Biological approach to explaining OCD

• Candidate genes

  researchers identified specific genes which create a vulnerability for OCD:

  serotonin genes, e.g. 5HT1-D beta, are implicated in the transmission of serotonin across synapses

  dopamine genes are also implicated in OCD

  dopamine and serotonin are neurotransmitters that have a role in regulating mood
• OCD is polygenic- not caused by one gene, several genes are involved. Taylor found over 230 different genes may be involved in OCD.
• One group of genes may cause OCD in one person but a different group of genes may cause the disorder in another person- this is known as aetiologically heterogeneous.
• there is also evidence that different types of OCD may be the result of particular genetic variations, such as hoarding disorder and religious obsession.
• neurotransmitters are responsible for relaying information from one neuron to another.
• low levels of serotonin lower 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) is affected.
• some cases of OCD, and in particular hoarding disorder, seem to be associated with impaired decision making. this in turn may be associated with abnormal functioning of the lateral frontal lobes of the brain.
• the frontal lobes are responsible for logical thinking and making decisions.
• there is also evidence to suggest that an area called the left parahippocampal gyrus associated with processing unpleasant emotions, functions abnormally in OCD.
• strength of OCD- strong supporting evidence for genetic explanation

  evidence from variety of sources which suggests some people are vulnerable to OCD as a result of their genetic make-up, e.g. nestadt et al. reviewed twin studies and found 68% of identical twins (MZ) shared OCD as opposed to 31% of non-identical (DZ) twins.
• limitation of biological explanations of OCD- too many candidate genes identified

  twin studies strongly suggest OCD is largely genetic, but psychologists have been less successful at pinning down all genes involved. one reason for this is that it appears several genes are involved and that each genetic variation only increases the risk of OCD by a fraction. the consequence is that a genetic explanation is unlikely to ever be very useful as it provides little predictive value.
• strength of biological explanations of OCD- supporting evidence for neural explanations

  antidepressants that work purely on the serotonin system are effective in reducing OCD symptoms and this suggests the serotonin system may be involved in OCD. also, OCD symptoms form part of biological conditions such as Parkinson's disease. this suggests the biological processes that cause the symptoms in those conditions may also be responsible for OCD.
• limitation: serotonin-OCD link may not be unique to OCD

  many people who suffer from OCD become depressed. having two disorders together is called co-morbidity. this depression probably involved (though is not necessarily caused by) disruption to the serotonin system. thus leaves us with a logical problem when it comes to the serotonin systems as a possible basis for OCD. it could simply be that the serotonin system is disrupted in many patients with OCD because they are depressed as well.