Biological Explanations Flashcards
How many genetic explanations of SZ are there?
3
What are the 3 genetic explanations of SZ?
1) Family studies
2) Twin studies
3) Adoption studies
What are family studies for SZ?
They find individuals who have SZ and determine whether their biological relatives are similarly affected more often than non-biological relatives
What have family studies found for SZ?
Established SZ more common among biological relatives of person with SZ, and the closer the degree of genetic relatedness, the greater the risk - children with SZ parents have a concordance rate of 46%, children with 1 have 13% and siblings is 9%
Outline twin studies for SZ
If MZ twins who share 100% of their genes are more concordant in terms of SZ than DZ twins who only share 50% of genes, suggests greatest similarity is due to genetic factors
Name the 2 studies for twin studies for SZ
1) Gottesman (91)
2) Joseph (04)
Outline Gottesman (91)
Suggests SZ inherited through genes - studied 40 pairs of twins and found concordance rate for MZ twins was 48% and only 17% for DZ twins
Outline Joseph (04) for twin studies
Calculated that pooled data for all SZ twin studies carried out prior to 2001 shows concordance rate for MZ as 40.4% and for DZ twins as only 7.4%
What have twin studies shown recently for SZ?
More recently, methodologically sound studies (blind diagnoses) tended to report lower concordance rates for MZ twins - despite this, researchers still argue even these findings support the genetic position as provide a MZ concordance rate many times higher than DZ concordance rate
Outline adoption studies for SZ
Due to difficulties of disentangling genetic and environmental influences for individuals who share genes and environment, studies of genetically related individuals who have been reared apart can be used
What is the main study for adoption studies for SZ?
Tienari (00)
Outline Tienari (00)
Of the 164 adoptees whose biological mothers diagnosed, 11 (6.7%) also received diagnosis compared to just 4 (2%) of the 197 control adoptees born to non-SZ mothers - concluded showed genetic liability to SZ had been ‘decisively confirmed’
What are the other 2 biological explanations for SZ besides the genetic ones?
1) The dopamine hypothesis
2) Neuroanatomy
What does an agonist mean?
A drugs that binds to and alters the activity of a receptor
What does an antagonist mean?
A drug that binds to a receptor but which does not alter the activity of the receptor
What is dopamine?
A neurotransmitter found in the brain
Outline the dopamine hypothesis
States brains of SZ patients produce more dopamine - states messages from neurons that transmit dopamine fire too easily or too often, leading to characteristic symptoms of SZ - SZs thought to have abnormally high numbers of D2 receptors on receiving neurons, resulting in more dopamine binding and therefore more neurons firing
Name a big study relating to the dopamine hypothesis
Comer (03)
Outline Comer (03)
Dopamine neurons play a role in guiding attention so disturbances in process may lead to the problems relating to attention, perception and thought found in people with SZ
What are the 4 sources of evidence which support the role of dopamine in SZ?
1) Amphetamines
2) Antipsychotic drugs
3) Parkinson’s disease
4) Post-mortem studies
What are amphetamines relating to dopamine?
Dopamine agonists
Outline how amphetamines support the dopamine hypothesis
It is a drug which stimulates nerve cells containing dopamine, causing the synapse to be flooded with the neurotransmitter - large doses can cause characteristic hallucinations and delusions of SZ episode
What are antipsychotic drugs relating to dopamine?
Dopamine antagonists
Outline how antipsychotic drugs support the dopamine hypothesis
There are many different types but all block the activity of dopamine in the brain - by reducing stimulation of dopamine system, drugs eliminate symptoms like hallucinations and delusions - the fact that these drugs alleviated many symptoms of SZ strengthened the case for dopamine being a significant contributory factor in this disorder
Outline how Parkinson’s disease supports the dopamine hypothesis
Those with the disease have low levels of dopamine and Grilly (02) found some taking drug L-dopa to increase dopamine were developing SZ-like symptoms
Outline Grilly (02)
Found some taking drug L-dopa to increase dopamine were developing SZ-like symptoms
What is the main post-mortem study supporting the dopamine hypothesis?
