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The repeated thoughts and urges of obsessive compulsive disorder (OCD) may be caused by an inability to learn to distinguish between safe and risky situations. A brain-scanning study has found that the part of the brain that sends out safety signals seems to be less active in people with the condition.

People with OCD feel they have to carry out certain actions, such as washing their hands again and again, checking the oven has been turned off, or repeatedly going over religious thoughts. Those worst affected may spend hours every day on these compulsive “rituals”.

To find out more about why this happens, Naomi Fineberg of Hertfordshire Partnership University NHS Foundation Trust in the UK and her team trained 78 people to fear a picture of an angry face. The team did it by sometimes giving the volunteers an electric shock to the wrist when they saw the picture while they were lying in an fMRI brain scanner. About half the group had OCD.


The team then tried to “detrain” the volunteers, by showing them the same picture many times, but without any shocks.

Lasting fear

Judging by how much the volunteers sweated in response to seeing the picture, the team found that people without OCD soon learned to stop associating the face with the shock, but people with the condition remained scared.

Compared with those without the condition, the people with OCD had less activity in their ventromedial prefrontal cortex, an area of the brain involved in signalling safety and predicting rewards.

Fineberg says the study shows that people with OCD aren’t always more fearful – they sweated in response to the face the same amount as the control group during the initial training. However, they sweated more than people without the condition during the detraining.

This fits with why situations that trigger OCD rituals often have at least some potential for things to go wrong if the task isn’t done correctly. Leaving the oven on might start a fire, for example.

“They’re not usually off-the-wall bizarre,” says Fineberg. “The obsessions are the sorts of things that most people would understand as being rational but exaggerated – for example, the need to wash your hands after going to the toilet.”

Focused therapy

Exposure response prevention therapy is usually used to treat OCD. It involves people trying to experience their triggers without doing their accompanying rituals – such as touching a toilet seat without washing their hands afterwards – to learn that nothing bad happens. But few people manage to drop all their repetitive behaviours, and about half of those with the condition aren’t helped at all.

The new findings may explain why people with OCD find this approach so difficult and it can take so long, says Fineberg. “The bit of their brain that should be telling them it’s safe isn’t working. Now we can say to them this is why it’s taking so long and we should stick with it.”

Annemieke Apergis-Schoute at the University of Cambridge says it may be helpful to give drugs during therapy that would help people to pay attention to the fact that nothing bad happens when they don’t do their rituals. One option would be psilocybin, for instance, a compound in magic mushrooms that causes euphoria. “We can boost this experience of things being safe or going right.”

Journal reference: PNAS, DOI: 10.1073/pnas.1609194114

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