The biological approach to explaining OCD

• Genetic explanation

  COMT Gene

  • COMT regulates the production of the neurotransmitter dopamine which has been implicated in OCD

  • One form of the COMT gene has been found to be more common in OCD patients

  • This variation produces lower activity of the COMT gene and higher levels of dopamine
• Genetic explanation

  SERT Gene

  • Also known as 5-HTT

  • Affects the transport of serotonin, creating lower levels of this neurotransmitter

  • A mutation of this gene has been found in two unrelated families where six of the seven members had OCD (Ozaki et al)
• Neural explanation for OCD

  Abnormal levels of neurotransmitters
• High dopamine levels and OCD


  • High doses of drugs that enhance levels of dopamine induced stereotyped movements resembling the compulsive behaviours found in OCD
• Lower levels of serotonin associated with OCD


  • Antidepressant drugs that increase serotonin activity have been shown to reduce OCD symptoms, whereas antidepressants that have less effect on serotonin do not reduce OCD symptoms
  • Serotonin also plays role in operation of OFC and CN (Comer)
• Abnormal brain circuits in OCD


  • Several areas in the frontal lobes of the brain are thought to be abnormal in people with OCD
  • The orbitofrontal cortex (OFC) sends worry signals to thalamus – if caudate nucleus is damaged these signals not suppressed – thalamus is alerted & sends signals back to OFC (worry circuit)
  • PET scans show a heightened activity in the OFC for OCD patients when their symptoms are active