Biological explanation of schizophrenia - abnormal dopamine functioning (the dopamine hypothesis)

What is the central idea of the dopamine hypothesis?

That the neurotransmitter dopamine is linked to the onset of the disorder. Dopamine generally has an excitatory effect and is associated with the sensation of pleasure. If too much dopamine is released into the synapse it can lead to the onset of schizophrenia.

Why has this theory developed?

Antipsychotic drugs ‘phenothiazines’ work by decreasing dopamine activity. These drugs lessen the symptoms of schizophrenia. The dopamine-releasing drug L-dopa (used to treat Parkinson’s disease) can create schizophrenic symptoms in non-schizophrenics particularly if dose is too high. LSD a hallucinogenic which influences the dopamine system creates schizophrenic-like behaviour in non-schizophrenics and heightens symptoms in sufferers. It is probable that genetic factors are linked to faulty dopamine systems in those with schizophrenia.

The theory was updated as high levels of dopamine are not found in all schizophrenics. Also, the modern anti-schizophrenic drug clozapine has very little dopamine-blocking activity and works effectively.

Hyperdopaminergia in the ..

& what is this associated with

Hyperdopaminergia in the subcortex.

The original version of the dopamine hypothesis focused on the possible role of high levels/activity of dopamine (Hyperdopaminergia) in the subcortex (central areas of the brain e.g. Broca’s area - speech production). This may be associated with poverty of speech or experience of auditory hallucinations.

Hypodopaminergia in the …

Hypodopaminergia in the cortex.

More recent versions of the of the dopamine hypothesis have focused on abnormal dopamine systems in the cortex. Low levels of dopamine (Hypodopaminergia) in the prefrontal cortex - responsible for thinking and decision making, has been linked to negative symptoms of schizophrenia.

What else may be involved? (Neurotransmitter)

Both Hyperdopaminergia and Hypodopaminergia may be correct explanations; both high and low levels of dopamine in different brain regions are involved in schizophrenia.

The neurotransmitter glutamate may be involved too, as there is reduced function of the NMDA glutamate receptor in people with schizophrenia, with dopamine involved, as dopamine receptors restrict the release of glutamate.

Evaluation

- biological reductionism

- dopamine seems to be associated more with the positive symptoms, so may contribute only to certain aspects of the disorder. Or only certain types of schizophrenia have a link with dopamine. The dopamine hypothesis may be accused of being over simplistic, as many other neurotransmitters may also be involved in the development of schizophrenia.

- it has been argued that pharmaceutical companies were keen to see the dopamine theory promoted, as they would make huge profits from anti-schizophrenic drugs that inhibited dopamine production. The theory cannot explain why sufferers only recover slowly when given neuroleptic drugs, when the medication has an instant effect on dopamine levels.

+ Iverson (1979); reported that post-mortems on people who had had schizophrenia found excess dopamine in the limbic system. Suggesting the neurotransmitter is involved in the disorder.