Reduced fMRI-complexity in pre-adolescent children with comorbid-free and comorbid ADHD, ODD, and OCD diagnoses

Motivation: Previous studies have shown reduced resting-state fMRI (rsfMRI)-complexity in attention-deficit/hyperactivity disorder (ADHD). However, the impact of comorbidity remains unclear. Goal(s): To investigate rsfMRI-complexity in ADHD, oppositional defiant disorder (ODD), and obsessive-compulsive disorder (OCD) for both comorbid-free and comorbid presentations. Approach: Hierarchical models with Generalized Estimating Equations compared sample entropy within executive function networks of pre-adolescents with comorbid-free and comorbid ADHD, ODD, and OCD. Results: RsfMRI-complexity was reduced in more regions in ADHD than in ODD compared to healthy controls in the comorbid-free presentations. In comorbidity, ADHD dominated complexity reduction. OCD had no significant impact on complexity in either scenario. Impact: Resting-state fMRI-complexity for ADHD comorbidity remains poorly understood, although reduced complexity in ADHD was reported. Our study demonstrates reduced complexity in ADHD pre-adolescents, both in comorbid-free cases and in those comorbid with oppositional defiant disorder, obsessive-compulsive disorder, and other conditions.