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Emma Kwiecinska 13S
The Dopamine Hypothesis (Biochemical)
To what extent does this theory provide a full explanation for the cause of SZ?
This explanation states that SZ is caused by a chemical imbalance at the synapse,
more specifically an excess of the neurochemical dopamine (DP) causing an
overstimulation of the D1 and D2 pathways, in particular the mesolimbic and
mesocortical pathways, that control emotion + aggression and thinking + reasoning.
Evidence for the DH comes from research into drugs that alter the levels of DP in
the brain, most notably amphetamines, which increase DP levels in the brain and have
often shown to worsen SZ symptoms. If this is the case, then it is possible that SZ is
caused by excess levels of DP.
1. Post mortem studies
a. One problem with this sort of research is that DP studies are usually carried
out post mortem.
b. This is an issue here because it raises the question of causality, we cannot be
sure if the excess DP levels shown are caused by the disorder or are the
result of having it.
c. For instance, in a post-mortem study by Owen (1978), SZ pps showed a
greater density of DP receptors in comparison to individuals without SZ.
These sorts of findings are used as evidence to support the DP hypothesis,
but, if the increase in DP receptor sites were a result of having SZ instead of
causing it, then this would challenge biological explanations and suggest SZ
may instead have a psychological cause.
2. Psychological cause?
a. Modrow (2003) has criticised biochemical theories of SZ for this very reason,
generally focusing on the DP hypothesis.
b. He points out that a study by Wong et al (1986) that found a 2 fold increase
in the density of DP receptors in SZ patients that had not been treated with
anti-psychotics (used as strong evidence for the DP hypothesis) has failed to
be replicated by many researchers, for instance Farde (1994) found a group
of SZ pps with normal levels of DP receptors, even in the preliminary
research by Wong an increase in receptors was not able to be found.
c. These results clearly shows that an excess of DP does not have to be present
in order for SZ to be, highlighting a very major flaw in biological explanations
of SZ; that there must be a physical abnormality.
d. Because of this, biological explanations of SZ may not be providing a full
explanation of the disorder.
3. Over simplistic?
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Emma Kwiecinska 13S
a. Psychological factors (which this theory discounts) have shown in various
studies to have a clear effect on brain chemistry. For example Rapopport
found that after 3 years, over 70% of the group on anti-psychotics had been
re-hospitalised in comparison to only 8% of the placebo group.