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Causes of Obsessive-Compulsive Disorder (OCD)

It is becoming clear that there are abnormalities of certain brain functions that underlie the symptoms of OCD, specifically in a circuit that connects the orbitofrontal cortex, anterior cingulate gyrus and limbic system with the basal ganglia [ref, ref, ref]. However, the nature of these changes remain incompletely understood, and other brain structures are likely involved as well.

The basal ganglia function as a filter that help one decide which actions one will execute from among the various different impulses for action that may be going through one's minds at any given time. These impulses originate from various areas of the brain. Planned action originates from the orbitofrontal cortex and the anterior cingulate gyrus, while more impulsive action, like aggressive or defensive responses, originate from the limbic system. Most of these processes happen at an unconscious level.

One hypothesis is that OCD may be caused by a dysfunction in the ability of the basal ganglia to act as an efficient filter of one's impulses for action [ref, ref, ref]. This may allow for certain impulses to get too much clearance or acceptance from the basal ganglia and to rise up into one's consciousness in the form of thoughts, images and urges.

The individual then senses that certain inappropriate thoughts and urges are on the verge of being acted out. This unsettling feeling is what we call an obsession. These thoughts feel intrusive, foreign and unwanted because it is as if they have trespassed through a backdoor of the mind that was mistakenly left open, and now one is left scrambling to get rid of them.

Compulsions may be the mind's way of dealing with these unwanted thoughts and urges by sending very strong signals for action from the orbitofrontal cortex and anterior cingulate gyrus back to the basal ganglia so as to occupy the basal ganglia fully and thus force it to abandon the other unwanted impulses. To an observer, these actions can appear excessive or unrelated to the impulses that they are meant to prevent. However, the point is that they work, if only temporarily, to expunge the unwanted impulses from consciousness.

The fact that this strategy works means that these compulsions get learned and reinforced so that the next time that an obsession enters the person's mind, the same compulsions are once again enacted. The reinforcement of this behaviour is likely mediated by the dopaminergic reward systems that are part of the circuit connecting the frontal cortex to the basal ganglia. This means that over time one's compulsions become more and more entrenched and difficult to unlearn.

There is likely a genetic basis to OCD. Studies have shown that about half of the risk of developing this condition can be attributed to genetic effects [ref]. However, so far it remains unclear as to which genes are responsible.

In children, OCD can sometimes be triggered following a common Streptococcus bacterial infection, which is the same bacteria that causes "Strep throat." This phenomenon is known as Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS), and has also been linked to the development of Tic Disorders. It is the body's immune response to the Streptococcus infection, and in particular the antibodies that the body produces, that are responsible for triggering OCD in these cases [ref].

Finally, there is some evidence to suggest that having been abused in childhood can increase one's chances of developing OCD [ref]. It has also been observed that OCD often begins shortly after an individual experiences a very stressful event [ref].


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Course & Prevalence