Biological Explanations SZ AO1

• what does the genetic explanation suggest about SZ?

  • Evidence suggests that the closer the biological relationship, the greater the risk of developing schizophrenia. 
  • For example, you will have a greater risk if both your biological parents have schizophrenia compared with just one of them having it. 
• how is SZ polygenetic?

  • There isn’t one single gene that seems to be responsible, but a number of genes. 
  • For example, COMT, DRD4 , AKT1 - have all been associated with excess dopamine in specific D2 receptors, leading to positive symptoms, including delusions and hallucinations.
• what do twin studies suggest about SZ?

  • Twin studies have also been done to look at the concordance rates of developing schizophrenia. 
  • As MZ twins share 100% of their genetics, whereas DZ twins share only 50%, we would expect that if one MZ twin develops schizophrenia there will be a stronger likelihood the other twin will, compared with if one DZ twin develops schizophrenia
  • useful as you can isolated nature and nurture in MZ twin studies
• what are assumptions of the biological explanation?

  • all mental disorders have a physical cause - micro-organisms, genetics, biochemistry or neuroanatomy
  • mental illnesses can be described in terms of clusters of symptoms
  • symptoms can be identified, leading to diagnosis of an illness
  • diagnosis leads to appropriate physical treatments
• what did Gottesman and Shields do?

  • reviewed 5 studies looking for concordance rates of SZ
  • 210 MZ twins and 319 DZ twins
  • found strong concordance rates - MZ - 48% risk, DZ - 17% risk
  • compared to general population of 1 % - supports a biological view as prevalence doesn't vary with environment - nature
• what is the neural correlates explanation?

  • refers to brain structure and how this may explain schizophrenia.
  • Dopamine is a neurotransmitter and the original dopamine hypothesis stated that schizophrenics suffered from an excessive amount of dopamine.
  • This causes the neurons that use dopamine to fire too often and transmit too many messages.
  • The symptoms this can then cause include positive symptoms, such a delusions, hallucinations and psychomotor disturbances.
• what does a more recent dopamine hypothesis suggest?

  A more recent dopamine explanation suggests that it is not excessive dopamine but that there are more dopamine receptors. More receptors lead to more firing and an over production of messages.
• what is hyperdopaminegia?

  • Excessive levels of dopamine in the Subcortex & Broca’s Area
• what is hypodopaminergia?

  • Low levels of dopamine in the prefrontal cortex
• where did the dopamine hypothesis come from?

  • The hypothesis is based principally on the knowledge that antipsychotic drugs reduce dopamine activity.
  • Antipsychotic drugs can cause side effects similar to Parkinson’s disease, a disease that is known to be caused by low levels of dopamine in the brain
• what is an antagonist?

  a substance that depresses the effects of an agonist
• what is an agonist?

  a substance which initiates a physiological response when combined with a receptor
• what is the Grilly 2002 study?

  • Individuals with Parkinson’s disease suffer from low levels of dopamine.
  • They were prescribed L-Dopa (the precursor to dopamine) to raise dopamine in the brain.
  • Some individuals went on to develop schizophrenia-like symptoms
• what are amphetamines?

  • Drugs that act as a dopamine agonist.
  • Synapses get flooded with dopamine.
  • Large doses can cause hallucinations and delusions.
  • Can exacerbate the symptoms of schizophrenia in individuals with the disorder.
  • shows why there's a high comorbidity between SZ and substance abuse
• what does Gottesman and Shields graph suggest?

  • a correlation between number of shared genes and risk of developing schizophrenia
  • MZ twins 100% genes - 48% - most at risk, whereas general population - 1%
  • risk increases with number of shared genes
  • strong empirical evidence for genetics driving SZ
• what does the most recent dopamine hypothesis suggest?

  • that there is too much dopamine in subcortex - hyperdopaminegia
  • there is a deficit of dopamine in cortex - hypodopaminegia