The Biological Approach - EXPLAINING

• genetic explanation for OCD


  - disorder is inherited; genetic analysis revealed around 230 separate 'candidate genes' found more frequently in people with OCD
• SERT gene - OCD


  - affects reuptake in the serotonin system

  - serotonin (chemical messenger) is released from the presynaptic neuron and detected by receptors on the postsynaptic neuron

  - if signal is strong enough, message is passed on, CM detaches from receptors and are taken back to presynaptic neuron (reuptake)
• what are other identified genes affecting OCD?


  - gene 9, COMT gene, 5HT1-D gene
• what is meant by polygenic?


  - as so many candidate genes have been identified, suggests that a predisposition to OCD requires a range of genetic changes
• neural explanation for OCD


  - low serotonin levels; the low level of serotonin is due to it being removed too quickly from the synapse

  - before it has been able to transmit its signal/influence the postsynaptic cell
• the 'worry circuit' - OCD


  - a set of brain structures, including the orbitofrontal cortex, the basal ganglia system (caudate nucleus, thalamus)

  - communication between these structures in the worry circuit appears to be overactive in people with OCD

  - results in obsessive thinking
• the 'worry circuit' - normal functioning


  - the basal ganglia filter out minor worries coming from the OFC, but if this area is hyperactive..

  - even small worries get to the thalamus, which is passed back to the OFC, forming a loop (recurring obsessive thoughts)
• compulsions, in link to the 'worry circuit;


  - repetitive motor functions (compulsions) are an attempt to break this loop

  - carrying out a compulsion may give temporary relief, but the hyperactive basal ganglia will soon resume the WC
• parahippocampal gyrus


  - an area of cortex close to the hippocampus, also linked to OCD

  - responsible for regulating and processing unpleasant emotions and has been seen to function abnormally in cases of OCD
• A03 - Nestadt (MZ/DZ)


  - DZ twins have 31% concordance rate, MZ twins have 68%, MZ and DZ twins grow up sharing similar environments

  - suggests additional shared DNA is responsible for increased concordance
• A03 - correlation

  - correlation in twin studies does not equal causation

  - as CR for MZ twins is 68%, there must be an environmental role as we would expect 100% for an entirely genetically determined factor
• A03 - CROMER: diathesis-stress


  - the diathesis-stress explanation combines a genetic vulnerability to OCD and environmental factor needed for the disorder to develop

  - Cromer: showed 54% of 265 people with OCD reported at least 1 traumatic life event