The dopamine hypothesis Flashcards
What is an excessive amount of dopamine?
Hyperdopaminergia
What is the deficiency in dopamine?
Hypodopaminergia
What is the dopamine hypothesis?
Biochemical explanations argue that SZ is caused by elevated levels of DA at key synaptic sites within the subcortical regions of the brain (mesolimbic pathway and the limbic system). This excess of DA is argued to cause a system overload where too many impulses are being transmitted, which causes the positive symptoms in SZ. This can be caused by a number of factors, including the presynaptic neurons releasing too much DA.
How do amphetamines support the DA hypothesis?
This is a dopamine agonist, which stimulates nerve cells containing dopamine causing the synapse to be flooded - large doses of the drug can cause the hallucinations and delusions of an SZ episode
How does cocaine support the DA hypothesis?
Increases the levels of DA within the brain and can cause the positive symptoms of SZ and exaggerate them in people who already have this disorder.
How do AP drugs support the dopamine hypothesis?
They block the activity of dopamine in the brain by reducing the stimulation of the dopamine system, eliminating hallucinations and delusions. By alleviating the many symptoms for SZ, AP drugs strengthen the case for dopamine being a significant contributing factor.
What is the revised dopamine hypothesis?
Modification is due to some inconsistencies in the findings. Davis pointed out that in the prefrontal cortex there are no D2 receptors and actually there appears to be a deficiency of dopamine in this region. This is more likely to be responsible for negative symptoms of SZ like avolition. This is hypodopaminergia.
DOPAMINE HYPOTHESIS - Research support?
Randrup and Munkrad created SZ-like behaviour in a sample of rats by giving them DA agonists. The rats were given amphetamines to raise DA levels three times a day for six days. They showed long lasting abnormalities including being unable to filter out irrelevant sounds. This was then reversed using AP drugs. This adds credibility to the explanation.
DOPAMINE HYPOTHESIS - Incomplete?
AP drugs were effective in 85% of patients with SZ, which raises the question of why reducing DA levels in the other 15% of patients does not alleviate symptoms. Implies that the neural explanation has limited explanatory power and there must be other factors.
DOPAMINE HYPOTHESIS - Cause and effect?
Unclear whether high levels of DA causes SZ or SZ causes high levels of DA. Therefore some treatments may not be effective. A third factor could cause both, such as excessive drug or alcohol use. This implies that the explanation is more limited.
DOPAMINE HYPOTHESIS - Practical applications?
Led to clinicians prescribing AP drugs to patients. AP drugs work by blocking the activity of DA and have been shown to be effective in up to 85% of patients. Implies that the neural explanation has tangible effects on society.
DOPAMINE HYPOTHESIS - Scientific?
Explanation is on brain chemistry, which can be studied in a controlled, objective and falsifiable manner. We can study NT levels by analysing blood samples, cerebrospinal fluid and PET scans. This promotes psychology as a scientific discipline.
