Biological explanation Flashcards
What is the genetic basis of schizophrenia?
- schizophrenia runs in families it has been noted for many years that schizophrenia runs in families
- this is quite weak evidence in itself for a genetic link because family members tend to share aspects of their environment as well as many of their genes
- however there have been systematic investigations of the extent to which greater genetic similarity between family members is associated with the likelihood of both developing schizophrenia
- for example we share 100% of our genes with an identical twin, 50% with a sibling or parent and so on
- there is. Strong relationship between the degree of genetic similarity and shared risk of schizophrenia
- this is shown in the gap below left, which presents the findings from Irving Gottesman’s large-scale family study
What are candidate genes?
- individual genes are believed to be associated with risk of inheritance
- because a number of genes each appear to confer a small increased risk of schizophrenia it appears that schizophrenia is polygenetic i.e. it requires a number of factors to work in combination
- because different studies have identified different candidate genes it also appears that schizophrenia is astrologically heterogeneous i.e. different combinations of factors can lead to the condition
- Ripe et al carried out a huge study combining all previous data from genome-wide studies I.e. those looking at the whole human genome as opposed to particular genes of schizophrenia
- the genetic make-up of 37000 patients was compared to that of 113000 controls; 108 separate genetic variations were associated with increased risk of schizophrenia
- genes associated with increased risk included those coding for the functioning of a number of neurotransmitters including dopamine
What are the factors of the dopamine hypothesis?
- neurotransmitters
- hyperdopaminergia in the subcortex
- hypodopaminergia in the cortex
What are neurotransmitters?
- the brains chemical messengers appear to work differently in the brain of a patient with schizophrenia
- in particular dopamine is widely believed to be involved
- dopamine is important in the functioning of several brain systems that may be implicated in the symptoms of schizophrenia
What are the neural correlates of schizophrenia?
- measurements of the structure or function of the brain that correlate with an experience, in this case schizophrenia
- both positive and negative symptoms have neural correlates
What are neural correlates of negative symptoms?
- one negative symptom abolition involves the loss of motivation
- motivation involved the anticipation of a reward and certain regions of the brain for example the central stratum, are believed to be particularly involved in this anticipation
- it therefore follows that abnormality of areas like the central stratum may be involved in the development of evolution
- Juckel et al have ,measured activity levels in the central stratum in schizophrenia and found lower levels of activity than those observed in controls
- moreover they observed a negative correlation between activity in the central stratum is a neural correlate of negative symptoms of schizophrenia
What are neural correlates of positive symptoms?
- positive symptoms also have neural correlates
- Allen et al scanned the brains of patients experiencing auditory hallucinations and compared them to a control group whilst they identified pre-recorded speech as theirs or others
- lower activation levels in the superior temporal gurus and anterior consulate gurus were found in the hallucination group, who also made more errors than the control group
- we can thus say that reduced activity in these two areas of the brain is a neural correlate of auditory hallucination
What are the evaluation points of the biological explanations for schizophrenia?
+ finish adoption study forming that adoptees with schizophrenic mothers had a higher chance of developing schizophrenia not matter what family they were adopted into
- radioactive labelling studies found that dopamine was produced faster in schizophrenic brains however some genes that increased schizophrenia were linked to other neurotransmitter production
- monozygotic twins have more similar environments So barre vs nurture
- biological reductionist as it tries to narrow down the cause to one gene ignoring psychological explanations
How do multiple sources of evidence for genetic susceptibility support biological explanations for schizophrenia?
- there is now very strong evidence for genetic vulnerability to schizophrenia from a variety of sources
- the Gottesman’s study clearly shows how genetic similarity and shared risk of schizophrenia sufferers are still at heightened risk of schizophrenia if adopted into families with no history of schizophrenia
- there is also evidence showing that particular genetic variations significantly increase the risk of schizophrenia
- there is thus overwhelming evidence for the idea that genetic factors make some people much more vulnerable to developing schizophrenia than others
How is mixed evidence for the dopamine hypothesis a weakness of biological explanations for schizophrenia?
- there is support from a number od sources for abnormal dopamine functioning in schizophrenia
- antipsychotic drugs, work by reducing dopamine activity
- radioactive labelling studies have found that chemicals needed to produce dopamine are taken up faster in the brains of schizophrenia sufferers that controls, suggesting that they produce more dopamine
- there is also evidence to suggest that dopamine does not provide a complete explanation for schizophrenia
- some of the genes identified in the study code for the production of other neurotransmitters, so it appears that although dopamine Is likely to be one important factor in schizophrenia so are other neurotransmitters
How is the fact that monozygotic twins encounter more similar environments a weakness of genetic factors?
- a crucial assumption underlying all twin studies is that the environments of monozygotic twins and dizygotic twins are equivalent
- it is assumed therefore that the greater concordance if schizophrenia for M.D. twins is due to genetic similarity
- however my twins are treated mir similarly and encounter similar environments and experience more identity confusion than DZ twins
- this suggests that the difference in concordance rates between me and do twins is due to environmental differences between the twins rather than genetic differences
Biologically reductionist weakness?
-a weakness of the genetic explanation of schizophrenia is that it is biologically reductionist. The Genome Project has increased understanding of the complexity of the gene. Given that a much lower number of genes exist than anticipated, it is now recognised that genes have multiple functions and that many genes behavior. Schizophrenia is a multi-factorial trait as it is the result of multiple genes and environmental factors. This suggests that the research into gene mapping is oversimplistic as schizophrenia is not due to a single gene.
