The biological approach to explaining OCD

• Genetic explanations for OCD

  Lewis (1936)- 37% parents and 21% siblings. Diathesis-stress model: certain genes increase vulnerability, but environmental stress is needed to trigger.

  Candidate genes- create vulnerability. E.g., 5HT1-D is implicated in efficiency of transport of serotonin across synapses.

  OCD is polygenic- several genes are involved. Taylor (2013): up to 230. Genes studied include ones related to dopamine and serotonin (neurotransmitters that regulate mood)
• Genetic explanations for OCD 2

  Different types of OCD- aetiologically heterogeneous- different groups of genes can cause OCD in different people. Different types of OCD caused by genetic variations (hoarding disorder and religious obsession)
• Neural explanations for OCD

  The role of serotonin- neurotransmitters relay information from one neuron to another. Some cases of OCD can be explained through the reduction in the functioning of serotonin system.

  Decision making systems-Some cases (particularly hoarding disorder) seem to be associated with impaired decision making. This in turn may be associated with abnormal functioning of the lateral of the frontal lobes (responsible for logical thinking and decision making). Parahippocampal gyrus (processing unpleasant emotions) functions abnormally in OCD.
• Genetic explanations- evaluation

  There is good supporting evidence- Nestadt et al. (2010) reviewed previous twin studies and found 68% of identical twins shared OCD as opposed to 31% of non-identical twins. Strongly suggests there is genetic influence. BUT may just have similar environments.

  Too many candidate genes- Difficult to pin down all genes involved and each genetic variation only increases risk of OCD by a small amount. Genetic explanation is unlikely to be useful as it provides little predictive value.
• Genetic explanations- evaluation 2

  Environmental risk factors- environmental factors can also trigger OCD (diathesis-stress model). Cromer et al. (2007) over half of OCD patients experienced a traumatic event. Not all cases have a genetic origin.
• Neural explanations- evaluation

  There is some supporting evidence- Some antidepressants work purely on increasing serotonin levels which reduce OCD symptoms. Proves serotonin system is involved in OCD.

  We should not assume the neural mechanisms cause OCD- there is evidence that various neurotransmitters and structures don't function normally in OCD. BUT they could be the result of OCD, not the cause.