Transcript Biological explanations of schizophrenia

Psychopathology:
Schizophrenia
UNIT 4: PSYA4
[email protected]
Topic Content
In relation to their
chosen disorder:
1.
2.
3.
4.


Schizophrenia
Depression

Phobic disorders
OCD

Candidates should
be familiar with the
following:


Clinical characteristics of the chosen disorder.
Issues surrounding the classification and diagnosis of
their chosen disorder, including reliability and
validity.
Biological explanations of their chosen
disorder, for example, genetics, biochemistry.
Psychological explanations of their chosen disorder,
for example, behavioural, cognitive, psychodynamic
and socio-cultural.
Biological therapies for their chosen disorder,
including their evaluation in terms of appropriateness
and effectiveness.
Psychological therapies for their chosen disorder, for
example, behavioural, psychodynamic and cognitivebehavioural, including their evaluation in terms of
appropriateness and effectiveness.
Family Studies
 Gottesman (1991) carried out a meta-analysis and
reviewed 40 studies that had investigated family
history of schizophrenia.
 He found that the closer the degree of geneticrelatedness, the greater the risk of schizophrenia.
 Children with two schizophrenic parents have a
concordance rate of 46%, children of one
schizophrenic parent 16% and siblings 8%.
 This supports the genetic hypothesis of
schizophrenia because…
Twin studies
 Gottesman (1991) carried out a meta-analysis and
reviewed 40 studies that had investigated family
history of schizophrenia.
 Found a concordance rate of 48% for MZ twins
and 17% for DZ twins.
Problems?
 If there is solely a genetic cause for schizophrenia,
the concordance rate for MZ twins would be 100%,
and it isn’t (48%).
 Therefore genetics cannot offer a complete
explanation for schizophrenia.
Problems considered…
 It could be that the 48% concordance rate in MZ
twins is not because they share 100% genes but
because they share very similar experiences in life.
 For example, they look the same, may dress the
same, may be treated the same and reacted to in the
same way by others around them.
 Therefore it could be environmental factors that
cause the schizophrenia rather than genetics.
Evaluation (A02)
 Twins are very rare in the general population and so
is schizophrenia.
 Therefore it is unusual to find twins with
schizophrenia.
 This means that the samples studied are small and
therefore limits the findings (i.e. may not be a true
reflection of actual concordance rates).
Adoptive Studies
 Kety et al (1988) studied 5483 Danish children who
were adopted (who had a schizophrenic biological
parent) between 1923-1947.
 A higher concordance rate (32%) for schizophrenia, or a
related disorder (e.g. schizotypal personality disorder),
was found for those who had been adopted and had a
schizophrenic biological parent compared to a control
group who had been adopted but didn’t have a
schizophrenic biological parent.
 This suggests…
Adoptive Studies
 However in this study the concordance rate of 32%
included related disorders, not purely schizophrenia.
 Therefore this reduces the validity of the findings for
a genetic basis of schizophrenia.
Evaluation: The search for relevant genes
 The biological location of a specific gene for the
cause of schizophrenia has not yet been identified,
although several have been implicated in the
development of the disorder.
 Therefore it is likely that multiple, interacting genes
lead to schizophrenia.
 The search for a specific gene continues.
IDA: Nature vs. Nurture
 Controversy surrounding origins of schizophrenia.
 Considerable evidence for genetic contribution.
 Environmental factors have also been shown to be
important (more later).
 Most agree that schizophrenia arises from a
combination of factors.
Biochemical factors
 Biochemical abnormalities should be
detectable in the brain of those
diagnosed with SZ.
The dopamine hypothesis
 SZ patients have excessive levels of
dopamine in the brain.
Biochemical Factors
Drugs to treat schizophrenia: Phenothiazines
 Phenothiazines (neuroleptic, antipsychotic drugs),
which work by reducing the action of dopamine
(known as dopamine antagonists) can reduce the
symptoms of SZ.
 This suggests that, because these drugs alleviate
many of the symptoms of SZ, the case for dopamine
being a significant contributory factor in the
development of SZ is strengthened.
Biochemical Factors
 Studies of drugs like amphetamines (dopamine
agonists – enhance the actions of dopamine) have
provided further support for the role of dopamine
in SZ.