Falkai (88)
Outline Falkai (88)
Looked at autopsies and found SZs had larger than normal numbers of dopamine receptors - there was an increase of dopamine in brain structures and receptor density so concluded dopamine production was abnormally high in SZs
Outline the role of neuroanatomy in SZ
There is growing evidence that SZ is associated with physical abnormalities in the brain - Szesko found asymmetry that was found in normal brains and that SZs tend to have symmetrical brains - also tend to have abnormally large ventricles in the brain which means brains of SZs are lighter than normal
What are ventricles?
Fluid-filled cavities in the brain
What is the main study for the role of neuroanatomy in SZ?
Andreasen (90)
Outline Andreasen (90)
Conducted a very well controlled CAT scan and found significant enlargement of the ventricles of SZs when compared to controls, however, only the case for men and not for women so cannot generalise to everyone - it is gender biased
Outline family studies for SZ
Many researchers accept SZ appears to run in families but may be more to do with common rearing patterns and environment that has nothing to do with heredity - e.g. research on expressed emotion has shown negative emotional climate in some families may lead to stress beyond an individual’s coping mechanisms, thus triggering a SZ episode
Name 4 negative points for twin studies for SZ
1) Crucial assumption that environments of MZ and DZ twins are equivalent
2) Sample sizes of studies always small
3) Do not all use same diagnostic criteria so different diagnoses will produce different concordance
4) Concordance calculated differently depending on method which questions reliability of these studies
Outline how the crucial assumption that environments of MZ and DZ twins are equivalent is a negative point for twin studies for SZ
It is therefore assumed greater concordance for SZ between MZ twins is the produce of greater genetic similarity rather than greater environmental similarity
What study looks into the crucial assumption that environments of MZ and DZ twins are equivalent for SZ?
Joseph (04)
Outline Joseph (04) for the assumption about twin studies
It is widely accepted MZ twins treated more similarly, encounter more similar environments and experience more ‘identity confusion’ (treated as ‘the twins’ rather than 2 distinct individuals) than DZ twins - as a result, there is reason to believe that differences in concordance rates between MZ and DZ twins reflect nothing more than the environmental differences that distinguish the 2 types of twin
Outline adoption studies for SZ
The central assumption is adoptees are not ‘selectively placed’ (adoptive parents who adopt children with SZ parent are no different from adoptive parents who choose children whose background is normal)
What 2 studies are associated with the evaluation of adoption studies for SZ?
1) Joseph (04)
2) Kringlen (87)
Outline Joseph (04) for adoption studies of SZ
Claims assumption is unlikely particularly in early studies,, in countries like Denmark and US, potential adoptive parents would have been informed of the genetic background of the children prior to selection for adoption
Outline Kringlen (87)
‘Because the adoptive parents evidently received info about child’s biological parents, one might wonder who would adopt such a child’
Name 4 negative points about genetic explanations of SZ
1) Methodological problems with heredity studies
2) Methodological problems in general
3) Very difficult to separate out the influence of nature or nurture
4) Lack population validity
Outline the methodological problems with heredity studies
Most adoption studies would not have found statistically significant differences between adoptees born to SZ and non-SZ parents without broadening the definition of SZ to include non-psychotic ‘SZ spectrum disorders’ - Kety (68) no cases of full SZ found among 1st degree relatives of adopted children identified with a SZ spectrum disorder
Outline Kety (68)
No cases of full SZ found among 1st degree relatives of adopted children identified with a SZ spectrum disorder
Outline methodological problems in general for genetic explanations of SZ
Retrospective and diagnoses may be biased by knowledge that other family members who may have been diagnosed - there may be problems with demand characteristics
Outline why it is very difficult to separate out the influence of nature or nurture in genetic explantions of SZ
Concordance rates not 100% meaning SZ cannot wholly be explained by genes and could be individual has a pre-disposition to SZ which suggests biological account cannot give a full explanation of the disorder
Outline how genetic explanations of SZ lack population validity
Small samples and only a select number of families are used so there are issues with the results being generalised to the whole population
What is the problem of drugs in terms of the dopamine hypothesis?
