Elucidating Distinct and Common fMRI-Complexity Patterns in Preadolescent Children With Attention-Deficit/Hyperactivity Disorder, Oppositional Defiant Disorder, and Obsessive-Compulsive Disorder.

Objective: The pathophysiology of attention-deficit/hyperactivity disorder (ADHD) is complicated by high rates of psychiatric comorbidities; thus, delineating unique vs shared functional brain perturbations is critical in elucidating illness pathophysiology. We investigated resting-state functional magnetic resonance imaging (rsfMRI)-complexity alterations among children with ADHD, oppositional defiant disorder (ODD), and obsessive-compulsive disorder (OCD), respectively, and comorbid ADHD, ODD, and OCD, within the cool and hot executive function (EF) networks. Method: We leveraged baseline data from 9- to 10-year-old children in the Adolescent Brain and Cognitive Development (ABCD) Study. Data for children who singularly met all Results: SampEn was reduced in comorbidity-free ADHD and ODD in overlapping regions of both EF networks compared with the healthy controls, including the bilateral superior frontal gyrus, anterior/posterior cingulate gyrus, and bilateral caudate (Wald statistic = 5.682-10.798, Conclusion: ADHD and ODD shared common impairments underlying the EF networks in the comorbidity-free presentations, with ADHD showing more widespread complexity reduction. When ADHD co-occurred with other psychiatric disorders, the reduction in SampEn extended beyond the regions affected in comorbidity-free ADHD, indicating that comorbidities amplify neural complexity deficits. In contrast, no significant SampEn alterations were observed in OCD, whether presented alone or in combination with ADHD.