 Large doses of these drugs can induce positive
symptoms very similar to SZ (e.g. hallucinations
and delusions) in healthy individuals.
 This supports the suggestion that schizophrenia is
due to an excess of dopamine in the brain.
Randrup and Munkvad (1966)
 Observed behaviour similar to that found in those
suffering from SZ in rats who were given
amphetamines.
 The effects were then reversed by neuroleptic drugs
(e.g. phenothiazines which work by reducing the
action of dopamine).
Post-mortems and PET scans
1.
Excessive levels of dopamine.
2.
Increased dopamine receptor density (more
dopamine receptors tightly packed into the caudate
nucleus putamen).
Consequently, from the research using postmortems and PET scans, it is now thought that,
rather than an excess of dopamine,
schizophrenia is actually a result of overly
sensitive dopamine receptors.
Evaluation
 Neither post-mortems nor PET scans can reveal
whether increased dopamine activity/increased
dopamine receptor density causes schizophrenia or
whether schizophrenia interferes with the
dopaminergic system (problem of cause and effect).
Evaluation
Effectiveness of drug treatments
 Drugs that affect levels of dopamine do not benefit all
sufferers of schizophrenia.
 Whilst many people recover fully after medication with
dopamine-based drugs, others only partially respond and
others show no effects at all.
 This suggests that a faulty dopamine system is not always
a causal factor in schizophrenia and implicates other
biochemical factors in the disorder.
Evaluation continued…
Effectiveness of drug treatments
 It may be that drugs work differently according to
the type of SZ and the type of symptoms (i.e. positive
or negative).
 E.g. amphetamines (known to affect dopamine
activity) worsen positive symptoms and lessen
negative symptoms of schizophrenia whereas
phenothiazines alleviate positive symptoms but are
not as effective with negative symptoms.
IDA: Reductionist
 Biochemical explanation is reductionist.
 It reduces a complex behaviour such as
schizophrenia down to a relatively simple level of
explanation i.e. an imbalance in brain chemicals,
specifically dopamine.
 Ignores all other potential influences in the course of
this disorder, for example…
Independent task
 In your booklets draw a visual representation of: -
Drugs to treat schizophrenia: Phenothiazines
2. The use of amphetamines
3. Post-mortems and PET scans
1.
Demonstrate what happens in terms of dopamine.
Neuroanatomical Factors
 Research examining neuroanatomical factors that
may play a role in the development of schizophrenia
have used MRI (magnetic resonance imaging)
scans.
 This is a non-invasive technique used to record radio
waves from the brain.
 These recordings are computerised and assembled
into a 3D image of the brain.
Research
 Brown et al (1986) – found decreased
brain weight and enlarged ventricles (which
are the cavities in the brain that hold
cerebrospinal fluid) in schizophrenic
patients.
Research
 Suddath et al (1990) used MRI to obtain images
of brain structure from MZ twins in which only one
twin had schizophrenia.
 The twin with schizophrenia had more enlarged
ventricles than the twin without schizophrenia.
 The differences were so large that the twin with
schizophrenia could be identified easily from the
brain images in 12/15 twin pairs.
Evaluation
 Humans do not have brains which are exactly the same size,
weight and shape. Therefore it is not easy to measure ventricle
enlargement accurately, and there are no set criteria for what
constitutes enlargement. Ventricles enlarge naturally with age
and are usually larger in male brains anyway. Therefore this
limits the validity of the research and questions the role of
structural abnormalities in the development of schizophrenia.
 Most MRI studies have been carried out on individuals
already diagnosed with schizophrenia. A problem with this is
that it is not clear whether structural abnormalities lead to
schizophrenia or whether the development of schizophrenia
causes structural changes – the problem of cause and effect.
Pair task
Exam Focus: June 2011
‘There is considerable evidence that schizophrenia is
caused by biological factors. These can be genetic,
neuroanatomical, biochemical, viral or a combination of
such factors.’4
Discuss biological explanations of schizophrenia. (8 marks
+ 16 marks)
Plan your answer – use P.E.E.L for A02.
Look at sentence starters in your booklet to help you…
Colour-code
 Decide if the term belongs to the genetic,
biochemical or neuroanatomical explanation of
schizophrenia.
 Q&A!!!