Biological approach to OCD

• Genes make up chromosomes and consist of DNA which codes the physical and physioloical characteristics of an organism
• Genes are transmitted from parents to offspring, i.e. inherited
• OCD is an example of a disorder that is largely understood as biological in nature. One form of the biological explanation is the genetic explanation
• Genes are involved in individual vulnerability
• Lewis (1936) observed that 37% of patients who had OCD, also found their parents had OCD, and 21% of their siblings had OCD
• Lewis's study suggests OCD has a genetic vulnerability, but it is not the only factor, environmental factors can trigger it
• The diathesis-stress model suggests that people gain a vulnerability towards OCD through genes, but an environmental stressor is also required
• environmental stressor could be a negative life event or trauma
• genetic predisposition plus environmental stress equals mental disorder
• genes create vulnerability for OCD, called candidate genes
• SERT gene

  • responsible for the transportation of serotonin
  • serotonin regulates mood
• • variation in the SERT gene
  • impaired transmission of mood relevant information
  • low levels of serotonin
  • lowered mood in OCD patients
• COMT gene

  • responsible for regulating dopamine levels
  • COMT gene gets rid of excessive dopamine
  • dopamine is responsible for satisfaction and motivation
• • low activity of COMT gene
  • high levels of dopamine
  • associated with compulsions
• OCD is polygenic
• Polygenic- not caused by a single gene, multiple that increases vulnerability
• Taylor (2013) found up to 230 genes may be involved in OCD
• one group of genes may cause OCD in one person, but a different group of genes may cause OCD in another person
• OCD may be aetiologically heterogenous- different combinations of genes cause different types of OCD (e.g. hoarding or religious obsession)
• STRENGTH of genetic explanation

  • supporting evidence- Nestadt et al (2000) found those with a first degree relative who has OCD are 5 times more likely to have OCD
• LIMITATIONS of genetic explanation

  • environmental risk factor- Cromer et al (2007) found over half the OCD patients had a traumatic event in their past, OCD was more severe in those with more than one trauma
• A neural explanation is the view that physical and psychological characteristics are determined by the behaviour of the nervous system, in particular the brain and neurotransmitters
• serotonin is a neurotransmitter which helps to regulate mood
• Neurotransmitters are responsible for relaying information from one neuron to another
• 1. Patients with OCD have lower levels of serotonin
  2. Normal transmission of mood-relevant information does not take place
  3. Person may experience low mood
• Some cases of OCD can be explained by a reduction of the functioning of the serotonin system in the brain
• It is believed that several regions in the frontal lobe of the brain have abnormal brain circuits in patients with OCD
• Brain areas involved:

  • orbitofrontal cortex
  • Caudate nucleus
  • Thalamus
• Orbitofrontal cortex- responsible for anxiety. Send worry signals
• Caudate nucleus- Suppresses worry signals from the OFC
• Thalamus- Responsible for safety behaviours
• What happens in healthy people:

  • OFC sends a worry signal to the thalamus
  • Caudate nucleus suppresses the OFC's signal as it is a minor worry
  • Thalamus does not respond and only responds to major worries/ concerns
• STRENGTHS of the neural explanation

  • Supporting evidence- Piggot et al (1990) found drugs increase the levels of serotonin in the synaptic gap which reduces OCD symptoms
• LIMITATIONS of the neural explanation

  • unable to understand brain areas involved- other areas are occasionally involved, no brain system is consistent in all OCD patients