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Biology 202
2002 Third Paper
On Serendip

Is There a "Criminal" Brain?

Kathryn Rorer

It is very rare these days to turn on the news and not hear about a crime or a murder. Crime is a common occurrence yet many times it is difficult to understand how someone could bring themselves to do these things. It does seem to make any sense why a young handsome man from a good family would want to kill someone and then be able to go through with it. This leads one to wonder if the brains of people who behave in socially unacceptable ways are different from everyone else's brains. There is a substantial amount of evidence that suggests some criminals do have differences in their brains that most likely contribute to their behavior. Many of these individuals have Antisocial Personality Disorder and some are considered sociopaths.

Everyone's brain is made up slightly differently, which is good because it provides individual variation. These biological differences can greatly influence how the individual behaves. For example, the frog brain and the human brain look very different structurally and the behaviors exhibited by a frog and a human are very different. Differences in brain structure are not limited to different species, there can be differences within the same species. Wildcats and domestic cats are a good example of this. The visual system of the wild cat and the domestic cat differ in substantial ways. Domestic cats have fewer ganglion cells in the retina and have a smaller lateral geniculate nucleus, which is a part of the thalamus (9). In addition, they have fewer total neurons involved in the visual system of the brain, however the sizes of neurons do not change between the wild and domestic cats (9). It may be possible to explain these changes by looking at "domestication". Through cohabitation with humans, different reproductive and food-search patterns, this process has caused significant changes in the behavior of cats (9). Wildcats are more aggressive and independent than domestic cats, which makes sense since these characteristics are more beneficial to their survival.

Structural brain differences also occur in humans. One significant behavior difference is between men and women. Men tend to be more sexually aggressive and aroused more often. Women are generally more fluent verbally. The suprachiasmatic nucleus is usually about 2.5 larger in the male brain than the female brain and there is a part in the amygdala that is also larger (9). The suprachiasmatic nucleus affects sexual behavior and larger amounts of testosterone cause it to be larger. In females, the corpus callosum and the anterior commissure are larger (9). Both of these structures are responsible for communication between the two hemispheres in the brain. The better communication between the two sides leads to better verbal fluency. These examples show how small differences in the brain can greatly affect human behavior. This means that it is possible that criminals have differences in their brains which cause them to act in socially unacceptable ways.

In order to understand why people act in antisocial ways, one needs to pinpoint which area of the brain controls social behavior. The prefrontal cortex has been thought to have something to do with control of social behavior ever since Phineas Gage's famous accident in 1848 (1). Phineas Gage was a construction foreman who as a result of demolition accident had a tamping rod go into his cheek, through the front part of his brain and out through the top of his head again. He remained conscious through all of this and retained his intelligence and memory. However, the damage to his prefrontal cortex caused Gage's personality to change. He became impulsive, selfish and aggressive, which greatly contrasted the gentle, level-headed personality he possessed before the accident.

The characteristics that Gage exhibited after his accident closely resemble some of the symptoms involved with Antisocial Personality Disorder (1). Some of the symptoms included in the DSM-VI are apathy towards others, a disregard for rights of others, a sense of entitlement, unremorseful, unconscienceable, blameful to others, manipulative, and affectively cold (7). About a 25% of the US inmate population have this disorder (6). A 1992 FBI report said that almost half of the killers of law enforcement officers fit the criteria for antisocial personality disorder (6).

The prefrontal cortex of men who have antisocial personality disorder (ASPD) has 11% less gray matter (1). PET scans, which measure the uptake of glucose to determine the amount of cell activity, have shown that the prefrontal cortex is less active in those with ASPD (8). In one study, 38 murderers were tested; twelve came from bad backgrounds and 26 from good backgrounds. The subjects from good backgrounds showed 5.7% less activity in the medial prefrontal cortex compared to the subjects from bad backgrounds (8). The activity was 14.2% less than the bad background subjects in the right orbital frontal cortex (8).

