The Dopamine Hypothesis

Question 1

What is Dopamine?

Answer 1

It is an excitatory neurotransmitter (that causes neurons to fire). Too much causes overload and leads to schizophrenic symptoms.

Question 2

What are the brain differences between those with schizophrenia and those without?

Answer 2

Ventricles are larger, Frontal lobes are smaller, there is a higher incidence of head injuries in childhood.
This suggests schizophrenia is caused by brain damage and malformation.

Question 3

Give a brief outline of each draft of this theory

Answer 3

First Draft- High levels of dopamine cause schizophrenia.
Second- The presence of excess dopamine receptors at the synapse cause it.
Third and final- There are too many dopamine receptors in the mesolimbic pathway causes positive symptoms and excess in the mesocortical pathway cause negative symptoms.

Question 4

What are the evaluatory strengths of this hypothesis?

Answer 4

Brain differences. They may link to dopamine sensitivity, and those with the disorder have been found to have brain differences.
Amphetamines. These produce symptoms similar to schizophrenia and use of amphetamines cause excess dopamine and psychosis.
Sensitivity to dopamine uptake. Those with it are more likely to release higher amounts of dopamine when given amphetamines.

Question 5

What are the evaluatory weaknesses of this hypothesis?

Answer 5

PET scans showing blocked receptors. PET scans have found that blocking dopamine using drugs doesn’t lessen the symptoms of schizophrenia.
Amphetamines produce positive symptoms only. This shows that the dopamine hypothesis is reductionist.
Glutamate hypothesis. The glutamate hypothesis suggests that other neurotransmitters (particularly glutamate) have an effect on schizophrenia.
Social and Environmental factors are involved. Environmental factors are seen to induce schizophrenic behaviour, but this hypothesis doesn’t take it into account.