Biological explanations of OCD

• Genetic explanations 

  • OCD has been explained in a number of ways but the biological approach offers particularly useful suggestions as to how it is caused. 
  • It has been proposed that there is a genetic component to OCD which predisposes some individuals to the illness. 

  The genetic explanation suggests that whether a person develops OCD is at least partly due to their genes. This may explain why patients often have other family members with OCD.
• Genetic explanations

  • Bellodi et al (2001) claim that genetic factors play a role in the disorder. Using evidence from twin studies and family studies, they showed that close relatives are more likely to have the disorder than more distant relatives.
  • Mckeon and Murray patients with OCD are more likely to have first degree relatives who suffer from anxiety disorders.

  Pauls et al there is a much higher % of OCD sufferers in relatives of patients with OCD than in the control group without OCD.
• Genetic explanations 

  • Candidate genes are ones which, through research, have been implicated in the development of OCD.
  • A possible candidate gene is the SERT gene which is involved in regulating serotonin, a neurotransmitter which facilitates message transfer across synapses. 
  • Another possible candidate gene is the COMT gene – this regulates the production of dopamine
  • Dopamine affects motivation and drive
• What is the main genetic factor associated with OCD?


  OCD is thought to be polygenic.
• What does it mean that OCD is polygenic?


  It means that its development is influenced by multiple genes, possibly as many as 230.
• Why does the polygenic nature of OCD imply little predictive power?


  Because multiple genes are involved, making it difficult to predict OCD based on genetics alone.
• What is the diathesis-stress model in relation to OCD?


  It suggests that a genetic vulnerability to OCD is triggered by environmental stressors.
• What type of event could act as an environmental stressor in the diathesis-stress model for OCD?


  A stressful event, such as a bereavement.
• What are the key components of the diathesis-stress model as it relates to OCD?


  • Genetic vulnerability to OCD
  • Environmental stressor required to trigger OCD
  • Example of stressor: bereavement
• AO3 - Genetics

  (+)There is evidence to suggest there is a genetic component to the disorder. One of the best sources of evidence for the importance of genes is twin studies (Nestadt – 2010)

  (+)Family studies could also be used to explain environmental influences.

  (-)Close relatives of OCD sufferers may have observed and imitated the behaviour (SLT).

  (-)It is difficult to untangle the effects of environment and genetic factors.
• AO3 - Candidate genes

  (+)Candidate genes are ones which, through research, have been implicated in the development of OCD.

  (-)There are too many genes involved

  (-)Psychologists have not been successful at pinning down all the genes involved

  (-)Each genetic variation only increases the risk of OCD by a fraction
• AO3 - Environmental factors

  (-)Individuals may gain a vulnerability towards OCD through genes that is then triggered by an environmental stressor.

  (-)Cromer (2007) found that over half the OCD patients in their sample had a traumatic event in the past, and that OCD was more severe in those with more than one trauma.

  (-)This means that it may more productive to focus on environmental causes as it seems that not all OCD is entirely genetic in origin
• Neural explanations

  The genes associated with OCD are likely to affect the levels of key neurotransmitters as well as structures of the brain.

  • Abnormal levels of certain neurotransmitters
  • Certain brain circuits may be abnormal
• Neural explanations

  Neuroimaging (brain scanning) techniques have enabled researchers to study the brain in detail and to identify normal brain patterns - this therefore allows for comparisons with abnormal brain patterns.

  1. Low levels of serotonin lowers mood

  Low levels of the neurotransmitter serotonin will affect the processing of mood-relevant information, if this doesn’t take place effectively, mood is affected
• Neural explanations

  2. Impaired decision making can be a characteristic of some cases of OCD

  This may be linked to abnormal functioning of the lateral frontal lobes of the brain. 

  The frontal lobes are responsible 

  for logical thinking and making 

  decisions
• Neural explanations

  3. The Parahippocampal gyrus doesn’t function normally

  This part of the brain is associated with processing unpleasant emotions
• Neural explanations

  Other brain areas believed to be involved in OCD include the orbitofrontal cortex (OFC) and the thalamus

  The thalamus is the brain area responsible for functions include cleaning, checking and other safety behaviours. 
• Neural explanations

  The OFC is involved in decision making and worry 

  about social and other behaviour.  In OCD the OFC 

  and the thalamus are believed to be overactive.  

  An overactive thalamus would result in an increased motivation to clean or check for safety.  If the thalamus was overactive the OFC would also become overactive as a result.

  An overactive OFC would result in increased anxiety and increased planning to avoid anxiety.
• AO3 - Neurotransmitters

  (+)Allows medication to be developed which helps sufferers. 

  (-)Drugs are not completely effective

  (-)Just because administering SSRIs decreases OCD symptoms does not mean that this was the cause in the first place

  (-)There is time delay between taking drugs to target the condition and any improvements being made and yet the chemical imbalance is addressed in hours
• AO3 - Areas of the brain

  (+)Advances in technology have allowed researchers to investigate specific areas of the brain more accurately, and OCD sufferers do seem to have excessive activity in the orbital frontal cortex

  (+)Cleaning and checking behaviours are "hard-wired" in the thalamus

  (+)The repetitive acts (compulsions) may be explained by the structural abnormality of the basal ganglia but not necessarily the obsessional thoughts.
• AO3 - Areas of the brain

  (-)There are inconsistencies found in the research as no system has been found that always plays a role in OCD

  (-)These neural changes could be as a result of suffering from the disorder, not necessarily the cause of it