Biological Factors The Dopamine Hypothesis

Question 1

The dopamine hypothesis suggests

Answer 1

That over activity of the neurotransmitter dopamine causes schizophrenia and possibly has a genetic origin

Question 2

Causes of DA overactivity

Answer 2

Abnormally high levels of DA being released into the synapse by the pre synaptic neuron

Abnormally high numbers of DA receptors on the post synaptic dendrites

Over sensitivity of DA receptors on the post synaptic dendrites

Question 3

Any of the above conditions would mean hat more DA would

Answer 3

Bind to the receptors and because dopamine is an excitatory neurotransmitter, increases the amount of neurons that fire

Question 4

Links between dopamine overactivity and symptoms

Answer 4

Excess of DA in central areas of the brain that make up the mesolimbic pathway could explain disturbances in speech functions which could explain positive symptoms

such as disorganised speech and auditory hallucinations

Question 5

Revised DA hypothesis

Answer 5

Over activity causes positive symptoms
Low activity in prefrontal cortex May cause negative symptoms

Prefrontal cortex: planning and decision making, deficit of DA could explain avolition

Question 6

Supporting evidence for DA from neuro imaging research

Wong
Lindstroem

Answer 6

PET scans schizophrenics had twice the density of DA receptors compared to healthy controls

Chemicals needed to produce DA are taken up faster in the brains of schizophrenia sufferers compared to controls

Increases the validity, implies difference in the brains could be the cause

Question 7

Supporting evidence for DA hypothesis from drug trials
Grilly
Leucht

Answer 7

Drugs act as DA agonists eg amphetamines can make schiz patients worse, can create schizophrenia like symptoms in non sufferers

Drugs that act as DA antagonists eg antipsychotics reduce symptoms such as hallucinations and delusions
Antipsychotics tested in 212 studies significantly more effective that placebos in treating symptoms of schizophrenia
Increases validity implies link between high levels of DA and schiz, could be the cause

Question 8

Contradictory evidence against dopamine hypothesis
Noll
Ripke

Answer 8

Argues that antipsychotics (antagonist) do not help alleviate symptoms eg hallucinations and delusions in 1/3 of patients prescribed
Some schiz patients have hallucinations/delusions with normal DA levels
Not all genes associated with schizophrenia are responsible for DA production
Reduces the reliability of DA hypothesis, over activity can’t explain all cases, other neurotransmitters involved