Biological Explanation of Schizophrenia

• Genes


  Consist of DNA strands. DNA produces 'instructions' for general physical features of an organism such as eye colour.
• Dopamine


  A neurotransmitter that generally has an excitatory effect and is associated with pleasure. High levels are associated with schizophrenia
• Neural correlates


  Patterns of structure or activity in the brain that occur when symptoms are experienced
• Genetic Basis of Schizophrenia

  • Schizophrenia runs in families
  • There is quite weak evidence to suggest a genetic link as family members tend to share aspects of the same environment as well as genes
  • There is a strong relationship between genetic similarity and shared risk of schizophrenia
• Twin studies

  • Twin studies have identified strong concordance rates
  • Monozygotic twins have a 48% concordance rate
  • Dizygotic twins have a 17% concordance rate
• Candidate genes

  • Schizophrenia is polygenic meaning a number of different genes are involved
  • Different studies have identified different genes (aetiologically heterogenous) so it may be caused by a number of different genes
  • A meta analysis of genome wide studies and found 108 separate genetic combinations were identified as increasing risk
• The role of mutation

  • Schizophrenia can also have a genetic origin in the absence of a family history of the disorder
  • One explanation for this is 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
• Dopamine hypothesis

  • The brain's chemical messengers appear to work differently in the brain of a person with schizo
  • Dopamine is said to be involved
  • Dopamine is important in the functioning of several brain systems that may be implicated in the symptoms of schizophrenia
• Hyperdopaminergia in the subcortex

  • High levels of dopamine
  • An excess of dopamine in Broca's area (responsible for speech and language) may result in speech poverty or speech or auditory hallucinations
• Hypodopaminergia in the subcortex

  • Low levels of dopamine
  • Low levels of dopamine in the pre frontal cortex (thinking and decision making) are linked with negative symptoms of schizophrenia
• Neural correlates of negative symptoms

  • One negative symptom avolition involves the loss of motivation
  • Motivation involved the anticipation of a reward
  • The ventral striatum is involved in anticipation and any abnormality in this area could lead to avolition
  • Negative correlation was observed between activity levels in ventral striatum and the severity of negative symptoms
• Neural correlates of positive symptoms

  • People with auditory hallucinations had their brains scanned and were compared to control group whilst they identified pre recorded speech as their own or others
  • Lower activation levels in the superior temporal gyrus and anterior cingulate gyrus were found in the hallucination group who also made more errors than the control group
  • Reduced activity in these 2 areas is a neural correlate of auditory hallucinations
• AO3 Genetic basis: Research Support

  • Genetic similarity and shared risk of schizo are strongly related
  • Adoption studies show how children of people with schizo are at a heightened risk of developing schizo if adopted into a family with no history of schizo
  • Genetic factors are important but are not the sole explanation of schizo
• AO3 Genetic Basis: Mixed Evidence for dopamine hypothesis

  • Amphetamines increase dopamine making schizo worse
  • Anti-psychotic drugs work by reducing dopamine activity
  • Dopamine does not provide the full picture for schizo and is only one important neurotransmitter involved
• AO3 Genetic Basis: Genetic Counselling

  • One application of our understanding of the likely role of genes in schizo is genetic counselling
  • If one or more potential parents have a relative with schizo they risk having a child with schizo
  • The risk estimate provided by genetic counselling is just an average figure
  • Does not really reflect the probability of a child developing schizo and environment plays a part
• AO3 Correlates: Correlation-causation problem

  • The studies on this flag up specific brain systems not working normally
  • But does the unusual brain activity cause the symptom
  • We do not know if the unusual brain activity is causing the symptom or if the symptom causes the unusual brain activity
  • There may be a third factor that influences both
• AO3 Biological Explanation: Environment

  • Biology is not the sole thing involved in the formation of schizo
  • Family functioning during childhood plays a part also
  • Developing schizo when your identical twin has it is still under 50% meaning another 50% of other factors are involved in schizo