Extensive research has been conducted that explains the neurological, genetic, and environmental factors that predispose individuals to criminal behavior. There are several critical differences in the brain scans of incarcerated versus non-incarcerated individuals . The low-activity form of the MAO-A gene correlates with increased levels of aggression . Abuse in childhood, both physical and psychological, is often seen in individuals demonstrating psychopathic tendencies . These factors, along with others, allow us to determine individuals at risk of becoming criminals. However, there are ethical quandaries regarding the implications of this research on treatment and how accountable individuals should be held for their crimes.
Autonomic Functioning and Associated Theories
Heart rate and skin conductance are two psychophysiological measures that indicate how the autonomic nervous system functions. There is a proven association between lower autonomic functioning and increased anti-sociality and violence. For example, there are studies proving that a low resting heart rate in adolescence can be associated with an increased likelihood of becoming a criminal. There are several different theories that explain the relationship between blunted autonomic functioning and increased anti-sociality. The sensation-seeking hypothesis, for example, explains that individuals engage in antisocial behavior to increase arousal levels. On the other hand, the fearlessness hypothesis explains that antisocial individuals engage in criminal behavior because they do not experience the same physiological responses that the average individual does .
It is interesting to think about the way the average person responds to certain situations as opposed to individuals engaging in criminal behavior. On a fundamental level, we view and understand our environment differently. My next question was: could this be genetic?
Monoamine Oxidase A
Monoamine oxidase A, also known as MAOA, is a gene that codes for an enzyme responsible for breaking down monoamines, including serotonin, epinephrine, dopamine, and noradrenaline. These neurotransmitters regulate emotion, sleep, stress, among other important bodily functions . There are several studies that prove a link between MAOA and aggression. Individuals possessing the low activity form of this gene (MAOA-L) tend to be more aggressive. Negative experiences affect them more, so they react more aggressively in defense. One study investigated the behavior of people when provoked. Results showed that MAOA-H individuals showed lower levels of aggression than MAO-L individuals .
Environmental factors also play a key role. In the study mentioned above, the level of provocation impacted the levels of aggression displayed by the subjects. For example, when the level of provocation was low, both MAO-L and MAO-H individuals reacted with similar levels of aggression. However, when the level of provocation was high, there was much more aggression displayed from MAO-L subjects. In another study, MAO-L individuals who were maltreated as children were accurately predicted to commit crimes. Though the MAOA gene correlates with aggressive behavior, it is clear that the environment is a factor to be considered, too .
After discovering possible genetic factors, it was clear that genetics was only part of the equation. I knew that there were specific sections of the brain that regulated things like behavior, emotions, and more. So I wondered: could disparities in these sections be another important factor?
Brain scans of over 800 incarcerated men were reviewed in a research study that spanned over ten years, eight prisons, and two states. This study was conducted by dividing participants into groups based on what they were convicted of. Results indicated that those who attempted or actually committed homicide had reduced gray matter in their brains, especially in regions associated with social cognition, emotional processing, and behavioral control. According to Professor Jean Decety at UChicago, “More gray matter means more cells, neurons, and glia…That’s what you need to make computations, to process information – whether it’s emotional information that you use to feel empathy for someone else, or information that you use to control your behavior, to suppress your tendencies to react.” It is important to note that studies are still being conducted to determine if reduced gray matter is a causal factor of homicide; we have yet to gain enough evidence to prove this link .
Twenty-one people with antisocial personality disorder were examined. Compared to individuals with no mental disorders, the brain scans of these individuals (on average), showed an eighteen percent reduction in the volume of the brain’s middle frontal gyrus and nine percent reduction in the volume of the orbital frontal gyrus . These structures are located in the frontal lobe, which controls important cognitive skills such as emotional expression, judgment, and more .
Dr. Helen Morrison, a forensic psychiatrist, studied and interviewed 135 serial killers. By doing this, she was able to discover many similarities between them. She believes that a chromosome abnormality that manifests itself around puberty may be the trigger for their violent behavior. Their brain scans show that they lack empathy toward their victims and that they never really develop a sense of belonging in the world .
A study conducted in 2009 compared the brains of psychopaths to the brains of non-psychopaths. Researchers discovered that in the psychopaths, the amygdala was deformed, there was a thinning in the outer layer of the cortex, and there was approximately an eighteen percent reduction in the volume of the cortex. As Adrian Raine, chair of the Department of Criminology at the University of Pennsylvania explains, “The amygdala is the seat of emotion. Psychopaths lack emotion. They lack empathy, remorse, [and] guilt…” .
It is clear that many different parts of the brain play a role in criminal behavior. But now that we have all of this knowledge, what is the next step? Can we move from simply learning to actually implementing solutions? But then, at what point does human interference become immoral?
Many of the brain differences that typically lead to an individual becoming a criminal can be measured early in life. For example, criminologist Nathalie Fontaine studies tendencies toward being callous and unemotional (CU) in children ages seven to twelve. She explains that “CU traits can be used to identify a subgroup of children who are at risk,” but these traits can change as children grow. There is debate over the ethics of helping children who are at risk of becoming criminals. Experts are hesitant because brain procedures can be invasive and risky, and the individuals in question have not committed any crime. However, there are also non-invasive options. Fontaine’s studies show that emphasizing positive reinforcement instead of punishing bad behavior can make a difference. Raine is testing the impact of omega-3 fatty acids (fish oil) to see if it can reduce aggressive behavior in children. Because it is used in cell growth, it is possible that fish oil will help brain cells grow larger. Since it is relatively harmless, it is more likely to be accepted than surgical treatment .
Research also poses questions about accountability. For example, psychopaths know right from wrong, but they do not feel it the same way as the average individual. They did not choose to have a differently functioning amygdala, so what does that mean for how they should be punished? Or, with the MAO-A gene, individuals cannot control their genes, so how responsible should they be held for their actions? 
I believe that we should still hold criminals accountable for their behavior. Though genetics and brain composition do incline them to act in one way or the other, it does not force them to do so. Furthermore, as the story of James Fallon proves, one can have all of the biological traits that make a killer but still take a different path.
Why Environment Matters Too
James Fallon is a neuroscientist who has been studying the brain of psychopaths for over twenty years. He explains that serial killers tend to have lower activity in the orbital cortex, the area of the brain involved with ethical behavior, decision making, and impulse control. When there is low activity here, there is less suppression of behaviors, which can include rage and violence  .
Fallon himself has the same low orbital cortex activity that he saw in serial killers during his research. Furthermore, he has the low-activity form of the MAO-A gene. Not only that, but he explains that psychopathic tendencies can be passed down from generation to generation, and there were many killers in Fallon’s lineage. However, he grew up to research killers, not to become one. According to Fallon, genes don’t determine your fate. Instead, they play a role in tipping you one way or the other. An important factor that was luckily missing in Fallon was abuse. Fallon grew up in a happy, non-abusive household . Results of one study of fifty serial killers indicate that approximately seventy percent of them experienced maltreatment, and approximately fifty percent suffered from psychological abuse . Thus, though patterns in one’s brain or genes can make them more inclined to behave a certain way, the environment is a major factor in determining what ends up happening.
In conclusion, though there are neurological, genetic, and environmental factors that may help tip the scales in a particular direction, there is no exact formula that will determine one’s likelihood of becoming a criminal with a one-hundred percent guarantee.
Hi! My name is Aarsha Shah, and I'm currently a junior at the Academy for Health and Medical Sciences. I am president of my school's IYNA chapter and am so happy to be working with the organization outside of school, too. Some of my favorite activities involve running cross-country and volunteering as an EMT at my local rescue squad. My other hobbies include reading, dancing, and hiking!