Explore what we currently know about the OCD and the Brain


Obsessive compulsive disorder, or OCD, is a mental illness that affects about 1-3% of the population. While this on its own may not sound like a very big number, this means that across the world, millions of people are affected by OCD. People with OCD typically experience obsessions (intrusive thoughts, doubts, urges or images that can make the person feel very distressed and anxious), and compulsions (repetitive behaviours or thoughts typically aimed at reducing the anxiety, fear and disgust caused by obsessions).

Silhouette of a person in distress because of their OCD symptoms.

OCD is a disorder of the brain – meaning that OCD symptoms are caused by how the brain works. Knowing more about the relationship between OCD and the brain may help some people living with OCD and others to better understand the condition.

"Knowing the science behind my OCD and its treatment, i.e., how they work in the brain, has been a big motivator in my recovery. It has demonstrated to me that what I'm dealing with is real and that the treatment addresses the neurobiological issue at hand. Knowing how OCD and its treatments work in the brain has also helped me educate my support system on OCD, as it's a highly misunderstood disorder."

Maya Tadross,
Community Gatekeeper

"Knowing more about OCD and the brain matters to me because it helps arm me with information to help combat the stigma associated with this mental illness. Finding out more gives me hope as it relates to improved treatments for OCD, and understanding more helps me to learn the connections between brain chemistry and the neurological effects on the body."

Kathy Stocking,
Community Gatekeeper

This website serves as a knowledge hub designed by researchers, charities and people living with OCD, to make the latest brain research on OCD more accessible. Discover what we currently know about OCD and the brain below.

This website focuses on what we know about OCD and the brain. If you would like to find out more about OCD in general, or about treatment and support, please go to our OCD Resources section. 

The brain

To understand more about OCD and the brain, we first need to know a few basics about the brain and how it works.

The brain processes information and informs behaviour

One of the main purposes of the brain is to enable us to navigate the world. We can think about it as an information processing device (a bit like a computer). This means that through our senses (seeing, hearing, touch, smell and taste), we get information about the world around us. The brain then makes sense of this incoming information and responds through our behaviour.

A brain with the frontal, parietal, temporal and occipital lobes labelled according to different colours.

So, for example, what happens if you see a spider? The visual information (the image of a spider) goes from your eyes to the area of your brain in charge of processing vision – the visual cortex. Your brain then sends signals to other parts of the brain, which interpret the information and recognise that this is an animal, more specifically a spider. Now that you know this information, you need to decide what to do next. Will you run away? Or will you take a step closer to examine what kind of spider it is? Perhaps you don’t like spiders, and so decide to run away. That is, in essence, what the brain does: it receives information, processes it in a meaningful way and then allows us to act upon it.

The brain is the most complex organ in the body. It has over 86 billion brain cells, called neurons, which work closely together to form different brain areas. These brain areas communicate with each other to exchange information, forming networks within the brain. 

Many brain cells forming networks, with some of them exchanging information with each other.

In OCD, networks known as the frontostriatal loops are thought to be especially important. Each person’s brain has several different frontostriatal loops. These connect brain areas in the so-called prefrontal cortex with areas deeper in the brain (for example the striatum) allowing for an exchange of information in a back and forth manner – therefore, a ‘loop’. The frontostriatal loops are very important in prioritising information, and in selecting between competing bits of information – essentially, they decide what is important, and what is not. 

A brain with frontal areas and the striatum highlighted in different colours, with arrows between them depicting frontostriatal loops.

To help us to think about what they do, imagine a frontostriatal loop as a busy traffic junction – there are cars, bikes and pedestrians that need to be managed effectively for the traffic to move smoothly. Traffic light signals help to direct how the traffic flows. In the brain, the frontostriatal loops control the information flow – allowing certain information to go, while stopping others. It can even prioritise specific types of information, over others, effectively determining what reaches its destination quicker.

An effectively managed traffic junction viewed from above.

The frontostriatal loops control the information flow and thus make the call on how we respond in a certain situation: whether to approach or avoid something, what information to focus on, or whether to continue thinking about something or move on. These loops have a big impact on how we react. So, if we see a spider, our frontostriatal loops will help us to move closer or run away. 

Within the frontostriatal loops, brain chemicals, called neurotransmitters are very important and can change how the loops work. Neurotransmitters act as messengers in the brain and allow brain cells to talk to each another. Different levels of neurotransmitters, like dopamine or serotonin, can change how we make decisions. 

These frontostriatal loops also play an important role in OCD. We’ll explore more about these loops and OCD later on.

Diverse influences make each brain unique

Although all brains follow these general principles of information processing, it is important to note that each one of our brains is unique and processes things differently.

