Biological explanations Flashcards
What are the 3 biological explanations for schizophrenia?
- Genetics
- Dopamine (Hyperdopaminergia/ Hypodopaminergia)
- Neural correlates
What have researchers suggested in relation to genetics as an explanation of schizophrenia?
- Some people may have a genetic disposition to schiz.
- So the condition is at least partly inherited
- disorder will run through families through faulty genes
- No one gene is likely to be responsible for all cases but several genes are involved (polygenic)
What did Ripke et al 2014 report on how many genes & what genes were responsible?
What did Hong 2001 find in relation to Chinese patients with Schiz?
- 108 genetic variants
- variations of chromosome 8 & 11
- C4 gene
- variation of the TPH gene was more common with Chinese patients, which codes for serotonin production
What is the function of the C4 gene & how does it relate to the development of schiz?
- Immune molecule outside of the CNS (Central Nervous System) that helps to contain infection
- C4 gene is expressed by neurons & located at synapses
- C4 mediates synapse pruning during development, something different from C4’s role in the immune system
- excessive pruning could lead to symptoms of schiz.
- This may explain why schiz. arises in adolescence & why schiz. patients have a thinner cerebral cortex with fewer synapses
What 4 instances did Gottesman & Shields 1991 find between schiz & genetics?
(Children of parents)
(MZ identical twins)
(First degree)
(Second degree)
- Children of 2 schiz patients who share 100% genetic similarity: 46% chance of developing schiz
- MZ twins (identical) who share 100% genetic similarity: 48% chance of developing schiz
- First degree relatives (children) share 50% genetic similarity: 13% chance of developing schiz IF a parent was diagnosed
- Second degree relatives (grandchildren) share 25% genetic similarity: 5% chance of developing schiz IF a grandparent was diagnosed
Why do adoption studies have an advantage over twin & family studies?
- If adopted you can solely look at genetics rather than schiz family members in their direct environment
- adopted child is isolated from their schiz family
Adoption study by Tienari 2000?
(164 Finnish kids)
- Used 164 adopted kids in Finland who’s biological mothers were schiz.
- Kids were matched with kids who’s mothers did not have schiz
- results: 11/164 (schiz mother) kids had been diagnosed with schiz v.s. 4/164 kids (control group helping to validate data)
- Shows schiz has a genetic component as adopted children do not share environmental influences with their biological mothers
AO3 genetic explanation of schiz
Jospeh 2004?
- Genetic similarity increases development of schiz
- Before 2001 pooled data showed 40% concordance rate with MZ twins (100% similarity)
- also showed &% concordance rate for DZ twins (50% share)
- Higher concordance for MZ shows genes have an influence on the development of schiz
AO3 genetic explanation of schiz
Psychological explanation instead?
(can use eval for all biological explanations of schiz)
- Psychological explanation is more influential
- Claims poor family relationships & maladaptive behaviour affects a growing child’s perception of reality & how they interact with their environment
- If these problems persist into adulthood, schiz may develop
- Shows biological explanation may not be the sole reason for schiz development
AO3 genetic explanation
Biological is reductionist?
(maybe that’s a good thing?)
- reductionist
- Highlights genetics & neurological imbalances in the brain
- this is viewed as the main catalyst of the disorder
- However the reductionism can be useful in developing treatments for sz
- anti-psychotic drugs work by reducing the effects of dopamine & so reduce symptoms of disorder
AO3 genetic explanation
Issues with cause & effect?
(environment/genes)
- Genetics results in issues with cause & effect
- Despite mothers sharing 50% genetic similarity with a parent that may be a sufferer/other first degree relatives
- family members tend to share an environment as well as genes
- Environmental factors can disrupt associated cause & effect through genetics
- behaviour can be adopted through the environment, imitating schiz symptoms or contribute towards the development of schiz
Outline the dopamine hypothesis?
- Aka Hyperdopaminergia (Hyper - high)
- Biochemical explanations argue schiz is caused by elevated levels of dopamine (DA)
- High DA activity in key synaptic sites e.g. mesolimbic pathway & limbic system
- Excess of DA causes a ‘system overload’ due to increases in impulses, triggering positive symptoms of schiz e.g. Hallucinations
- Pre synaptic neurons can be a factor by releasing too much DA
Outline 2 observations that support the dopamine hypothesis of schiz?
- Antipsychotics: relieve some symptoms by blocking DA
- These have been shown to be effective in up to 85% of patients (antagonistic) - Post-Mortem studies have shown a higher concentration of DA in schiz patients
Outline the revised dopamine hypothesis?
