Evaluation of the dopamine hypothesis

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Supporting Studies

Iverson - found that post mortem studies of diagnosed 'SZ' showed higher than normal concentrations of dopamine in the limbic system. Falkai et al found the same but in the amygdala (associated with aggression, emotion and language comphrension).

Wong et al - he discovered that SZ sufferers (who had never taken drugs, this is important as you can rule out drug abuse effects on the brain) had a greater density of dopamine receptors in the 'Caudate nuclei' compared to the control group who had fewer. Caudate nuclei (associated with learning, memory and language comphrension).

Davis et al - In non 'SZ', cocaine and amphetamines produce delusions and hallucinations similar to those who have 'SZ'. Both drugs are known to stimulate dopamine receptors and both exacerbate 'SZ' symptoms. Davis et al - found that 'SZ' have 6 times more D4 receptors than non 'SZ'. D4 is a particular type of dopamine found in the brain.

Kimble - Drugs which treat 'SZ' reduce the concentration of brain dopamine by blocking dopamine receptors.

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Opposing Studies

Crow et al - Drugs are helpful in treating positive symptoms and not negative symptoms. So dopamine may cause positive symptoms but not negative symptoms.

Davis - the dopamine hypothesis can not be a complete explanation as it can take several weeks for antipsychotic medication to reduce positive symptoms even though they begin blocking D2 receptors very quickly. The drugs may work because of the effect they have on other brain areas not the effect thry have on dopamine levels.

Davidson and neal - New antipsychotic drugs implicate serotonin. Serotonin neurons regulate dompamine neurons in the mesolimbic system.

Kane - discovered that the drug clozaphine (an antipsychotic) was effective in the treatment of negative symptoms in SZ such as disturbances of speech. However Clozaphine works by blocking serotonin receptors in the brain and thus may suggest that dopamine is not the only chemical in that brain that may cause 'SZ'.

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Other points

  • It is now thought that SZ is caused by oversensitive dopamine receptors or a larger number of receptors.
  • Drugs used to treat SZ are not always effective indicating factors other than biology e.g. social factors or cognitive.
  • We do not know if the excess dopamine causes SZ or if the illness causes levels of dopamine to increase.
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