diagnoses can experience a wide range of ADHD-related symptoms. Research into the pediatric ADHD phenotype has traditionally employed categorical approaches, comparing children with ADHD to typically developing children. As individuals with ADHD symptom burden, regardless of diagnosis, are at risk for negative-long term outcomes, the current project investigated the ADHD phenotype categorically and dimensionally to increase the understanding of the behavioral and neural substrates of ADHD symptom burden in clinical and nonclinical populations. The first study determined whether variability in behavior and functional connectivity (FC) differed between children with and without ADHD (i.e., a categorical approach), and the second study examined whether there were relationships between ADHD symptom burden and variability in behavior and FC in a large sample of children with continuous ADHD-related symptom measures (i.e., a dimensional approach). While there were no significant differences in behavioral nor FC variability in children with and without ADHD in the first study, the second study revealed that dimensional relationships exist between ADHD symptom burden and variability in behavior and FC. Specifically, elevated ADHD symptoms were associated with increased behavioral variability, reduced FC variability in the frontoparietal network, and increased FC variability in the cinguloopercular network. The third and final study further explored the heterogeneity that exists within and across ADHD diagnostic categories by using a community detection approach to identify symptom-based subgroups of individuals with and without ADHD. This study revealed four unique subgroups that were transdiagnostic in nature, such that children with ADHD were included in each of the four subgroups. Together, the findings discussed here suggest that both categorical and dimensional approaches can be used to characterize the behavioral and neural substrates of the ADHD phenotype. The results of this project additionally contribute to identification and treatment efforts for individuals experiencing ADHD symptoms, regardless of clinical diagnostic status.