Obsessive-compulsive disorder (OCD) is a mental health condition that involves symptoms of obsessive thoughts and compulsive behaviors. Obsessive thoughts consist of repetitive, unwanted thoughts, mental images or urges. Compulsive behaviors are rituals that are performed repetitively. For example, individuals with OCD may wash their hands constantly due to fear of germs or may have a compulsion to arrange objects in a specific manner.
Individuals with OCD are often aware that their thoughts and behaviors are counterproductive, but are unable to stop performing those behaviors. The symptoms of OCD may consume a considerable amount of time and interfere with an individual’s social and work life.
Treatment for OCD generally involves cognitive behavioral therapy, but antidepressants may also be used. Only half of individuals respond to those types of treatment, therefore, a better understanding of the biological basis of OCD is needed. Brain scans may be helpful in showing the differences in the structure and function of brain regions in individuals with OCD. Such studies can provide new targets for the treatment of OCD.
The Brain Cortex Structure in People with OCD
The cerebral cortex is the outer, wrinkly layer of the brain that is made up of tightly packed neurons. The cerebral cortex is divided into multiple regions by their function or their location. Three cortical regions have been consistently found to be different in individuals with OCD relative to people without OCD. These regions include the anterior cingulate cortex, the orbitofrontal cortex (OFC) and the caudate nucleus.
- The orbitofrontal cortex is involved in the detection of errors, determining which stimuli are rewarding and registering an error when previously rewarding experiences are no longer rewarding.
- The anterior cingulate cortex, located in the frontal cortex, also plays an important role in the detection of errors and the processing of conflicting information that occurs during decision making.
- The caudate nucleus receives information from neurons in the orbitofrontal cortex and anterior cingulate cortex. It also serves as a relay point between these areas and the thalamus. The thalamus then sends information regarding the error to different parts of the brain for further processing and relays it back to the orbitofrontal cortex. The caudate nucleus prevents overstimulation of the thalamus when an error signal is detected.
For people with OCD, the brain circuit involving the anterior cingulate cortex, the orbitofrontal cortex and the caudate nucleus is dysfunctional. As a result, people with OCD cannot stop worrying about the elements they obsess over, even if they know that their obsession is counter-productive.
Magnetic resonance imaging (MRI) scans conducted to compare the volumes of different brain regions in people with and without OCD have found smaller volumes of the orbitofrontal cortex and the anterior cingulate cortex in individuals with OCD. Furthermore, the volume of the thalamus tends to be larger in individuals with OCD than in individuals without OCD. The volume of the thalamus is associated with the severity of OCD symptoms. Additionally, the parietal lobe of the brain that is involved in attention, planning and response inhibition tends to be thinner in individuals with OCD.
Understanding Brain Circuitry and OCD
The previously mentioned MRI studies involved scanning the brains of individuals while they are at rest. These studies provided information regarding the structure of each individual region. However, multiple brain regions, connected to each other by axons, are involved during any behavior. Differences in behavior (OCD vs. non-OCD) are associated with differences in the strength of connectivity between the brain regions.
Studies in humans generally involve measuring activity in different brain regions during a task to gain insight into which brain regions are activated simultaneously. To understand which brain circuits are involved in a particular task, individuals are asked to perform a task while in a functional magnetic resonance imaging scanner (fMRI). A fMRI detects changes in blood flow to different brain regions that are indicative of neuronal activity in a particular region.
One example of the tasks used to compare differences in brain circuits of people with and without OCD is the stop signal task. The stop signal test involves a stimulus (left or right arrow) that the subjects are supposed to respond to. However, if there is a stop signal in the form of an audio tone or color change after the presentation of the stimulus, then the person must withhold their response to the initial stimulus. This task measures the ability to override their initial response and thus, measure the ability to control unwanted behavior. Similarly, other tasks measure the ability of individuals to detect interfering stimuli or errors and adjust their behavior. Many studies involve people with and without OCD performing such a cognitive task while lying in an fMRI scanner.
During a study, people with OCD and people without the disorder were shown two faces while in the fMRI scanner. A small electric shock was delivered when they were shown one of these faces. Both groups of individuals came to recognize this face as being threatening. After a few trials, the pairing between the shock stimulus and the faces were switched. People without OCD came to associate the previously safe face as being threatening. However, individuals with OCD began to identify both faces as being threatening after the reversal. The individuals with OCD failed to update information regarding the threat levels associated with the faces. The neuroimaging data collected from the fMRI scans indicated that the ventromedial prefrontal cortex (vmPFC) communicated with the anterior cingulate cortex, the insula and thalamus when the first face was paired with the electric shock. However, the vmPFC did not communicate with these regions when the other face was paired with the shock.
The vmPFC plays an important role in evaluating emotional stimuli and did not communicate to other brain regions that the first face was safe. Deficits in the network involving vmPFC and the other three regions may be responsible for some of the behavioral deficits in OCD patients. This study suggests that individuals with OCD may perform repetitive behaviors such as washing their hands because washing their hands once does not trigger the safety signal from the vmPFC.
How Brain Scans Are Helping Develop New OCD Treatments
Studies involving brain scans do not establish a causal link between the brain regions or circuits and behavioral deficits. The abnormal activity in these brain regions may simply be a consequence of the impaired functioning of other brain regions. However, studies may provide new therapeutic targets for the treatment of OCD. For example, the FDA approved repetitive transcranial magnetic stimulation for the treatment of OCD.
Transmagnetic stimulation is a non-invasive procedure involving the activation of neurons using magnetic fields. Transmagnetic stimulation is being used to target some of the brain regions identified in the previously mentioned studies. Other, more invasive treatment options for severe OCD include neurosurgery to sever the connection between brain regions or placing an electrode in a particular brain region to provide stimulation.
Once the findings from brain scan studies are consolidated with data from other studies, these two invasive procedures may become viable treatment alternatives. The information from the brain scans may also help the development of new medications that may be used with behavioral approaches to address the various deficits observed in OCD individuals.
Some people attempt to self-medicate their OCD by using drugs or alcohol. This type of behavior can quickly lead to addiction. If you or a loved one struggle with substance use and co-occurring mental health disorder, learn how professional treatment can address addiction and any co-occurring mental health disorders.
Huey, Edward; et al. “A psychological and neuroanatomical model of obsessive-compulsive disorder.” The Journal of neuropsychiatry and clinical neurosciences, April 2008. Accessed September 22, 2019.
Apergis-Schoute, Annemieke; et al. “Neural basis of impaired safety signaling in obsessive compulsive disorder.” Proceedings of the National Academy of Sciences, March 2017. Accessed September 22, 2019.
U.S. Food and Drug Administration. “FDA permits marketing of transcranial ma[…]compulsive disorder.” August 17, 2018. Accessed September 27, 2018.
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