Biological Explanation for Schizophrenia

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Concordance Rates

  • MZ twins- 48%
  • DZ twins- 17%
  • Siblings- 10%
  • This supports the genetic explanation showing that the more closely related you are, the higher your risk of also developing schizophrenia
  • The concordance rate of 17% for DZ twins is unexpected as like ordinary siblings they only share 50% of their genes, however they have a higher concordance rate than ordinary siblings (10% vs 17%)- suggests upbringing aka environmental factors may have an effect
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1. Biological Explanations

The diathesis-stress model

  • People have a genetic predisposition to schizophrenia which extreme stress can trigger
  • This supports the idea of both environmental and genetic factors having an affect on the development of schizophrenia--> abnormal brain structures
  • This view of a genetic susceptability, is supported by studies of relatives, twins and adoption cases

Studies of relatives

  • Studies have found that schizophrenia is more common among relatives of people with the disorder
  • The more closely related the relatives are to the person with schizophrenia, the greater the likelihood of developing the disorder
  • Possible environmental influences- relatives, in particular close relatives, often live within close proximity to each other, therefore offering an alternative explanation to these findings and they will be living in the same stressful environment that is created by a schizophrenic individual. This could result in relatives developing a schizoid personality (charaterised by apathy, emotional coldness, a lack of interest in social relationships and secretiveness)
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2. Biological Explanations

Adoption Studies

  • Allows researchers to rule out environmental influences
  • Similarities found between the adopted child and the biological parents would indicate biological influences
  • Similarities found between the adopted child and the adoptive parents would indicate environmental influences
  • Kety et al- Out of a sample of 5,500 apopted adults in Denmark (issues with generalisation), 33 developed schizophrenia who were then matched to 33 control subjects from the same sample. 365 biological and adoptive relatives of the 66 people were traced and interviewed.37 of these relatives were found to have schizophrenic symptoms, of which almost all were biological relatives- supports genetic explanation for schizophrenia
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The Viral Connection

  • Pre-birth exposure to the influenza A virus has been presented as a possible cause for schizophrenia
  • The 25-30 week foetus is the most vulnerable
  • Suggested that the virus lies dormant until it is activated by hormonal changes at puberty
  • High peaks in schizophrenia diagnosis have been shown to correspond with major flu epidemics occuring at the time those individuals would have been in utero
  • Could account for structural abnormalities (link) of the brain
  • Could account for higher than expected concordance rates (link) in DZ twins
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The Dopamine Hypothesis

  • Proposes that the nervous system of schizophrenics produces too much of the neurotransmitter dopamine
  • More recent research however suggests thhat there are too many D2 receptors meaning there is greater synaptic activity but normal dopamine levels

Evidence to support dopamine hypothesis

  • Schizophrenics who were administered anti psychotic medication experienced reduced symptoms but developed Parkinsonian symptoms- Parkinson's diseases is caused by abnormally low dopamine levels, suggesting the medication was lowering dopamine levels too much
  • L-dopa is a drug used to treat patients with Parkinson's disease, if the dosage is too high their will develop schizophrenic symptoms
  • Amphetamine psychosis- Amphetamines are known to increase dopamine activity, individuals who take amphetamines over a long period of time have been known to develop amphetamine psychosis, a syndrome that closely mimics schizophrenia. Antipsychotic drugs can correct an amphetamine psychosis by lowering dopamine levels again
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Abnormal Brain Structures

  • New scanning techniques have shown that many schizophrenics have enlarged ventricles- brain cavities that contain cerebrospinal fluid
  • These enlargements appear at the onset os the disorde, before treatment- not caused by anti psychotic medication
  • These patients are type 2 schizophrenic as opposed to type 1 and do not respond well to antipsychotic medication- suggests that different types of schizophrenia have different causes (type 1- dopamine levels, type 2- enlarged ventricals)
  • People with these brain abnormalities can never develop schizophrenia- suggests that it gives an individual a predisposition to schizophrenia but perhaps an environmental factor must be present to trigger it--> diathesis stress model

Suddath et al- to investgate discordant twin pairs for structural abnormalities

  • Method- 15 MZ twins where only one had schizophrenia were given MRI scans to look at brain structure
  • Results- In 14 out 15 pairs, the twin with schizophrenia had a smaller hippocampus and enlarged ventricles
  • Conclusion/evaluation- Supports brain structure hypothesis, scientific, small sample size, cause and effect issues
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