No two brains are exactly alike, and each person’s brain constantly changes throughout their lifetime. When we are born, our brain is only a fraction of its final size, and it will grow and become increasingly complex and sophisticated throughout childhood, adolescence, and into adulthood. In particular, the brain regions that are part of the frontostriatal loops are some of the last areas to fully develop, usually not until late adolescence. This may play a critical role in the emergence of conditions such as OCD. You can find out more about this in the next section.

A large brain surrounded by piano and balls for different sports, a DNA strand, nature and city, as well as the silhouette of a grown-up woman and a baby.

The changes that our brain goes through are influenced by many different factors. One of these factors is our genes – the biological building blocks that we receive from our parents. Genes will, to some extent, determine how our brains are built. But they are not the only influence. We know that the environment also has a big impact on our brain – everything we see, experience and do throughout our life has an effect on our brain. For example, learning how to play the piano can affect the brain in both structure and function, in order to support the coordination of very detailed finger movements that are needed in piano playing. This means the brain is not a static organ, but a very dynamic one. It adjusts to demands and what it has been exposed to. This is known as plasticity – the brain’s ability to change. All influences on the brain, both internal (such as your genes or changes of your hormones and neurotransmitters), and external (such as learning new skills), have a substantial effect on the brain and how it works.

All of this means that each of our brains is unique. Researchers are currently looking into how differences in the way that our brains work can lead to OCD. In the same way that all of our brains are very different, the reasons underpinning OCD may also differ from person to person. We explore this in the next section.

What is the brain’s role in OCD?

Researchers are still unravelling the mechanisms in the brain that are involved in OCD. It is very likely that OCD is not caused by changes to one single brain process, but instead, it appears due to changes in a number of different brain mechanisms. 

As we explored in the previous section, the brain and its development is influenced by several factors, including genes, environment, experiences, and behaviours. These all contribute to the unique structure and way that each person’s brain works.

It is likely that OCD arises when several brain processes develop in a certain way. Although the causes might be different between people, very similar symptoms (obsessions and compulsions) may appear. This is similar to why people might experience a headache, for example. A headache is a symptom (your head hurts) that may be caused by various things. It could be because of a migraine, too much sun, or consuming the wrong substances. Similarly, there might be different reasons why someone experiences OCD symptoms. In this section, we will explore the role of frontostriatal loops, which are at the centre of one of the long-standing scientific theories of what causes OCD.

A brain with frontal areas and the striatum highlighted in different colours, with arrows between them depicting frontostriatal loops.

Over the past few decades, researchers have come to believe that changes in frontostriatal loops lie at the core of OCD. These loops are important for prioritising and processing information.

In OCD, researchers think that when the control of this information flow is disrupted – for example because of an imbalance within the frontostriatal loops – OCD symptoms such as obsessions and compulsions may appear. 

  • For example, if the control of a signal about a movement action is disrupted, this may lead to the person having urges to perform movement actions when they come across an OCD-related trigger (e.g. a stove, knife, or light switch). This results in compulsive acts being performed (eg checking the stove is turned off, avoiding sharp objects, turning a light switch on and off). 

  • Similarly, an imbalance in frontostriatal loops can turn common intrusive thoughts into obsessions. Many people, with and without OCD, often experience intrusive and distressing thoughts. However, in people living with OCD, these intrusive thoughts tend to stick in the mind and are challenging to dismiss. This is where the frontostriatal loops once again are thought to play a role. If the loops have an imbalance, the brain might not be able to suppress the thought intrusions and dismiss them as irrelevant. As a result, the thoughts may stay present and become obsessions. Often, this leads to increasing levels of distress, and continues the cycle of performing compulsions to try to reduce the thoughts and distress that have become overwhelming.

A traffic jam represented by an frustrated cyclist and stopped cars, with a bus in the background, which contains an advert with words and sentence that normally arise during OCD symptoms.

In summary, researchers believe that difficulties in switching between processing different types of information or suppressing the flow of information in the brain can lead to people experiencing ongoing obsessions and compulsions. 

Going back to our traffic comparison, imagine if the timing of the traffic lights is off at a busy traffic junction. The junction would no longer be managed effectively and there would be disruptions in the traffic flow. For example, if a particular traffic light rarely switches to red, the traffic on that lane will get priority, causing major traffic jams for the other lanes. Even minor imbalances in such a complex and dynamic system can have significant consequences downstream.

A badly managed traffic junction viewed from above.

Although there has been great progress in this area of research, exactly how the regulation of the frontostriatal loops becomes imbalanced is still being actively looked into. Similar to complex traffic junctions in big cities, in the brain, this balance can be altered in many different ways: 

  1. Imbalances of brain chemicals (called neurotransmitters) which regulate these loops may play a role. 

  2. The strength of the connection between brain areas may also influence the overall flow. 

  3. Or changes can happen if the balance between the different loops is off. 

A brain with frontal areas and the striatum highlighted in different colours. The arrows between them, which depict frontostriatal loops, are broken up.

