People suffering from obsessive-compulsive disorder (OCD) struggle to learn about the safety of specific stimuli and this may explain why overcoming their compulsions is so difficult.

OCD was once considered to be a rare condition, because there was a lack of understanding of what the condition is and people were often misdiagnosed. They often also hesitated to share their stories with doctors out of shame.

However, things have progressed quickly and it is now estimated that in the UK, 12 out of every 1,000 people have OCD. The condition is a serious anxiety-related mental health problem where a person experiences frequent intrusive, repetitive and unwelcome obsessional thoughts (the obsessive part of OCD).

This then leads to an increase in anxiety and can be followed by repetitive impulses or urges (the compulsive part of OCD) – such as repetitive hand washing.

But while OCD has been studied in a lot more depth in recent years. there are still a lot of uncertainties about how to best treat it. A common method used to help people overcome their compulsions is to expose then to a stimulus they consider threatening, and to show them that it is in fact safe.

This is called exposure therapy and it may involve, for instance, having them touch something they consider to be dirty and preventing them from washing their hands afterwards. The problem is that this technique does not work well on the long term, as the compulsions can come back after a while when the person is feeling stressed. The new research published in PNAS looks at why this may be the case and why it is so hard for these patients to learn about safe stimuli.

Green face, red face

The team from Cambridge University recruited 43 people with ICD and 35 healthy volunteers to study how they learnt about different stimuli and if they were able to tell what was safe and what wasn't.

Their brain activity was measured with functional magnetic resonance imaging (fMRI) scanner during an specific task. They were shown pictures of faces – a red one and a green one. When the participants were shown the green one, they would sometimes receive a mild electric shock, so that they would associate this image with a threatening stimulus.

Then, the researchers conducted another experiment during which they made the red face to be paired with an electric shock while the green face was safe.

OCD patients are unable to learn what stimuli are safe. Thomas Trutschel / Getty Images

While healthy volunteers were able to learn quickly, in both experiments, which stimuli were safe and which were not, this was not the case of OCD patients. At first, they were able to identify which stimulus was threatening, but they never learned that the second stimulus was safe. When the stimuli were changed in the second experiment, OCD patients failed to differentiate a safe from a
threatening stimulus.

These observations were backed up by the brain scans, as they showed decreased activity in an area at the front of the brain known as the ventromedial prefrontal cortex, which is thought to contribute to learning about the safety of stimuli.

"Our study suggests that something is going wrong in the brains of people with OCD when they are learning what is safe, and this in turn affects how they perceive threats under updated circumstances," Dr Annemieke Apergis-Schoute, the study's first author, said.

"This needs to be taken into consideration when we're developing future therapies to tackle the disorder. Current exposure therapies may help the patient take control over their compulsions, but our work suggests that they might never learn that their compulsions are unnecessary and they may return in times of stress."