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Describe and Evaluate
Biological Explanations for Schizophrenia
Diathesis-Stress Model
A theory that explains behaviour as both a result of biological and genetic
Factors ("nature"), and life experiences ("nurture").
This model thus assumes that a disposition towards a certain disorder may
result from a combination of one's genetics and early learning.
The term "diathesis" is used to refer to a genetic predisposition toward an
abnormal or diseased condition.
According to the model, this predisposition, in combination with certain kinds
of environmental stress, results in abnormal behaviour.
This theory is often used to describe the pronunciation of mental disorders,
like schizophrenia that are produced by the interaction of a vulnerable
hereditary predisposition, with precipitating events in the environment.
We can think of it like this….
Vulnerability
•
In the diathesis–stress model, a biological or genetic vulnerability or predisposition
(diathesis) interacts with the environment and life events (stressors) to trigger
behaviours or psychological disorders.
•
The greater the underlying vulnerability, the less stress is needed to trigger the
behaviour or disorder.
•
Conversely, where there is a smaller genetic contribution greater life stress is
required to produce the particular result.
•
Even so, someone with a diathesis towards a disorder does not necessarily mean
they will ever develop the disorder.
•
Both the diathesis and the stress are required for this to happen.
•
This theory was created by Holmes & Rahe.
Here comes the Science!
• DNA contains a set of instructions. It is the carrier of information.
• Half of their genes come from their maternal line, and half from
their paternal.
• The DNA is composed of a series of genes, each of which ‘codes’ for
a particular protein.
• Minute differences in the DNA code create different shaped /
functions in the proteins made.
• As each persons DNA is different from anyone
else’s, this is their specific Genotype.
• This results in a completely unique Phenotype
(the characteristic show, as a result of both
the genes and the way in which it interacts
with the environment).
• Some genes always lead to certain characteristics; these are
known as dominant genes. To produce a characteristic,
dominant genes need to be on only one pair of chromosomes
(one copy).
• Some genes need more than one copy to produce a
characteristic, there are known as recessive genes – if a
Recessive gene is present on only one chromosome, the
characteristic will not appear.
• HOWEVER, they may be passed on and appear in a future
generation.
• Characteristics can be aspects of appearance, personality,
physical health and behaviour.
• Dizygotic twins (non-identical twins) share similar
characteristics, much like a siblings.
• Monozygotic twins (identical twins) are the result of an
embryo viably splitting early on in development. They share
almost exactly the same Chromosomal DNA.
Genes and Schizophrenia
•Researchers have looked for a particular ‘Schizophrenia Gene’ without success.
•It is now thought that combinations of certain genes might make people more
vulnerable to Schizophrenia, but this does not necessarily mean that they will
develop the symptoms.
•The evidence shows that people who have a parent with Schizophrenia are
more likely to develop it themselves.
•Biochemical research has been centred on Dopamine, which is one of the
chemicals that carry messages between brain cells.
•The theory is that an excess of dopamine, or dopamine receptors may be
involved in the development of Schizophrenia.
•Complete the Gottesmann and Sheilds research worksheet.
Evaluate
Pass the Pen Activity
A Genetic Explanation – The Synapse
How does this explain the
Dopamine Hypothesis
DOPAMINE HYPOTHESIS
The Dopamine hypothesis states that the
brain of schizophrenic patients produces
more dopamine than normal brains.
–Evidence comes from
–studies with drugs
–post mortems
–pet scans
Disturbance in the
Neurochemistry
• The first discovery in the mid 1950s was that chronic usage of large daily
doses of Amphetamines could produce a psychosis that was virtually
indistinguishable from schizophrenia.
• It was found that Amphetamine could enhance neurotransmission of
Dopamine, Norepinephrine and (to a lesser extent) Serotonin Synapses.
• The second discovery was that Chlorpromazine could improve symptoms
for schizophrenia.
• It was also discovered that Chlorpromazine could prevent Dopamine from
activating it’s D2 receptor subtype.
• The knowledge that Chlorpromazine improves symptoms of schizophrenia
while blocking D2 receptors for Dopamine has led to the development of
drugs that have similar pharmacological properties to chlorpromazine.
Normal Level of
Dopamine In The
Human Brain
Elevated Level of Dopamine
In The Brain of a
Schizophrenic Patient
(specifically the D2 receptor)
 Neurons that use the transmitter ‘dopamine’ fire too often and
transmit too many messages or too often.
 Certain D2 receptors are known to play a key role in guiding attention.
 Lowering DA activity helps remove the symptoms of schizophrenia
ROLE OF DRUGS
–Amphetamines (agonists) lead to increase in DA
levels
–Large quantities lead to delusions and hallucinations
–If drugs are given to schizophrenic patients their
symptoms get worse
Parkinson’s disease
• Parkinson’s sufferers have low
levels of dopamine
• L-dopa raises DA activity
• People with Parkinson's develop
schizophrenic symptoms if they take
too much L-dopa
–Chlorphromazine (given to schizophrenics) reduces
the symptoms by blocking D2 receptors
POST MORTEM
Falkai et al 1988
Autopsies have found that people with
schizophrenia have a larger than usual number
of dopamine receptors.
Increase of DA in brain structures and receptor
density (left amygdala and caudate nucleus
putamen)
• Concluded that DA production is abnormal for
schizophrenia
PET SCANS
Lindstroem et al (1999)
• Radioactively labelled a chemical L-Dopa
• administered to 10 patients with
schizophrenia and 10 with no diagnosis
• L-Dopa taken up quicker with schizophrenic
patients
• Suggests they were producing more DA than
the control group
Chickens hatch
from eggs, but a
mother chicken
must keep an egg
warm in order for
it to hatch
Which Came First?
The Chicken or the Egg?
Schizophrenia or Faulty
Chemicals?
Faulty chemicals cause
schizophrenia but schizophrenia
may cause faulty chemicals
Drugs may influence other systems that impact on
schizophrenia so cant be 100% sure about their
effects
Evaluate the
Dopamine Hypothesis for
Schizophrenia
Enlarged Ventricle Hypothesis
Evaluate