Biological explanations of schizophrenia

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  • Created by: Natalie
  • Created on: 17-10-13 13:43
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  • Biological Explanations
    • Genetic factors
      • Schizophrenia more common among biological relatives of person with schizophrenia (Gottesman, 1991).
      • Twin studies - Joseph (2000) pooled data shows concordance rate for MZ twins of 40% and DZ twins 7%.
        • Differences in concordance rates may reflect environmental similarity rather than role of genetic factors.
          • Environments of MZ twins may be more similar than for DZ twins.
        • Use of 'blind' diagnoses produces lower concordance rate for MZ twins, but still much higher than DZ.
      • Adoption study by Tienari et al. (2000) - if biological mother schizophrenic, 6.7% of adoptees also schizophrenic (2% of controls).
        • Schizophrenia more common among biological relatives of person with schizophrenia (Gottesman, 1991).
        • Adopted children from schizophrenic backgrounds may be adopted by particular type of adoptive parent, making conclusions difficult to draw.
    • Dopamine hypothesis
      • Neurons that transmit dopamine fire too easily or too often, leading to symptoms of schizophrenia.
      • Schizophrenics - abnormally high levels of D2 receptors.
      • Evidence from large doses of amphetamines (dopamine agonist) causes hallucinations and delusions.
      • Anti-psychotic drugs - block dopamine and eliminate symptoms.
      • Parkinson's disease - treatment with l-dopa raises dopamine levels and can therefore also trigger schizophrenia symptoms.
      • Drugs can increase schizophrenic symptoms as neurons try to compensate. Haracz (1982) found elevated dopamine levels in post-mortems of schizophrenics who had taken medication.
      • Neuroimaging studies failed to provide convincing evidence for altered dopamine activity in schizophrenics.
    • Enlarged ventricles
      • Ventricles of person with schizophrenia 15% bigger than non-schizophrenic.
      • Display negative rather than positive symptoms.
      • May be result of poor brain development or tissue damage.
      • Meta-analysis found substantial overlap in ventricle size among schizophrenic and control populations.
      • Enlarged ventricles may be due to effects of anti-psychotic medication.


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