The biological theory of OCD

• Orbitofrontal cortex: alerts the brain to potential worries in the envrironment
• Cingulate gyrus: connects thalamus to orbitofrontal cortex
• Caudate Nucleus: Inhibits the action of the globus palidus fibres (if overactive - does not work)
• Globus Pallidus fibres: acts as a breaking mechanism - control activity of the thalamus
• Thalamus: contains primitive checking and clearing behaviours, hardwired in the brain
• Left parahippocampal gyrus: associated with processing unpleasant emotions - functions abnormally in OCD sufferers cauing anxiety and obsessions
• Lateral frontal lobes (side front): responsible for logical decision making - faulty in OCD sufferers - leads to compulsions
• Caudate nucleus: inhibits the action of globus pallidus fibres - overactive in OCD sufferers and so does not work
• Lewis found that 37% of his patients had parents with OCD and 21% had siblings with OCD - therefore there must be a genetic element
• Candidate genes: researchers have identified candidate genes which make you more likely to develop OCD, such as the 5HTI D Beta gene (efficiency of serotonin) or CCOMT or SERT
• Polygenic: OCD is polygenic. This means it is caused by various different genes/ neurotransmitters. Dopamine is also implicated.
• Aetiologically heterogeneous: some genes may cause one type of OCD in someone but same genes may cause a different type of OCD in others. This is known as aetiologically heterogeneous.
• Serotonin is a mood transmitter and is responsible for?


  contributes to well-being and happiness, helps sleep cycle and digestive system regulation. Affected by exercise and light exposure - in OCD lower levels of serotonin - affects mood - anxiety
• Brain structure: strengths

  1. Whiteside et al (2004) - they cingulate gyrus, Basal Ganglia and Orbitofrontal cortex become more active when OCD is stimulated
  2. Menzies et al (2007) - brain scans show that OCD sufferers have more grey matter in orbitofrontal cortex compared to non sufferers
• Brain structure: weaknesses:

  1. Brain activity is too complex to isolate areas as explanations for OCD
• Genetics - Strengths:

  1. Nestadt reviewed twin studies and found 68% of identical twins with OCD, also have a twin with OCD, compared to 31% of non-identical twins
  2. Murphy et al - there is a genetic marker for early onset OCD
• Genetics - weaknesses:

  1. There may be too many candidate genes - psychologists have not been able to pin down all the genes involved
  2. Close relatives of OCD sufferers may have observed and imitated the behaviour (SLT)
  3. Just because someone has a candidate gene it doesn't mean they will get OCD, some people need a stressful life event - the diathesis stress model
• Brain chemistry - strengths:

  1. There is some supporting evidence - antidepressants which try and increase serotonin in the brain work for people with OCD
• Brain chemistry - weaknesses:

  1. OCD is often combined with depression. Depression affects serotonin levels - which is causing the change in serotonin? - establish cause and effect
• OCD could be caused by environmental factors:

  Cromer found that over half their sample has a past traumatic life event
• Hard to say is brain activity issues cause OCD or accompany symptoms - cause and effect cannot be established
• It is not always clear which neural mechanisms are involved. No system in the rain has been found to always and consistently play a role in OCD
• OCD is often comorbid with depression. Depression affects serotonin levels - which is causing the change?
• It is a scientific theory that can be tested objectively