Biological explanation for OCD

• Genetic explanations

  Researchers have identified specific genes which create a vulnerability for OCD, called candidate genes :

  • Serotonin genes, e.g. 5HT1-D beta, are implicated in the transmission of serotonin across the synapse
  • Dopamine genes are also implicated in OCD and may regulate mood

  Both dopamine and serotonin are neurotransmitters
• Genetic explanations

  OCD is not caused by one single gene but several genes are involved. Taylor found evidence that up to 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 which is known as aetiologically heterogeneous

  There is evidence that different types of OCD may be the result of particular genetic variations like hoarding disorder and religious obsessions
• Neural explanations

  Neurotransmitters are responsible for relaying information from one neuron to another

  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 function of 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
• Evaluation

  One strength is evidence for genetic explanation of OCD. Nestadt reviewed twin studies and found that 68% of MZ twins shared OCD as opposed to 31% of DZ twins. Marini and Stebnicki found that a person with a family member with OCD is around four times more likely to develop it as someone without. This means that people who are genetically similar are more likely to share OCD, supporting a role for genetic vulnerability.
• Evaluation

  One limitation is animal studies used as evidence in genetic explanations. Evidence from animal studies show particular genes are associated with repetitive behaviours in other species like mice. However, the human mind is much more complex, so it may not be possible to generalise from animal repetitive behaviour to human OCD. This means that animal studies of candidate genes are probably not relevant to understanding OCD.
• Evaluation

  One strength is the neural model is supporting evidence. Antidepressants that work on serotonin reduce OCD symptoms. This suggests that serotonin may be involved in OCD. Also, OCD symptoms form part of conditions that are known to be biological in origin like parkinson's disease. This means that biological factors are likely to be involved in OCD
• Evaluation

  One limitation of the neural model is there is no unique neural system. Many people with OCD experience depression. This depression probably involves disruption to the action of seritonin. It could simply be that serotonin activity is disrupted in many people with OCD as they are depressed as well. This means that serotonin may not be relevant to OCD symptoms.