Biological Explanations of OCD
There should be no surprises here. The biological model, true to form, believes OCD to be the result of either genes, neurochemistry or brain structure. Keep in mind of cause, if there is an issue with brain chemistry or brain structure then it’s our genes that would have caused this.
Genetic explanation
No psychological disorder is entirely genetic bur some appear to be more genetic than others. OCD seems to fall into the category of high level of heritability.
There is clear evidence that OCD runs in families. Offspring with OCD have a 37% chance that one or more parents also has the disorder. There is also a 21% concordance rate for siblings. Compare these figures to the 2% incidence of OCD in the general population and there is clear evidence of something genetic going on.
As always with family studies of this sort we cannot rule out environmental and social factors. Family members, brothers and sisters, parents and offspring, don’t just share genes but also living environment. It is quite likely that some of this concordance is down to nurture.
Nestadt et al 2010 looked at the concordance rate for MZ and DZ twins.
MZ had a 68% concordance rate
DZ had a 31% concordance rate
Both of these figures are very high in comparison to other psychological disorders such as schizophrenia.
In an essay, if twin studies or family studies are mentioned always evaluate by pointing out the obvious. We cannot rule out environmental factors. Therefore we cannot assume that the similarity reported is just the result of genes!
Diathesis Stress
One conclusion we can draw however; OCD is not entirely genetic, otherwise the concordance rate for MZ would be 100%. Other factors must therefore be involved.
There appears to be a genetic predisposition, an increased likelihood of developing OCD that some people inherit from their parents. However, this doesn’t guarantee that OCD will develop. Other factors such as stress, upbringing, life events are needed to trigger the OCD.
Diathesis: the genes that make OCD more likely (nature)
Stress: environmental and social factors that trigger the genes into action (nurture).
Candidate Genes
These are the genes that predispose the development of the disorder. In the case of OCD it seems there may be hundreds of them. OCD is therefore said to be polygenic.
Other evaluation
With so many candidate genes involved it is quite likely that each one is only having a very minor effect. Therefore the model is of limited practical value in
Cromer et al (2007) when not being a seaside resort on the north Norfolk coast, reported that about half of OCD patients could recall a specific, traumatic, event that may have triggered their OCD. Again this supports the idea of a diathesis-stress cause for the disorder.
Umbrella disorder
OCD is complex and comes in many forms (hoarding, checking, tapping, illness, sexual, contamination, symmetry…). It’s unlikely that all of these will have the same cause. Therefore it isn’t surprising that there are so many potential candidate genes.
Neural Explanations
Brain chemistry
Abnormal levels of serotonin and/or dopamine may be involved in some patients with OCD. Some of the candidate genes mentioned in the previous section are known to be involved in serotonin pathways. Serotonin is also involved in the regulation of mood with low levels of the chemical preventing the transmission of mood-related messages at the synapse.
Evidence
Some antidepressants such as SSRIs target only serotonin pathways in the brain. These appear to be the most effective in treating cases of OCD. This would appear to provide strong evidence for the involvement of serotonin. However, beware the treatment aetiology fallacy! We cannot make these assumptions about the functioning of the brain. Aspirin treats headache but we do not assume it was lack of aspirin that caused it in the first place.
The levels of dopamine in some patients with OCD appear to be higher than usual. Dopamine is involved in a number of psychological and neurological disorders such as addiction, schizophrenia and Parkinson’s Disease.
Brain structure
Poor decision making is a characteristic symptom of many types of OCD such as hoarding, tidying and hand-washing. As we saw in memory, executive functions (for example those carried out by the central executive) are largely located in the pre-frontal cortex (PFC) of the brain. Not only is PFC involved in making the right decisions it also helps to over-ride the wrong ones (it has been implicated in addiction).
Although some patients with OCD have been shown to have damage to this area, most don’t. Again it could be the same old issue. OCD is not a single disorder so it’s not surprising that different types will have different causes.
Behaviourist Explanations
Mowrer’s two stage approach that we looked at in phobias can clearly explain some forms of OCD.
Acquisition: A classically conditioned association between something like dirt or germs and anxiety or disgust.
Maintenance: Negative reinforcement in the form of avoidance that prevents the patient ever facing up to the issue.
It’s not surprising that some forms of systematic desensitisation (behaviourist treatments) have been successful in treating patients with OCD.
Conclusion
Biology clearly has a role to play. However, as always with brain structures and function it is almost impossible to prove a causal relationship. Brain structures and chemicals may be involved but what comes first, the disorder or the faulty functioning? It could be that a third factor is causing both.
