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

What you need to know

• The largest brain imaging study of obsessive-compulsive disorder (OCD) to date found widespread differences in brain connectivity compared to healthy individuals
• People with OCD showed reduced connectivity, especially within brain regions involved in sensory processing and movement
• The findings suggest current models of OCD should place more emphasis on the role of sensorimotor brain networks
• While differences were seen at the group level, brain connectivity patterns could not reliably distinguish individuals with OCD from those without

How brain connectivity differs in OCD

Obsessive-compulsive disorder (OCD) is a mental health condition characterized by recurring, intrusive thoughts (obsessions) and repetitive behaviors or mental acts (compulsions). It affects about 1-3% of people worldwide and can significantly impact quality of life. To better understand the brain basis of OCD, researchers conducted the largest brain imaging study of the disorder to date.

The study combined brain scans from over 2,000 people - about half with OCD and half without. They looked at functional connectivity, which measures how different brain regions communicate and work together. By pooling data from many research sites, the study aimed to find reliable differences in brain connectivity associated with OCD.

Widespread differences in connectivity

The most striking finding was that people with OCD showed reduced connectivity throughout much of the brain compared to those without the disorder. This pattern of “global hypoconnectivity” suggests OCD involves altered communication between many brain regions, rather than just a few specific areas.

The reduced connectivity was especially prominent in sensorimotor brain networks. These networks process sensory information from the body and environment and control movement. Specifically, there was lower connectivity within and between regions like:

• The primary sensorimotor cortex, which processes touch sensations and controls voluntary movements
• The supplementary motor area, involved in planning and executing movements
• The insula, which integrates sensory, emotional and cognitive information

This focus on sensorimotor regions is a new emphasis compared to earlier, smaller studies of OCD. It suggests altered sensory processing and motor control may play a bigger role in the disorder than previously thought.

Connections with existing models

The results partially align with existing models of OCD but also suggest some updates may be needed. Current theories emphasize the role of circuits connecting the frontal lobes, basal ganglia, and thalamus. These circuits are thought to be involved in habit formation, reward, and cognitive/motor control.

The new study did find some altered connectivity in these circuits. For example, there was reduced connectivity between the thalamus and caudate nucleus, both part of the basal ganglia. The thalamus also showed increased connectivity with some sensorimotor regions.

However, the widespread nature of the connectivity differences, especially in sensorimotor networks, was not predicted by current models. The researchers suggest OCD theories should be revised to incorporate these findings.

Possible implications for symptoms

The altered sensorimotor connectivity seen in OCD may relate to several aspects of the disorder:

• Sensory phenomena: Many people with OCD report uncomfortable bodily sensations that drive compulsive behaviors. Altered sensory processing networks could contribute to these experiences.

• Difficulty suppressing actions: Reduced connectivity in motor control regions may make it harder to inhibit compulsive behaviors.

• Impaired sensorimotor gating: This is the brain’s ability to filter out irrelevant sensory information. Poor sensorimotor gating in OCD could contribute to feelings of being bombarded by stimuli.

• Habit formation: The sensorimotor circuit is involved in forming habitual behaviors. Altered connectivity here may relate to the repetitive nature of compulsions.

However, more research is needed to directly link these brain connectivity patterns to specific symptoms.

Differences based on medication use

The study also looked at how brain connectivity differed based on whether people with OCD were taking psychiatric medications. Those on medication showed more prominent differences from the healthy comparison group than those not taking medication.

This could mean medications are changing brain connectivity patterns. However, it’s also possible that those with more severe symptoms are more likely to be on medication and show greater brain differences. The cross-sectional nature of the study (looking at one point in time) makes it difficult to determine cause and effect.

Challenges in using connectivity as a diagnostic tool

While clear differences emerged when comparing groups, the study found brain connectivity patterns could not reliably distinguish individuals with OCD from those without. Attempts to use machine learning algorithms to classify people based on their brain scans were only modestly successful.

This highlights the challenges of developing brain-based diagnostic tools for mental health conditions. There is likely significant variation in brain patterns both among people with OCD and those without. A person’s brain connectivity snapshot may not clearly indicate whether they have the disorder.

Conclusions

• OCD involves widespread differences in brain connectivity, especially reduced connectivity in sensorimotor networks
• These findings suggest current models of OCD should place more emphasis on sensory processing and motor control circuits
• While clear differences exist at the group level, brain connectivity patterns alone cannot yet reliably identify who has OCD
• More research is needed to understand how these connectivity differences relate to specific OCD symptoms and develop over time

This large-scale study provides important new insights into the brain basis of OCD. The results suggest promising directions for future research to refine our understanding of the disorder and potentially develop new treatments targeting sensorimotor brain circuits.