Explain OCD: the biological approach

• Can we assume that the neural mechanisms cause OCD?

  No.

  • There is evidence suggesting various neurotransmitters and structures of the brain do not function normally in patients with OCD
  • Not the same as saying that abnormal functioning causes OCD. These abnormalities could be a result of OCD.
• how is the neural explanation for OCD not clear what neural mechanisms are involved ?

  Studies of decision making have shown that these neural systems are the same systems that function abnormally in OCD ( Cavedini et al 2002)

  • Research has also identified other brain systems that may be involved sometimes but no system has been found that always plays a role in OCD
• 2 Limitations Neural explanation of OCD

  • not clear exactly what are neural mechanisms are involved
  • should not assume the neural mechanisms are involved
• How is there supporting evidence for the neural explanation of OCD?

  Some antidepressants work purely on the serotonin system, increasing levels.

  • effective in reducing OCD symptoms ( suggesting serotonin is related to OCD)
  • OCD symptoms form part of other are biological in origin (Parkinson’s Disease)
  • Suggests that biological processes that cause the symptoms in those conditions may also be responsible for OCD
• 1 strength of neural explanation of OCD there is updating evidence
• Abnormal functioning of parts of the brain as a neural explanation for OCD

  Frontal lobes

  • responsible for logical thinking and making decisions
  • abnormal functions of the lateral of the frontal lobes can cause hoarding disorders Parahippocampal gryus associated with processing unpleasant emotion functions abnormally in OCD
• Abnormal levels of neurotransmitters as an neural explanation for OCD


  • serotonin is believed to regulate mood
  • if a person has low levels of serotonin than normal > transmission of mood
  • relevant information does not take place > mood is effective
  • OCD may be explained buy by a reduction in the functioning of the serotonin system in the brain
• How does the Genetic explantation for OCD not focus on environmental risk factors?

  Environment mental factors can also trigger or increase the risk of OCD (diathesis-stress model)

  
  

  Corner er al (2007)

  • Found that over half of the OCD patients have in their sample have had a traumatic experience —> more trauma = more server
  • Suggests that OCD is not entirely genetic ; may be more productive to focus on the environmental factors
• Genetic explanations for OCD : Too many candidate genes

  Psychologists have been much less successful at pinning down all the genes involved

  • it appears that several genes are involved at that each genetic variation only increases the risk of OCD by a fraction
  • Genetic explanation is unlikely to ever be very useful because it provides little practical value
• 2 limitations of the Genetic explanation for OCD

  • Too many candidate genes
  • environmental risk factors
• How is there good supporting evidence for the genetic expansions for OCD?

  Evidence form a variety of sources that OCD is result of our genetic make-up:

  
  

  Nestadt et al (2010)

  • Twin studies
  • Reviewed previous twin studies
  • 68% of identical twins shared OCD as opposed to 31% of non-identical twinsStrongly suggest a genetic influence
• 1 strength of using genetic explanation to explain OCD

  
  

  There is good supporting evidence
• What is the diathesis-stress model?

  Suggests that certain genes leave some people more likely to suffer a mental disorders, a person may gain vulnerability towards OCD through an environment stressor
• What is the evidence that OCD can caused buy inherited genes ?

  Lewis (1936)

  • 37% had parents with OCD
  • 21% had siblings have OCD
  • suggesting that OCD is runs in the family
  • not a definite diagnosis
• What Candidate Genes were identified in creating a vulnerable to OCD?

  - A mutated SERT gene causing low levels of serotonin

  - A mutated COMPT causing high levels of dopamine
• OCD is aetiologically heterogeneous, what does this mean?


  Origins have different causes
• What is polygenic and what is the evidence that OCD is polygenic?


  More than 1 specific gene has been identified for the onset of OCD

  
  

  Taylor (2013)

  • carried out a meta-analysis that 230 different genes implicated in developing OCD
• What are the 2 explanations for OCD ?

  • Genetic Explanation
  • Neural explanation