Biological Approach to Explaining OCD

• OCD= an anxiety disorder where anxiety arises from both obsessions (persistent internal thoughts) and compulsions (external behaviours that are repeated over again).
• Compulsions are a response to the obsessions, and the person believes the compulsions will reduce anxiety.
• The genetic explanation of OCD suggests that a person inherits the gene from their parents which are related to the onset of OCD.
• Researchers have identified some specific genes which create vulnerability for OCD- known as candidate genes.
• The SERT Gene:

  • These genes are involved in regulating transportation within the serotonin system (lower serotonin= increased chance of OCD).
  • Serotonin= a neurotransmitter associated with feelings of well-being, calm & happiness.
  • Eg, Ozaki et al (2003) found a mutation of SERT gene in 2 unrelated families, where 6 of the 7 family members had OCD.
• The COMT Gene:

  • This gene is involved in the production of dopamine, altering the COMT enzyme and thus creating excess amounts of dopamine in the nervous system.
  • Dopamine= a neurotransmitter associated with motivation & drive- it is part of our 'reward circuit'.
  • Eg, Tukel et al (2013) found one form of the COMT gene to be more prevalent in OCD patients versus healthy controls.
• Diathesis Stress Model:

  • It's unlikely that just because you have a gene linked to OCD, you will automatically develop the disorder.
  • It is more likely that genetic makeup creates a vulnerability (diathesis), and other factors such as life stressors, affect whether the condition actually develops.
  • Indicates genetics & environment interact (nature nurture).
• Genetic Explanations Evaluation- Strength:

  • Good supporting evidence for the role of genetics.
  • Nestadt et al- twin studies showed a genetic influence of OCD.
  • 68% identical twins shared OCD compared to just 31% of non- identical twins.
  • However, these concordance rates (chance both people have the disorder) are never 100%, which indicates that there must also be environmental factors.
• Genetic Explanations Evaluation- Weakness:

  • OCD is polygenic.
  • Neither the SERT gene or the COMT gene are solely responsible for the development of OCD.
  • OCD is thought to be explained by several genes rather than a single one.
  • Eg, Taylor (2013) analysed findings of previous studies & found evidence that up to 230 genes are involved in OCD- this weakens the theory overall.
• Neural Explanations:

  • The neural explanation of OCD suggests that if a person has abnormal levels of certain neurotransmitters or faulty brain circuits then they are likely to develop OCD.
• Abnormal levels of neurotransmitters:

  • Serotonin helps to regulate mood and normal levels are associated with feelings of well-being & happiness.
  • If a person has low levels of serotonin, then normal transmission of mood relevant information does not take place & mood is affected.
• Abnormal levels of neurotransmitters:

  • OCD may be explained through a reduction in the functioning of the serotonin system in the brain.
  • Dopamine is linked to motivation, drive & reward.
  • Higher levels of dopamine than normal are associated with OCD.
  • This is particularly the case with compulsive behaviours which may be 'driven' by abnormal dopamine levels.
• Abnormal Brain Circuits:

  • Two brain regions have been implicated in OCD, including the basal ganglia and orbitofrontal cortex.
• Abnormal Brain Circuits:

  • Basal ganglia- brain structure involved in multiple processes including the coordination of movement.
  • Patients who suffer head injuries in this region often develop OCD-like symptoms following their recovery.
• Abnormal Brain Circuits:

  • Orbitofrontal cortex- a brain region which converts sensory information into thoughts & actions.
  • One suggestion is that the heightened activity in the orbitofrontal cortex increases the conversion of sensory information to actions (behaviours) which results in compulsions.
  • The increased activity also prevents patients from stopping their behaviours.
• Neural Explanations Evaluation- Strength:

  • Has good supporting evidence- treatments affecting neurotransmitters.
  • Antidepressants that increase activity of the serotonin system are effective in reducing OCD symptoms (Pigott et al, 1990).
  • This suggests the serotonin system is involved in OCD, as well as providing support for treatment.
• Neural Explanations Evaluation- Strength:

  • Good supporting evidence of Orbitofrontal cortex.
  • PET scans of the brains of OCD patients show increased activity in the Orbitofrontal cortex when their symptoms are active (eg a person who is germ obsessed is asked to hold a dirty cloth).