Despite being listed as one of the top ten most debilitating illnesses by the World Health Organization (WHO), the physical cause of OCD is unclear. This lack of understanding has enabled the trivialization of this illness and makes it difficult to develop new treatments. Recent research has uncovered evidence of inflammation in the brains of people with OCD, and specifically in regions associated with behavior. The severity of the inflammation is also in step with the severity of the symptoms: those with more severe OCD show higher levels of inflammation. These exciting findings highlight the physical nature of mental illness and may lead to new treatments.

Inflammation is an immune response which can be triggered by the presence of a foreign entity, such as an infection, or by an over-active immune system. In both cases, blood flow to an affected area increases. When this occurs in the brain it is called neuroinflammation, and the activity of cells called microglia, which protect our brain and spinal cord from infection, can be used as a proxy marker that it's occurring. During inflammation, microglia produce an immune response protein called ‘translocator protein’, or TSPO. The presence of high levels of TSPO in specific areas of the brain can therefore pinpoint areas of inflammation.

Using a radioactive probe for TSPO, scientists analyzed the levels of brain inflammation in OCD-suffering and healthy study participants. Significantly higher levels of inflammation were visible in the brains of OCD sufferers compared with the healthy controls. More specifically, higher levels of inflammation were found in regions of the brain that form a system called the cortico-striato-thalamo-cortical (CSTC) circuit, which is know to play a role in behavior.

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