PET Scans and Crime

 by Annabel Heaton

PET scans, positive emission tomography scans, are used to track how well certain parts of the body are performing, rather than simply showing you what they look like. PET scans are particularly useful for determining how far cancer has progressed and how well it is responding to therapy in confirmed instances of cancer. However, they can be more targeted on regions such as the brain, indicating where brain activity is most active at certain points of activity.

Everyone's brains perform differently, with no set way of how a brain is “truly active”, yet there is a significant difference between the brain of a criminal and the average person's brain. Genetic and environmental variables, such as childhood impoverishment, according to the researchers, may have altered their brains early in life. Other subsequent variables, such as smoking, alcohol, or drug misuse, might have contributed to the brain abnormalities. However, on PET scans, scientists can see what part of the brain is more active than others through the use of colour and the vibrancy of which this is shown. These colours are seen in the scans using the injection of a small amount of radioactive glucose (a sugar) is injected into a vein.

The PET scanner takes a picture of where glucose is being used in the brain. PET scanning utilises a radioisotope tracer that is an analog to glucose, called fluorodeoxyglucose (FDG). This is where certain parts of the brain are highlighted to be more active than the other sections. In every level of criminal law, the inner workings of a defendant's mind are frequently a significant issue. In criminal trials, however, different rules apply to the admission of scientific evidence during the guilt and sentence phases. During the pre-trial phase, counsel may request that a criminal defendant's competency to stand trial be evaluated. If a defendant is ruled unfit to stand trial, the examiner must provide a diagnosis as to what caused the mental incapacity, as well as a prognosis for when and how competency can be restored.

A PET scan may be used in circumstances when a doctor feels a defendant's mental abilities will not be restored owing to brain injury, and can assist in demonstrating the examiner's finding of a brain-based problem. The everyday human, with no crimes committed, tends to have large amounts of brain activity in both regions of the frontal lobe, represented in vibrant reds, oranges and yellows. The frontal lobe is responsible for maintaining optimal mood, behaviour and social judgement, this is essential for homeostasis. This activity is lesser, but still present in the parietal lobe, represented in colours of yellows and greens, indicating less activity than in the frontal lobe. The frontal lobe of the brain is responsible for processing information from the body's senses, whereas the parietal lobe is responsible for processing information from the body's senses. It houses the somatosensory cortex, which is in charge of processing sensory information from all over the body such as touch, temperature, and pain.

Finally, with the occipital lobe being actively represented in colours red and yellow, this is the sector of the brain responsible for visuospatial processing, distance and depth perception, color determination, object and face recognition, and memory formation. This is contrasting to the activity in the average criminal’s brain, with the only similarity between the average person and the criminal being they have the same level of activity in the occipital lobe, showing reds and yellows. In the criminals PET scan, the colour in the frontal lobe sector of the brain is blue and black, indicating a huge lack of activity in this part of the brain. With this part of the brain being responsible for major “human” attributes and functions such as social judgement and behaviour are not as controlled, meaning they will be more impulsive and lack social judgement before acting on their impulses. Additionally, the parietal lobe has less activity than the “normal” person’s brain, indicating green and blue tones, indicating that the criminal would be more likely to not feel as much as the average person. This overall shows that there is a significant difference in PET scans and brain activity between the average member of society and the average criminal.