Dopamine hypothesis
Evaluate 1 bio explanation of schizophrenia (20)
One strength of the dopamine hypothesis is that it has supporting evidence.
Excess dopamine is produced by overactive dopaminergic neurons, which leads to
symptoms seen in schizophrenia. This is because patients overreact to the presence of
dopamine in their brains, which leads to hallucinations as the brain is too active.
Lieberman et al. (1987) found that 75% of patients with schizophrenia have an increase
in psychosis after taking amphetamine which is known to increase dopamine activity
and lead to “cocaine psychosis”. This means that dopamine may be the chemical
responsible for the psychotic symptoms seen in schizophrenia. This is a strength as it
provides objective evidence for the dopamine hypothesis as a scientifically credible
explanation for schizophrenia. However, in Lieberman’s study, only a small proportion of
regular users of amphetamine continued to have psychotic symptoms. This suggests
that there must be a different factor as to how brains react to the presence of dopamine
and how this leads to symptoms of schizophrenia since the dopamine hypothesis
would predict the regular users to keep having psychotic symptoms as amphetamine
increases dopamine activity, but they did not.
One weakness of the dopamine hypothesis is that it may be reductionist. This
explanation explains schizophrenia, a disorder that has many complex features, by the
imbalance of a single neurotransmitter (dopamine). For example, it would suggest that
schizophrenia may result from high levels of dopamine in the brain or a greater number
of D2 receptors in the brain which have a higher affinity to dopamine and are more likely
to bind to it. This leads to hypersensitivity of D2 dopamine receptors. As a result though,
this explanation ignores other environmental factors that may contribute to the onset of
schizophrenia. For example, Brown and Birley (1968) found that 50% of patients with
schizophrenia reported a major life event 3 weeks prior to relapse. This implies that
social conditions may be involved in triggering relapse in schizophrenic patients. This is
a weakness as the complex interrelationship between neurotransmitter levels and other
biological, physiological and social factors is ignored, but this may be a more valid
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