How Do Brain Structures Differ Among ADHD, Autism, and OCD?

What you need to know

• This large study compared brain structure differences between ADHD, autism, OCD and healthy controls across different age groups
• Few brain differences were shared across the disorders, suggesting mostly distinct patterns for each condition
• ADHD showed smaller overall brain volume in children/adolescents, while autism showed thicker frontal brain regions in adults
• Brain differences were subtle overall, highlighting the complexity of these conditions
• More research is needed to understand how brain structure relates to symptoms and behavior in these disorders

Background and aims of the study

Attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and obsessive-compulsive disorder (OCD) are common neurodevelopmental disorders that often have overlapping symptoms. However, it’s unclear whether they also share underlying brain structure differences.

This study aimed to directly compare brain structure across ADHD, ASD, and OCD to look for shared and distinct patterns. It was the largest study of its kind, analyzing brain scans from over 12,000 people across 151 research sites worldwide.

How the study was done

The researchers examined MRI brain scans to measure:

• Volumes of subcortical brain regions (deeper structures like the hippocampus)
• Thickness of the cortex (outer brain layer)
• Surface area of cortical regions

They compared these measurements between patients with ADHD, ASD, or OCD and healthy controls. Analyses were done separately for children, adolescents, and adults to look at age-related differences.

Key findings

The study found mostly distinct patterns of brain differences for each disorder, with few shared features:

ADHD-specific findings:

• Smaller overall brain volume in children and adolescents compared to ASD, OCD and controls
• Smaller hippocampus volume in children compared to those with OCD

ASD-specific findings:

• Thicker cortex in several frontal brain regions in adults compared to ADHD, OCD and controls

OCD-specific findings:

• No major OCD-specific brain differences were found

Shared findings:

• Adults with both ASD and OCD showed smaller hippocampus volume compared to controls, but this was not significant for ASD after statistical correction
• Some overlapping cortical thinning in children with ADHD and ASD, but this did not survive statistical correction

Conclusions

The key conclusions from this study are:

• Brain structure differences in ADHD, ASD and OCD are mostly distinct rather than shared across disorders
• Brain differences were subtle overall, with small to moderate effect sizes
• ADHD showed signs of delayed brain maturation, with smaller brain volumes persisting into adolescence
• The thicker frontal cortex in adults with ASD may relate to differences in cognitive control
• More research is needed to link these brain differences to specific symptoms and behaviors

Implications for patients and families

For patients and families affected by ADHD, ASD or OCD, this study provides some important insights:

1. These conditions involve subtle brain differences that vary by disorder and age, rather than major obvious abnormalities.

2. The distinct patterns for each disorder support the idea that they are separate conditions, despite some overlapping symptoms.

3. Brain differences in ADHD may normalize somewhat in adulthood, consistent with symptom improvement for some individuals.

4. The lack of major shared brain features suggests treatments may need to be tailored for each specific disorder.

5. More research is still needed to understand how these brain differences relate to symptoms and behavior in each condition.

6. Brain scans alone cannot diagnose these disorders - symptoms and behavior remain key for diagnosis and treatment planning.

Overall, this study advances our understanding of the neurobiology of ADHD, ASD and OCD. However, the subtle and complex nature of the findings highlights that there is still much to learn about the brain basis of these conditions. Patients and families should continue to work closely with their healthcare providers to find the most appropriate treatments based on each individual’s symptoms and needs.

Conclusions

• ADHD, autism and OCD show mostly distinct patterns of brain structure differences
• Brain differences are subtle overall, indicating the complexity of these conditions
• ADHD is associated with delayed brain maturation that may persist into adolescence
• Autism involves thicker frontal brain regions in adults, possibly related to cognitive differences
• More research is needed to connect these brain findings to symptoms and behavior
• Brain scans alone cannot diagnose these disorders - clinical evaluation remains essential