(A01)The Biological Explanation Of OCD

• Genetic explanations

  OCD is a good example of a condition that may be largely understood as biological in nature. The genetic explanation is one form of a biological explanation as genes are involved in individual vulnerability to OCD
• Lewis's study


  Observed OCD patients and 37% of patients had parents with OCD and 21% of patients had siblings with OCD. Lewis suggested OCD runs in families
• Diathesis-stress model


  Certain genes leave some people more likely to suffer a mental disorder - but some environmental stress is necessary to trigger the condition
• Candidate genes


  Researchers identified genes which create vulnerability for OCD called candidate genes which are involved in regulating the development of the serotonin system
• 5HTI-D beta


  The gene 5HTI-D beta is implicated in the efficiency of transport of serotonin across synapses
• OCD is polygenic


  Several genes cause OCD not one meaning OCD is polygenic
• Taylor et al study


  Analysed findings of previous studies and found 230 different genes involved with OCD. Also genes associated with dopamine as well as serotonin, both of these neurotransmitters believed to have a role in regulating mood
• The different types of OCD

  The aetiology (origin) of OCD are heterogenous (has different causes). Suggests that different types of OCD may be a result of particular genetic variations such as hoarding disorder/religious obsession
• Neural explanations

  Genes associated with OCD are likely to affect the levels of key neurotransmitters as well as structure of the brain
• Role of neurotransmitters


  Neurotransmitters are responsible for relaying information from neuron to another
• Role of serotonin

  If a person has low levels of serotonin then normal transmission of mood-relevant information does not take place and mood/mental processes are affected. Some cases of OCD can be explained by reduction in function of serotonin system in the brain
• Decision making systems


  Some cases of OCD (hoarding disorder) seem to be associated with impaired decision making. May be associated with abnormal decision making/functioning of the lateral (sides) of the frontal lobes which are responsible for logical thinking/making decisions
• Parahippocampal gyrus

  Left parahippocampal gyrus functions abnormally in OCD - associated with processing unpleasant emotions