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Schizophrenia
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Explanations – Biologicalvs Psychological
Nature vs Nurture
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Biological Explanations
GeneticsBio chemicals
Brain Structure
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Genetics – Twin Studies• Gottesman 1991 suggests that
schizophrenia is inherited through genes. Studied 40 twins - the concordance rate for MZ twins is about 48% and only about 17% for DZ twins.
• Also Cardno 2002 – showed concordance rate of 26.5 MZ and 0% for DZ.
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Evaluation – Twin Studies
• However, the fact that the concordance rate for twins is not 100% means that Schizophrenia cannot be accounted for by genetics alone
• As we already know, the higher concordance between MZ twins could be explained by greater environmental similarity rather than genetic similarity – MZ twins elicit more similar treatment than DZ twins (so can be explained by other theories)
• Also the sample size of such twin studies is always going to be very small, so ……..
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Further Twin Evaluation
Twin studies do not all use the same diagnostic criteria – Therefore different diagnosis will produce different concordance rate.
Concordance rates can also be calculated differently depending on the method used – questions the reliability of such studies.
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Genetics - Adoption Studies
• Tienari – 155 adopted children – who biological mothers had schizophrenia –they had a concordance of 10% compared to 1% in adopted children without schizophrenic parents.
• This is very strong evidence that genetics are a risk factor for schizophrenia
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Genetics – Family Studies
• Gottesman also studied families – he concluded that if both your parents suffer from Schizophrenia, then you have a 46% chance of developing it yourself (compared to a 1% chance of someone selected at random will suffer)
• The more genetically similar relatives are, the more concordance is found.
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Family Evaluation
• This evidence again strongly suggests genetics is a factor
However:• It could also be explained in terms of
the fact that genetically similar family members tend to spend more time together and so environment could also affect.
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Biochemical Factors – The Dopamine Hypothesis• This theory claims that excessive
amounts of dopamine or an oversensitivity of the brain to dopamine is the cause of schizophrenia
• Eval: There is strong empirical support which suggests that dopamine plays an important role in schizophrenia – e.g drugs which block dopamine (Phenothaiazines) also seem to reduce the symptoms of schizophrenia.
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The Dopamine Hypothesis - Evaluation
• L-Dopa – a drug for Parkinson’s disease actually increases dopamine – this in turn can produce symptoms of schizophrenia.
• Post mortems of schizophrenics, show an increase of dopamine in parts of the brain. (Seeman 1987)
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Dopamine Evaluation - Negatives
• Phenothiazines do not seem to work for everyone therefore....
• Cause or effect?
• This theory is over simplistic and has been criticized for using the treatment to determine the cause. This is an AETIOLOGY FALLACY
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Neuroanatomy - Brain Structure
There is growing evidence that schizophrenia is down to physical abnormalities in the brain.
Szesko et al found that the ‘asymmetry’ found in normal brains – in the prefrontal cortex is absent in people with schizophrenia.
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Brain Structure
People with schizophrenia have abnormally large ventricles in the brain. Ventricles are fluid filled cavities. This means that the brains of schizophrenics are lighter than normal.
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Brain Structure Evidence• Andreasen et 1990 –
conducted a very well controlled CAT scan study and found significant enlargement of the ventricles in schizophrenics compared to controls.
• However this was only the case for men and not for women. Therefore cant generalise to everyone.
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Evaluation
• Research is difficult to interpret and there have been contradictory findings.
• Difficult to establish cause and effect – as many participants have suffered from schizophrenia for a while and have been undergoing treatment. So.......
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Further Evaluation
• The main problem with such studies is that it is not found in all schizophrenics. This has lead to further research done by Crow 1985.
• He suggested two types of schizophrenia with two biological causes.
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Two Syndrome Hypothesis - Crow 1985
• Type one - genetically inherited associated with dopamine – characterised by positive symptoms.
• Type Two – Neurodevelopmenal disorder – to do with Brain structure – characterised by negative symptoms.
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Summery
• Biological explanations do account for schizophrenia,
however the fact that there is no conclusive explanation that accounts for all schizophrenics – psychological explanations
need to be considered.