Biological Explanations for Schizophrenia

• What are the 2 biological explanations for schizophrenia?

  - Neural

  - Genetic
• According to Irving Gottesman, if you have a parent with schizophrenia, you have a _% of developing schizophrenia


  parent = 6%
• According to Irving Gottesman, if you have a sibling with schizophrenia, you have a _% of developing schizophrenia


  sibling = 9%
• According to Irving Gottesman, if you have an identical twin with schizophrenia, you have a _% of developing schizophrenia


  identical twin = 48%
• schizophrenia is polygenic (What does this mean?)


  multiple genes are responsible for the development
• What are the most likely genes responsible for schizophrenia development?


  Those coding for neurotransmitter development, mainly dopamine
• How many genetic variations were associated with schizophrenia development as found by Ripke et al (2014)


  180 gene variations
• aetiologically heterogeneous definition


  different combinations of factors, including genetic variation, can lead to the condition
• How do we know schizophrenia is aetiologically heterogeneous?


  Different studies have identified different genes
• How may mutation occur to encourage the development of schizophrenic genes


  Radiation, Poison, Viral infection, Mieosis
• Evidence for mutation


  positive correlation between paternal age (increased risk of sperm mutation) and schizophrenia development = Brown et al 2002

  0.7% fathers under 25, over 2% fathers over 50
• Research Support (AO3) for the genetic basis of schizophrenia

  • Family studies (Gottesman) show risk increases with genetic similarity to a family member with schizophrenia
  • Adoption studies (Tienari, 2004) show biological children of parents with schizophrenia are at a heightened risk even if they grow up in an adopted family
  • Twin studies (Hilker, 2018) show concordance rates of 33% for identical twins, 7% for non-identical
• Limitation of Genetic explanation = Environmental factors

  risk factors include birth complications (Morgan et al 2017) and smoking THC-rich cannabis in teenage years (Di Forti et al 2015)

  psychological risk factors -> childhood trauma which leaves people more vulnerable to adult mental health problems in general.

  Nina Morkved(2017) = 67% of people with schizophrenia reported at least one childhood trauma, 38% with non-psychotic mental health issues
• Define 'Neural correlate' in terms of schizophrenia?

  patterns of structure or activity in the brain that occur in conjunction with schizophrenia and may be implicated in its origins
• What is the best-known neural correlate of schizophrenia?

  Dopamine (DA)
• What was the original Dopamine Hypothesis? (how it came about)

  Discovery made that drugs used to treat schizophrenia, which reduces DA, caused symptoms close to those of Parkinson’s disease, a condition of low DA levels (Seeman 1987)

  ∴ schizophrenia might be the result of high levels of DA (hyperdopaminergia) in subcortical areas of the brain. 
• How may the original dopamine hypothesis being used to explain speech Poverty/ auditory hallucinations?

  e.g. an excess of dopamine in receptors in pathways from the subcortex to Broca’s area may explain specific symptoms like speech poverty and/or auditory hallucinations. 
• What was the theory of the updated dopamine hypothesis?

  Kenneth Davies(1991)

  addition of cortical hypodopaminergia (abnormally low levels of DA in cortex).  

  Also suggested that cortical hypodopaminergia leads to subcortical hyperdopaminergia – so both high and low levels of DA in different brain regions. 
• How can the updated dopamine hypothesis explain the symptoms of shizophrenia?

  Low DA in prefrontal cortex (thinking) could explain cognitive problems, i.e. negative symptoms of the disorder. 
• AO3 in support of the neural explanation for schizophrenia =

  3 evidencestudies

  • (Curran, 2004) Amphetamines increase DA, they worsen symptoms in people with schizophrenia and induce symptoms in people without.
  • (Tauscher, 2024) Antipsychotic drugs reduce DA activity and reduce the intensity of symptoms
  • (Tenn, 2003) induced schizophrenia-like symptoms in rats using amphetamines and then relieved symptoms using DA-reducing drugs. 
• What is the AO3 limitation of the explanation of neural correlates for schizophrenia?

  evidence for the central role of glutamate

  • Post-modern and live scanning studies have consistently found raised levels of the neurotransmitter glutamate in several brain regions of people with schizophrenia (McCutcheon et al 2020).
  • Also, several candidate genes for schizophrenia are involved in glutamate production and processing.