GENETIC EXPLANATIONS
– OCD is a condition that largely understood as biological in nature.
– Genes are involved in individual vulnerability to OCD.
– Lewis (1936) observed that of his OCD patients 37% had parents with OCD and 21% had siblings with OCD.
– This suggests that OCD runs in families, although what is probably passed on from one generation to the next is genetic vulnerability not the certainty of OCD.
– According to the diathesis-stress model certain genes leave some people more likely to suffer a mental disorder but it is not certain – some environmental stress is necessary to trigger the condition.
CANDIDATE GENES
– Researchers have identified genes, which create vulnerability for OCD, called candidate genes.
– Some of these are involved in regulating the development of the serotonin system.
OCD IS POLYGENIC
– This means that OCD is not causes by a single gene but that several genes are involved.
DIFFERENT TYPES OF OCD
– One group of genes that cause OCD in one person but a different group of genes may cause the disorder in another person.
– The term used to describe this is aetiologically heterogeneous.
– There is also some evidence to suggest that different types of OCD may be the result of particular genetic variations, such as hoarding disorder and religious obsession.
EVALUATION OF GENETIC EXPLANATIONS
STRENGTHS
Research Support
– There is evidence from a variety of sources for the idea that some people are vulnerable to OCD as a result of their genetic makeup.
– One of the best sources evidence are twin studies.
– For example, in 2010 Nestadt reviewed previous twin studies and found that 68% of identical twins shared OCD as opposed to 31% of non-identical twins.
– This strongly suggests a genetic influence on OCD.
LIMITATIONS
Can’t Find Genes Involved in OCD
– Psychologists have been unsuccessful in pinning down all the genes involved in OCD.
– One reason for this is because it appears that several genes are involved and that each genetic variation only increases the risk of OCD by a fraction.
– The consequence is that a genetic variation is unlikely to ever be very useful because it provides little predictive value.
Other Factors
– Environmental factors can also trigger or increase the risk of developing OCD.
– For example, in 2007 Cromer found that over half the OCD patients in his sample had a traumatic event in their past, and that OCD was more severe in those with more than one trauma.
– This suggests that OCD cannot be entirely genetic in origin, at least not in all cases.
– It may be more productive to focus on the environmental causes because we are more able to do something about these.
NEURAL EXPLANATIONS
– The genes associated with OCD are likely to affect the levels of key neurotransmitters as well as structures of the brain.
– These are neural explanations.
THE ROLE OF SEROTONIN
– This is a neurotransmitter which is believed to help regulate mood.
– If a person has low levels of serotonin then normal transmission of mood-relevant information does not take place and mood and sometimes other mental processes are affected.
– At least some cases of OCD may be explained by a reduction in the functioning of the serotonin system in the brain.
DECISION-MAKING SYSTEMS
– Some cases of OCD seem to be associated with impaired decision making.
– This in turn may be associated with abnormal functioning of the lateral (side bits) of the frontal lobes of the brain as these are responsible for logical thinking and making decisions.
– There is also evidence to suggest that an area called the left parahippocampal gyru, associated with processing unpleasant emotions, functions abnormally in OCD.
EVALUATION OF NEURAL EXPLANATIONS
STRENGTH
Research Support
– There is evidence to support the role of some neural mechanisms in OCD.
– For example, some antidepressants work purely on the serotonin system, increasing levels of this neurotransmitter.
– Such drugs are effective in reducing OCD symptoms and this suggests that the serotonin system is involved in OCD.
LIMITATION
Causal Relationship
– There is evidence to suggest that various neurotransmitters and structures of the brain do not function normally in patients with OCD.
– However, this is not the same as saying that this abnormal functioning causes the OCD.
– These biological abnormalities could be a result of OCD rather than its cause.
– Therefore, it is hard to say what influenced what