Biological Explanation of Schizophrenia Flashcards
Describe the genetic explanation
Individuals are born with an innate vulnerability to SZ in their DNA
How do family studies support the genetic explanation?
- They show that the risk of developing SZ is greater for those most closely related to the schizophrenic
- Concordance rates are important (measure of similarity between 2 people on a give trait)
- If the concordance rate is high, this would suggest a biological basis for SZ
Give an example of a family study to support the genetic explanation
- Gottesman found that the closer the genetic similarity with the schizophrenic individuals , the higher the likelihood of them developing SZ
- e.g. for identical twins it was about 48% compared to 6% likelihood when having schizophrenic parents
Give an example of twin studies to support the genetic explanation
- If SZ is genetic disorder, we should find that if MZ twin develops SZ then the other MZ twin will also
- Joseph collected data from SZ twin studies and the concordance rates for MZ twins was 40% and 7% for DZ twins
Describe candidate genes as support for the genetic explanation
- There’s no individual gene linked to SZ, a number of genes confer a small increased risk SZ meaning it may be polygenetic.
- e.g. Ripke et al looked at the genetic make-up of 37,000 patients compared to 113,00 controls, and found 108 separate genetic variation associated with increased risk of SZ,
Give evaluation for the genetic explanation (support from adoption study)
- Tienari compared 164 adopted children whose biological parent had SZ (group 1) against a group of adopted children whose parents had no history of SZ (group 2)
- In group 1, 6% of children developed SZ while in group 2, 2% of children developed SZ
- The difference supports the genetic hypothesis of SZ as environment seems to have a limited impact, as those with ‘schizophrenic’ genes were more likely to develop SZ
Give evaluation for the genetic explanation (concordance rate isn’t 100%)
- There must be an environmental influence
- e.g. Joseph suggested that MZ twins are treated more similar, so have more similar environments and experience ‘identity fusion’ (being treated as ‘the twins’ rather than as 2 individuals) than DZ twins
- This means that the differences in concordance rates in twin studies only reflect the environmental differences between the 2 types of twins
What is a neural correlate?
Patterns of structure or activity in the brain that occur together with an experience, may be implicated in the origins of SZ
What is dopamine?
A neurotransmitter that has an excitatory effect and is associated with the sensation of pleasure
Describe the original dopamine hypothesis
- It’s an explanation of SZ based on dopamine, and it has been found that schizophrenics have excess levels of dopamine in the subcortex
- This may be due high levels of D2 receptors on the receiving neurons, meaning more dopamine binding and more neuron fire
- These dopamine neurons play a key role in a person’s attention, perception and thought, which are all affect with SZ
Give an example of applying the original dopamine hypothesis
e.g. excess dopamine receptors in Broca’s area (responsible for speech production) may be associated with auditory hallucinations
Describe the revised dopamine hypothesis
- Goldman-Rakic et al identified a role for low levels of dopamine in the prefrontal cortex (responsible for thinking and decision making), could explain negative symptoms
- This hypothesis suggests both high levels of dopamine (hyperdopaminergia) in the subcortical areas and low levels of dopamine (hypodopaminergia) in the prefrontal cortex are involved in SZ
Give evaluation for the dopamine hypothesis (evidence suggests dopamine plays a big role in development and continuation of SZ)
- Dopamine agonists stiumalete nerve cells and increase dopamine levels, amphetamines are dopamine agonists
- Curran et al found people without SZ who take larges does of these drugs show characteristics of SZ, like hallucinations and delusions
- Indicates dopamine is involved in the development of symptoms of SZ
Give evaluation for the dopamine hypothesis (support from treatment of SZ +counter)
- Anti-psychotics are dopamine antagonists (they block dopamine receptors)
- e.g. Chlorpromazine is anti-psychotic often used in the treatment of SZ, and reducing the symptoms by reducing the productions of dopamine, supporting the involvement of dopamine in SZ
- However, Noll argues that anti-psychotics don’t alleviate hallucinations and delusions in a about a third of people with these symptoms. And some with typical levels of dopamine may still experiences these symptoms
- Suggests that dopamine may not play as a big of a role in SZ as once was thought
Give evaluation for the dopamine hypothesis (dopamine doesn’t provide a complete explanation of SZ)
- There’s evidence for a central role of the neurotransmitter called glutamate, and research has shifted to the role of this neurotransmitter
- McCutcheon et al used post-mortems and live brain scans of schizophrenics have consistently found raised glutamate levels
- Suggests that other neurotransmitters, other than dopamine, may be involved in SZ
