Biological Explanation

• Diathesis stress

  • genetic vulnerability to develop forms of the COMT and SERT gene
  • Individuals inherit genes from their parents that are related to OCD
  • Lewis found that from his patients, 37% had parents with OCD and 21% with siblings
  • It is unlikely that either gene causes the disorder - polygenic
• COMT

  • higher dopamine levels
  • it regulates the production of the neurotransmitter dopamine
  • all genes come in different forms and one form of the COMT gene has been found to be more common in OCD patients than people without the disorder
  • this variation produces lower activity of the COMT gene and higher levels of dopamine
• SERT

  • lower levels of serotonin
  • it affects the efficiency of transport of serotonin, creating lower levels of it
  • Ozaki et al (2003) found amutation of this gene in two unrelated families where 6/7 family members had OCD
• Neural Explanations

  • behaviour of the nervous system and the brain
  • synaptic transmission is the process by which one neuron communicated with the other
  • e.g. serotonin and dopamine diffuse from one neuron to the next to travel around the body
• Abnormal Levels of Neurotransmitters

  • dopamine levels are supposed to be abnormally high in people with OCD
  • this is based on animal studies
  • lower levels of serotonin are associated with OCD
  • antidepressant drugs have been shown to reduce OCD symptoms (Pigott, 1990) whereas antidepressants that have less effect on serotonin do not (Jenicke, 1992)
• Which brain lobes are thought to be abnormal in OCD?

  Frontal lobes
• What brain area is associated with high activity in OCD?

  Orbital frontal cortex
• What does the orbital frontal cortex convert?

  Sensory information into thought
• What does the orbital frontal cortex signal to the thalamus?

  Worrying thoughts
• What happens when the thalamus receives signals from the orbital frontal cortex?

  It leads to an impulse to act
• What is the role of the caudate nucleus in OCD?

  It suppresses worry signals
• What issue do individuals with OCD face regarding impulses?

  Difficulty switching off or ignoring impulses
• What happens when the caudate nucleus fails to suppress signals?

  The thalamus is alerted
• What does the thalamus do after being alerted?

  It sends signals back to the OFC
• What do PET scans reveal about patients with OCD?

  Heightened activity in the OFC
• Which neurotransmitter is linked to OCD and the caudate nuclei?

  Serotonin
• What did Corner (1998) report about serotonin's role in OCD?

  It plays a key role in OCD operation
• What may cause malfunction in the caudate nuclei?

  Abnormal levels of serotonin
• What is dopamine's role in the brain related to OCD?

  It is the main neurotransmitter of basal ganglia
• What effect do higher levels of dopamine have on the basal ganglia?

  They lead to overactivity of this region
• What are the key components of the abnormal brain circuits in OCD?

  • Abnormal areas in frontal lobes
  • High activity in orbital frontal cortex
  • Signals sent to thalamus about worries
  • Caudate nucleus suppresses signals
  • Thalamus alerts when signals are not suppressed
  • Heightened activity in OFC shown by PET scans
  • Serotonin and dopamine linked to these regions
• Evidence to Support Genetic Explanation

  • Nestadt (2000) identified 80 patients with OCD and 343 of their first degree relatives
  • he compared them with 73 control patients without mental illness and 300 of their first-degree relatives
  • they found that poeple with a first-degree relative with OCD had a 5 times greater risk of having the illness themselces at some opint in their life, compared to the general population
  • a meta-analysis of 14 twin studies found that on average MZ twins were more than twice as likely to develop OCD if their twin had the disorder, than was the case for DZ twins