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Obsessive-Compulsive Disorder: An Information Guide Centre for Addiction
and Mental Health

What causes OCD?

What causes OCD?

From: Obsessive-compulsive disorder: An information guide ( © 2001 CAMH)

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"As far back as I can remember, my family and friends referred to me as a worrywart. When I was about the age of 16, my experiences with OCD began. I had just started high school and things were stressful with all the changes. A friend of mine had been afflicted with a case of food poisoning, and that was when I acquired my fear of being poisoned. I can still remember how it started as a tiny concern, and proceeded to snowball into the major preoccupation of my life."

Despite considerable research into the possible causes of OCD, no clear answer has emerged. As with most psychiatric conditions, different factors may be involved. At the present time, the most we can say is that OCD appears to be caused by a combination of psychological and biological factors. We will explore the theories in this chapter and the related treatments in Chapters 3 and 4.

Psychological Factors

Many psychological theories have been introduced to explain the development of OCD. The two that have received the greatest support are the behavioural and cognitive theories.

Behavioural Theory

The behavioural theory suggests that people with OCD associate certain objects or situations with fear, and that they learn to avoid the things they fear or to perform rituals that help reduce the fear.

This pattern of fear and avoidance/ritual may begin when people are under periods of high emotional stress, such as starting a new job or ending a relationship.

At such times, we are more vulnerable to fear and anxiety. Often things once regarded as "neutral" may begin to bring on feelings of fear. For example, a person who has always been able to use public toilets may, when under stress, make a connection between the toilet seat and a fear of catching an illness.

Once a connection between an object and the feeling of fear becomes established, people with OCD avoid the things they fear, rather than confront or tolerate the fear. For instance, the person who fears catching an illness from public toilets will avoid using them. When forced to use a public toilet, he or she will perform elaborate cleaning rituals, such as cleaning the toilet seat, cleaning the door handles of the cubicle or following a detailed washing procedure. Because these actions temporarily reduce the level of fear, the fear is never challenged and dealt with and the behaviour is reinforced. The association of fear may spread to other objects, such as public sinks and showers.

In behavioural therapy (discussed in detail in the following chapter), people with OCD learn to confront and reduce their anxiety without practicing avoidance or ritual behaviour. When they learn to directly confront their fears, they become less afraid.

Cognitive Theory

While the behavioural theory focuses on how people with OCD make an association between an object and fear, the cognitive theory focuses on how people with OCD misinterpret their thoughts.

Most people have intrusive or uninvited thoughts similar to those reported by people with OCD. For example, parents under stress from caring for an infant may have an intrusive thought of harming the infant. Most people would be able to shrug off such a thought. Individuals prone to developing OCD, however, might exaggerate the importance of the thought, and respond as though it represents an actual threat. They may think, "I must be a danger to children if I have thoughts of harming children." This can cause a high level of anxiety and other negative emotions, such as shame, guilt and disgust.

People who come to fear their own thoughts usually attempt to neutralize feelings that arise from their thoughts. One way this is done is by avoiding situations that might spark such thoughts. Another way is by engaging in rituals, such as washing or praying.

Cognitive theory suggests that as long as people interpret intrusive thoughts as "catastrophic," and as long as they continue to believe that such thinking holds truth, they will continue to be distressed and to practice avoidance and/or ritual behaviours.

According to cognitive theory, people who attach exaggerated danger to their thoughts do so because of false beliefs learned earlier in life. Researchers think the following beliefs may be important in the development and maintenance of obsessions:

  • "exaggerated responsibility," or the belief that one is responsible for preventing misfortunes or harm to others
  • the belief that certain thoughts are very important and should be controlled
  • the belief that somehow having a thought or an urge to do something will increase the chances that it will come true
  • the tendency to overestimate the likelihood of danger
  • the belief that one should always be perfect and that mistakes are unacceptable.

