1. Dopamine Hypothesis
Schizophrenia

2. What is dopamine?
Helps control the brain's reward and pleasure centres
Helps regulate movement and emotional responses
Enables us to see rewards and to take action to move toward them
Low dopamine = Parkinson’s, more prone to addiction
High dopamine = links to schizophrenia

3. Dopamine Hypothesis EXCESS dopamine = schizophrenia
Observations of patients overdosing on major stimulants (methamphetamine and cocaine)
Showed positive symptoms (hallucinations/delusions)
HYPERSENSITIVITY of receptors (too much is taken in)
++ receptors in MESOLIMBIC pathway = positive symptoms
++ receptors in MESOCORTICAL pathway = negative symptoms

4. Supporting Evidence
Opposing Evidence
Application
Specific Criticisms
Randrup and Munkvad (1966) raised dopamine in rats – became more aggressive and isolated
Carlsson et al 1999/2000 – SZs given amphetamine show a greater release of dopamine than those without SZ – those with SZ are more sensitive to dopamine
Post mortem examinations of SZ patients show a higher density of dopamine receptors than non SZ patients (Owen et al, 1978)
Wong et al 1986 discovered that SZ sufferers had a greater density of dopamine receptors in the 'Caudate nuclei' compared to the control group who had fewer
Lieberman (1987) 75% of SZ patients show an increase in psychosis after using amphetamine
Alpert & Friedhoff (1980) some patients show no improvement after taking dopamine antagonists
Schwabe et al (2004) more neurotransmitters may be involved than just dopamine – it is suggested there is a relationship between dopamine and glutamate
Drugs can be developed (antagonists) to help block dopamine receptors and reduce the symptoms of schizophrenia
Some antagonists can cause up-regulation, causing more dopamine to be absorbed and more symptoms to occur (Haracz, 1982)
The biological theory ignores social and environmental factors
A lot of research into the dopamine hypothesis is conducted on animals
Evidence can only be collected from the brains post-mortem - hard to know what came first
The use of PET scans to test SZ patients is reliable and objective BUT does not provide lots of detail