Biological explanation of OCD

• Which approach explains OCD?

  Biological
• what does the biological approach believe determines OCD?

  Physiology
• which two explanations are involved in explaining OCD?

  genetic and neural explanations
• What is genetic explanations?

  inheritance of genes from mother and/or father.
• What is neural explanations?

  our brains work differently and this explains OCD. Neurotransmitters and abnormal brain function.
• What did Lewis (1936) show about genetics and OCD?

  studied OCD patients. 36% has a parent with OCD and 21% had a sibling with OCD. this suggests OCD runs in families (vulnerability.)
• what did Nestadt (2010) show about genetics and OCD?


  Concordance for OCD in monozygotic twins was 62% and in dizygotic twins 31%. This suggests a biological basis to OCD.
• what is the diathesis stress model used to illustrate?

  used to illustrate the interaction of genes and environment to bring about a disorder.
• What is the factor that makes some vulnerable to OCD more likely to experience it?

  a stressful and negative environment
• OCD is polygenic, what does this mean?


  there are probably many genes which play a part in OCD.
• what are these polygenic genes in OCD known as?

  candidate genes - they are believed to create a vulnerability for OCD.
• What did Taylor's 2013 meta-analysis show?

  found that up to 230 genes may be involved in OCD. These 230 include genes that affect serotonin and dopamine levels in the brain, in particular.
• what is SERT (serotonin transporter) responsible for?

  the reuptake of serotonin at the synapse.
• what will happen if someone has a variant in SERT?

  they may have less serotonin left in the synapse because reuptake of serotonin happens more quickly in their brains.
• Why might someone with a variant in SERT feel overstimulated?

  Serotonin calms down too much activity in the brain, with a variant the inhibitory effect is not enough for the next neuron.
• What does the Neural explanation of OCD look at?

  - abnormal brain area function.

  - abnormal levels of certain neurotransmitters
• What does neuroimaging (brain scan) techniques enable researchers to do?

  enables researchers to study the brain in detail and to identify normal brain patterns. This then allows for comparisons with abnormal brain patterns.
• which parts of the brain have researchers implicated to be overactive in someone with OCD?

  - Basal Ganglia

  - Orbitofrontal cortex

  - thalamus

  
  

  The functioning of any of these affects the others.
• what is the function of the Basal Ganglia?

  Repetitive motor actions. Clusters of neurons in areas of the brain, associated with innate psychomotor (voluntary) function.
• what did Rapoport and Wise (1998) propose about the basal ganglia?


  proposed that over activity of the basal ganglia gives rise to the repetitive motor behaviours seen in OCD.
• what is the function of the orbitofrontal cortex (OFC)?

  involved in decision making and worry about behaviour.
• what did Saxend and Rauch (2000) say about the orbitofrontal cortex?

  it is overactive in those with OCD.
• what is the function of the thalamus?


  involved in checking and safety behaviours.
• what have studies shown about the thalamus?


  suggested it is overactive in people with OCD.
• what do SSRI medications do?

  increase the amount of serotonin at the synapse of the brain, are effective for most people (2/3) at improving the symptoms of OCD.
• How do SSRI's work?

  1) SSRI blocks re-uptake channel.

  2) as a result serotonin remains in the synapse for longer, delivering its message more.
• What may abnormal dopamine action cause?

  an imbalance in the reward system may lead to carrying out repetitive behaviours which provide little relief.
• Why are the genetic and neural explanations not opposing?

  because our genes determine neurotransmitter activity.
• what are strengths of the genetic explanation?

  - evidence through family and twin studies e.g Nestadt.

  - research has implicated a number of candidate genes in the development of OCD.

  - Research supports individuals may have a genetic vulnerability towards OCD that is then triggered by an environmental stressor.
• what are limitations of the genetic explanation?

  - concordance rate is never 100%

  - people who share genes usually also share the same environment so is difficult to determine how much each has on the outcomes.

  - OCD is aetiological heterogeneous, so it is difficult to predict genes definitely involved.

  - we can control environment but not yet genes, so this may be more useful explanation.
• what did Cromer (2007) find?

  found that over half of 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 the environment may play a very important role in OCD, at least in some people.
• what are strengths of the neural explanation?

  - Advances in technology have allowed accurate investigations in brain function.

  - an understanding of the role of neurotransmitters has allowed medication to be developed which helps many sufferers.
• what are limitations of the neural explanation?

  - compulsions can be explained by abnormality of the basal Ganglia but doesn't explain obsessions, so not one area has been found to always play a role in OCD.

  - data does not show cause and effect, neural changes could be as a result of OCD itself.

  - drugs are only 70% effective

  - SSRI decreasing OCD symptoms could be due to aetiological fallacy (low serotonin may not be the cause.)
• What gene regulates serotonin?

  SERT
• What gene regulates dopamine?

  COMT
• What does high dopamine in those with OCD lead to?

  repetitive behaviours, due to imbalance in the reward centre.
• What can the overstimulation due to lack of serotonin at the synapse lead to?

  heightened anxiety and intrusive thoughts.
• What are the overactive parts in the brain referred to as?

  The worry circuit.