Transcript Schizophrenia_Biological_explanations File

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 twofold 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
• http://www.youtube.com/watch?v=WCUWkQszA_g&feature=
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.