A03

• What are the strengths of the genetic explanation?

  1. Multiple sources of evidence for genetic susceptibility
  2. Role of mutation
• What are the limitations of the genetic explanation?

  1. Environmental influences
• What are the strengths of neural correlates?

  1. Evidence from brain scanning research
  2. Evidence for dopamine hypothesis from drugs
• What are the limitations of neural correlates?

  1. Correlation-causation problem
  2. Drugs are not always effective
• Strength (genetic explanation) = multiple sources of evidence for genetic susceptibility

  • Family studies - e.g. Gottesman (1991)
  • Children with 2 schizophrenic parents = concordance rate of 46%
  • Children with 1 schizophrenic parent = 13%
  • Siblings = 9%
  • Twin studies - e.g. Joseph (2004)
  • Calculated that the pooled data for all schizophrenia twin studies carried out prior to 2001 showed a concordance rate for MZ twins of 40.4% and 7.4% for DZ twins
• Strength (genetic explanation) = role of mutation

  • Has been found that schizophrenia can take place in the absence of a family history of the disorder
  • A possible explanation for this is mutation in parental DNA, this can be caused by radiation, poison or viral infection
  • Evidence has shown a positive correlation between parental age (associated with increased risk of sperm mutation) and risk of schizophrenia, increasing from around 0.7% with fathers under 25 to over 2% in fathers over 50
  • Also highlights genetic influence on schizophrenia
• Limitation (genetic explanation) = environmental influences

  • MZ twins are treated more similarly and encounter more similar environments compared to DZ twins
  • The differences in concordance rates could be nothing more than environmental differences rather than genetic differences
• Strength (neural correlates) = evidence from brain scanning research

  • Juckel et al. (2006)
  • Measured activity levels in the ventral striatum in schizophrenics and found lower levels of activity than those observed in controls
• Strength (neural correlates) = evidence for dopamine hypothesis from drugs

  • There has been successful drug treatment for schizophrenics which attempt to change levels of dopamine activity in the brain
  • (1) Drugs that increase dopaminergic activity: Amphetamines = increase levels of dopamine
  • ‘Normal‘ individuals exposed to amphetamines can develop characteristic symptoms of a schizophrenic episode, which disappear when they stop taking the drug
  • (2) Drugs that decrease dopaminergic activity: antipsychotic drugs block activity of dopamine and so eliminate symptoms e.g. hallucinations
• Limitation (neural correlates) = correlation-causation problem

  • Evidence does not show a causal relationship, only correlational
  • Not possible to confidently conclude that unusual activity in the region of the brain causes symptoms
  • E.g. the correlation between activity in the ventral striatum and negative symptoms of schizophrenia
  • Possible that negative symptoms themselves mean that less information passes through the striatum, resulting in the reduced activity
• Limitation (neural correlates) = drugs are not always effective

  • It has been argued that psychotic drugs do not alleviate hallucinations and delusions in about one third of people
  • In addition, in some people, hallucinations and delusions are present despite levels of dopamine being normal