How Does Brain Structure Differ in People with Obsessive-Compulsive Disorder?

What you need to know

• This study examined differences in brain structure between people with obsessive-compulsive disorder (OCD) and healthy individuals.
• No overall differences were found between OCD patients and controls, but differences emerged in subgroups of OCD patients with depression, anxiety, or medication use.
• The study found changes in the shape of brain regions like the hippocampus, pallidum, and thalamus in these OCD subgroups.
• The findings suggest that comorbid conditions and medication use may influence brain structure in OCD more than the disorder itself.

Background on OCD and brain imaging

Obsessive-compulsive disorder (OCD) is a mental health condition that affects 1-3% of people. It involves unwanted, intrusive thoughts (obsessions) and repetitive behaviors or mental acts (compulsions) that a person feels compelled to perform. OCD can significantly impact quality of life and daily functioning.

Researchers have long been interested in understanding how OCD affects the brain. Brain imaging studies have found some differences in certain brain regions in people with OCD compared to those without the disorder. However, results have been inconsistent across studies.

This study aimed to take a closer look at the shape of specific brain structures in a large group of people with OCD. The researchers were particularly interested in deep brain structures like the basal ganglia, which are thought to play a role in OCD symptoms.

What the study did

This study combined brain MRI scans from 412 people with OCD and 368 healthy controls from multiple research sites. The researchers used advanced techniques to analyze the shape of seven key brain structures:

• Pallidum
• Hippocampus
• Amygdala
• Thalamus
• Caudate nucleus
• Putamen
• Nucleus accumbens

They compared the thickness and surface area of these structures between the OCD group and control group. The researchers also looked at how factors like medication use, having depression or anxiety in addition to OCD, and duration of OCD symptoms related to brain shape.

Key findings

No overall differences between OCD and control groups

Surprisingly, when comparing the full OCD group to the control group, the researchers found no significant differences in the shape of the examined brain structures. This contradicts some previous smaller studies that had found brain differences in OCD.

Differences emerge in OCD subgroups

While there were no differences overall, the researchers did find brain shape differences when they looked at specific subgroups of OCD patients:

1. OCD patients with depression:

   • Lower thickness and surface area in the hippocampus
   • Higher thickness and surface area in the pallidum
   • Changes in the thalamus, caudate nucleus, putamen, and nucleus accumbens

2. OCD patients with anxiety:

   • Lower thickness in the hippocampus
   • Higher thickness in the pallidum
   • Changes in the caudate nucleus and putamen

3. OCD patients taking medication:

   • Lower thickness in the hippocampus, putamen, and thalamus
   • Higher thickness in the pallidum and caudate nucleus
   • Lower surface area in the hippocampus and amygdala
   • Higher surface area in the putamen, pallidum, and caudate nucleus

Importantly, OCD patients without depression/anxiety or medication use did not show significant brain differences compared to controls.

What do these findings mean?

The results of this study suggest that having depression or anxiety along with OCD, or taking medication for OCD, may have a greater impact on brain structure than OCD itself. This highlights the complexity of studying brain differences in psychiatric disorders, where comorbid conditions are common.

The specific brain regions showing differences in shape - like the hippocampus, pallidum, and thalamus - are involved in functions relevant to OCD symptoms. For example:

• The hippocampus plays a role in memory and emotional processing
• The pallidum is part of the basal ganglia and involved in movement and behavioral control
• The thalamus acts as a relay station for sensory and motor signals in the brain

Changes in the shape of these structures could potentially relate to symptoms like intrusive thoughts, compulsive behaviors, and heightened anxiety in OCD. However, more research is needed to directly connect brain shape differences to specific symptoms.

Limitations and future directions

This study had some key strengths, including its large sample size and use of advanced brain imaging techniques. However, there are also some limitations to keep in mind:

• The study only looked at brain structure at one point in time, so it can’t show how brain shape might change over the course of OCD.
• Information on depression and anxiety wasn’t available for all participants.
• The study couldn’t determine if medication use causes brain changes or if pre-existing brain differences influence who takes medication.

Future research could address these limitations by:

• Following people with OCD over time to see how brain shape changes
• More carefully assessing comorbid conditions in all participants
• Examining brain structure before and after starting OCD medication

Conclusions

• No overall brain shape differences were found between people with OCD and healthy controls.
• OCD patients with depression, anxiety, or taking medication showed changes in the shape of brain regions like the hippocampus and pallidum.
• Comorbid conditions and medication use may influence brain structure in OCD more than previously thought.
• More research is needed to understand how brain shape relates to OCD symptoms and treatment.