Biological explanations for schizphrenia Flashcards
What are 2 biological explanations for schizophrenia?
- Genetic factors
- Neural correlates- the dopamine hypothesis, reduced activity in ventral striatum and enlarged ventricles
What are genetic factors?
Inherited factors make certain individuals more likely to develop a behaviour or mental disorder
What are neural correlates?
Changes in neuronal events and mechanisms that result in the characteristic symptoms of a behaviour or mental disorder.
What is the dopamine hypothesis?
Claims that an excess of the neurotransmitter dopamine in certain regions of the brain is associated with the positive symptoms of schizophrenia and lack of dopamine with negative symptoms.
What is hyperdopaminergia?
Excessive levels of dopamine in the subcortex and Broca’s area
What is hypodopaminergia?
Low levels of dopamine in the prefrontal cortex
What are two other changes in the brain linked to symptoms of schizophrenia?
- Reduced activity in the ventral striatum (reward system)- linked to avolition
- Enlarged ventricles- linked to negative symptoms
What is the strength of genetic explanations?
Multiple sources of evidence for genetic susceptibility:
Family studies: Gottesman (1991):
- Children with 2 schizophrenic parents= concordance rate of 46%.
- Children with 1 schizophrenic parent= 13%
- Siblings= 9%
Twin studies: Joseph (2004)= calculated that the pooled data for all schizophrenia twin studies carried out prior to 2001 showed a concordance rate for MZ twins of 40.4% and 7.4% for DZ twins.
COUNTER-ARGUMENT: MZ twins are treated more similarly and encounter more similar environments compared to DZ twins. The differences in concordance rates could be nothing more than environmental differences rather than genetic differences.
What is the limitation of genetic explanations?
Role of mutation:
It has been found that schizophrenia can take place in the absence of a family history of the disorder. A possible explanation for this is mutation in parental DNA. This can be caused by radiation, poison or viral infection.
Evidence has shown a positive correlation between parental age (associated with increased risk of sperm mutation) and risk of schizophrenia, increasing from around 0.7% with fathers under 25 to over 2% in fathers over 50. This evidence also highlights the genetic influence on schizophrenia.
What is the strength of neural correlates?
Evidence from brain scanning research:
Juckel et al. (2006)- measured activity levels in the ventral striatum in schizophrenics and found lower levels of activity than those observed in controls.
COUNTER-ARGUMENT: Correlation-causation problem= does not show a causal relationship, only correlational. Can we confidently conclude that the unusual activity in the region of the brain causes the symptom?
E.g. The correlation between activity in the ventral striatum and negative symptoms of schizophrenia- it is possible that the negative symptoms themselves mean that less information passes through the striatum, resulting in the reduced activity.
What is the limitation of neural correlates?
Evidence for dopamine hypothesis from drugs:
There has been successful drug treatment for schizophrenics which attempt to change levels of dopamine activity in the brain.
1. Drugs that increase dopaminergic activity:
- Amphetamines (not used as a medicine)= increase levels of dopamine. ‘Normal’ individuals exposed to amphetamines can develop characteristic symptoms of a schizophrenic episode, which disappear when they stop taking drug.
2. Drugs that decrease dopaminergic activity:
- Antipsychotic drugs- block activity of dopamine and so eliminate symptoms such as hallucinations and delusions. This strengthens the case for the important role of dopamine in schizophrenia.
COUNTER-ARGUMENT: It has been argued that psychotic drugs do not alleviate hallucinations and delusions in about one third of people. In addition, in some people, hallucinations and delusions are present despite levels of dopamine being normal.
