Biological explanations of OCD

• Genetic explanations  

  Genes involved in individual vulnerability to OCD  

  • Lewis found that 37% of OCD patients had parents with OCD and 21% of patients had siblings with OCD  
  • Could be the genetic vulnerability that is being passed on rather than the certainty of OCD 

  OCD is Polygenic  

  • Caused by several genes -> up to 230 identified by Taylor et al  

  Candidate genes  

  • Identifies genes which create vulnerability for OCD  
  • COMT gene = regulate the production of dopamine  
  • SERI gene = affects the transcript of serotonin and involved in creating lower levels of neurotransmitters  
• Genetic explanations - candidate genes

  COMT gene = High in people with OCD as dopamine is part of the learning pathway argued that because its high people preform the behaviour to respond to an obsession and repeat to develop into compulsions  

  SERI gene = Low serotonin levels in those with OCD means that they would have lower connectivity of neural pathways meaning their thoughts aren't entirely complete leading to obsessive thoughts
• Genetic explanations A03

  Supporting evidence as variety of sources provide evidence that a patients genetic makeup makes them more vulnerable -> billet et al completed meta-analysis of twin studies and found MZ twins if 1 had OCD then both had 68% of the time but DZ twins only 31% of the time  

  Concordance rates are never 100% which means that environmental factors may also play a role 
• Genetic explanations A03 continued

  Difficult to untangle effects of environment and genetic factors 

  Environmental risk factors -> diathesis stress model suggests that environmental factors also have a role in development of OCD -> Cramer et al found that over 50% of patients suffered a traumatic event in the past and those who suffered more than 1 had severe OCD
• Neural explanations

  Low serotonin levels  

  • Mood to relevant information doesn't take place and so the mood is affected  

  Basal Ganglia  

  • Area of the brain is responsible for innate psychomotor functions  
  • Rapport and wise proposes that the hypersensitivity of basal ganglia gives rise to repetitive motor behaviours seen in OCD 

  Decision making systems  

  • Orbitofrontal cortex in frontal lobes is responsible for logical thinking and making decisions which function abnormal in OCD suffers   
• Neural explanations

  Caudate Nucleus  

  • Normally supresses signals from the OFC to the thalamus but when its faulty it doesn't stipe the worry signal  

  Diathesis stress model  

  • Predisposition + environmental trigger = behaviour 
• Neural explanations A03

  Supported by PET scans while their symptoms are active  

  Supporting evidence oof the neural role in OCD -> anti-depressants that work on serotonin system by increasing levels of serotonin are effective in decreasing symptoms of OCD 

  Drug treatments are only effective 50% of the time so must be alternative methods 

  Evidence that suggests various areas of brain and neurotransmitters and involved in OCD and don't function normally in OCD patients  

  Alternative explanations -> e.g. mowers 2 process theory