biological explanations for schizophrenia

• Genes

  Consist of DNA strands
• DNA

  • Produces instructions for general physical features of an organism (such as eye colour, height)
  • Produces instructions for specific physical features (such as neurotransmitter levels and size of brain structures)
  • May impact on psychological features (such as intelligence and mental disorder)
• Inheritance

  Genes are transmitted from parents to offspring
• Neural correlates

  Patterns of structure or activity in the brain that occur in conjunction with an experience and may be implicated in the origins of that experience
• Dopamine

  • A neurotransmitter that generally has an excitatory effect and is linked to the sensation of pleasure
  • Unusually high levels are associated with schizophrenia
  • Unusually low levels are associated with Parkinson's disease
• The genetic basis of schizophrenia - family studies

  • Gottesman - large scale family study
  • the risk of schizophrenia increases in line with genetic similarity
  • BUT family members tend to share aspects of their environment as well as many of their genes

  A) 48%

  B) 2%

  
• the genetic basis of schizophrenia - candidate genes

  • schizophrenia is polygenic
  • Ripke - combined all previous data from genome-wide studies of schizophrenia
  • genetic make-up of 37,000 people with a diagnosis of schizophrenia was compared to 113,000 controls - 108 separate genetic variations were associated with risk of schizophrenia
  • different studies have identified different candidate genes - schizophrenia is aetiologically heterogeneous
• aetiologically heterogeneous

  different combinations of factors including genetic variation can lead to condition
• the genetic basis of schizophrenia - the role of mutation

  • mutation in parental DNA which can be caused by radiation, poison or viral infection
  • evidence for mutation comes from positive correlations between paternal age and risk of schizophrenia
  • fathers under 25 - 0.7%
  • fathers over 50 - over 2%
• AO3- genetic basis of schizophrenia - limitation

  P: clear evidence to show that environmental factors also increase the risk of developing schizophrenia

  E: These environmental factors include birth complications and smoking cannabis in teenage years

  psychological risk factors include childhood trauma which leaves people more vulnerable to adult mental health problems

  E: Morkved - 67% of people with schizophrenia and related psychotic disorders reported at least one childhood trauma

  L: genetic factors alone cannot provide a complete explanation for schizophrenia
• AO3 - genetic basis of schizophrenia - strength

  P: supporting evidence from twin studies

  E: Joseph - calculated that pooled data for all schizophrenia twin studies showed concordance rate for MZ twins of 40.4% and 7.4% for DZ twins

  E: strong evidence - MZ twins share 100% rather than 50% DNA as environments are the same.

  L: strongly suggests genes can account for the increased concordance rate in schizophrenia
• neural correlates of schizophrenia - the original dopamine hypothesis

  • drugs used to treat schizophrenia caused symptoms similar to those in people with Parkinson's disease a condition associated with low dopamine levels
  • schizophrenia results from high levels of dopamine in subcortical areas of the brain
  • excess of dopamine receptors in pathways from the subcortex to Broca's area may explain specific symptoms- poverty of speech
• neural correlates of schizophrenia - new dopamine hypothesis

  • Davis - abnormally low dopamine in the brain's cortex - could explain symptoms of schizophrenia
  • low dopamine in prefrontal cortex could explain cognitive problems
  • abnormally low levels of dopamine in cortex lead to high levels of dopamine in subcortex
  • genetic variations and early experiences of stress make people more sensitive to low dopamine levels in cortex
• AO3 - neural correlates of schizophrenia - strength

  P: support for the idea that dopamine is involved in schizophrenia

  E: amphetamines increase dopamine and worsen symptoms in people with schizophrenia

  antipsychotic drugs reduce dopamine activity and reduce intensity of symptoms

  some candidate genes act on the production of dopamine

  L: suggests that dopamine is involved in the symptoms of schizophrenia
• AO3 - neural correlates of schizophrenia - limitation

  P: evidence for a central role of glutamate

  E: post-mortem and live scanning studies have consistently found raised levels of the neurotransmitter glutamate in several brain regions of people with schizophrenia - candidate genes for schizophrenia are believed to be involved in glutamate production

  L: an equally strong case can be made for a role for other neurotransmitters