Because the frontostriatal loop imbalances may be caused by such different things, this may be one reason why some people benefit from one type of treatment, whereas others benefit from another approach. Researchers are actively looking into this – you can find out more in the next section.

The emergence of OCD symptoms

OCD symptoms often start to emerge either during late childhood, adolescence, or in the early twenties. Researchers think that because the brain undergoes lots of development during this time, there is a lot of room for certain brain systems to change in various ways. Both neurotransmitters and brain regions linked to the frontostriatal loops mature well into adolescence and even early adulthood. Therefore, if the development of these brain systems goes awry, this is likely to play a significant role in triggering the start of OCD. As such, the unique development of the brain may result in OCD. However, it is also important to note that OCD can manifest at any stage of life, often triggered by significant stressful events.

Researchers are still uncertain about why obsessions and compulsions focus around such diverse themes, ranging from health-related washing compulsions to uncertainty checking and harm avoidance mental rituals. It is possible that imbalances in frontostriatal loops may particularly affect things that someone considers most stressful, anxiety-provoking, or personally significant. In other words, the specific content of obsessions and compulsions may vary, and they may align with what certain people prioritise or care about the most. This would mean that even if the type of OCD is different, the biological causes might still be similar.

In summary, when looking at how brain networks work, OCD is likely to be caused by changes in frontostriatal loops, which are critical for prioritising and suppressing information flow in the brain. When there are imbalances in regulating this information flow, it may result in the development of obsessions and compulsions. Researchers are actively studying the specific processes within these frontostriatal loops that can be changed, the different things that might cause these imbalances, and what treatments might be effective in addressing these imbalances. 

The text

You can read more about how researchers are exploring these questions, as well as other exciting and promising research, in the next section. 

Research into OCD and the brain

Brain researchers (or neuroscientists) use different methods and techniques to look at the brain. Some study single genes or brain cells in a laboratory. Others study the entire, living human brain using large machines, such as MRI scanners that take pictures of the brain. 

Each of these methods has advantages and disadvantages. For example, animal research has allowed scientists to study how changes in specific genes might affect behaviour. Human research looking at behaviour and how the brain works has allowed scientists to study how different areas of the human brain communicate and work together to produce different behaviours and understanding. Combining methods and findings from all research fields helps us to better understand what is going on in the brain, especially in people living with conditions such as OCD. Here, we focus mostly on human research techniques as this is the expertise of the research team behind this website, and these are the techniques that people with lived experience of OCD are most likely to come across if they decide to take part in research studies. 

Researching behaviour

Scientists who study how people think and behave often use tasks or specific games to investigate how the brain works. One example is the Brain Explorer app. These tasks give insight into what’s going on inside the brain and so can help researchers to understand how people make decisions in different situations. Questionnaires or interviews are also used to gather information on people’s behaviour and thinking. This gives researchers a clearer overall view of different influences that could be related to people’s individual difficulties, changes in their mental health condition, or even how they respond to different treatments. For example, with games and tasks, researchers have uncovered that people with OCD often experience high levels of uncertainty and a lack of confidence in their thoughts and actions. These findings align with common OCD symptoms, such as difficulties in making decisions-making and repetitive checking.

If you are interested in participating in research and playing such a game or completing such a questionnaire, you can download our lab’s app, Brain Explorer, and give them a try. Everyone is welcome to take part.

Looking at the brain

Over the past few decades, neuroscientists have developed different techniques that allow us to have a glimpse into how the brain works. Usually this is done with large brain scanners, such as magnetic resonance imaging (MRI), magnetoencephalography (MEG) or electroencephalography (EEG). All of these scanners do not use any radiation, are routinely used in hospital procedures, and are very safe. 

The image is split into three, with a person in an MEG scanner in one part, a person in an MRI scanner in another part, and a person with a EEG cap on in the last part.

By using all of these techniques, we are able to understand when the human brain is processing information, what and how. To understand how information is processed in the brain, researchers often ask volunteers to perform tasks, like the ones mentioned above, whilst they are in a scanner. By looking at how people solve these games or react to certain pictures or sounds, we can see which brain areas are activated differently between people with and without lived experience of OCD. This allows us to pinpoint the exact moment when and how information is processed differently, and how this leads to different perceptions and actions. For example, we can look at brain networks involved in processing uncertainty, and test if these networks show differences in activity between people living with OCD compared to people who do not have OCD. This also offers potential future targets for new treatments. 

In summary, using different scientific methods, researchers look at how the brain is changed in OCD and how treatments and therapies may affect these changes, which will hopefully lead to improved future treatments. We explore more about OCD treatments and how they work in the brain in the next section. 

Treatments for OCD

We have seen how OCD is linked to brain functions, and especially how it is linked to imbalances in how the frontostriatal loops work. But how do the existing treatments for OCD try to change these imbalances?