- Modified due to inconsistencies in research
- Davis (1991) pointed out in PFC (Pre-Frontal Cortex) there are no D2 receptors instead there is a deficiency of DA
- Davis suggested low levels DA are responsible for negative symptoms (avolition) this is called Hypodopaminergia (Hypo - low)
- PFC responsible for executive functions (rational thoughts, decision making e.g. things associated with negative symptoms)
AO3 Dopamine research support
Randrup & Munkvad (1966)?
P - Randrup & Munkvad created schiz behaviour in a rat sample by giving them dopamine agonists (amphetamines)
E - The rats dopamine levels were raised 3 times a day for 6 days
- Rats then displayed prolonged abnormalities including inability to filter out external sounds
- This was reversed using anti-psychotic drugs
L - supports dopamine hypothesis towards development of schiz
AO3 Dopamine Alternative explanation of cognitive explanation?
P - There are alternative explanations towards development of schiz
E - Cognitive psych explanation argues many schiz sufferers have faulty information processing & dysfunctional thought processes
E - A malfunction within the central monitoring system (CMS) could explain positive symptoms
L - Shows dopamine explanation may not be the primary cause for schiz
AO3 Dopamine
Practical application?
P - Real world application is that drug treatment can be introduced can be introduced to aid sufferers of schiz by reducing DA levels
E - Antipsychotic drugs block activity of DA working as an antagonist against DA NT’s
E - Medication been effective in up to 85% of pt’s
L - Therefore dopamine explanation has helped to create medication aiding sufferers with their symptoms
AO3 Dopamine
Strength in contributing to Diathesis-Stress model?
P - Strength of high dopamine explanation of schiz is that it contributes to diathesis-stress model
E - Dopamine would be the diathesis (biological element) & this would interact with environmental factors e.g. urban living (stressors)
E - Could potentially result in the development of schiz through interactionism between biological & environmental facotrs
L - Dopamine hypothesis of schizophrenia is a vital element in wholly explaining the causes of schiz
Outline further Neural correlates of schiz?
- Schizophrenia is a result of further abnormalities in the brain & biochemistry
- Abnormalities can be genetically inherited or through experience
Outline Enlarged Ventricles as a neural correlate?
- Neuroimaging techniques suggest anatomical differences between brains of schiz & those non-schiz people
- Schiz - enlarged ventricles found in brain fluid-filled cavities
- Only 15% difference found in unmedicated patients, so drugs not relevant
- Enlargements appear in onset of schiz
Outline Hypofrontality as a neural correlate?
- Hypofrontality correlates with reduced blood flow in PFC (Pre Frontal Cortex)
- This is seen with negative symptoms of schiz patients (emotional & cognitive kind) e.g. avoltion (social withdrawal) & speech poverty (alogia)
Outline Hippocampus - amygdala region as a neural correlate?
- Hippocampus - Amygdala is reduced in size
- Exacerbates positive symptoms (Hallucinations/Illusions of Grandeur)
- Amygdala (emotion)
- Hippocampus (memory)
AO3 Neural correlates research against
McEwen (2007)?
P - Research against from McEwen (2007)
E - Argues that nurturing influences could cause structural changes in the brain, making explanation incomplete
E - Children & Adolescent brains more sensitive to chronic stressors (physical abuse) which shapes the structure of cortical regions
L - Therefore environmental factors can cause schiz maybe more so than biological/supports diathesis-stress model
AO3 Neural correlates
Alternative explanation due to cause & effect?
P - Other explanations may prove to be more substantial as NC has issues with cause & effect
E - Just because there’s a correlation between brain areas & symptoms does not mean the neural mechanism has caused the symptoms
E - Maybe the difference in activity levels could be a consequence of schiz and the changes in brain areas is due to the schizophrenia
L - So it is ambiguous as to what is causing the symptoms
AO3 Neural correlates
Research support Suddeth (1990)?
P - Research support from Suddeth (1990) suggests there are neural correlates that cause schiz
E - Suddeth conducted study on MZ twins we can assume neuro-physical differences cause schiz
E - It is therefore unlikely for schiz to be due to external factors as twins are genetically identical & grow up in a similar environment
L - This strengthens the neural explanation for the development of schiz
AO3 Neural correlates
Cross illness issues for enlarged ventricles?
P - Issue with Neural correlates as an explanation for schiz is enlarged ventricles, not exclusive to schiz
E - They may occur in brains of Parkinson’s disease sufferers & other disorders
E - Only some patients have enlarged ventricles, not all
- ‘Normal’ individuals also have enlarged ventricles & are schiz
L - Implies we cannot use enlarged ventricles as a biological explanation for NC’s with credibility
