biological explanations

• the main assumption of the biological explanation is that all behaviour has a physical cause, therefore OCD has a physical cause.
• the genetic explanation states that OCD is inherited, and having a certain gene gives you a vulnerability to OCD. the main ways of studying this is through twin and adoption studies. family studies have shown that relatives of OCD sufferers have a greater likelihood to suffer from OCD and anxiety related problems
• Nestadt et al


  first degree relatives of OCD sufferers had an 11.7 % chance of developing the disorder compared to a 2.7 % chance for those without an OCD relative
• Lewis 


  37 % of his OCD patients had parents with OCD

  21 % had siblings with OCD
• taylor

  230 different genes may be involved in OCD, its polygenic
• Miguel et al 


  if one MZ twin has OCD there is a 53 - 87 % chance that the other twin will also develop it whilst in DZ twins theres only a 22 - 47 % chance
• Nestadt et al

  interviewed previous twin studies and found that 68% of identical twins shared OCD as opposed to 31 % of non identical twins. however, MZ had the same environment
• Carey and Grottesman

  MZ concordance 87% for obsessive symptoms compared to 47% in fraternal twins
• evaluation

  because OCD is polygenic, it may be the case that its difficult to conclusively link OCD to genetics

  environmental factors have also been seen to play a role in OCD Cromer et al found that over half of OCD patients in a sample had a traumatic event in their past, and OCD seemed to be worse in those who had more than one trauma

  higher concordance may be due to nurture

  concordance is not 100%

  genes only create vulernability, not a direct cause

  diathesis stress model - not all develop it - a trigger is needed
• the neural explanation outlines how certain illnesses, such as throat infections, lymes disease, and influenza, have been associated with the onset of OCD.
• PET scans have been used to show low levels of seretonin in OCD sufferers, and drugs that increase seretonin have reduced symptoms.
• PET scans also show high activity in the orbito frontal cortex, this part of the brain is responsible for higher thinking, and converting sensory information into thoughts. its also involved in recieving impulses and acting accordingly. then when the impulses lessen the brain stops us. with OCD this is overactive and doesn't stop the impulses.
• Pichichero 


  reported that case studies from the US national institution of health showed that children displayed symptoms of OCD and tourettes safter contracting streptococcal infections. supports the idea that some infections may be linked to OCD
• Fallon and Nields

  40 % of people contracting lymes disease incur neural damage that resulted in psychiatric conditions resulting in OCD. this supports neural explanation
• Zohar et al

  gave a serotonin reducing drug to 12 OCD patients and 20 non - OCD sufferers as a control. the OCD symptoms got significantly worse for the participants with OCD.
• Hu


  compared seretonin activity in 169 OCD sufferers and 253 non sufferers and found that serotonin levels were lower in OCD sufferers
• evaluation

  its thoughts that the infection doesn't cause OCD, but may trigger symptoms in those more genetically vulnerable
• evaluation

  it hasn't been established if low serotonin and over activity in the orbito frontal cortex are causes or effects of OCD
• evaluation

  despite research showing the OCD sufferers and non sufferers have neural differences, its not clear how this relates to the specific mechanisms of OCD
• evaluation

  not all OCD sufferers respond well to serotonin increasing drugs. this goes against the idea that its the sole cause of OCD