According to scientific research, coupled with clinical interventions, obsessive compulsive disorder (OCD) is considered to share both biological and psychological factors. The first part of this article explains briefly the biology of OCD. This includes a review on certain areas of the brain which show how particular structures in the basal ganglia seemingly play a role in this disorder. The second part explains how psychology plays a part and how thinking errors attached to intrusive thoughts link to faulty beliefs which compound and strengthen the symptoms. It further demonstrates how cognitive behavioural therapy with exposure response prevention – a scientifically established based therapy – is able to correct the disorder at a bio-behavioural level.


The Basal Ganglia

Let’s first look at the brain parts that seem likely to play a role in OCD:

  • The orbito cortex
  • The cingulate gyrus
  • The amygdala (this is included as one of the basal ganglia due to its anatomical proximity, although properly it is part of the limbic system, important for emotions, instincts and desires)
  • The thalamus
  • The striatum which has two parts and therefore collectively known as the neostriatum.

 Orbito cortex, cingulate gyrus and the amygdala

The orbito cortex and the cingulate gyrus are interactively involved whereby the first stores the value of things as good or bad and the latter signals that something doesn’t feel right (Prof. F. Toates). Further, the amygdala puts us in that “fight or flight” situation when, for example, fear or danger faces us.

The Thalamus

The thalamus acts as a kind of “relay station” whereby motor and sensory information (except smell) are received by it and projected to the cerebral cortex (Arthur S. Reber.) The cerebral cortex is responsible for the so-called “higher-mental processes” of language, thinking and problem solving (Reber).  Given the nature of its role, it makes sense how the thalamus loops the same information to and from the cerebral cortex in those who have obsessive compulsive disorder (OCD).

 The Striatum

The striatum transmits information involved in thinking, automatic filtering and movement (Reber). This part of the brain exists as two identical cell types which are known as the:

  • Caudate nucleus for controlling automatic thinking and filtering and the
  • Putamen for controlling automatic movement

How do these brain parts cause obsessions?

Example: When “Lucy” brushes past someone, she experiences a sudden and fearful intrusive thought that she’s been infected with a sexually transmitted disease (STD).

Let’s look at what happens here.

Lucy’s orbito cortex interacts with the cingulate gyrus to signal that something is wrong. An additional interactional signal involving the amgydala puts Lucy in a “fearful” situation. Her response is to repeatedly de-contaminate without delay. This response shows that Lucy has developed a contamination obsession. Her corresponding compulsion (de-contaminating) acts as an irrational attempt to remove the “disease” or “dirty” sensation and to relieve anxiety momentarily.

What is the outcome?

In this example (and in all subtypes of OCD), the transmission that involves automatic thinking, filtering and movement (neostriatum) has become affected. As such, the network of interacting brain regions become locked (J.M. Schwartz). So after de-contaminating Lucy is less able to move to another thought/behaviour automatically because her thoughts loop the same information, hence further attempts to decontaminate.. [1]

Is it true that everyone get intrusive thoughts?

Studies show that mostly everyone gets intrusive thoughts from time to time. [2] However, obsessions are much stronger since these are rooted in the brain and repeatedly appear in the person’s consciousness without their will, causing intense fears. Put simply, obsessions are classed as intrusions that are activated and driven on a biological level, and therefore termed a psychiatric disorder.

The question still arises, if everyone gets intrusive thoughts, does this mean that all people to some degree have OCD?

On the contrary, it would seem that people who aren’t vulnerable to OCD may become fleetingly aware of intrusive thoughts but these are automatically filtered out via the caudate nucleus, and so alarm bells probably don’t even get the chance to ring. In this respect, the person doesn’t suffer from obsessions and for that reason isn’t affected by the fear and anxiety associated with those who have OCD; as a result, and following an intrusive thought, they move directly to another thought/behaviour with little or no concern (see neostriatum).


The interacting parts of the brain that cause OCD become locked.  Subsequently, sensible reasoning gets confused. What follows are attempts to correct the obsessional problem with a corresponding compulsive behaviour (emotional response).

If you like part 1 please share below before going to part 2 to discover how OCD can be corrected on a bio-behavioural level – thank you.

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[1] Brainlock by Jeffrey M. Schwartz, M.D. with Beverley Beyette covers a cognitive bio-behavioural approach that can help you free yourself from obsessive-compulsive disorder.

[2] Radomsky and his colleagues found that the thoughts, images and impulses symptomatic of obsessive compulsive disorder (OCD) are widespread. “Almost everyone has these kinds of thoughts. They’re normal, and they’re a part of being human,” Radomsky said. For people who suffer from OCD, this knowledge “can be incredibly helpful to change the meaning that they ascribe to the intrusive thoughts.”