The Biological approach to explaining OCD

• What is thought to be the main cause of OCD in a neural explanation?

  • Abnormalities in the frontal lobe
  • Frontal lobe = logical thinking + decision-making
• What is the worry circuit?

  • Abnormalities in OFC (orbitofrontal cortext) + caudate nucleus (part of basal ganglia) = these parts of brain fail to suppress worry signals
  • OFC = stops initial unnecessary worry signals
  • Caudate nucleus stops unnecessary worry signals that got past OFC
  • = more worry signals sent to thalamus than needed = increased worry signals sent back to OFC = worry circuit
  • Worry circuit = feedback loop of escalating anxiety -> provokes desire to perform actions to address anxiety
• What do the provoked actions resulting from the worry circuit explain in OCD?

  • Obsessions
  • Compulsions
• What could be causing the failure to suppress worry signals by the OCF + caudate nucleus?

  • An imbalance in NTs resulting from variations in genes (e.g. COMT + SERT)
  • OCD usually means less serotonin than no OCD = neurons fire more frequently = more worry signals passed on than should be
  • OCD usually means more dopamine too = more nerve impulses (signalling need for action) fire = increased compulsion to perform repetitive tasks
• What do genetic explanations for OCD say to explain it?

  • There is an innate predisposition towards OCD inherited from parents through genes
  • This innate predisposition is polygenic -> (up to) 230-gene combination (Taylor 2013)
• What are the 2 main examples of gene variations that increase chances of developing OCD?

  • COMT gene variation
  • Low activity
  • SERT gene variation
  • High activity
• What is the SERT gene?

  • 5-HTT
  • Involved in production of protein that helps transport serotonin from synaptic gap back into presynaptic neuron
• What is the SERT gene variant?

  • High activity variant of SERT gene (5-HTI-D) = found more commonly in people with OCD than those without OCD
  • Variant produces more of the protein that aids the reuptake of serotonin = less serotonin in synapse overall
  • People with this gene have less serotonin available in synapses during synaptic transmission
  • This contributes to failure of OFC + caudate nucleus to suppress worry signals
• What is the COMT gene?

  • Helps regulate production of dopamine through production of COMT enzyme (catechol-0-methyltransferase)
• What is the COMT gene variant?

  • Low activity COMT gene -> found more frequently in people with OCD than those without OCD
  • Produces less COMT enzyme = less effective at regulating dopamine (ineffective at ensuring only enough is produced)
  • = higher levels of dopamine -> dopamine = excitatory NT = neurons fire more often in basal ganglia = overactivity
  • = more nerve impulses signalling need for action -> linked to compulsions
• Neural explanations for OCD A&E point: research support that atypical brain function is present in those with OCD

  • Ursu + Carter (2009) -> used fMRI to find evidence of hyperactivity in OFC of 15 people with OCD (small sample size tho)
  • Further supported by Saxena + Rauch (2000) -> meta-analysis using PET, fMRI + MRI scans to find consistent evidence of association between OFC + OCD symptoms
  • Neural explanations cannot be dismissed!! -> clear correlations between abnormal brain activity + obsessions/compulsions seen in people with OCD
• Genetic explanations for OCD A&E point 1: research support for genetic element to developing OCD

  • Nedstadt et al. (2000) -> 1st degree relatives of people with OCD had an 11.7% chance of developing OCD, but people with no 1st degree relatives with OCD had a 2.7% chance of developing it
  • 1st degree relatives share 50% of your genes -> 9% increase in chances of developing OCD if you have a 1st degree relative with OCD strongly suggests OCD is heritable
• Genetic explanations for OCD A&E point 2: further research support for genetic element to developing OCD

  • Twin studies -> Nedstadt et al. (2010) meta-analysis of twin studies = 68% concordance rate in MZ twins but only 31% in DZ twins
  • MZ twins = 100% shared DNA, DZ twins = 50% shared DNA
  • Increased concordance rates in MZ twins = both of them will have same gene variation linked to OCD
  • If environmental factors were causing OCD, concordance rates between MZ + DZ twins would be much more similar
• Genetic explanations for OCD A&E point 3: the biological approach to explaining OCD is insufficient

  • Nedstadt et al.'s (2010) meta-analysis of twin studies -> environmental factors contributing to the development of OCD
  • If OCD = solely genetic, there would be 100% concordance rates between MZ twins -> if all DNA is shared, they would both have OCD
  • There must be environmental factors that trigger OCD's development that either both or only one twin would experience -> need for an environmental trigger to initiate onset of OCD explains concordance rates being high but not 100%