The repetitive behavior of obsessive-compulsive disorder (OCD), such as excessive hand-washing or turning the lights on and off multiple times before leaving a room, sounds like the product of a mind in overdrive. But it may actually be the result of an underactive brain, according to a new study.
If scientists had to single out a part of the brain responsible for OCD, they'd point to the orbitofrontal cortex. The region, located behind the eyes, helps us make decisions and keeps compulsive behaviors, such as gambling and excessive drinking, in check. Some studies have found abnormalities in this region in people with OCD, but its role in the disorder is unclear.
Samuel Chamberlain, a psychiatrist at the University of Cambridge in the U.K., hoped brain scans would help. He and colleagues monitored 14 OCD patients, 12 unaffected relatives, and 15 people without a family history of the disorder as they engaged in a task intended to stimulate the orbitofrontal cortex. As a functional magnetic resonance imaging machine measured blood flow to various parts of their brains, the participants viewed two superimposed images--a face over a house, for example--on a screen and had to figure out through trial and error which images were "correct" and which ones were "incorrect," as determined by the researchers. Once the subjects caught on to which image was the right choice, the researchers switched it up and made the other image the correct choice. That forced the participants to change their newly acquired habit, something previously shown to activate the orbitofrontal cortex. But although normal subjects exhibited the expected activity in this region, those with OCD and their relatives showed reduced activity, even though their performance on the task was normal, the researchers report in tomorrow's issue of Science.
Peter Remijnse, a psychiatrist at the Vrije Universiteit Medical Center in Amsterdam, the Netherlands, praises the findings for helping shed some light on the cause of OCD. But he says that one question still remaining is what triggers the reduced activity in the orbitofrontal cortex in the first place.
Chamberlain says the answer might lie in the genes. This is the first study to show that relatives of patients also have abnormalities in the orbitofrontal cortex, so it's possible that there are genes that have yet to be identified that play a role in triggering OCD, he says.
Reduced activity in the orbitofrontal cortex could be a way to identify those who are at risk for OCD but have not yet developed symptoms, says Murat Yücel, a neuropsychologist at the University of Melbourne in Australia. Early identification "is important because people with OCD often only seek help late in the disease process, such as when they develop secondary depression, or the disease has very much affected their quality of life," says Chamberlain. Spotting those at risk could enable them to get early treatment.