Researchers have yet to pinpoint the exact cause of obsessive-Compulsive Disorder (OCD), but brain abnormalities, genetic (family) influences, and environmental factors are being studied. Brain scans of people with OCD have shown that they have different patterns of brain activity than those without OCD and that abnormal functioning of circuitry within a certain part of the brain (striatum) may cause the disorder. Abnormalities in other parts of the brain and an imbalance of brain chemicals, especially serotonin, may also contribute to OCD.¹