Biological approach to explaining OCD

• Genetic explanation of OCD -

  Genes are involved in individual vulnerability

  Lewis - OCD patients: 37% had parents with OCD, 21% had siblings with OCD

  Suggesting OCD runs in families - genetic vulnerability (diathesis stress model)
• Genetic explanation of OCD - Candidate genes

  • genes that create vulnerability for OCD
  • involved in regulating the development of the serotonin system
• Genetic explanation of OCD - Polygenic

  OCD is caused by a combination of genetic variations that together increase vulnerability

  Taylor - analysed findings and found evidence that up to 230 different genes may be involved in OCD e.g dopamine and serotonin
• Genetic explanation of OCD - different types

  • one group of genes cause OCD in 1 person but a different group cause disorder in another person - AETILOGICALLY HETEROGENEOUS
  • origins of OCD vary from one person to another
• AO3 genetic explanation - research support

  Twin study Nestadt - 68% of identical twins shared OCD as opposed to 31% of non-identical twins

  Family study - A person with a family member diagnosed with OCD is 4x likely to develop it
• AO3 genetic explanation - environmental risk factors

  OCD is not entirely genetic in origin

  environmental risk factors can also trigger risk

  Cromer - over half the OCD clients had experienced a traumatic event in their past
• Neural Explanation of OCD

  • genes associated with OCD are more likely to affect the levels of key neurotransmitters as well as structures of the brain
• Neural Explanation - the role of serotonin

  • low levels of serotonin then normal transmission of mood-relevant information does not take place so person experienced low mood
  • some cases of OCD can be explained by a reduction in the functioning of the serotonin system in the brain
• Neural Explanation - decision-making systems

  • impaired decision-making
  • abnormal functioning of the lateral of the frontal lobes of the brain
  • the frontal lobes - responsible for logical thinking and making decisions
  • left parahippocampal gyrus functions abnormally - associated with processing unpleasant emotions
• AO3 neural explanation - research support

  • Antidepressants that work purely on serotonin are effective in reducing OCD symptoms - suggests that serotonin may be involved in OCD
  • OCD symptoms form part of conditions that are known to be biological in origin - Parkinson's disease causes muscle tremors.
  • Biological disorder produces OCD symptoms then biological processes underlie OCD
• AO3 neural explanation - Serotonin-OCD link may not be unique to OCD

  • many people with OCD also experience clinical depression
  • two disorders - co-morbidity
  • depression involves disruption to the action of serotonin
  • could simply be that serotonin activity is disrupted in people with OCD because they are depressed as well