"When I first experienced my OCD I thought I was losing my mind. I had never worried about these ideas before and now I was totally enveloped with them. I knew what I was feeling was unreasonable but I still had this terrifying feeling of 'what if?' What if it was at all possible for these things to happen? I knew that the odds were .0001 per cent but I would still be overwhelmed with the fear that something disastrous might occur to me or someone else."

In cognitive therapy, (discussed in detail in the following chapter), people "unlearn" their mistaken beliefs and change their patterns of thought. By doing so, they are able to eliminate the distress associated with such thoughts and to discontinue their compulsive behaviours.

Biological Factors

Regulating of Brain Chemistry

Research into the biological causes and effects of OCD has revealed a link between OCD and insufficient levels of the brain chemical, serotonin. Serotonin is one of the brain's chemical messengers that transmit signals between brain cells. Serotonin plays a role in the regulation of mood, aggression, impulse control, sleep, appetite, body temperature and pain. All of the medicines used to treat OCD raise the levels of serotonin available to transmit messages.

Changes in Brain Activity

Modern brain imaging techniques have allowed researchers to study the activity of specific areas of the brain. Such studies have shown that people with OCD have more than usual activity in three areas of the brain. These are:

The caudate nucleus, specific brain cells in the basal ganglia, located deep in the centre of the brain
This area of the brain acts as a filter for thoughts coming in from other areas. The caudate nucleus is also considered to be important in managing habitual and repetitive behaviours.

When OCD is successfully treated with drugs or therapy, the activity in this area of the brain usually decreases. This shows that both drugs and a change in "thinking" can alter the physical functioning of the brain.

The prefrontal orbital cortex, located in the front area of the brain
The level of activity in the prefrontal orbital cortex is believed to affect appropriate social behaviour. Lowered activity or damage in this region is linked to feeling uninhibited, making bad judgments and feeling a lack of guilt. More activity may therefore cause more worry about social concerns. Such concerns include: being meticulous, neat and preoccupied with cleanliness, and being afraid of acting inappropriately. All of these concerns are symptoms of OCD.

The cingulate gyrus, in the centre of the brain
The cingulate gyrus is believed to contribute the emotional response to obsessive thoughts. This area of the brain tells you to perform compulsions to relieve anxiety. This region is highly interconnected to the prefrontal orbital cortex and the basal ganglia via a number of brain cell pathways.

The basal ganglia, the prefrontal orbital cortex and the cingulate gyrus all have many brain cells affected by serotonin. Researchers believe that medicines that raise the levels of serotonin available to transmit messages may change the level of activity in these areas of the brain.

Streptococcus and OCD

Some researchers believe that cases where children suddenly develop OCD or TS may be linked to a recent infection with streptococcus, the bacteria that cause the common "strep throat." In these cases, the body may be forming antibodies to the infection, which may mistakenly react to the basal ganglia, an area of the brain linked to OCD.

There is no evidence, however, that streptococcus plays a role in adult-onset OCD. And in most cases where children develop OCD, the symptoms begin gradually, not suddenly as described above. At this time, then, the link between streptococcus infection and OCD is not certain. Further research into this possible link may lead to a better understanding of the causes of OCD.

Genetic Factors

OCD often seems to "run in the family." In fact, almost half of all cases show a familial pattern. Research studies report that parents, siblings and children of a person with OCD have a greater chance of developing OCD than does someone with no family history of the disorder.

One might ask if OCD is "taught" by one family member to another. If this were the case, though, why do individual family members often have very different symptoms of OCD?

Researchers looking for genes that might be linked to OCD have not been able to find them. It is believed there may be genes, though, that are involved in regulating serotonin and passed on through the generations. One study involving identical twins showed that if one twin develops OCD, the other is likely to follow, which suggests that the tendency to develop obsessions and compulsions may be genetic. Other studies have shown a relationship between OCD and Tourette's syndrome (TS). Families of individuals with TS also seem to have high rates of OCD, suggesting a genetic relationship between these two conditions.
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