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

## TL;DR

This study uses brain scans to compare ADHD, ODD, and OCD in children, finding that ADHD and ODD share brain complexity issues, while OCD does not show similar patterns.

## Contribution

The study identifies shared and distinct neural complexity patterns in ADHD, ODD, and OCD using rsfMRI data from preadolescent children.

## Key findings

- ADHD and ODD share reduced brain complexity in overlapping regions of executive function networks.
- Comorbid ADHD with other disorders shows more widespread complexity reductions than ADHD alone.
- OCD does not show significant complexity alterations, whether alone or with comorbidities.

## Abstract

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.

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 DSM-5 behavioral criteria for ADHD (n = 61), ODD (n = 38), and OCD (n = 48), respectively, were extracted, alongside data for children with comorbid ADHD, ODD, OCD, and/or other psychiatric diagnoses (n = 833). Data for a control sample of age-, sex-, and developmentally matched children were also extracted (N = 269). Voxel-wise sample entropy (SampEn) was computed using the LOFT Complexity Toolbox. Mean SampEn within all regions of interest (ROIs) of the EF networks was calculated for each participant. Hierarchical models with generalized estimating equations compared SampEn of comorbidity-free and comorbid ADHD, ODD, and OCD within the EF networks.

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, p < .05, and Benjamini–Hochberg [BH] corrected), with ADHD additionally affected in the right inferior/middle frontal gyrus and bilateral frontal orbital cortex (Wald statistic = 7.231-9.420, p < 0.05, and BH corrected). Among comorbid presentations, the presence of ADHD symptomatology was associated with significantly lower SampEn in every ROI (z = −3.973 to −2.235, p < .05, and BH corrected).

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.

Attention-deficit/hyperactivity disorder (ADHD) and its comorbidities may be better understood by examining differences in the brains of those with ADHD versus ADHD with other psychiatric diagnoses. Using data from the Adolescent Brain and Cognitive Development℠ (ABCD) study, this study compares the resting-state fMRI executive function networks in 9- to 10-year-old children. Researchers found ADHD and oppositional defiant disorder (ODD) shared common impairments in the comorbid-free presentations, with ADHD showing more widespread reductions in functional brain complexity. When ADHD co-occurred with other psychiatric disorders, the reduction in complexity extended beyond the regions affected in comorbid-free ADHD, indicating that comorbidities amplify deficits in neural complexity. In contrast, no significant complexity alterations were observed in obsessive-compulsive disorder (OCD), whether presented alone or in combination with ADHD.