Insights into obsessive-compulsive disorder

10 March 2017

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Scientists have come up with a potential new way to help patients affected by obsessive compulsive disorder (OCD).

About one person in fifty suffers with OCD and feels compelled by anxiety to perform repetitive, ritualistic behaviours, like washing their hands a certain number of times or getting dressed in a certain way. Failing to comply leads to an overwhelming sense of dread that something terrible will happen.

One approach therapists use to treat the problem is to prevent sufferers from fulfilling their rituals - for instance, making them touch a toilet seat and then stopping them from washing their hands more than once. But this only works for about half of patients, so what’s needed is a deeper understanding of what causes OCD in the first place so that better therapies can be developed.

Now Annemieke Apergis-Schoute, at Cambridge University, has discovered that OCD patients are very good at learning when things are unsafe or a threat, but they fail to be flexible and learn when a former perceived threat is actually safe.

Writing in PNAS, she showed OCD sufferers and a group of unaffected control volunteers a series of images of faces. One of the faces was a "threat stimulus" and when shown to the volunteers was accompanied by the administrations of an electronic shock. Another photo was a "safe" image that was not associated with a shock.

After the volunteers learned this association the researchers abruptly switched the stimuli around, so they started to receive a shock when they saw the safe face and no shock with the former "threat" face.

"We wanted to see how flexible the subjects would be in learning to distinguish a safe from a threatening stimulus," explains Apergis-Schoute. This was done by simultaneously measuring the the amount of sweat on the skin of the subjects as an index of stress.

"We can tell when they think they are going to get a shock, because the level of sweating goes up!"

Normal individuals quickly adapted to the switch in stimuli, recognising the new threat and no longer showing a stress response to the old threat image. In contrast, the OCD patients completely failed to do this and instead now showed stress responses to both faces.

By scanning the individuals as this was going on, it was clear that one brain region was behaving quite differently between the two groups. "The ventromedial prefrontal cortex, which is involved in making decisions about safety, was completely inactive in the OCD patients during the trial," Apergis-Schoute explains."

Instead, she thinks that the OCD patients become so absorbed in contemplating their obsession that this brain area becomes unavailable to pay attention when things are actually safe or rewarding.

But can this help us to better treat the 40% of OCD patients for whom exposure therapies won't work? According to Apergis-Schoute, the answer is yes, because it might be that by fortifying the brain's reward process, either behaviourally or with the help of medications, the perception of safety can be made more meaningful, which will help patients to overcome and "unlearn" their obsession.

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