1. DOPAMINE
HYPOTHESIS

2. LEARNING OBJECTIVES
You must:
• Describe the role of Dopamine (DA)
in schizophrenia
You should:
• Outline evidence to support the
hypothesis
You could:
• Evaluate the Dopamine Hypothesis

3. Lets remind ourselves how
neurotransmitters work

4. Lets remind ourselves how
neurotransmitters work

5. 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

6. Elevated Level of
Normal Level of
Dopamine In The Brain of a
Dopamine In The
Schizophrenic Patient
Human Brain
(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

7. 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

8. 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

9. 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

10. 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

11. hatch from
eggs, but a Which Came First?
mother
chicken The Chicken or the Egg?
must keep
an egg warm
in order for
it to hatch
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

12. ACTIVITY
• Use the evaluation points to write effective
AO2 commentary for the studies on the
handout
• You must comment on how the evidence you use supports or
challenges the DA hypothesis.
• You should comment on evidence both for and against the
hypothesis.
• You could use your own skills and knowledge to make
additional critical and evaluative points.

13. EVALUATION POINTS
• There is a lack of correspondence between taking the drugs and
signs of clinical effectiveness. It takes 4 weeks to see any sign that
the drugs are working when they begin to block dopamine
immediately. We can not seem to explain this time difference.
• It could be that the development of receptors in one part of the brain
may inhibit the development in another.
• Type 1 cases respond well to conventional anti-psychotic drugs.
Drugs such as CHLOPROMAZINE: Only effective at relieving the
Positive Symptoms of the Illness.
• Not good at explaining negative symptoms. Therefore suggested that
Type 2 is related to a different kind of abnormality such as brain
structure.
• PET scans have suggested that drugs did not reduce symptoms of
patients diagnosed with disorder for 10 yrs or more
• There may be other neurotransmitters involved.
• Possible that social and environmental factors trigger the condition.