How Does Obsessive-Compulsive Disorder Affect Brain Structure?

What you need to know

• This large brain imaging study found changes in the white matter structure of certain brain regions in adults with obsessive-compulsive disorder (OCD).
• The white matter changes were associated with having OCD symptoms for a longer time, but not with how severe the symptoms were.
• No differences in brain structure were found in children with OCD compared to those without OCD.
• The findings suggest OCD may involve problems with connections between different brain regions, especially those linking the front and back of the brain.

How the brain’s structure relates to OCD symptoms

Obsessive-compulsive disorder (OCD) is a mental health condition that causes unwanted, intrusive thoughts (obsessions) and repetitive behaviors or mental acts (compulsions). While we know OCD involves differences in how the brain functions, less is known about whether there are also changes in the brain’s physical structure.

A large international study has now found evidence of structural changes in the brains of adults with OCD. Specifically, the study looked at the brain’s white matter - the tissue that contains nerve fibers connecting different brain regions. Using a brain imaging technique called diffusion tensor imaging (DTI), the researchers examined the white matter structure in 700 adults with OCD and 645 adults without OCD.

What did the study find?

The study found that adults with OCD had differences in the structure of white matter in several brain regions compared to those without OCD. These differences were seen in areas that connect the front of the brain to regions further back, including:

• The sagittal stratum, which connects areas involved in visual processing and attention
• The posterior thalamic radiation, which links the thalamus (a relay center for sensory information) to the back of the brain

In these regions, the white matter showed signs of reduced structural integrity in people with OCD. This could potentially mean the connections between different brain areas are not as strong or efficient.

Interestingly, the white matter changes were related to how long a person had been experiencing OCD symptoms. People who had OCD for a longer time tended to show more pronounced white matter differences. However, the changes were not related to how severe a person’s current OCD symptoms were.

The researchers also looked at brain scans from 174 children with OCD and 144 without. Unlike in adults, they did not find any differences in white matter structure in children with OCD.

What might this mean?

The findings suggest that OCD in adults involves alterations in how different brain regions are connected, particularly between frontal areas and more posterior regions. This fits with the idea that OCD may arise from problems in how the brain integrates information across different regions.

The fact that white matter changes were associated with how long someone had OCD, but not current symptom severity, is intriguing. It could mean these brain changes accumulate gradually the longer someone experiences OCD symptoms. Alternatively, it’s possible that pre-existing differences in brain structure might make some people more vulnerable to developing long-lasting OCD.

The lack of brain differences in children with OCD is also noteworthy. It suggests the brain changes seen in adults may develop over time, rather than being present from early in the disorder. However, the researchers caution that the group of children studied was relatively small, so more research is needed to confirm this.

Limitations to consider

While this was a large study, it only provides a snapshot of people’s brains at one point in time. To really understand how OCD and brain structure are related, we would need studies that follow people over time.

The brain imaging technique used (DTI) also has some limitations. While it can detect differences in white matter structure, it can’t tell us exactly what’s causing those differences at the cellular level.

Additionally, many of the OCD patients in the study were taking medication. The researchers found some evidence that medication use was associated with white matter changes. However, the study design makes it impossible to know if the medications caused changes, or if people with certain brain characteristics are more likely to be prescribed medication.

Conclusions

• Adults with OCD show differences in the structure of white matter connecting the front and back regions of the brain.
• These brain differences are related to how long someone has had OCD symptoms, but not to current symptom severity.
• Children with OCD do not show the same brain differences, suggesting the changes may develop over time.
• More research is needed to understand exactly how these brain changes relate to OCD symptoms and treatment.

This study provides important new evidence about the brain basis of OCD. By highlighting which brain regions and connections are altered in OCD, it may eventually lead to new treatment targets. However, we still need to learn much more about how these brain changes develop and whether they can be reversed. Future studies that follow people over time and look at the effects of treatment on brain structure will be crucial for advancing our understanding of OCD.