explaining OCD (biological approach)

• explaining OCD

  • genetic explanations (GE)
  • neural explanations (NE)
• candidate genes (GE)

  • researchers have identified specific genes which create a vulnerability for OCD (candidate genes):
  • serotonin genes = eg 5HT1-D beta, are implicated in the transmission of serotonin across synapses
  • dopamine genes = also implicated in OCD and may regulate mood
  • both dopamine and serotonin are neurotransmitters
• OCD is polygenic (GE)

  • 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
• different types of OCD (GE)

  • one group of genes may cause OCD in one person but a different group of genes may cause the disorder in another person
  • known as aetiologically heterogenous
  • there is also evidence that different types of OCD may be the result of particular genetic variations (such as hoarding disorder and religious obsession)
• strength = supporting evidence (GE)

  • Nestadt et al = revised twin studies and found that 68% of identical twins (MZ) shared OCD as opposed to 31% of non-identical (DZ) twins (concordance rates)
  • Marini and Stebnicki = found that a person with a family member with OCD is ~4x more likely to develop it as someone without
  • means that people who are genetically similar are more likely to share OCD => supporting a role for genetic vulnerability
• limitation = existence of environmental risk factors (GE)

  • genetic variation affects vulnerability to OCD, but there are also environmental risk factors that trigger or increase the risk of OCD
  • Cromer et al = found in one sample, over half of people with OCD experienced a traumatic event (OCD severity correlated positively with the number of traumas)
  • means that genetic vulnerability only provides a partial explanation for OCD
• extra evaluation = animal studies

  • evidence from animal studies show particular genes are associated with repetitive behaviours in other species (eg mice)
  • HOWEVER = the human mind is much more complex, so it may not be possible to generalise from animal repetitive behaviour to human OCD
  • means that animal studies of candidate genes are probably not relevant to understanding OCD
• low levels of serotonin lowers mood (NE)

  • neurotransmitters are responsible for relaying information from one neuron to another
  • eg = if a person has low levels of serotonin then normal transmission of mood-relevant information doesn't take place and mood (and sometimes other mental processes) is affected
• decision-making systems in frontal lobes are impaired (NE)

  • some cases of OCD (in particular hoarding disorder) = seem to be associated with impaired decision-making
  • this is turn may be associated with abnormal functioning of the lateral (side bits) frontal lobes of the brain
  • the frontal lobes = responsible for logical thinking and making decisions
• parahippocampal gyrus dysfunctional (NE)

  • also evidence suggesting that an area (called the left parahippocampal gyrus) associated with processing unpleasant emotions, functions abnormally in people with OCD
• strength = supporting evidence (NE)

  • antidepressants that work on serotonin reduce OCD symptoms
  • suggests that serotonin may be involved in OCD
  • ALSO = OCD symptoms form part of conditions that are known to be biological in origin (eg Parkinson's disease)
  • means that biological factors (eg serotonin and processes underlying Parkinson's disease) are likely to be involved in OCD
• limitation = there is no unique neural system (NE)

  • many people with OCD also experience depression = this depression probably involves disruption to the action of serotonin
  • it could simply be that serotonin activity is disrupted in many people with OCD because they are depressed as well
  • means that serotonin may not be relevant to OCD symptoms
• extra evaluation = correlation and causality (NE)

  • some neural systems don't work normally in people with OCD = the biological model suggests this is explained by brain dysfunction causing the OCD
  • HOWEVER = this is just a correlation which does not necessarily indicate a causal relationship - OCD (or depression) might cause the abnormal brain function
  • means that there is a lack of strong evidence for a neural basis to OCD though correlations may eventually lead us to a cause