Concordance rates suggest there is a genetic influence to Sz
as MZ twins share 100% genes while DZ twins share 50%
CR appears higher for MZ twins
Joseph
Pooled data from no of studies + found CR of
40.4% for MZ twins + 7.4% for DZ twins
Suggests while you may expect CR to be 100% if Sz was
100% bio there is evidence of genetic influence
A02
Environmental differences
rather than bio ones
MZ twins are treated more similarily
Leading to experience of more 'identity confusion', as they are
commonly viewed as 'the twins' rather than 2 separate people
With this in mind, Joseph argued higher CR may simply be distinguishing
environmental differences of 2 types of twins
Studies focusing on other genetic relatives show greater genetic
relatedness = greater risk for person to develop disorder if relative has it
Gottesman
One researcher who wanted to determine whether bio relatives are similarly affected
more often than non-bio relatives when there is diagnosed Sz in fam
Research has shown children w/ 2 Sz parents have CR of 46%,
children w/ 1 Sz parent 13% + siblings 9%
Genetic factors: Adoption studies
A01
Further develop theory of Sz having genetic basis as
they separate biological + environmental influences
Allows researchers to differentiate between influence of indivi. genes +
environment they were raised in - away from Sz family member
Can be used to defend findings of twin + fam studies
because they remove environmental influences
Means if results are similar it further supports
all other results
A02
Research support
Tienari et al
Conducted study looking at differences between adopted children
w/ bio mothers who had Sz compared to those who didn't
Found out of 164 adoptees whose bio mothers had been diagnosed w/ Sz
11 were also diagnosed with disorder
These findings were compared to control group of 197 adoptees born
to non-Sz mothers were only 4 received diagnosis of Sz
Knowledge of adoptive parents is questionable
Would have likely been informed about child's genetic
predisposition + may have treated them differently due to this
May have meant adoptive environment either helped or hindered them as
adoptive parents may have been apprehensive about predisposition
Kringlen
Pointed out that 'one might wonder who would adopt
such a child'
Suggesting they may have had high levels of expressed emotion due from
adoptive parents or double-bind due to parents knowlesge
Diathesis stress model
Dopamine hypothesis
A01
DH claims Sz have chemical imbalance caused by messages from
neurons that transit dopamine being fired too easily or too often
High levels of D associated w/ characteristic symptoms of disorder
Suggests by controlling levels of D in brain one might be able
to lessen symptoms of Sz
A02
Research support
Amphetamines
Are a D agonist which stimulates nerve cells
containing D causing synapse to be flooded
Large doses of these cause characteristic
hallucinations + delusions of a Sz episode
Antipsychotics
Block activity of D in brain
By reducing stimulation of D system these drugs eliminate
symptoms such as hallucinations + delusions
Effects of these drugs demonstrate role D plays in Sz episode +
also demonstrate how effects can be counteracted
Post-mortem studies
Shown antipsychotics may actually have opposite effect than
that desired + may actually cause D levels to rise further
Haracz
Found these anomalies in post-mortems of those Sz who had received
antipsychotic drugs shortly before death showed elevated levels of D
Those who hadn't received medication had normal levels of D
Suggests D's role in symptoms of Sz could be
over exaggerated + potentially misleading
Brain structure: ventricles
A01
Ventricles in Sz have been found to be bigger while
other areas are smaller (frontal + temporal lobes)
than that of a normal indivi.
Torrey
Found ventricles were 15%
larger in sufferers of Sz
However, suggested ventricles were not cause of Sz but that
decreased brain tissue due to size of ventricles was cause
Suggests certain brain structures
may cause onset of Sz
A02
Ho et al
Conducted research which supports theory as they found that Sz had larger
ventricles + their brains made more cerebrospinal fluid compared to a
control group
Due to longitudinal nature of study they found that larger ventricles
became less easy it was for patients to cope w/ their symptoms
Suggests symptoms experiences by Sz could get worse as they grow older as ventricles generally become larger in males + older people
Cause and effect?
Idea is inconclusive as psychologists can't state whether
enlarged ventricles are cause or consequence of Sz
Due to fact that you can't operationalise ventricle size
from 1 person to next as we all develop differently
'Enlargement' itself is questionable as ventricles naturally get bigger in everyone
So what counts are Sz-causing enlargement and what doesn't?