Background and aim

1. People with schizophrenia show under-activity of the prefrontal cortex, the part of the brain used for planning, reasoning and switching strategy.
2. On the dopamine hypothesis, dopamine activity is what drives that prefrontal work, so weak prefrontal activity should go with weak dopamine signalling there.
3. If that is right, a drug that stimulates dopamine ought to raise prefrontal activity and improve scores on a task the prefrontal cortex is needed for.
4. Amphetamine is one such drug, because it increases the amount of dopamine acting at the synapse.
5. Aim: to investigate activity in the prefrontal cortices of people with schizophrenia.

Method

1. Design: a laboratory experiment using repeated measures, so each participant was tested with and without amphetamine on two different days.
2. Counterbalanced: half the participants took amphetamine on the first day and half took the placebo first, which cancels out order effects such as practice on the task.
3. The placebo meant participants did not know which they had been given, so their own expectations could not shape their scores.
4. Sample: ten in-patients from mental health research wards in the USA.
5. Controls: every participant's symptoms had already been stabilised with medication before testing began.
6. None of them was physically ill, and none was using alcohol or other drugs.

Variables and apparatus

1. Independent variable: whether participants were given a placebo or 0.25 mg/kg of oral dextroamphetamine.
2. Dependent variable: performance on a cognitive task, the Wisconsin Card Sort Test, which needs the prefrontal cortex to plan and to switch strategy.
3. In that test a person sorts cards by a rule they are never told, and the rule changes without warning, so they have to notice the change and switch.
4. Apparatus: brain activity was measured by a SPECT (single-photon emission computed tomography) scan, which tracks regional cerebral blood flow as a sign of how hard an area is working.
5. Participants also performed a sensori-motor control task alongside the cognitive task, so any change could be tied to the cognitive demand rather than to general arousal.

Results

1. There was a significant difference between the amphetamine and placebo conditions on the cognitive task, but not on the sensori-motor task.
2. Amphetamine significantly increased prefrontal cortex activity during the cognitive task, and task scores were higher.
3. That rise happened despite the drug reducing overall blood flow in the brain, so the effect was specific to the prefrontal region under cognitive demand.

Conclusions

1. Dopamine modulates and enhances cortical activity, since amphetamine stimulates dopamine activity and prefrontal activity went up.
2. The prefrontal under-activity seen in schizophrenia is therefore at least partly reversible by dopaminergic means.
3. Link to the theory: this supports the dopamine hypothesis, the biological explanation of schizophrenia, in which dopamine activity at the synapse shapes how the brain functions.

Criticisms

1. Strength, the design: repeated measures removes individual differences, counterbalancing cancels order effects, and the placebo blinds the participant.
2. Strength, the data: scan readings and task scores are objective and quantitative, so another team could repeat the study and check the figures.
3. Strength, the control task: the sensori-motor task pins the effect to the cognitive demand rather than to general arousal from the drug.
4. Sample: ten in-patients is too small to represent everyone diagnosed with schizophrenia.
5. Validity: sorting cards to a hidden rule is too artificial to say much about everyday thinking.
6. Extraneous variable: the medication that stabilised symptoms was itself altering dopamine activity, so its effect cannot be separated from the amphetamine's.
7. Dated findings: schizophrenia is diagnosed differently now, so these ten patients may not match who would be diagnosed today.
8. Ethics: using scanning equipment for research alone carries risk, and so does giving amphetamine to people who are already unwell.
9. Nature and nurture: the biological explanation sits on the nature side of this debate, because it explains schizophrenia through dopamine and brain function.
10. That leaves out nurture, such as upbringing, stressful life events and rejection by other people.

Turning this into marks

1. When two criticisms are asked for, make them genuinely separate rather than one criticism rephrased.
2. Name the SPECT scan and the Wisconsin Card Sort Test, because a general reference to a brain scanning study does not secure the knowledge mark.
3. The mark most often lost is reporting the rise in prefrontal activity without saying that overall blood flow fell.