Biological explanations for schizophrenia

• Genetic basis of schizophrenia - Schizophrenia runs in families

  • Weak for a genetic link - Share aspects of their environments as well as genes

  Systematic investigations:

  • Share 100% of our genes with identical twin
  • 50% with sibling or parent

  Strong relationship with degree of genetic similarity and shared risk of schizophrenia
• Genetic basis of schizophrenia - Candidate genes

  • Individual genes believed to be associated with risk of inheritance
  • Schizophrenia is polygenic - Needs a number of factors to work in combination
  • Aetiologically heterogenous - Different studies identified different candidate genes

  Ripke et al: Study combining all previous data from genome-wide studies of schizophrenia

  • 37 000 S compared to 113 000 controls - 108 genetic variations associated with higher risk of S
  • Genes with higher risk - Coding for neurotransmitters such as dopamine
• The dopamine hypothesis - Neurotransmitters

  • Work differently in the brain of a S

  Dopamine:

  • Believed to be involved
  • Important in functioning of multiple brain systems that may be implicated in symptoms of S
• The dopamine hypothesis - Hyperdopaminergia in the subcortex

  OG version of the dopamine hypothesis:

  • High levels or activity of dopamine (Hyperdomainergia) in the subcortex - Central areas of the brain
  • E.g. excess dopamine receptors in Broca's area - Associated with speech poverty and/or auditory hallucinations
• The dopamine hypothesis - Hypodopaminergia in the cortex

  • Recent version of the dopamine hypothesis
  • Focus on abnormal systems in the brains cortex

  Goldman-Rakic et al:

  • Identified low levels of dopamine (hypodopaminergia) in the prefrontal cortex - Negative symptoms of schizophrenia

  (Both high and low levels can be a reason why schizophrenia exists)
• Neural correlates of schizophrenia - Measurements of the structure or function of the brain that correlate with an experiences

  • Produce both positive and negative symptoms of schizophrenia
• Neural correlates of schizophrenia - Neural correlates of negative symptoms

  Avolition - Loss of motivation:

  • Includes anticipation of a reward
  • Certain region of the brain e.g. ventral striatum - Believed to be involved

  Juckel et al: Measured activity levels in the ventral striatum in S

  Findings:

  • Low levels of activity than controls
  • Negative correlation with activity in levels in the VS and severity of negative symptoms

  Activity in the VS is a neural correlate of negative symptoms
• Neural correlates of schizophrenia - Neural correlates of positive symptoms

  Allen et al: Scanned brains of people with auditory hallucinations and compared with control group

  Identified pre-recorded speech as theirs or others

  Findings:

  • Lower activation level in superior temporal gyrus + anterior cingulate gyrus
  • Made more errors

  Can say reduced activity in two areas of the brain is a neural correlate of auditory hallucination
• Evaluation of biological explanations for schizophrenia - Multiple sources of evidence for genetic susceptibility

  Gottesman: Shows how genetic similarity and shared risk of S are closely related

  Pekka Tienari et al:

  • Adoption studies
  • Children of S - Higher risk even if adopted into families with no history of S
  • Overwhelming amount of evident genetic factors lead to vulnerability

  HOWEVER does not mean S is genetic - Factors in environment

  Strength: Supports validity of the claim
• Evaluation of biological explanations for schizophrenia - Mixed evidence for the dopamine hypothesis

  Support for number of sources for abnormal dopamine functioning:

  • Dopamine agonists e.g. amphetamines - Increase levels
  • Radioactive labelling studies - Chemicals needed to produce dopamine are taken up faster in S brains showing they produce more dopamine

  Evidence suggesting dopamine does not provide a complete explanation:

  • Some genes code for other neurotransmitters
  • E.g. other neurotransmitter - glutamate

  Limitation: Dopamine hypothesis can be described as mixed
• Evaluation of biological explanations for schizophrenia - The correlation-causation problem

  • Questioned whether neural correlates for negative and positive S symptoms

  Other explanations for the correlation:

  • Something wrong with striatum causing negative symptoms - Possible that negative symptoms mean less info passes through the striatum leaning to reduced activity
  • Could be another factor influences both the negative symptoms and ventral striatum activity

  Limitation: Neural correlates in S tell us little in its self