Raine et al Flashcards
What brain parts did Raine look at in particular?
Raine looked at the role played by the prefrontal cortex, the corpus callosum, the amygdala, the medial temporal lobe (MTL)/hippocampus and the thalamus in predisposing people towards aggression
What was the aim of the study?
To find out if there is a difference in the structure of brain activity between people who have committed murder (NGRIs) and non-murderers.
What was the Independent Variable?
Whether the participant is an offender pleading Not Guilty by Reason of Insanity (NGRI) to murder, or a non-murderer in the Control group.
What was the Dependent Variable?
Relative glucose levels in the prefrontal cortex, the other lobes of the brain, the corpus callosum, the amygdala, the MTL/hippocampus and thalamus, as revealed by Positron Emission Tomography (PET).
What was the sample like?
- 41 offenders pleading NGRI to the crime of murder and 41 Controls. The NGRIs were 39 men and 2 women (mean age 34.3);
- 23 had a history of brain damage, 3 with a history of drug abuse, 6 suffered from schizophrenia, 2 with epilepsy and 7 with other emotional or learning disorders.
- The Controls were people of the same age and sex with no history of crime or mental illness, except 6 Controls who had schizophrenia.
What type of sample was used for the NGRIs?
- Opportunity Sample
What was the procedure like?
The participants were tested at the University of California. Each was injected with the glucose tracer and then performed the Continuous Performance Task (CPT) for 32 minutes. Then the PET scan was carried out.
Raine used other experimental controls:
- The participants were allowed to practice the CPT ten minutes before the glucose tracer was injected to make sure they were all equally familiar with it.
- Raine made sure none of the participants (NGRIs or Controls) was on medication; the NGRIs had been kept medication-free for 2 weeks before the PET scan.
RESULTS - What was activity like in the prefrontal cortex?
As expected, the NGRIs showed less activity in the frontal lobe, especially the prefrontal cortex which is associated with rational thinking, self-restraint and memory.
RESULTS - What was activity like in the parietal lobe?
There was also less activity in the parietal lobe, which is associated with abstract thinking (such as “morality” or “justice” but more activity in the occipital lobe (vision).
RESULTS - What was activity like in the corpus callosum?
In the sub-cortical region, the NGRIs had less activity in the corpus callosum: the “bridge” of nerve fibres connecting the brain’s two hemispheres
RESULTS - What was activity like in the amygdala and hippocampus?
There was also an imbalance of activity between the left and right hemispheres in the limbic system. There was less activity on the left and more on the right in the amygdala and MTL/hippocampus; more activity on the right side of the thalamus. These are areas of the brain associated with aggression in animals.
What conclusions were drawn?
- Prefrontal deficits (deficits are lack of activity) might make someone more impulsive and emotional
- Deficits in the limbic system might make someone aggressive, as was observed in cats; the amygdala controls urges and desires, the thalamus processes information and the hippocampus processes memory. Deficits might make it hard for someone to learn from mistakes or understand their emotions.
- Deficits in the corpus callosum make it harder for the brain’s hemispheres to communicate, making it difficult to think through long term consequences and make decisions
- Areas like the parietal lobe, amygdala and hippocampus have a part to play in recognition; deficits here might make it harder for someone to judge social situations, leading them to overreact.
