Biological Explanations Of Schizophrenia

• Biological explanations of schizophrenia

  •Biological explanations emphasise the role of inherited factors and dysfunction of brain activity in the development of schizophrenia.•Most modern psychologists believe that schizophrenia is at least partly biological.
• •There are three main biological explanations:–Genetics–The dopamine hypothesis (role of neurotransmitters)–Neural correlates
• Explanation 1: genetics

  •These are the results of Gottesman’s (1991) large-scale family study.•There is considerable evidence that schizophrenia runs in families and is in part genetic (inherited as genes are transmitted from parent to child).•Gottesman (1991) conducted a large-scale family and found much higher concordance rates in MZ twins (48%) in comparison to DZ twins (17%).
• Explanation 1: Genetics

  •Schizophrenia is thought to be polygenic (it requires a number of different factors to work in combination) and so different combinations of genes can lead to the condition. Research suggests that there are 108 genetic variations associated with increased risk of schizophrenia.
• Dopamine hypothesis


  Explanation for schizophrenia
• Brain's chemical messengers (neurotransmitters)


  • Work differently in the brain of a patient with schizophrenia
• Dopamine


  A neurotransmitter that generally has an excitatory effect and is associated with the sensation of pleasure
• Unusually high levels of dopamine


  Associated with schizophrenia, particularly the positive symptoms
• Dopamine transmission in schizophrenia

  1. Messages from neurons that transmit dopamine fire too easily or too often

  2. Schizophrenics have abnormally high levels of D2 receptors on post-synaptic neurons

  3. More dopamine binding and therefore more neurons firing
• Abnormal dopamine transmission

  Leads to hallucinations and delusions
• Revised dopamine hypothesis

  Proposed by Davis and Khan (1991)
• Revised dopamine hypothesis

  • Positive symptoms of schizophrenia are caused by higher levels or activity of dopamine in the subcortex (central areas of the brain)
  • Negative symptoms of schizophrenia are thought to arise from lower levels of dopamine in the pre-frontal cortex
  • Both high and low levels of dopamine in different brain regions may be involved in schizophrenia
• Positive symptoms of schizophrenia

  • Speech poverty
  • Auditory hallucinations
• An excess of dopamine receptors in Broca's area may be associated with speech poverty and/or auditory hallucinations
• Neural correlates


  Measurements of the structure or function of the brain that occur in conjunction with (correlate with) the characteristic symptoms of schizophrenia, and so may be implicated in the origins of schizophrenia
• Neural correlates

  • Of positive symptoms
  • Of negative symptoms
• Lower activation levels in the superior temporal gyrus and anterior cingulate gyrus


  Found in those experiencing auditory hallucinations
• Reduced activity in the superior temporal gyrus and anterior cingulate gyrus is a neural correlate of auditory hallucinations (positive symptom)
• Neural correlates of negative symptoms

  •The ventral striatum is thought to be involved in the anticipation of reward.•Avolition involves the loss of motivation.•Juckel et al. (2006) found a negative correlation between activity levels in the ventral striatum and the severity of overall negative symptoms.•Therefore, activity in the ventral striatum is a neural correlate of the negative symptoms of schizophrenia.