These results provide a lot of evidence that the brains of those with antisocial personality are different from normal brains. The prefrontal cortex is known to inhibit the limbic system, which is an area of the brain that gives rise to aggressive behavior (8). Adrain Rain describes the prefrontal cortex as an "emergency brake" that prevents people from lashing out in fits of rage (1). The right frontal orbital cortex is involved with fear conditioning, which is the nonconscious process of making an association between socially unacceptable behavior and punishment (8). Fear conditioning is thought to be important in forming the conscience (8). However, since individuals with ASPD seem to lack fear, their emotions often seem blunted. Rain describes it by saying, "While some people have biological systems that make it easy, others have biological systems that make it hard. If you're an individual whose right orbital cortex is not functioning well, you're biologically disadvantaged in developing a conscience (8)."

There have also been many studies done that examine murderer's brains. In one such study, PET scans were again used to determine cell activity in 41 murderers (3). The results showed a lower level of communication between the two hemispheres of the brain. The activity in the corpus callosum, which is the bridge that links the two sides of the brain, was 18% less active than normal (3). This is significant because the left side is usually considered the rational side, and the right side is the irrational side (3). If the bridge that links the two sides isn't very active, then the rational and irrational sides would not be communicating very well. In most people, the left side of the brain has more control, but in murderer's brains neither side rules. The study also showed some evidence that murderer's emotions might be stronger than normal. The PET scans showed increased activity in the thalamus, amygdala, and limbic system by 6% compared to controls (3). All of these areas control basic emotions, such as aggression, sexual desire, and anger, and therefore increased activity in these regions would suggest stronger emotions.

Of course one question that is raised by these differences is whether the brain is different because of genetic reasons or environmental factors. Although the causes of antisocial disorder are unknown, there is some evidence that points to a few possible causes. The first is that it is due to genetics. People who have antisocial fathers are also likely to be antisocial (8). This is also true for people who were not raised by their biological antisocial father. Birth and pregnancy complications also seem to produce ASPD. Fetal Alcohol Syndrome and Heavy Cigarette smoking during pregnancy correlate with conduct disorder (5). Other factors lead exposure and undernourishment (4). It appears that these deficiencies in the child's early developmental stages can create the type of brain damage that leads to ASPD.

The factors that cause these brain differences do not appear to be things that the individual can control. This brings in the question of how accountable are these criminals for their actions. It is fairly clear that the differences in their brains influence how they act, and they could not prevent having these differences, so how much control do they really have over their actions. The reason why these people are punished and held accountable is because people have the power to decide how to act. However there is evidence that suggests that people do not have as much control over their actions as they think. For example, phermones are chemical signals that people emit but are not consciously perceived. The signals can affect how sexually attracted people are to each other yet people do not realize that this is why they are attracted to certain people. This attraction however can affect how this person behaves towards the other person. This feeling of attraction is what provides the motive for how the person responds. However, it is important to point out that the person can respond to this feeling a variety of ways.

It is very likely that criminals may perceive and feel things differently, but it the end it is up to them to decide how to act (1). It may be more difficult for criminals to act in socially responsible ways because their brains cause them to have feelings that contradict these principles, however it can be done. The may brain influence all aspects of behavior, but it doesn't determine behavior. It is important to understand and recognize these differences because it may be able to help prevent crime. If potential criminals are identified and taught how to control their different emotions, it may be possible to prevent hearing about crime everyday on the news.


1)Brain Differences in Antisocials
2)What Lurks Within Murderous Minds?
3)Neural Roots of Murder
4)Crime & Nourishment
5)Prenatal Smoking Linked to Conduct Disorder in Boys
6)Psychopathy and Antisocial Personality Disorder: A Case of Diagnostic Confusion
7)The Psychopath's Brain: Tormented Souls, Diseased Brains
8)Functional Families, Dysfunctional Brains
9)>Different Brains, Different Behaviors

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