Biological Explanations for OCD

• Obsessive compulsive disorder (OCD)


  An anxiety disorder characterised by obsessions and compulsions
• Symptoms of OCD


  • Obsessions
  • Compulsions
• Biological explanations for OCD

  • Genes
  • Neurochemistry
  • Neural functioning
• Genetic explanation


  • OCD is inherited (passed on through genes) from generation to generation
  • People inherit a candidate gene which creates a vulnerability to OCD but a life stressor is needed to trigger it
• COMT


  Candidate gene managing the production of dopamine (increase)
• SERT


  Candidate gene for transportation of serotonin (decrease)
• Diathesis stress model


  • Genes such as COMT and SERT only create a vulnerability (risk of developing) for OCD
  • Other factors (stressors) need to be present to trigger the development of the disorder
• Neurochemistry explanation


  • OCD is caused by abnormal levels of specific neurotransmitters
• Neural functioning explanation


  • Several areas of the frontal lobe are abnormal in people with OCD
  • The Orbitofrontal cortex (OFC) is the brain's 'worry detector'
  • The caudate nucleus suppresses signals from the OFC reaching the thalamus
  • When the caudate nucleus is damaged it cannot suppress minor 'worry' signals which causes the thalamus to be alerted
• Supporting research


  • Point - supporting research from family and twin studies for genetic causes of OCD
  • Evidence - Nestadt et al. (2010) reviewed previous twin studies and found that 68% of identical twins shared OCD as opposed to 31% of non-identical twins.
  • Explain - suggests that the cause of OCD is partly genetic.
  • Link - increase the validity of genetic explanations of OCD.
• Research support for the diathesis-stress model


  • Point - supporting research evidence that environmental factors may also trigger or increase risk of developing OCD.
  • Evidence - Cromer et al. found that over half the OCD patients in their sample had a traumatic event in their past and that OCD was more severe in those with more than one trauma.
  • Explain - This suggests that OCD may be best explained as the result of environmental causes.
• Research support for genes and OFC


  • Point - One strength of neural explanations of OCD is that there is supporting evidence of the genetic link to abnormal levels of neurotransmitters.
  • Evidence - Menzies et al used MRI to produce images of brain activity in OCD patients and their family without OCD and a control group of unrelated healthy patients. OCD patients and their close relatives had reduced grey matter in key regions of the brain, including the OFC.
  • Explain - suggests that anatomical differences are inherited and these may lead to OCD in certain individuals.