Melinda W. Moyer starts and ends her article on causes and treatments of obsessive-compulsive disorder (OCD) for Scientific American Mind with a description of progress of a person with OCD, one of ten most disabling conditions: from obsession with one number and endlessly performing repetitive rituals seemingly cause by fear, to her academic and social success after an exposure and response prevention therapy.

In the diagnostic manual of mental disorders, DSM, because of accompanying nervousness, OCD was listed among anxiety disorders. Does anxiety cause repetitive behaviors? It looks like it is the other way around: a drive to perform actions over and over again may make a person worry. More researchers now see the urges for repetitiveness as the defining feature of the condition. Obsessive-compulsiveness is closer to body dysmorphic disorder or hypochondriasis - they often develop together and may have common genetics. Also, OCD runs in families.

An excitatory neurotransmitter glutamate, the brain-signaling chemical, drives the neural circuit involved in making decisions for positive outcomes.  This brain circuit  operates abnormally in OCD patients. Increasing the amounts of another one, serotonin, with its reuptake inhibitors (SRIs), is most effective for OCD, and its regulating protein is affected by a single gene variation.

The cortical-basal ganglia circuit consists of the orbitofrontal cortex (decision making area), the striatum (learning and rewards), the thalamus (data), and the anterior cingulate cortex (error detection). Nonsensical behaviors may be caused by dysregulation in this neural wiring. Immune cells in the brain microglia regulate neuronal cell death. Insufficient cellular pruning may also cause compulsive behaviors. Abnormal immune responses may play a role as well.