the biological approach to explaining OCD

• what does the COMT gene do?

  regulates dopamine production
• what does the COMT gene contribute to?

  OCD
• what is a less active level of the COMT gene common with?

  OCD patients & produces higher dopamine levels
• how does the SERT gene contribute to OCD?

  by reducing serotonin levels
• what did Ozaki et al. 2003 find about the SERT gene?


  A mutation of this gene has been found in two unrelated families where 6/7 members had OCD
• what is diathesis-stress?

  each gene only creates a vulnerability (a diathesis) for OCD. Other factors, such as childhood experience, provide the trigger (stress) for the condition to develop
• what are the 3 genetic explanations of OCD?

  • the COMT gene
  • the SERT gene
  • Diathesis-stress
• what are the neural explanations for explaining OCD?

  • dopamine levels
  • serotonin levels
  • The orbitofrontal cortex (OFC)
• What levels of dopamine & serotonin are associated with OCD

  • dopamine = high levels
  • serotonin = low levels
• what do high doses drugs that enhance dopamine induce?

  stereotypical movements in rats
• what do antidepressants do?

  • increase serotonin activity
  • reduce the symptoms of OCD
• what 2 things are thought to be abnormal in OCD patients?

  • The orbitofrontal cortex (OFC) of the frontal lobes
  • The caudate nucleus (part of the basal ganglia)
• what can damage to the caudate nucleus lead to?

  fails to suppress minor 'worry' signals from the OFC, creating a worry circuit
• what do low serotonin levels cause


  the malfunction of these structures
• what is dopamine in relation to the basal ganglia?

  the basal gangia's main neurotransmitter, so high dopamine levels lead to overactivity of this region
• The worry circuit

  Label

  A) Thalamus

  B) Orbitofrontal cortex

  C) Caudate nucleus

  D) basal ganglia

  E) putamen & globus pallidus

  
• A03: Research support for genes and the role of the OFC...

  • Menzies et al. (2007) used MRI to produce images of brain activity in OCD patients and their immediate family members without OCD
  • OCD patients and they close relatives had reduced grey matter in key regions of the brain, inducing the OFC
  • This supports the view that inherited anatomical differences may lead to OCD in certain individuals. in the future, brain scans may be used to detect OCD
• A03: Evidence for the genetic basis of OCD comes from family & twin studies...

  • Nestadt et al. (2000) found that people with a first-degree relative with OCD had a 5x greater lifetime risk of OCD themselves, compared to risk levels in general population
  • A meta-analysis found that identical MZ twins were more than twice as likely develop OCD if their twin had the disorder than non-identical Dz twins (Billett et al. 1998)
  • This evidence supports a genetic basis for OCD, but the concordance rates are never 100% so environmental factors must also play a role
• What disorders are suggested to have genetic links to OCD?

  Tourette's and autism
• How is OCD related to Tourette's syndrome according to Pauls and Leckman (1986)?

  OCD is a form of expression of the same gene
• What type of behavior is found in children with autism related to OCD?

  Obsessional and compulsive behavior
• What does the research suggest about the uniqueness of genes for OCD?

  There are no specific genes unique to OCD
• What role do genes play in relation to obsessive-type behavior according to the study material?

  They act as a predisposing factor
• What are the implications of the genetic links to OCD?

  • OCD may express genes linked to other disorders
  • It is characteristic of multiple disorders
  • Supports the idea of shared genetic factors