Biological explanations for schizophrenia

• Concordance rate in family studies for schizophrenia:

  • Both parents = 46%
  • One parent = 13%
  • Siblings = 9%
• Concordance rate in twin studies for schizophrenia:

  • MZ twins = 40%
  • DZ twins = 7%
  • Greater similarity is due to genetic factors
• In an adoption studies, 7% of adoptees with biological schizophrenia mothers were diagnosed with schizophrenia
• Dopamine hypothesis


  Positive symptoms of schizophrenia are caused by an excess of the neurotransmitter dopamine in certain areas of the brain due to increased D2 receptors
• Revised dopamine hypothesis


  Positive symptoms are caused by an excess of dopamine in sub cortical areas of the brain, the negative symptoms are caused by a deficit of dopamine in areas of the prefrontal cortex
• Biological explanations for schizophrenia:

  • Genetic factors
  • Dopamine hypothesis
  • Neural correlates: the prefontal cortex, the hippocampus, grey matter, white matter
• Neural correlates - Prefontal cortex


  Cognitive symptoms are due to deficits within the prefontal cortex (which is involved in reasoning & judgement) & its connections with other brain areas
• Neural correlates - Hippocampus


  Anatomical changes in the hippocampus in schizophrenics
• Neural correlates - Grey matter


  Schizophrenics have grey matter deficits & enlarged brain ventricles which is a consequence of nearby parts of the brain not developing properly
• Neural correlates - white matter


  schizophrenics have reduced myelination of white matter pathways. Myelination helps to conduct information properly
• Dopamine Hypothesis for explanations of schizophrenia AO3

  • Evidence from treatment - meta-analysis shows antipsychotic drugs which reduce dopamine are more effective than placebo in treatment of positive & negative symptoms
  • Challenges to dopamine hypothesis - antipsychotic drugs don't allieviate hallucinations & delusions for a third of people. Some people have halluncinatons & delusions despite normal levels of dopamine