Biological approach to explaining OCD

• OCD is widely understood and explained as biological in nature  
• Genes are involved in vulnerability to OCD  
• Aubrey Lewis (1936)  

  • Looked at OCD in his patients  
  • 37% had parents with OCD  
  • 21% had siblings with OCD  
• What does Lewis's research suggest? (1936)

  Suggests that OCD runs in families. However, familial DNA doesn't guarantee OCD only a genetic vulnerability to it. 
• Diathesis-stress model  

  • Certain genes leave some more likely to develop a mental disorder, but it isn't certain  
  • Environmental stress may trigger conditions  
• Biological psychologists have identified individual genes (candidate genes)  
• Some candiate genes like 5HT1-D beta implicated in the transport of serotonin across the synapse
• OCD is polygenic  


  Apart from being a result of candidate genes, it’s also assumed that OCD polygenic (the result of several genes). 
• Taylor (2013)  

  • Analysed findings of previous studies done on the genetic nature of OCD  
  • Found that 230 genes may be involved in OCD  

  These genes are associated with the action of dopamine and serotonin both believed to have a role in regulating mood.  
• One group of genes may cause OCD in one person, but a different gene may cause OCD in another person  

  Therefore, OCD is aetiologically heterogenous - meaning the origin of OCD has different causes 
• Some evidence to suggest that different types of OCD may be a result of particular gene variation (alleles) 
• Serotonin

  Neurotransmitter which is believed to help regulate mood. Responsible for for relaying information from one neuron to another.
• Low levels of serotonin....

  • Normal transmission of mood relevant information does not take place from one neuron to another. 
  • Therefore, individual may experience lowered mood
• In some cases of OCD, it can be explained by a reduction in the functioning of the serotonin system in the brain.
• Some cases of OCD, particularly hoarding disorder, may be associated with impaired decision making.   
• Two brain regions thought to be involved in OCD

  • The orbitofrontal cortex - responsible for decision making
  • The basal ganglia - monitors voluntary movement
  • A impaired functioning between these tow bran region may explain obsessions (reoccurring thoughts) and a desire to continue to carrying out action(compulsions)
• Research support for genetic explanation - AO3

  P - Strength of genetic explanation for OCD is it's strong evidence base

  E - Nestasdt et al (2010) - reviewed twin studies and found that 68% of MZ twins shared an OCD diagnosis as a posed to 31% of DZ twins

  A - Further research conducted by Mariani and Stebnicki (2012) has found that that person with a family member who has a diagnosis of OCD is around 4 times more likely to develop the condition that someone without it

  L - This impressive research support suggests that there must be some genetic influence on the development of OCD
• Environmental risk factors - AO3

  P - One weakness is that the genetic model for OCD fails to consider some it's environmental risk factors

  E - Although there is evidence that a certain genetic makeup increases vulnerability to OCD. It's still not completely genetic in origin.

  A - Cromer et al (2007) found that half the people in the sample had experience a traumatic event their past. It was also evident that the more sever types of OCD was a result of one or more trauma

  L - This highlights that genetic vulnerability is only a partial explanation for the development of OCD
• Research support for neural explanation - AO3 


  P - One strength of neural model for OCD is the existence of supporting evidence

  E - Antidepressants which work purely on increasing serotonin are effective in reducing the symptoms of OCD. This suggests that serotonin is involved in OCD.

  A - Also Nestasdt et al (2010) suggests OCD symptoms form part of a number of other conditions that are biological in origin e.g Parkinson's

  L - This suggests that neural factors including serotonin is at least somewhat responsible for OCD
• No unique neural model - AO3

  P - One large limitation of the neural explanation for OCD is that the serotonin-OCD link may not be limited to OCD

  E - Many with OCD also had a diagnosis of depression. Having both these condition is an example of co-morbidity.

  A -In that depression also involves a disruption action of serotonin. This means that it might juts be that serotonin activity is disrupted in people with OCD because they also have depression

  L - This means that dysfunction to serotonin may not be relevant in the behavioural, emotional and cognitive symptoms of OCD