There should be no surprises here. The biological model, true to form, believes OCD to be the result of either genes, neurochemistry or brain structure. Keep in mind of cause, if there is an issue with brain chemistry or brain structure then it’s our genes that would have caused this.
Genetic explanation
No psychological disorder is entirely genetic bur some appear to be more genetic than others. OCD seems to fall into the category of high level of heritability.
There is clear evidence that OCD runs in families. Offspring with OCD have a 37% chance that one or more parents also has the disorder. There is also a 21% concordance rate for siblings. Compare these figures to the 2% incidence of OCD in the general population and there is clear evidence of something genetic going on.
As always with family studies of this sort we cannot rule out environmental and social factors. Family members, brothers and sisters, parents and offspring, don’t just share genes but also living environment. It is quite likely that some of this concordance is down to nurture.
Nestadt et al 2010 looked at the concordance rate for MZ and DZ twins.
MZ had a 68% concordance rate
DZ had a 31% concordance rate
Both of these figures are very high in comparison to other psychological disorders such as schizophrenia.
In an essay, if twin studies or family studies are mentioned always evaluate by pointing out the obvious. We cannot rule out environmental factors. Therefore we cannot assume that the similarity reported is just the result of genes!
Diathesis Stress
One conclusion we can draw however; OCD is not entirely genetic, otherwise the concordance rate for MZ would be 100%. Other factors must therefore be involved.
There appears to be a genetic predisposition, an increased likelihood of developing OCD that some people inherit from their parents. However, this doesn’t guarantee that OCD will develop. Other factors such as stress, upbringing, life events are needed to trigger the OCD.
Diathesis: the genes that make OCD more likely (nature)
Stress: environmental and social factors that trigger the genes into action (nurture).
Candidate Genes
These are the genes that predispose the development of the disorder. In the case of OCD it seems there may be hundreds of them. OCD is therefore said to be polygenic.
Other evaluation
With so many candidate genes involved it is quite likely that each one is only having a very minor effect. Therefore the model is of limited practical value in
- predicting the onset of OCD
- in developing treatments for OCD. There are too many genes to target.
Cromer et al (2007) when not being a seaside resort on the north Norfolk coast, reported that about half of OCD patients could recall a specific, traumatic, event that may have triggered their OCD. Again this supports the idea of a diathesis-stress cause for the disorder.
Umbrella disorder
OCD is complex and comes in many forms (hoarding, checking, tapping, illness, sexual, contamination, symmetry…). It’s unlikely that all of these will have the same cause. Therefore it isn’t surprising that there are so many potential candidate genes.
Neural Explanations
Brain chemistry
Abnormal levels of serotonin and/or dopamine may be involved in some patients with OCD. Some of the candidate genes mentioned in the previous section are known to be involved in serotonin pathways. Serotonin is also involved in the regulation of mood with low levels of the chemical preventing the transmission of mood-related messages at the synapse.
Evidence
Some antidepressants such as SSRIs target only serotonin pathways in the brain. These appear to be the most effective in treating cases of OCD. This would appear to provide strong evidence for the involvement of serotonin. However, beware the treatment aetiology fallacy! We cannot make these assumptions about the functioning of the brain. Aspirin treats headache but we do not assume it was lack of aspirin that caused it in the first place.
The levels of dopamine in some patients with OCD appear to be higher than usual. Dopamine is involved in a number of psychological and neurological disorders such as addiction, schizophrenia and Parkinson’s Disease.
Brain structure
Poor decision making is a characteristic symptom of many types of OCD such as hoarding, tidying and hand-washing. As we saw in memory, executive functions (for example those carried out by the central executive) are largely located in the pre-frontal cortex (PFC) of the brain. Not only is PFC involved in making the right decisions it also helps to over-ride the wrong ones (it has been implicated in addiction).
Although some patients with OCD have been shown to have damage to this area, most don’t. Again it could be the same old issue. OCD is not a single disorder so it’s not surprising that different types will have different causes.
Behaviourist Explanations
Mowrer’s two stage approach that we looked at in phobias can clearly explain some forms of OCD.
Acquisition: A classically conditioned association between something like dirt or germs and anxiety or disgust.
Maintenance: Negative reinforcement in the form of avoidance that prevents the patient ever facing up to the issue.
It’s not surprising that some forms of systematic desensitisation (behaviourist treatments) have been successful in treating patients with OCD.
Conclusion
Biology clearly has a role to play. However, as always with brain structures and function it is almost impossible to prove a causal relationship. Brain structures and chemicals may be involved but what comes first, the disorder or the faulty functioning? It could be that a third factor is causing both.
