Biological Explanations for Schizophrenia (24 marks)

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Discuss biological theories of schizophrenia. (24 marks)
The basic idea of the genetic theory is that schizophrenia (Sz) can be inherited and run through families. This
is tested through family, twin and adoptive studies. Zimbardo and Gottesman suggested the general
population have a 1% risk of getting Sz. Monozygotic (MZ) twins have a 46% concordance rate, Dizygotic
(DZ) twins have a 17% concordance rate and general siblings have a 9% concordance rate. This means that if
your identical twin develops schizophrenia they is a 46% chance that you will develop it too. Twin studies
are generally completed on MZ twins who were reared apart; Gottesman found a 58% concordance rate
for this. Adoptive studies look at children born to schizophrenic mother but separated from them early on;
Heston found 11% of children developed Sz, while in a control group (with non-schizophrenic mothers) 0%
of them developed it. The final way to test for genetic links would be the search for the related gene or
genes. However, this has still not been found.
The family studies on concordance rates studied by Zimbardo and Gottesman suffer from Zeitgeist. The
studies in the meta-analysis were collected from 1920-1987. This is an issue as the definition, classification
and diagnosis of schizophrenia has changed significantly since then. Therefore, there may have been people
included in the study who didn't actually have schizophrenia, making the results unreliable. Meta-analysis
also poses the issue of reliability and validity; you can't be certain that each piece of research was collected
following scientific procedure. The concordance rate for MZ twins raises several important questions. Twins
have the same genes yet the concordance rate is 46%, not 100%. Therefore there must be some other
factor involved that causes some to develop it while others don't. It may just be that twins are treated
similarly by their parents and other important figures such as teachers, causing them to both develop
schizophrenia as upbringing can affect cognitive development.
The main issue with twin studies is that the twins were often not entirely separated. The often went to the
same schools and were able to interact with each other. This means their nurture and environment were still
similar which could be the cause of the higher concordance rate, rather than the genetic link. Similarly it may
also have the disruption and fear of separation from an identical twin that caused them to suffer from
mental problems as this can be a disturbing life event. In Gottesman's study the sample was only 12 sets of
twins; this poses a lot of issues with the ability to generalise results as the same size is so small. The sample
is also not big enough to complete inferential statistics meaning it can be hard to evaluate the results.
Adoption studies look at children whose biological moth had schizophrenia but adoptive parents don't.
Results in this area have been varied but Heston found an 11% link, while Tenari found a 7% link. The issue
with Tenari's study was that children were adopted by the age of four. This means that many children were
with their mother for the critical period (first two and a half years according to Bowlby) which means they
were able to build a relationship with them and their mother's state may have already affected them. Of
the 7% of children who did develop schizophrenia the adoptive parents also had several mental issues,
meaning it could have been their behaviour and upbringing that caused the schizophrenia, not the genetic
link.
The second biological theory that can be used to describe schizophrenia is the dopamine hypothesis. This
suggests that when messages from neurones which transmit dopamine fire too easily or too often type one
positive symptoms of schizophrenia can arise. Patients also tend to have more dopamine receptors at the
synapse indicating increased release of dopamine. It may be that you genetically inherit the tendency to
have increased dopamine levels so this theory often works in conjunction with the genetic theory. Drugs like
amphetamines and LSD are known to effect the dopaminergic system by increasing levels of dopamine.
These drugs can induce states that are very similar to acute schizophrenia, showing that schizophrenia is
linked to increased levels of dopamine.
One of the main studies used to support this theory is completed on rats. Rats that were given
amphetamines appeared to show behaviour that was similar in those suffering from schizophrenia,

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The issue with this is
that it is very hard to diagnose schizophrenia in rats; in humans it is usually diagnosed by talking to patients
about their symptoms but this is impossible with animals so the results may suffer from observer or
experimenter bias.
Research into Parkinson's disease is also common. Parkinson's is caused by a lack of dopamine but when
patients are given L-dopa to increase dopamine levels they often show signs of positive schizophrenia
symptoms.…read more

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