the biological approach to explaining OCD

• genetic explanations: COMT gene - regulates dopamine production, less active form of COMT gene more common in OCD patients, produces higher dopamine levels.

  
  

  SERT gene - may contribute to OCD by reducing serotonin levels, mutation of this gene has been found in 2 unrelated families where 6/7 members had OCD - Ozaki.
• genetic explanation: diathesis stress - each gene only creates a vulnerability (diathesis) for OCD. Other factors eg. childhood experiences provides trigger (stress) for the condition to develop.
• neural explanations: high dopamine and low serotonin in OCD. High doses of drugs that enhance dopamine induce stereotypical movements in rats. antidepressant drugs, increase serotonin activity, reduce symptoms of OCD.
• neural explanation: orbitofrontal cortex & caudate nucleus are thought to be abnormal in people with OCD, damage to the caudate nucleus fails to supress minor 'worry' signals from OFC, creating a worry circuit. - low serotonin levels may cause malfunction in these areas - high dopamine levels lead to overactivity of basal ganglia (caudate nucleus)
• • face validity for serotonin levels. since OCD can be treated with SSRIs it makes sense that serotonin is a contributor to OCD. SSRIs encourage more serotonin to bind with post synaptic neuron.
• • alternative - two process model. eg dirt can be associated with anxiety, compulsive behaviours like handwashing negatively reinforces fear by removing anxiety caused by dirt.
• • ignores environmental factors. eg twin and family studies often live in the same environment which could be why there is a high concordance rate.
• • serotonin link to OCD may not be unique to OCD, many people also experience clinical depression co-morbidity. This depression probably involves a disruption to serotonin so serotonin may not be relevant to OCD.