Biological explanations of schizophrenia

psychology aqa a A2 unit 4

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  • Created by: lauren
  • Created on: 14-06-12 10:31

Genetic factors

Family studies - Gottesman - show that schizophrenia is more common among biological relatives of a person than in the general population - the greater the degree of genetic relatedness, the greater the risk - children with two schizophrenic parents have a 46% risk of developing **** whilst with one schizophrenic parent a 13% risk and with a schiz sibling 9%

Problem for genetic explanations of schiz is that heritable traits that are maladaptive would be selected out during natural selection, so schiz would no longer exist - Stevens and Price - among our distant ancestors auditory hallucinations etc could have influenced the other group members to follow them and form a new group - grou-splitting hypothesis argues that schiz is an extreme expression of an adaptive trait

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Genetic factors

Twin studies - If MZ twins are more similar in terms of schiz than DZ twins this suggests a strong genetic influence for the disorder - meta-analysis of twin studies prior to 2001 - Joseph - found concordance rate of just over 40% for MZ twins and just over 7% for DZ twins - recent studies found lower concordance rates for MZ twins - meta-analysis - good size sample, low ethics however can introduce the file drawer effect (only choosing studies that benefit the hypothesis), studies that are being compared might not have the same methodology which could affect the accuracy and reliability of results

assumed that the greater concordance rate between MZ twins compared to DZ twins is the consequence of genetic similarity rather than greater environmental similarity for MZ's but joseph points out that MZ twins tend to be treated more similarly and experience more identity confusion - so there is reason to believe that differences in concordance rates for MZ and DZ twins reflect nothing more than the environmental differences that distinguish the two types of twin

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Genetic factors

Adoption studies - these studies are valuable because it is difficult to disentangle genetic and environmental influences for those who share genes and the environment - Tienari - found that for adoptees whose biological mothers had schiz 6.7% of these individuals also developed the disorder - 2% developed disorder born to non-schiz mothers

Assumption is that parents who adopt a child with schiz biological parent are no different from other adoptive parents - but its unlikley as adoptive parents are usually informed of the genetic background of potential adoptees prior to making a decision whether to adopt

Most adoption studies have only found differences between children born to schiz and non schiz biological parents by broadening the definition to include non-psychotic schiz spectrum disorder rather than restrciting it to full-blown schiz - so results may not reflect just the disorder itself

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The dopamine hypothesis

Neurons that transmit dopamine fire too easily or too often leading to the symptoms of schiz - schizophrenics have abnormally high numbers of D2 receptors, resulting in more dopamine neurons firing - dopamine neurons play a key role in guiding attention - disturbances in this process might lead to problems of perception and thought found in schiz

Psychologicsl factors such as expressed emotion influence the development of schiz or the recovery so this suggests that for those with a biological vulnerability such as high levels of dopamine, schizophrenia only develops in the presence of significant stressors - diathesis - stress model

a review of post-mortem studies  - Haracz - found that most who showed elevated dopamine levels recieved antipsychotics shortly before death - suggesting that high levels of dopamine may just be a consequence of this treatment

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The dopamine hypothesis

Evidence for the dopamine hypothesis - amphetamines are dopamine agonists, stimulating nerve cells containing dopamine, causing the synapse to be flooded with dopamine - large doses cause hallucinations and delusions - antipsychotic drugs are dopamine antagonists, blocking the activity of dopamine in the brain and so reducing the symptoms of schiz

reductionist - if schiz was solely caused by excess dopamine activity then antipsychotic drugs should be effective for all schizophrenics but this is not the case suggesting that the dopamine explanation alone cannot explain the development of schiz and other factors must be involved

development of PET scans has led to more accurate measurements but has failed to provide evidence of altered dopamine activity in brains of those with schiz - Copolov and Crook

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Enlarged ventricles

Brain scans have shown that the ventricles of a person with schiz are 15% bigger than normal in individuals - Torrey - these may be the result og poor brain development or tissue damage which lead ot the development of schiz

Meta-analysis - copolov and crook - of more than 90 CAT scans revealed a substantial overlap between the schizophrenic and control populations - possible explanation for why some **** have enlarged ventricles may be the use of antipsychotics - lyon found as the dose of medication increased, the density of brain tissue decreased leading to enlarged ventricles

meta-analysis - file drawer effect,researchers may only choose studies that benefit the hypothesis, all studies used may not have the same methodology - inaccuracy good sample size, low ethics

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