Although it’s not entirely clear what causes obsessive-compulsive disorder (OCD), neuroimaging studies suggest that people with the condition have distinct differences in their brain structure and function.

OCD is a mental health condition that involves persistent, unwanted thoughts (obsessions) and repetitive behaviors aimed at reducing the distress these thoughts cause (compulsions).

If you have OCD, learning more about your brain structure may help you understand your diagnosis better. It can also shed some light on why treatments like deep brain stimulation and some medications can help OCD.

Research suggests that people with OCD often show both biochemical and structural differences in the brain compared with people without OCD.

Biochemical differences relate to neurotransmitters (brain messengers) like serotonin, and structural differences relate to the size and function of certain parts of the brain.

Biochemical differences in OCD

OCD is associated with imbalances in levels of certain neurotransmitters. Neurotransmitters are chemical messengers that help parts of your body communicate among themselves so that they function optimally.

Differences in the following neurotransmitters are associated with OCD:

  • Glutamate: This is an excitatory neurotransmitter, which means it causes neurons to fire off a message to the next cell. People with OCD tend to have higher glutamate levels than other people.
  • Gamma-aminobutyric acid (GABA): GABA can have a calming effect on the brain, as it blocks certain alert signals. Low GABA levels are associated with OCD.
  • Serotonin: OCD is often associated with differences in levels of serotonin, a neurotransmitter that regulates mood.

More research is needed to fully understand the biochemical markers of OCD.

Structural brain differences in OCD

Studies have identified that certain areas of the brain are associated with OCD symptoms. In people with OCD, certain regions of the brain are overactive or differently sized.

The brain areas most closely associated with OCD symptoms are those involved in the cortico-striato-thalamo-cortical (CSTC) loop. These parts of the brain include the:

  • Orbitofrontal cortex: This is involved in decision making and evaluating risks. The cortex is often hyperactive in people with OCD, which may contribute to the intrusive, anxiety-provoking thoughts characteristic of the disorder (obsessions).
  • Anterior cingulate cortex: This plays a role in error detection and emotional regulation. Overactivity in this area may contribute to the heightened anxiety and the need for perfectionism common in some forms of OCD.
  • Striatum and thalamus: These brain structures are involved in habit formation and movement regulation. The striatum might be larger in people with OCD, and both areas tend to be different compared with those of people without OCD.

Although neuroimaging studies indicate that people with OCD tend to show these brain differences, doctors don’t use neuroimaging to diagnose OCD. Generally, they’ll diagnose the condition based on a number of behavioral and psychological symptoms.

Deep brain stimulation is a surgical treatment that involves implanting electrodes into specific areas of the brain. These electrodes deliver electrical impulses to modulate the activity of specific brain regions.

To treat OCD, deep brain stimulation usually targets the CSTC loop. According to an extensive review of studies, it’s a “promising therapy” for people who have severe symptoms of OCD.

The review notes that about 60% to 70% of study participants who underwent deep brain stimulation had a reduction in OCD symptoms. Also, the reviewers concluded that more research is needed to fully understand the effects of deep brain stimulation on OCD.

Because deep brain stimulation is a surgical treatment, doctors usually only recommend it for symptoms that haven’t responded to other OCD treatments. In other words, it’s for people who’ve experienced little to no relief from OCD symptoms after using psychotherapy and medications.

The Food and Drug Administration (FDA) has approved deep brain stimulation for these cases of OCD. Healthcare professionals consider deep brain stimulation a well-tolerated treatment with few to no side effects.

Doctors sometimes prescribe medications like selective serotonin reuptake inhibitors (SSRIs) to treat OCD. These drugs are a “first-line” treatment for severe symptoms, along with cognitive behavioral therapy (CBT).

Examples of SSRIs for OCD include:

As discussed before, according to some research, some people with OCD have dysregulated serotonin pathways. SSRIs increase the levels of serotonin in the brain by blocking its reabsorption (reuptake). This means you’ll have more serotonin available in the brain.

If SSRIs don’t work for your OCD symptoms, other medications may help balance the biochemical differences in your brain that may contribute to OCD. For example, doctors often suggest a tricyclic antidepressant called clomipramine for OCD.

Research suggests that people with OCD often show differences in brain structure and function, particularly in areas involved in decision making, emotional regulation, and habit formation.

For this reason, people with OCD can benefit from treatments that address the biochemical and structural brain differences. These include SSRIs and deep brain stimulation.

Although these treatments can be effective, doctors usually recommend them alongside other treatments, such as CBT and stress management strategies.