Brain abnormalities in murderers indicated by positron emission tomography Flashcards
What was Raine’s aim?
To investigate brain differences between murderers (who were pleading not guilty by reasons of insanity) and non-murderers.
What was the method?
Raine et al (1997) used a quasi-experiment with a matched pairs design. The IV is NGRI or not, and the DV is brain differences shown on a PET scan.
What are PET scans?
A brain positron emission tomography (PET) scan is an imaging test that allows doctors to see how your brain is functioning.
The scan captures images of the activity of the brain after radioactive “tracers” have been absorbed into the bloodstream. These tracers are “attached” to compounds like glucose (sugar). Glucose is the principal fuel of the brain. Active areas of the brain will be utilizing glucose at a higher rate than inactive areas. When highlighted under a PET scanner, it allows doctors to see how the brain is working and helps them detect any abnormalities.
Who were the participants?
41 murderers (39 men and 2 women=Gender bias) with an average age of 34.3 years, obtained by opportunity sampling. All had been charged with murder or manslaughter and all pleaded not guilty by reason of insanity (NGRI) or incompetence to stand trial. The participants were referred to the University of California for examination to obtain proof of their diminished capacity
What were the mental disorders?
SCHIZOPHRENIA
HISTORY OR HEAD INJURY OR ORGANIC BRAIN DAMAGE
HISTORY OF PSYCHOACTIVE DRUG USE
AFFECTIVE DISORDER
EPILEPSY
HISTORY OF HYPERACTIVITY AND LEARNING DISABILITY
PERSONALITY DISORDER
What did Raine control?
The participants were instructed to be medication free, which was checked with a urine scan, for two weeks prior to brain scanning.
Who were the control group?
The control group was formed by matching each murderer with a normal individual of the same sex and age. The six schizophrenics were matched with schizophrenics from a mental hospital. The other controls had no history of psychiatric illness, nor was there a history of psychiatric illness in any close relatives, and no significant physical illness. None were taking medication.
What was the procedure?
Opportunity sampling
A PET Scan was used to study brain activity.
All Ps were given an injection of a tracer-This tracer is taken up by the active areas of the brain and thus it was possible to compare the brains of the NGRI and control groups.
All Ps were asked to do a continuous performance task- In order to activate specific parts of the brain.
Ps were given a chance to practise the CPT before receiving the FDG injection.
Thirty seconds before the FDG injection participants started the CPT so that the initial task novelty wouldn’t be FDG labelled.
Thirty-two minutes after the FDG injection a PET scan was done of each participant. Ten horizontal slices of their brain were recorded using the cortical peel and box techniques. The article provides precise details of the scanning techniques so that the study could be replicated.
What was Raine’s findings?
The study found reduced activity in brain differences of NGRI’s in areas previously linked to violence
Prefrontal cortex
Left angular gyrus
Corpus callosum
Left hemisphere- amygdala, thalamus and hippocampus
The study found increased activity in brain differences of NGRI’s in areas previously linked to violence
Cerebellum
Right hemisphere amygdala, thalamus and hippocampus
The study found no difference in brain differences of NGRI’s in areas previously linked to violence
Caudate
Putamen
Globus Pallidus
Midbrain
What was the CPT performance like in Bothe groups?
They performed very similarly
What was Raine’s warning?
The results do not show that violent behaviour is determined by biology alone; clearly social, psychological, cultural and situational factors play important roles in predisposition to violence.
The results do not show that murderers pleading NGRI are not responsible for their actions, nor that PET can be used as a means of diagnosing violent individuals.
The results do not show that brain dysfunction causes violence. It may even be that brain dysfunction is an effect of violence.
The results do not show that violence can be explained by the results; the results relate only to criminal behaviour.
What was the conclusion?
Murderers pleading NGRI have significant differences in the metabolism of glucose in a number of brain areas compared to non-murderers. Nevertheless the findings do suggest a link between brain dysfunction and a predisposition towards violence in this specific group (NGRI murderers), which should be further investigated.
