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Many psychologists have theorised the possibility of criminals, especially those who have committed the most heinous of crimes, having brain abnormalities. These abnormalities are the potential source of dysfunction, and those who claim they are not guilty by reason of insanity (NGRI) lean heavily on the idea of biological causes for their behaviours.
Raine et al. (1997) sought to shed light on this claim by analysing a group of 41 murderers who had pleaded NGRI. Using a positron emission tomography (PET) scan, they investigated the brains of these murderers and found some interesting and revealing results.
Murder, flaticon.com/Freepik
Many areas of the brain are associated with specific functions, but truly identifying the areas and confidently saying they are responsible for said functions is not an easy task.
For instance, the amygdala is heavily associated with aggressive and violent behaviours. It helps regulate our interpretations of the world, inhibiting and producing responses that are appropriate for the current situation. If we perceive a threat, the amygdala helps us decide how to react, both fearfully and aggressively.
The amygdala also is involved in analysing the facial features of others, especially when they are also experiencing these emotions.
So, many psychologists have acknowledged the localisation of function within the brain, and have attempted to establish the areas responsible for specific behaviours and actions. They have also argued that dysfunction of these areas results in violence and sometimes criminal behaviours in psychology. Like the amygdala, dysfunction of the prefrontal cortex has also been associated with issues in regulating aggression.
Raine et al. (1997) sought to identify these potential areas of abnormalities in the brain. They hypothesized that violent offenders who plead NGRI would have dysfunction in the prefrontal cortex, angular gyrus, amygdala, hippocampus, thalamus, and corpus callosum.
Raine et al. (1997) carried out their experiment using the following methodology:
This was a quasi-experiment. The independent variable was whether the participant was a murderer who had pled NGRI or a normal person. The dependent variable was areas of brain dysfunction.
The participants consisted of 41 subjects who had been tried in California (US), comprised of 39 men and 2 women. They had been charged with murder or manslaughter, although for this experiment Raine et al. (1997) refers to all participants as 'murderers' for consistency's sake.
They were referred to the University of California for imaging services due to their plea of insanity/incompetence, or because they were believed to have diminished capacity by those overseeing them (which may help their cases in the sentencing phase). They were all in custody during this time period.
These referrals were made for the following reasons:
In 7 of these cases, unusual circumstances were noted in the crime, which alluded to the idea of there being diminished capability or mental impairment.
During their PET scan, the subjects were not taking any regulated psychoactive medications and were asked to remain drug-free for at least two weeks leading up to the scan. Raine et al. (1997) collected urine samples to ensure, whilst undergoing a PET scan, the subjects had tested negative for any medications.
To ensure the subjects being tested were indeed showing abnormalities, they were each matched with a normal subject of the same age, who had also been tested with a PET scan at the same location.
The exception was the 6 schizophrenic subjects (all of which were men) who were matched with 6 schizophrenics. Overall, there were 41 controls (39 men and 2 women).
Just like the murderers, the controls were medication-free. The controls consented to the experiment, and those with any history of mental disorders in themselves or first-degree relatives were excluded. Those with a history of seizures, head trauma and substance abuse were also excluded.
Raine et al. (1997) used fluorodeoxyglucose (FDG), a tracer that gives off radiation when injected into the body. A PET scan can detect the radiation as it gives off positrons, which then allows it to produce an image of areas of high activity (usually indicated by red/yellow colours) and low activity (usually indicated by blue/green colours).
Build up of FDG usually indicates activity in the area of the body.
FDG was injected and taken up by the brain (a brain metabolic rate of 32 minutes), during which Raine et al. (1997) had the subjects complete a continuous performance task (CPT).
The subjects completed a practice trial of the CPT 10 minutes before their FDG injection, and they started the task 30 seconds before the injection.
After the uptake period had ended (32 minutes), the subjects were taken to the PET scanner, and scans were taken at 10mm intervals. Overall, ten slices were obtained.
