Biological Explanations - Dopamine Hypothesis

What is the dopamine hypothesis?

• Positive symptoms are associated with excess dopamine in Mesolithic pathway \n evidence for it:

• drugs that increase dopaminergic activity

• drugs that decrease doaminergic activity

What is the revised dopamine hypothesis?

Davis and Kahn proposed that positive symptoms of sz are caused by an excess of dopamine in deeper regions of the brain

Drug increase dopaminergic activity?

Individuals exposed to large doses of amphetamines can develop the characteristic hallusinations and delusions of a sz episode or for those with sz these become worse

Drugs that decrease dopaminergic activity?

• Leucht et al carried out a meta-analysis of 212 studies that had analysed the effectiveness of different antipsychotic drugs and the placebo effect

• Found that all drugs were more effective than the placebo effect, positive and negative

(-) Inconclusive supporting evidence?

• Although antagonists induce sz episodes - they also affect other neurotransmitters \n inconclusive evidence for increased dopamine in post mortem - something youd expect to see

• The idea that sz is caused by activity in the dopamine system isn’t supported

(-) Other neurotransmitters?

• Noll - claims there is strong evidence against dopamine hypothesis - doesnt get rid of symptoms in 1/3, in some people hallucinations occur without excessive dopamine

• Blocking D2 receptors had no effect - dopamine is not the sole factor other neurotransmitters may produce symptoms

Can cause and effect be established?

• Correlational nature of the theory \n cant tell if its excess of dopamine that causes SZ or sz causing excess of dopamine - bidirectional ambiguity

• Most research focuses on people who were already diagnosed - looking retrospectively