Biological Explanations of Schizophrenia

AQA A2 Psychology A: Schizophrenia

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Biological Explanations of Schizophrenia by Mind Map: Biological Explanations of Schizophrenia

1. Genes

1.1. Gottesman (1991) - the higher the number of genes that a person shares with a SZ sufferer, the higher the risk of them also suffering

1.1.1. MZ twins 48%

1.1.2. Child of 2 affected parents 46%

1.1.3. DZ twins 17%

1.1.4. Child of 1 affected parent 17%

1.1.5. Grandchildren 5%

1.1.6. All of these statistics are below 100%, this suggests that other factors play an important part - not reductionist

1.1.7. 63% of people diagnosed have no family history of the disorder

1.2. Twin Studies

1.2.1. MZ twins - genetically identical, DZ twins - different genes (50% the same)

1.2.2. Cardno et al (2002) - Maudsley twin register - concordance rate of 26.5 for MZ twins and 0% for DZ twins - song evidence for a genetic component MZ twins are relatively rare and of these, only 1% are expected to have SZ - sample size is very small Twin studies don't all use the same diagnostic criteria - different definitions produce different concordance rates - comparisons cannot always be made Concordance rates can be calculated in different ways and vary widely depending on the method used Hard to separate the effects of hereditary from the effects of the environment because twins are usually raised together

1.3. Adoption Studies

1.3.1. Adoption studies allow researchers to look at people who are born to SZ mothers not raised by families without SZ - so SZ only effects their genes and NOT their environment

1.3.2. Tienari (1991) - Finland - 155 Ps - compared them with children with healthy parents - 10% of the adopted group developed SZ whereas in the control group was only 1% Provides strong evidence for a genetic component

2. Dopamine Hypothesis

2.1. Dopamine is a brain neurotransmitter which transmits messages across synapses to the brain. Excess dopamine activity at certain synapses has been linked to SZ.

2.2. It is likely that dopamine is somehow involved, but this is an oversimplified explanation on its own

2.3. Evaluation

2.3.1. Drugs Drugs (e.g. Phenothiazines) which act by blocking dopamine at the synapse are effective at alleviating symptoms However they do not work on everyone - they also tend to alleviate the positive symptoms and not the negative ones L-Dopa acts by increasing dopamine activity, this can produce SZ symptoms in previously unaffected individuals

2.3.2. PET scans PET scans show higher density of dopamine in the brains of SZs (Wong et al) These results have not been replicated (Farde et al)

2.3.3. Post Mortems Post mortems of SZs have shown an increase in dopamine in parts of the brain These are usually carried out on Ps who have taken neuroleptic drugs for years, so the results could be because of the drugs rather than because of the cause of SZ

3. Neuroanatomical factors

3.1. Frontal Lobe

3.1.1. The frontal lobe has an important role in higher intellectual functioning and fluent expression

3.1.2. Buchsbaum (1990) - PET scans reveal reduced cerebral blood flow in the frontal lobe

3.1.3. Szesko et al (1995) - the symmetry found in normal brains in the prefrontal cortex is absent in SZs

3.2. Ventricles

3.2.1. Fluid filled cavities in the brain, they are supposedly larger in SZ brains - more significant in males than females

3.2.2. Andreasen et al (1990) - CT scans revealed a significant enlargement of the ventricles in SZs compared to controls

3.3. Research is difficult to interpret as there are contradictory findings

3.4. Difficult to establish cause and effect

3.5. These abnormalities are not found in all people with SZ

3.5.1. This has lead to Crow (1985) defining two types of SZ with different underlying pathology Type 1: genetically inherited, associated with dopamine dysfunction, characterised by positive symptoms, responds well to anti-psychotics Type 2: neurodevelopmental disorder, arising from prenatal and perinatal insults, characterised by negative symptoms, develops over a period of time, does not respond well to anti-psychotics Accounts for the apparent contradictions of research Oversimplified - many Ps show aspects of both types

4. Given that no biological explanation accounts for all cases of SZ, it seems likely that social and psychological factors play a part.

5. The biological argument heavily rests on the nature side of the nature/nurture debate