They can actually increase dopamine as neurons struggle to compensate for the sudden deficiency
Name 4 studies that support the dopamine hypothesis
1) Haracz (82)
2) Wise & Stein (73)
3) Barlow & Durand (95)
4) Janowski (72)
Outline Haracz (82)
Reviewed post-mortem studies of SZs and found most of those who showed increased dopamine had received antipsychotic drugs shorty before death and those who had not, had normal levels of dopamine
Outline Wise & Stein (73)
Found SZ patients who dies in accidents showed abnormally low levels of dopamine beta hydroxylase (DBH) in the brain fluid - DBH is an enzyme whose function is to break down the neurotransmitter dopamine after release - means less dopamine is being broken down so more dopamine
Outline Barlow & Durand (95)
Report that chlorpromazine effective as reduces SZ symptoms in about 60% of cases - appears to have the most impact on positive symptoms and treated patients may still suffer from severe negative symptoms - suggests chlorpromazine effective in reducing symptoms by reducing dopamine suggesting high levels contribute to the symptoms
What are 2 negative points about Barlow & Durand (95)?
1) Only worked on 60% and not all suggesting not only factor
2) Still suffer from sever negative symptoms suggesting further dopamine not only factor
Outline Janowski (72)
Compared responses to amphetamine of SZ patients and normal controls given identical doses - low doses of amphetamine that produced slight increases in psychomotor agitation amongst normal controls resulted in a substantial exacerbation of symptoms amongst SZ patients - suggests using dopamine agonist which increases dopamine levels worsens SZ symptoms and even in normal people causes slightly SZ symptoms
What is a positive point Janowski (72)?
Supported by Timmons & Hamilton (90) who found high doses of amphetamine resulted in an acute psychosis resembling SZ in clinically normal people
What are 2 other types of research which support the dopamine hypothesis?
1) Neuroimaging research
2) Evidence from treatment
Outline how neuroimaging research supports the dopamine hypothesis
Development of neuroimaging techniques like PET scans has allowed researchers to investigate dopamine activity more precisely than in previous studies that relied on measure of metabolites (waste products) associated with dopamine
What has been a major disadvantage of neuroimaging research for the dopamine hypothesis?
It has failed to provide convincing evidence of altered dopamine activity in brains of those with SZ
Outline how evidence from treatment supports the dopamine hypothesis
Success of drugs treatments that attempt to change levels of dopamine - antipsychotic drugs reduce the effect of dopamine and so reduces the symptoms of SZ
What is some evidence from treatment which support the dopamine hypothesis?
Davis (80)
Outline Davis (80)
Carried out meta-analysis of 29 studies that analysed the effectiveness of antipsychotic drugs compared with a placebo and found relapse occurred in 55% of patients in placebo group but only 19% of those on actual treatment
Apart from research support, what is a major positive of the dopamine hypothesis?
Practical application as from research, new drugs developed like clozapine thus improving patients quality of life
Name 4 negative points for the dopamine hypothesis
1) Issues with cause and effect - not clear whether increased dopamine is cause or effect
2) Kasper (99)
3) Biologically deterministic
4) Antipsychotic drugs do not work on all SZs so cannot be the only factor
Outline Kasper (99)
Suggested there are a number of problems with the dopamine hypothesis - antipsychotic drugs are effective for only positive symptoms so excessive dopamine can only explain some types of SZ - secondly, newer atypical antipsychotic drugs proved more effective than typical ones - successfully treating symptoms despite blocking fewer dopamine receptors - this is contradictory evidence that dopamine is the main contributing factor associated with SZ
How is the dopamine hypothesis biologically deterministic?
Does not account for freewill in development of SZ and suggests individuals have no control in getting better when having treatment as it is all biologically based
What are 2 positive points about neuroanatomy explanations of SZ?
1) Research has high reliability as highly controlled environments with specialist high technology equipment like MRI and PET scans so high test-retest reliability
2) Supporting evidence comes from further empirical evidence from Suddath (90)
What are 2 negative points about neuroanatomy explanations of SZ?
1) Research difficult to interpret and there have been contradictory findings
2) Difficult to establish cause and effect as many ppts suffered from SZ for a while and have also been undergoing treatment - SZ may be caused by treatment itself
