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.
The Neurobiology of OCD
Gorka Jiménez Pajares

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.

“It’s like that song that plays over and over in your head, only you can’t get rid of it.”

-Kimberly Matthews-Cifra-

Woman thinking very worried
OCD deteriorates the fundamental areas of the individual’s life and produces great suffering.


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.


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).

“Having OCD is like being controlled by a puppeteer.”

-Toni Neville-


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.

“A physical sensation crawls up my arm as I avoid compulsions. But if I complete it, the world resets itself for a moment like everything will be just fine. But only for a moment.”

-Mardy M. Berlinger-

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.


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.

“In 87 percent of cases, OCD becomes chronic.”

-Claudia Urbistondo-


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.

blue lit brain
In OCD, the frontal cortex is highly active, while the basal ganglia are underactive.


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.

“It’s like you have two brains, a rational brain and an irrational brain. And they’re constantly fighting.”

-Emilie Ford-

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Belloch, A. (2023). Manual De Psicopatologia. Vol. Ii (2.a ed.). MCGRAW HILL EDDUCATION.
  • CIE-11. (s. f.).
  • First, M. B. (2015). DSM-5. Manual de Diagnóstico Diferencial. Editorial Médica Panamericana.
  • Pena-Garijo, J., Ruipérez Rodríguez, M. Á., & Barros-Loscertales, A. (2010). Neurobiología del trastorno obsesivo-compulsivo: aportaciones desde la resonancia magnética funcional (I).
  • Martínez Díaz, S., Peña, C., López, E., Guzmán, N., & Corominas, A. (2019).
  • Carrobles, J. A. S. (2014). Manual de psicopatología y trastornos psicológicos (2a). Ediciones Pirámide.
  • Urbistondo, C., Macbeth, G. E., Kichic, R., & Ibáñez, A. (2011). El modelo frontoestriado del trastorno obsesivocompulsivo: evidencia convergente de estudios de potenciales evocados relacionados a eventos. Psicología y Psicopedagogía, 25(1), 120-133.
  • Ortiz García, A. E. (2015). Marcadores genéticos y de neuroimagen en el Trastorno obsesivo-compulsivo de inicio en la infancia y la adolescencia.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.