Schizophrenia: Biological explanations

Overview Genetic hypothesis Biochemical factors Neuroanatomical factors Prenatal exposure to virus.

Genetic hypothesis AO1 Schizophrenia does run in families. Gottesman (1991) reported on the findings of many twin studies, and found: For monozygotic (MZ) twins the risk/concordance is 48 per cent. For children of 2 affected parents the risk is 46 per cent. For DZ twins the risk is 17 per cent. AO2/3  Twin studies do not all use the same diagnostic criteria.  Concordance rates related to ‘scientific rigour’ of the study. Marshall (1990) suggested that the better controlled the study, the lower the concordance rate.

Genetic hypothesis AO2/3 Adoption studies a.What were the findings of the Tienari (1991) adoption study? (The Finish Adoption Study) b.What does this indicate about the cause of schizophrenia? c.Is this study a support for nature or nurture? d.Why is the 1 per cent a significant figure in this study?

Biochemical factors Recap: what are neurotransmitters?  AO1. According to the dopamine hypothesis (Carlsson 1960s) schizophrenia is due to an excess of dopamine activity.  AO2/3 This is supported by several observations, including:  Schizophrenia-like psychosis in people who misuse amphetamines, a drug known to increase the release of dopamine.  All drugs that were effective antipsychotic agents were dopamine receptor antagonists (slows down the activity), e.g. Penothiazines.

Biochemical factors Dopamine hypothesis AO2/3 However:  Penothiazines do not work for everyone diagnosed with schizophrenia. They also are most effective in relieving the positive symptoms. This could lead us to the conclusion that different symptoms, or even different types of schizophrenia have different causes.  PET scans (3D imaging) studies, e.g Wong et al (1986) found a two- fold increase in the density of dopamine receptors in schizophrenic patients who had never been treated with drugs, compared to those who had.  However: Later PET scan studies have not replicated Wong’s results.

1.What is the risk of you developing schizophrenia if you have an identical twin with the disorder? 2.What is the risk if you have a non-identical twin with the disorder? 3.An excess of which neurotransmitter has been linked to the development of schizophrenia? 4.Give a piece of evidence supporting this link.

Neuroanatomical factors (brain structure) AO1 Frontal lobes found to be smaller in people with schizophrenia AO1 Ventricles, the fluid-filled cavities in the brain. Numerous studies have shown that these are larger in people with schizophrenia.

Neuroanatomical factors (brain structure) AO2/3 Andreasen et al. (1990) conducted a ‘very-well controlled CT scan study’ and found significant enlargement of the ventricles in schizophrenic patients compared to controls. This was only the case for men and not for women. AO2/3 Issues of ‘cause and effect’.  What is meant by this? AO2/3 Not all these abnormalities are found in people with schizophrenia Crow (1985) resolves this contradiction with his ‘two-syndrome hypothesis’. See booklet for Type 1 and Type 2 description.

Prenatal and Perinatal factors Viruses, e.g. Maternal flu virus Perinatal ‘insults’: problems that occur at birth.

Biological explanations: Conclusion Genetics clearly plays a role, and this genetic influence is expressed through biochemistry and neuroanatomy (brain structure). However, concordance rates for schizophrenia are always well below 100%, showing that other factors must be involved. Examiners Tip: do not state that biological explanations ignore environmental factors; biologists do see the cause as an interaction of biology and genetics. Neurodevelopmental factors include prenatal and perinatal complications.

The Schizophrenia Song endscreen&NR=1 endscreen&NR=1 Love it or hate it, learn it and you’ll have the key terms in your head, forever!

True or False 1.Concordance rates for schizophrenia in monozygotic twins is 100% 2.Schizophrenia has been linked to an excess of cortisol in the brain. 3. The dopamine hypothesis is supported by the effect of drugs such as phenothiazines. 4.Biological explanations can account for all cases of schizophrenia. 5.The Finish Adoption study found support for the genetic basis of schizophrenia.