Compulsive checking

Last update: February 20, 2024
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Reading time: 3 minutes
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By Brain Matters

Did I lock the car? Did I leave the gas on? Do I have my wallet with me? These are all very normal thoughts that everyone has from time to time. However, when it comes to compulsively checking to make sure the car is locked, it is called obsessive-compulsive disorder, also known as OCD.

What is OCD?

OCD is a mental disorder in which people feel a compulsion to repeatedly perform certain actions. These people have many compulsive thoughts (obsessions) and this comes with a lot of anxiety. To (temporarily) relieve this anxiety, they perform compulsive acts (compulsions). The rituals themselves are generally quite harmless, but stem from a great sense of nervousness and can completely disrupt a person's normal daily life. In addition to this, people can spend a great deal of time performing compulsions, which further disrupts daily life.

A look inside the brain

Previous research on Parkinson's patients with OCD had already shown that OCD symptoms are alleviated by deep brain stimulation, in which an electrode is inserted into the subthalamic nucleus (STN). The STN is a subcortical brain nucleus involved in motor skills, hence its role in Parkinson's disease. The reduction of OCD symptoms upon stimulation of the STN, suggests that this area is also involved in processing cognitive and emotional information. This was investigated by measuring the activity of individual STN neurons in OCD patients.

All subjects had Parkinson's in addition to OCD and had to undergo surgery to implant electrodes as treatment for Parkinson's disease. This surgery allowed the researchers to measure the activity of individual neurons in the STN. The main finding was that the activity of individual STN neurons was affected by the subject's uncertainty. With more uncertainty, the neurons fired more, resulting in more checking behavior. Thus, the STN appears to play an important role in the repetitive thoughts and actions of OCD patients, which could explain why deep brain stimulation of the STN reduces compulsive behavior. The study was extraordinary and difficult to do with humans since not every day someone has to perform a cognitive task during their surgery!

Difficulty learning which stimuli are safe and which are not

A team of British neuroscientists decided to study how well people with and without OCD could learn new associations and, more importantly, whether they could unlearn these again. While using fMRI to measure their brain activity, participants were repeatedly shown either a green face or a red face. In the first experiment, subjects received a mild electric shock when a green face was shown, but not when the red face was shown. All participants learned the association between the green face and the shock. This was demonstrated in part by sensors that recorded a slight increase in sweat production when a green face appeared on the screen.

After a while, the green and red faces were switched so that now the red faces were accompanied by shock. While the control group had learned fairly quickly that the green face was now no longer a danger, the OCD patients had more difficulty with it, as was shown by sweat production. The brain scans revealed that this group showed less activity in the ventromedial prefrontal cortex, an area involved in, among other things, making decisions under risky conditions.

The researchers argue that this may explain why people with OCD have trouble letting go of their compulsive behaviors. Their brain has a negative association with certain harmless stimuli and does not seem as ready to unlearn this negative association, even when it has been shown within safe conditions (such as in exposure therapy) that there is nothing to be anxious about. This insight helps scientists to investigate more effective treatments for OCD.

Author: This article is a combination of previously published Brainmatters articles written by Lorraine Fliek (22-02-2013) and Job van den Hurk (09-03-2017). It was edited by Anneke Terneusen in 2022.

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