Did I lock the car? Did I leave the gas on? Do I have my wallet with me? All 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. Specifically, we are talking here about the type of OCD that involves the intense urge to repeatedly check things. Researchers show that the activity of neurons in a subcortical brain region, the subthalamic nucleus, may underlie this obsessive behavior.
What is OCD? People with OCD suffer from compulsive thoughts (obsessions) accompanied by anxiety. To relieve this anxiety, they may perform compulsions (actions they feel that they have to perform) with the goal of reducing the obsession*. There are several forms of OCD, such as contamination obsession, symmetry fixation, and checking compulsions, to name a few.
Previous research in 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 brain nucleus involved in motor skills, hence its role in Parkinson's disease. Reducing OCD symptoms upon stimulation of the STN, suggests that this area is also involved in processing cognitive and emotional information. This was investigated by researchers in 2013 by measuring the activity of individual STN neurons in OCD patients with the checking variant.
Big doubt
Participating in the study were 10 patients with OCD who had the checking variant. They had to perform a task in which they had to link pictures together. The subjects were shown a picture and then given a short rest period. After this, they were shown another picture and had to decide if this picture was the same as the first picture. After the subjects made a decision about pairing the pictures, there were two options. The first option was to press a button to go back and check if the answer was right and the other button meant they confirmed the answer.
Measuring of individual neurons
In addition to checking OCD, all subjects also had Parkinson's disease and had to undergo surgery to implant electrodes as treatment for Parkinson's. 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 check behavior. STN thus appears to play an important role in the repetitive thoughts and actions of OCD patients with the check variant, which could explain why deep brain stimulation of the STN reduces compulsive behavior in these patients. The study was very extraordinary and difficult to do with humans. Of course, it is not everyday that someone has to perform a cognitive task during their surgery! Today, deep brain stimulation is used as treatment for OCD patients for whom regular forms of therapy do not work***. However, researchers are still busy searching for the exact spot in the brain that can best be stimulated.
*There is a variant of OCD called “Pure Obsessional OCD,” or Pure-O for short. This is a type of OCD in which people suffer from obsessions and these are accompanied by compulsions that take place only in the mind, and therefore do not manifest themselves in checking to see if you have your house keys, for example, or washing your hands for the tenth time. These intrusive thoughts and images tend to emerge in certain themes, such as worries about sexual orientation, relationship decisions, fears of doing something illegal, pedophilia or being overly concerned about honesty or religion. An associated compulsion is then, for example, analyzing what these thoughts say about you as a person and when this cannot be disproved, a Pure-O person does have to assume they are a bad person.
** Parkinson's is a neurological disorder caused by a deficiency of the messenger substance in the brain called dopamine. This messenger substance is important for movement, emotions, and other functions. In Parkinson's, the STN becomes overactive due to the loss of dopamine, leading to the typical symptoms such as tremors, stiffness and sluggishness.
*** Usually OCD patients receive a variant of cognitive behavioral therapy called exposure and response prevention where patients are exposed to situations that trigger obsessions (touching door handles) where you try to resist your compulsion (not washing your hands). In addition, OCD patients may be prescribed antidepressants.
Author: Lorraine Fliek
Adapted and updated: Joyce Burger
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