The slices depicted by Adrian Raine, Raine et al. (1997): Brain Abnormalities in Murderers
They identified brain regions using:
They used a MANOVA approach (two-way group repeated-measures multivariate analyses of variance) and a three-way MANOVA when necessary.
For Raine et al. (1997), the results indicate differences in both the cortical and subcortical regions in the brain in glucose metabolic activity in murders compared to controls.
For the prefrontal areas:
For the parietal areas:
For the temporal areas:
For the occipital areas:
For the corpus callosum:
For the amygdala:
For the medial temporal lobe (including the hippocampus):
For the thalamus:
For the cingulate:
For the caudate, putamen, globus pallidus, midbrain and cerebellum:
Overall, there were no significant differences between the groups on their performance on the CPT.
They found that left-handed murderers had higher levels of medial prefrontal activity, and less abnormal amygdala asymmetry than right-handed murderers.
Overall, ethnicity appears to have no significant influence on their findings, as white murderers and non-white murderers had no significant differences.
In regards to head injuries, 23 murderers reported such issues. They found no differences in these murderers when compared to murderers without head injuries, apart from one who showed lower activity in the corpus callosum.
Overall, considering the above results we can say that murderers have lower glucose metabolism in the brain than normal, healthy controls. Specifically, the areas of lower glucose metabolism are:
They also show asymmetrical levels of activity in their left and right hemispheres in different regions of the brain, specifically:
These results support the notion of there being a biological difference in murderers when they are compared to healthy people, and could even suggest that these biological differences may be the cause of the abnormal, violent behaviours; they predispose the murderers into committing violent crimes.
As some of these brain areas, specifically the amygdala, are associated with aggression and self-control, it is not surprising that dysfunction of these areas may result in aggressive behaviours, more impulsive actions, and a lack of self-control.
Areas of the limbic system specifically aid in the control of emotion and modulation of aggression, supporting the inhibition of impulsive behaviours. When confronted by stimulating situations, especially those that may evoke hostile or malicious emotions, these murderers would not be able to form an appropriate response due to the apparent dysfunction, and then would struggle to learn from the consequences of their actions.
This also relates to the fearlessness theory, referring to the amygdala, as reduced activity in the amygdala results in a lack of fear.
PET scan example of a normal, healthy brain, commons.wikimedia.org
Raine et al. (1997) stress that the results of this study do not indicate that:
Let's consider the strengths and weaknesses of Raine et al. (1997).
Raine, A., Buchsbaum, M., & LaCasse, L. (1997). Brain abnormalities in murderers indicated by positron emission tomography. Biological psychiatry, 42(6), 495-508.
The aim of Raine et al. (1997) was to identify if murderers had abnormalities in brain function which could help explain their violent behaviours and also aid the process of identifying if they were compos mentis. They wanted to identify if differences existed in the brain structures and functions of murderers who had pled NGRI when compared to healthy controls.
Raine et al. (1997) was a quasi experiment. The independent variable was whether the participant was a murderer who had pled NGRI or a normal person. The dependent variable was areas of brain dysfunction.
Raine et al. (1997) was a quasi experiment. The independent variable was whether the participant was a murderer who had pled NGRI or a normal person. The dependent variable was areas of brain dysfunction.
Raine et al. (1997) followed protocols laid out by the Human Subjects Committee of the University of California, Irvine. Controls gave prior consent due to the potential risks (PET scans carry radiation risks), and if the murderers had issues with consenting, due to the necessity of the results aiding their sentencing in court, a lawyer or their carer consented for them. Debriefing was not explicitly discussed by Raine et al. (1997).
They concluded that murderers showed lower glucose metabolism than controls, specifically in the bilateral prefrontal cortex, the posterior parietal cortex, and the corpus callosum. They also showed asymmetrical levels of activity. This indicates there's a biological predisposition for violent and impulsive behaviours in murderers, but Raine highlighted these biological considerations are not the only cause.
The bilateral prefrontal cortex, the posterior parietal cortex, and the corpus callosum.
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