A01

• Outline the two biological explanations for OCD

  1. Genetic explanations - the extent to which OCD is inherited and passed down from parents in our genes

  2. Neural (brain) explanations - the extent to which levels of neurotransmitters in the brain or malfunctioning of brain structures can lead to OCD
• What are candidate genes?

  Genes which create vulnerability for a specific disorder
• What are the two candidate genes for OCD?

  1. Allele of the COMT gene

  2. SERT gene
• How does an allele of the COMT gene lead to an increase in dopamine?

  - The allele produces less COMT, which regulates dopamine

  - This variation decreases the amount of COMT in the body which then results in increased levels of dopamine (associated with compulsive behaviour) as it is not regulated
• Explain how the SERT gene is implicated in OCD

  SERT gene affects the transport of serotonin, causing a decrease in serotonin levels
• What are two neural explanations for OCD?

  1. Influence of neurotransmitters

  2. Abnormal brain circuits - the 'worry circuit
• Outline two neurotransmitters that have been implicated in OCD

  1. Dopamine - levels are too high in people with OCD

  2. Serotonin - levels are too low in people with OCD
• Outline how serotonin is implicated in OCD

  Decreased levels lead to obsessive thoughts and anxiety
• Outline how dopamine is implicated in OCD

  Increased / excessive levels lead to compulsive behaviour
• What is the 'worry circuit'?

  - Orbitofrontal cortex (OFC) sends 'worry signals' to the thalamus

  - These are normally suppressed by the caudate nucleus

  - People with OCD tend to have a damaged caudate nucleus, which results in the thalamus being alerted and confirming the 'worry' to the OFC