Updated: Jul 22, 2021

Obsessive-compulsive disorder (OCD) is a psychiatric disorder mainly characterized by unwanted, recurring thoughts causing anxiety and the need to respond to those recurring thoughts. Atypical signs in some areas of the brain of OCD patients have been revealed through brain scans. However, the changes to the causes of the symptoms of OCD are still unknown.

OCD is a tendency toward repetitive habitual actions that the patient feels a need to perform, with untoward functional consequences such as detracting from overall life goals, or quality of life). Disorders of compulsivity include OCD and related disorders such as hoarding disorder, body dysmorphic disorder, trichotillomania, skin picking disorder, and Tourette syndrome. Imaging, surgical, and lesion studies suggest that the prefrontal cortex (orbitofrontal and anterior cingulate cortexes), basal ganglia, and thalamus are involved in the pathogenesis of obsessive-compulsive disorder (OCD). On the basis of these findings several models of OCD have been developed, but have had difficulty fully integrating the psychological and neuroanatomical findings of OCD.

The Root of OCD is problems with communication between three brain areas: the cortex, striatum, and thalamus. The pathways that connect these areas are involved in both the initiation and termination of behavior; researchers believe that an imbalance within these pathways may cause individuals with OCD to get stuck in repetitive loops of thought and behavior. Because selective serotonin reuptake inhibitors (SSRIs) can be helpful in treating OCD, it has been hypothesized that serotonin may play an important role in the disorder. Cortico-striato-thalamic pathways, however, also utilize dopamine heavily, so some have suggested that an imbalance between serotonin and dopamine levels may be at the root of the disorder.

In a study recently published in Nature Neuropscyhopharmacology, an international team of investigators (Radua et al.) focused on how white matter tracts in the brain might be affected in OCD. While the cell bodies of neurons make up what is known as grey matter, white matter is mostly made up of myelinated axons. Axons are the long extensions of neurons that carry information away from the cell body, making it possible for that signal to then be passed to an adjacent neuron. Myelin is a white insulatory material that covers axons and facilitates the conduction of a signal down the axon.

Radua et al. compiled the results of 34 studies that used methods like diffusion tensor imaging to examine white matter integrity in OCD patients. They found that widespread abnormalities in the white matter of OCD patients (as compared to non-OCD patients) had been reported. Aberrations were most frequently seen in tracts that make up the corpus callosum and cingulum. The corpus callosum is a large fiber bundle that connects the left and right hemispheres of the brain, while the cingulum is a group of fibers that connects different structures of the limbic system. Some of the reported abnormalities were related to the cortico-striato-thalamic pathways typically associated with OCD, but there were also published reports of anomalies beyond these pathways.

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