The Neurobiology of OCD

Obsessive-compulsive disorder (OCD) affects approximately three percent of the world's population. Research regarding its etiology is extensive. Here, we're going to talk about the neurobiology of OCD.

Written and verified by the psychologist Gorka Jiménez Pajares.

Last update: 14 March, 2023

Obsessive-compulsive disorder (OCD) is a serious clinical condition. It can occur in both children and adults and greatly impacts the daily functioning of sufferers. In fact, according to the WHO, it’s one of the 20 main objective factors for receiving a diagnosis of disability.

Sufferers of this severe disorder spend a great deal of time and energy on obsessions and compulsions. In addition, they struggle to get their tasks done on time because they’re quite inflexible. Furthermore, it can even affect an individual’s ability to raise their children.

OCD

According to the World Health Organization (WHO), sufferers of OCD tend to become obsessed with certain aspects of their lives. In effect, their obsessions make them behave in a ritualistic manner. This is called compulsion.

OCD causes intense suffering and the fundamental areas of the individual’s life deteriorate. For example, work and the interpersonal or academic sphere.

Obsessions

Imagine that the following thought occurs to you “What if I were to kill my neighbor?” Naturally, this causes you tremendous discomfort because you don’t really want to do it. However, the thought has popped into your mind, become integrated, and is constantly repeated. This is an obsession. It’s a thought, an impulse, or an intrusive image that causes a great deal of anxiety (APA, 2015).

Compulsions

Continuing with our example, say you try to free yourself from the previous thought. But, to do this, you have to count to the number 100 in twos, one every minute. A compulsion is a behavior. It can be both mental (like our example), or physical (like washing your hands). By carrying out the compulsion, you prevent both your feelings of discomfort and the negative situation.

An approach to the neurobiology of OCD

There are different biological hypotheses that attempt to shed light on the origins of OCD. That said, we still lack the biomarkers or laboratory tests that unequivocally confirm them. To date, the following findings have been obtained.

Genetics

If you’re the child, sibling, or parent of someone affected by OCD, you probably have twice the risk of developing the same disorder. Indeed, according to Belloch (2022), the children of those with OCD have a greater number of obsessions, compared to the normal population.

According to Carrobles (2014), obsessive-compulsive disorder is highly heritable. However, more research is required on the subject. Interestingly, monozygotic siblings (twins) present a risk of both suffering from OCD in up to 90 percent of cases.

Neurobiology

The most investigated brain regions are the frontal lobe (which supports higher mental functions), the basal ganglia (related to motor behavior), and the thalamus (the conductor of all sensory and motor information). Disorders that fall under the OCD spectrum share similar neural networks. More specifically, the frontostriatal region.

• In sufferers of OCD, the basal ganglia are underactive. This could partly be the cause of the motor compulsions. The greater the symptomatic severity, the greater the volume or size of this structure.
• The frontal cortex is excessively active in OCD sufferers. This could explain why patients get bogged down by their obsessions.

In obsessions related to the fear of being contaminated (“I’ve touched a pen, I’ve contaminated myself and I’m going to get sick”) which cause the need to wash constantly, or the compulsion (“If I wash myself 54 times, I’ll be clean”), specific regions have been found. In fact, in these cases, the ventromedial areas of the prefrontal lobe are more activated, as well as the caudate nucleus.

On the other hand, in obsessions involving verification compulsions (“I think I left the car unlocked, I’m going have to check it out”) the putamen, globus pallidus, and thalamic regions are intensely activated.

Neurotransmission

There are basically two hypotheses. Firstly, there’s the theory that the serotonin molecule is excessively low in these patients. Secondly, is the hypothesis that the dopamine molecule (involved in motor behavior and learning) is found in excess. This could explain why OCD patients exhibit excessive motor behavior.

Evidently, more research is required concerning the neurobiology of obsessive-compulsive disorder. For example, it’d be particularly interesting if diagnostic tests based on biomarkers were discovered. This would allow more precise diagnoses.

As a matter of fact, if this were the case, OCD could be diagnosed through an MRI or a blood test. However, to date, this is far from becoming a reality.