Various brain processes can be off-balance in people living with OCD. Similarly, different OCD therapies may influence the frontostriatal loops in different ways. This may be why treatments work more or less well for different people with OCD. In this section, we will explore the commonly recommended treatments for OCD and what we know about how they work. There are also other treatments that affect the brain, many of which are not as well established yet, or scientific evidence is still being collected for them. We do not cover other OCD treatments here, but you can read more about them here. Please note, the availability and approval of treatments varies between countries and is subject to change. 

Cognitive-behavioural therapy (CBT) with exposure and response prevention (ERP)

The most common way to treat OCD, especially in young people, is using evidence-based therapies, such as cognitive-behavioural therapy (CBT) with exposure and response prevention (ERP). CBT refers to a specific form of therapy, in which trained psychotherapists guide the person to alter behaviours and thought patterns. ERP is the most important type of CBT for people living with OCD, as it directly challenges the OCD cycle of obsessions and compulsions

Here, the person with OCD is put into situations that may normally trigger their OCD symptoms (like compulsions), but then tries to not carry out the compulsive acts. For example, in a person that experiences OCD focused on harm, they might be asked to experience exposures involving their triggers, such as handling sharp objects or looking at a photograph of an accident. With the guidance of the therapist, they confront the situation, embracing the discomfort or anxiety it may cause and resist the urge to engage with compulsive behaviours. By doing this, their brain learns that the situation itself is not truly threatening and over time, and that it does not always have to react with the same feelings (distress) and behaviours (compulsions) in those specific situations. Therefore, CBT with ERP changes the workings of the brain through the power of talking, learning and practicing changes in behavioural patterns. This approach is often challenging, but highly effective. For more information, see our OCD Resources section.

Silhouettes of two people talking to each other with the words

How does it work?

Engaging in ERP means that we can indirectly change imbalances in the frontostriatal loops through the power of plasticity – the brain's ability to change and adapt. We can do this by changing the anxiety linked to a situation, introducing new ways of responding to an obsession, and enabling re-learning of what to do in these OCD-related situations. Brain imaging research studies have indeed suggested that ERP does change how the frontrostriatal loops work (scientific journals on the subject can be found here and here).

Changing the levels of chemicals in the brain

A second way of altering these loop imbalances is by changing the level of brain chemicals called neurotransmitters, which influence the balance of frontostriatal loops. There are different medications that alter different neurotransmitters. The most commonly approved and prescribed medications affect a neurotransmitter called serotonin (so called SSRIs or SRIs). Sometimes additional medications that affect a neurotransmitter called dopamine are also prescribed. 

Different synapses with neurotransmitters being transmitted across neurons.

How does it work?

Even though we know these drugs are safe and work well for OCD, the exact mechanisms behind how these drugs re-balance frontostriatal loops is not known. Neurotransmitters have many roles in the brain which means it is unclear to pinpoint what exactly has changed. However, we do know that they have a direct impact on how information is being processed in brain areas that are part of the frontostriatal loops. If you think back to our traffic example, you can imagine that changing the levels of a neurotransmitter such as serotonin influences this entire system – just like changing how long traffic lights are on green can change how smoothly cars flow through traffic.

Changing brain activity

There are more experimental approaches to change frontostriatal loop imbalances too. However, these methods are still currently being assessed, and/or are reserved for people who do not respond to commonly recommended treatments. These methods directly alter brain activity, such as deep brain stimulation (DBS), where an internal electrical stimulator (similar to a pacemaker for a heart) is implanted in the brain or transcranial magnetic stimulation (TMS), where an external device using magnetic coils is positioned over the head.

How do they work? 

DBS and TMS work by changing activity in one area of the brain. Imagine that this is like changing just one specific traffic light in our traffic system. Just like traffic, our brain is all connected and changing the activity of one brain region has an impact on the entire network, in a similar way that one signal failure can affect traffic across the entire city.


OCD is much more treatable than many people assume and treatments benefit the majority of people living with OCD. However, it is important to note that none of these treatments are perfect or have a 100% success rate. People respond differently to treatment, and it may be challenging and a long journey for many. It is likely that some amount of imbalance in the brain will remain and for some people, the OCD symptoms might not go away completely or might come back after some time. Because the human brain is so complex, these treatment options can also affect different functions of the brain, leading to side effects. However, researchers are working hard to improve the treatments so that they help to reduce OCD symptoms as much as possible with minimal side effects.

Exactly which treatments work best for whom is a question that researchers are currently exploring. It could well be that people with different types of imbalances in the frontostriatal loops will benefit from different or a combination of treatments. This is why researchers are looking into which imbalances exist, how they can be measured, and whether we can predict who will benefit from which treatment.

Summary image of the website, with a brain surrounded by neurons, some questions that people with OCD might experience, neurons and neurotransmitters, as well as depictions of OCD symptoms.