University of Cambridge researchers have found that patients with obsessive-compulsive disorder (OCD) have reduced activity in the orbitofrontal cortex, the region that helps people make decisions and keep compulsive behaviors in check.

The researchers took fMRI scans as participants engaged in a task (changing a habit–learning new pattern-matching rules) intended to stimulate the orbitofrontal cortex. Normal participants exhibited the expected activity, but those with OCD did not, even though their performance on the task was normal. Unaffected relatives of OCD patients also had this reduced activity, suggesting that genes (not yet identified) may trigger OCD.

Brain scans could identity those who are at risk for OCD but have not yet developed symptoms, allowing them to get early treatment.