What was the experimental design?
Matched pairs design
What type of experiment was it?
Quasi-experiment
What was the IV and the DV?
- IV = NGRI
- DV = Brain differences
Describe the experimental group.
- 41 participants, 39 men & 2 women.
- Mean age of 34.3
- All charged with murder / manslaughter and pleaded NGRI.
- Referred to the University of California for examination to prove their diminished capacity.
- 6 were schizophrenic and 23 had a history of head injury / brain damage.
What was the experimental group instructed to do 2 weeks prior to scanning?
Be medication free
Describe the control group.
- Each murderer was matched with a normal individual of the same sex and age.
- The 6 schizophrenics were matched with 6 schizophrenics from a mental hospital.
- The other controls had no history of mental illness, nor any significant physical illness.
- None were taking medication.
What sampling method was used?
Opportunity sampling
What type of scan was used to study the active brain?
PET scans
What is the name of the tracer and what does it do?
- FDG
- The tracer is taken up by active areas of the brain, making it possible to compare the brains of the experimental and control group.
What does the CPT do?
Aims to activate the target areas of the brain to see how they function.
What is step 1 of the procedure?
Participants were given a chance to practice the CPT before receiving the FDG injection.
What is step 2 of the procedure?
30 seconds before the injection, participants start the CPT so the initial task wouldn’t be FDG labelled.
What is step 3 of the procedure?
- 32 minutes after the FDG injection, PET scans were done of each participant.
- 10 horizontal pictures of the brain were recorded.
- Precise details of the scanning techniques were recorded so that the study could be replicated.
What brain differences were found?
- Reduced activity in the brains of NGRI in areas previously linked to violence, e.g. the prefrontal cortex.
- Increased activity in the brains of NGRI in areas not previously linked to violence, e.g. the cerebellum.
- Abnormal asymmetries were found = Reduced activity on the left side of the brain, greater activity on the right.
How can violent behaviour be explained?
The disruption of a network of interacting brain mechanisms.
How was the study designed?
- Carefully
- Matched controls
- Large sample
What DON’T the findings show?
- Violent behaviour isn’t determined by biology alone; social, psychological, cultural and situational factors also play important roles in predisposition to violence.
- They don’t show that murderers pleading NGRI are not responsible for their actions.
What does reduced activity in the prefrontal cortex show?
- A deficit linked to impulsivity.
- Loss of control.
- Immaturity.
- inability to modify behaviour.
These are all associated with increased aggressive behaviour.
