Daniel et al (1991) Flashcards
Aim
To investigate the effects of dextroamphetamine on DLPFC and regional cerebral blood flow (rCBF) during Wisconsin
Card Sort Test in Schizophrenic patients.
IV of the experiment
whether participants had been given amphetamine or placebo.
DV of the experiment
performance on the Wisconsin Card Sorting Test
Hypothesis of the experiment
The researchers hypothesised that if dysfunction in the prefrontal cortex was related to problems in dopamine controlled synaptic transmission, then a substance that stimulated dopamine activity (known as an agonist) should increase the activity in that area during a cognitive task.
The agonist the researchers chose was amphetamine, a chemical that increases alertness and energy, and improves mood.
The researchers used Single-Photon Emission-Computed Tomography (SPECT) to scan the participants’ brain activity during the task
what was done in the design to control the experiment
Double-blind, placebo-controlled lab experiment
Placebo
A fake drug designed to have no effect (so it can be tested against a real drug)
Sample
Ten in-patients from the National Institute of Mental Health research wards in Washington, USA.
The study had the approval of the institutional review board and radiation safety committee, and the participants all gave informed consent to take part in it
Materials and apparatus
Images of brain activity were recorded during SPECT technology, which was capable of collecting a full set of 80 projections in five seconds. Each participant underwent two scans two to four days apart. During scanning, the participant was seated in a semi-reclined position in a comfortable chair, with their head positioned in the scanner. The head was kept still using foam-rubber inserts.
Each scan involved:
- A mock test to get the participants used to the set-up
- A test of simple sensori-motor control, where the participants match bars on screen based on their orientation (the BAR task)
- The prefrontal activation test (the WCST)
Procedure
Five participants did the BAR test first, and five did the WCST first - this is known as counterbalancing. On the two test days, each participant received either a dose of amphetamine or a placebo, again in order that was counterbalanced between the participants. Both tasks were carried out on computer and required similar motor responses.
Results (1)
Amphetamine had a minimal effect on regional cerebral blood flow when participants completed both the BAR task and the WCST
Cerebral blood flow
Supply of blood to the brain at any one given time
Results (2)
There was no significant differences in the effects of amphetamine and the placebo on brain activity when completing the BAR task. However, there were some significant differences in blood flow in particular regions of the brain when completing the WCST. The left dorsolateral prefrontal cortex, the occipital and anterior cingulate cortices were all affected
Results (3)
Amphetamine had a small but significant positive effect on two performance measures of the WCST, including the number of correct responses. There was no such effect when the placebo was used
Results (4)
Behaviour changes caused by the amphetamine were highly variable and generally mild, ranging from increased cooperation, optimism, and improved mood to irritability and dysphoria. Three patients showed clinically significant improvement, whereas one patient significantly deteriorated
Conclusions (1)
Conclusions made in this study are tentative due to the modest sample size.
Conclusions (2)
Amphetamine appeared to enhance the ability of the cortex to focus activity in response to the WSCT task.
Conclusions (3)
Amphetamine enhances task-specific activation in the DLFC (consistent with previous research).
Conclusions (4)
Amphetamine with regional and task specificity significantly increased DLPFC activation during performance of a PFC-linked cognitive task despite its globally reducing rCBF.
Criticisms (1)
The sample size was too small to be representative. It is difficult to generalise the results to other people with schizophrenia, as the sample may not been representative and the participants were all volunteers
Criticisms (2)
The sample was potentially culturally biased. The sample was drawn from a small area of the USA and consisted mainly of white people. Because there is evidence of different rates of schizophrenia between different ethnic groups and different countries, we should be cautious about making generalisations about the relationship between the brain and schizophrenia
Criticisms (3)
The study may lack temporal validity. The results may become outdated over time because the study used a different system for diagnosing schizophrenia than the one that is used today.
Criticisms (4)
Some psychologists would be concerned about the ethics of using scans when we are unclear on their long term consequences. This is an issue because the participants were scanned just for the sake of research and sometimes after only administrated a placebo
Criticisms (5)
The difference in brain activity may have been affected by the haloperidol given to the participants before the other drugs. Although haloperidol was necessary for stabilising the patients, it becomes an extraneous variable that makes it harder to establish cause and effect
