biological explanations of schizophrenia (genetics and neural correlates) Flashcards
where does evidence for the role of genetics in schizophrenia
family, twin, adoption studies, candidate gene studies and gene mutation
what % of their genes do monozygotic and dizygotic twins share
MZ 100%
DZ 50%
who are first degree relatives
biological parents, siblings
share 50% of genes
who are 3rd degree relatives
first cousins, great grandparents
who are second degree relatives
biological grandparent, aunt, uncle, half-siblings
what study gives evidence for the role of genetics in family, twin and adoption
gottesman
The more genetic ….. a person carries, the …. likely they are to develop schizophrenia.
risk alleles
more likely
According to the genetic explanation of schizophrenia, if some family members have schizophrenia, then it is ….. likely that you will develop schizophrenia.
This is because you may ….. a specific gene….. associated with schizophrenia.
more
inherit
allele
if you inherit a gene allele that increases the likelihood of developing schizophrenia it doenst mean you will get it, what else may it depend on
other gene alleles you carry
environmental factors
what does the genetic explanation say about the number of gene alleles responsible for increasing the risk
there are multiple not just one
in twin studies, who is compared
researchers compare monozygotic and dizygotic twins
in twin studies, a rate is calculated. what rate and what is it
concordance rare which is The percentage of twins that both share the same trait, given that at least one twin has the trait.
For a particular trait, there might be a difference in concordance rates between monozygotic and dizygotic twins. What does this difference tell us about the influence that genetics has on this trait?
A BIG concordance rate shows that genetics has a BIG influence on the trait COMPARED to other factors.
Gottesman & Shields twin study on schizophrenia found that there was a …..% concordance rate in MZ and a ….% concordance rate in DZ
mz= 74%
dz= 24%
what does Gottesman & Shields twin study indicate about the development of schizophrenia
Schizophrenia is partially influenced by our genetics.
Gottesman & Shields twin study: As the concordance rates for monozygotic twins was not ….% what can be said about schizophrenia development?
100%
Schizophrenia is not just caused by genetics.
Schizophrenia development is also influenced by the environment.
What is one assumption that twin studies make?
The environment will have the same impact on phenotype for both monozygotic and dizygotic twins.
eg dressed the same, treated the same/mistaken for each other if (mz) may not happen so much if dz
If monozygotic twins might also have a more similar environment than dizygotic twins, what does this mean for any differences in concordance rates between monozygotic and dizygotic twins?
they might be caused by environmental factors.
They might be caused by genetics.
what is an issue that twin studies may have? over exaggerate…
Twin studies might over exaggerate the importance of genetics.
example of how mz twins could have a more similar environment than dz twins
more likely to be both bullied at school so both get same stress which could contribute to high concordance rate
a weakness of Gottesman and Shields’ study?
The study assumes that monozygotic twins and dizygotic twins have a similar amount of shared environment.
mz are more likely to be treated the same than dz so high ccr observed in mz might be due to environmental factors as well as shared genetic factors
Explain what Tiernari’s study tells us about the role of genetics in schizophrenia.
Adopted children with biological mothers who have schizophrenia are more likely to develop the disorder than children whose biological mothers don’t have schizophrenia.
This suggests that genetics plays an important role in the development of schizophrenia.
what were the control and experimental groups for Tienaris study
The experimental group was adopted children whose biological mothers had schizophrenia.
The control group was adopted children whose biological mothers did not have schizophrenia
what study shows support for the genetic explanation using adoption studies
tienari
findings of tienaris adoption study (3 things)
Children of biological mothers with schizophrenia were more likely to develop schizophrenia themselves.
Similarities between the child and biological mother were due to genetics.
Genetics had more influence on schizophrenia development than the environment
What is one assumption made by adoption studies?
Biological parents of children adopted at birth can influence a child’s genes but not their environment.
what does the neural correlates hypothesis state
The neural correlates hypothesis states that abnormal brain structure, such as enlarged ventricles , causes schizophrenia.
what does dopamine do
Dopamine is involved in processing reward and in controlling attention.
In the mesolimbic system, dopamine has an excitatory effect. This means that, if there are higher levels of dopamine…
neurons generate more electrical activity than normal causing overactivity in the mesolimbic system > +symptoms eg delusions
What does the dopamine hypothesis suggest schizophrenia is caused by?
(general)
abnormal brain function
what did the revised dopamine H say about -symptoms
lower levels of dopamine in the frontal cortex than usual > underactivity causes -symptoms
what does the revised dopamine hypothesis say we should seen in the brains of people with schizophrenia
hypodopaminergia in the cortex (abnormal dopamine systems)
low levels of dopamine in cortex > negative symptoms
support for DH: According to the dopamine a, if a person takes an amphetamine, which increases dopamine levels, what should occur?
increased activity in the mesolimbic pathway.
healthy patients given amphetamines and get +symptoms
what happened in nolls study
Noll reviewed previously conducted drug studies.
In the studies, people with schizophrenia were given drugs that reduce dopamine levels.
In the studies, the positive symptoms of people with schizophrenia were monitored.
According to the dopamine hypothesis, what should we see in the brains of patients with schizophrenia? and link to an example
hyperdopaminergia in the subcortex (central regions of the brain)
eg in brocas area, an increase in the dopamine receptors which could be responsible for auditory hallucinations and speech poverty
Why did Montcrieff conclude that the evidence supporting the dopamine hypothesis is inconclusive?
Drugs that increase dopamine, like amphetamine, also increase the levels of other neurotransmitters, so we can’t be sure that it’s the increased dopamine that is causing these symptoms.
Some post-mortem studies reported increased levels of dopamine in the mesolimbic pathway, but other studies reported no difference compared to the control brains.
which neurotransmitters does amphetamines also increase as well as dopamine
serotonin and noradrenaline
Name the researcher that criticised the dopamine hypothesis, by finding that amphetamine also increases noradrenaline and serotonin, alongside dopamine
montcrieff
what is a strength of using antipsychotics as a treatment for sz - fully explained
comes from success of drug treatments.
eg meta-analysis of 212 studies found that all the antipsychotics tested they were SIGNIFICANTLY more effective than a placebo in treating + and - symptoms
done by reducing effects of dopamine
also challenges classification of APs into typ/atyp as there wasnt much difference between the 2
outline and evaluate genetics as a biological explanation for SZ (16)
AO1- explained
one of bio exp is genetics.
genetic exp see sz is heritable through transmission of dna.
predicts higher risk of developing sz if a bio fam member has compared to not.
and risk incr if genetic similarity is higher. eg 1st degree rel higher risk than 2nd and 3rd
also identifying specific genes that predict development of sz using candidate genes (early studies - single gene but now polygenic ie multiple genes influence development
also considers how gene mutation contributes ie genetics can still exp sz even in the absence of a family history of sz.
outline and evaluate genetics as a biological explanation for SZ (16)
