OCD Explanation - Biological

• What are candidate genes?

  A group of specific genes may cause OCD /other conditions
• What does polygenic mean?

  OCD isn’t caused by one single gene, conditions are caused by having multiple genes (must have mitigate genes to you the condition)
• What does Aetiologically Heterogeneous mean?

  One group of genes may cause OCD in one person but a different group of genes may cause OCD in another person. (Same groups or different groups could cause different symptoms)
• What did Taylor (2013) find?

  Up to 230 different genes may be involved in OCD
• What is the COMT gene?

  • too much dopamine
  • Gene decreases the amount of COMT available - therefore dopamine isn’t controlled and there is probably too much dopamine
  • associated with OCD
• What is the SERT gene?

  • too little serotonin
  • Affects transport of serotonin - lower levels
  • Associated with OCD
• How does dopamine (neurotransmitter) link to OCD

  • levels are thought to be abnormally high
  • based on animal studies
  • Given higher doses of drugs that enhance levels of dopamine induce stereotyped movements resembling compulsive behaviours in OCD patients
• How does serotonin link to OCD?

  • low levels =normal transmission of mood-relevant info doesn’t take place
  • Mood is affected
• What is the worry circuit?

  Thought serotonin and other neurotransmitters help the functioning of the OFC and the worry circuit
• What does OFC stand for?

  Orbitofrontal cortex
• Steps of the worry circuit:

  1. Serotonin deficiency initiates faulty signals from OFC
  2. OFC sends worry signal to thalmus
  3. Caudate nucleus monitors signals
  4. Thalmus sends filtered version of danger back
  5. OFC sends worry signal to thalmus
• Abnormal Brain Circuits

  • several areas in frontal lobes are thought to be abnormal in people with OCD (OFC sends worry signals)
  • These are normally suppressed by the caudate nucleus
  • If this is damaged, thalmus confirms the worry to OFC creating a worry circuit
  • Individual is driven more to think (anxiety) about them and take action (compulsive behaviour)
• Strength - evidence for genetic explanations

  • Nestadt (2000)
  • compared to general population, people with first degree relatives with OCD have a five times higher risk of having OCD in their life.
  • Billet- monozygotic twins are more than twice as likely to develop OCD if their co-twin has OCD.
  • means people who are genetically similar are more likely to share OCD, supporting a role for genetic vulnerability
• Weakness - counter for evidence for genetic explanations

  • concordance rates are not 100% therefore there must be other factors
  • e.g. environmental as the twins grow up in the same environment and they may observe and imitate.
• Strength - research support for the OFC

  • Menzies (2007)- compared to unrelated healthy people OCD patients + immediate relatives had reduced grey matter in key regions of the brain
  • including OFC
  • supports the view that anatomical differences are inherited and may lead to OCD.
• Strength - support for neurotransmitters

  • Pigott et al (1992)
  • Antidepressant drugs that increase serotonin activity have been seen to reduce OCD symptoms
  • suggests that serotonin may be involved in OCD
• Weakness - alternative explanations

  • As not one gene has been identified it is clear that the environment may play a part.
  • two process model is a credible alternative
  • behaviourist explanations for OCD e.g. a link between dirt and anxiety persists because compulsions such as hand-washing reduce the anxiety.
• Weakness - no unique neural system

  • Many people who experience OCD also experience depression
  • Depression likely involves disruption to the action of serotonin
  • so serotonin may not be relevant to OCD symptoms
  • it could just be disrupted due to the depression they are experiencing and NOT the OCD