Explanations – Biological vs Psychological Nature vs Nurture
Biological Explanations Genetics Bio chemicals Brain Structure
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.
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 ……..
Further Twin EvaluationTwin studies do not all use the same diagnosticcriteria – Therefore different diagnosis willproduce different concordance rate.Concordance rates can also be calculateddifferently depending on the method used –questions the reliability of such studies.
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
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.
Family Evaluation• This evidence again strongly suggests genetics is a factorHowever:• 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.
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.
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)
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
Neuroanatomy - Brain StructureThere 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.
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.
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.
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.......
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.
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.
Summery • Biological explanations do account for schizophrenia,however the fact that there is no conclusive explanation thataccounts for all schizophrenics –psychological explanations need to be considered.
Exam Question• TASK: Exam Question: PLAN THE QUESTION• Outline and evaluate one or more biological explanations for schizophrenia. In your evaluation you should refer to research evidence. (25 marks)