British researchers at the University of Cambridge have found that an area of the brain that regulates habitual behaviour is under-activated in people with obsessive compulsive disorder and their close family members.

Obsessive compulsive disorder (OCD) is a condition in which people often have obsessive thoughts concerning cleanliness, fear of contamination, or anxiety around the health or well-being of a family member.

To keep these thoughts at bay, sufferers frequently repeat the same actions over and over, such as stacking objects or washing their hands.

The condition runs in families, and it's thought that genetic changes account for the abnormal brain development.

The study found that in people with OCD the lateral orbitofrontal cortex — a section of the brain located in the frontal lobes which governs decision-making and behaviour — was underactive in MRI scans.

The scans compared the brains of those with OCD and their family members with people who did not have the condition.

In total, 40 participants in the study had their brains scanned as they watched and deciphered images on a screen.

"Impaired function in brain areas controlling flexible behaviour probably predisposes people to developing the compulsive rigid symptoms that are characteristic of OCD," said Samuel Chamberlain, a researcher at the University of Cambridge's department of psychiatry, in a release.

"This study shows that these brain changes run in families and represent a candidate vulnerability factor."

The researchers believe that the discovery could lead to better diagnosis of OCD, as well as treatments of the condition.

Chamberlain said further work is needed to identify the genes responsible for the abnormal brain function.

The study is published in the July 18 issue of Science.