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Biology 202
2003 Second Web Paper
On Serendip

The Brains of Violent Males: The homicidal & suicidal brain

Nicole Jackman

"It becomes increasingly evident that some of the destruction which curses the earth is self-destruction; the extraordinary propensity of the human being to join hands with external forces in an attack upon his own existence is one of the most remarkable of biological phenomena."
-Karl Menninger (1).

Violence is everywhere in our society- in movies, television programs, video games, and professional sports such as boxing and wrestling. In 2000, 28,663 deaths were related to firearms. 58% were reported as suicides and 39% were reported as homicides (2). The objective of this paper is to qualitatively evaluate and compare the brains of male murderers and male suicide victims. Even though more females attempt suicide, males are used for comparison because males are four times more likely to die from a suicide attempt (3). Male suicidal individuals have a higher success rate because they are more likely to kill themselves in a violent manner (i.e. using a gun).

At first glance, most people would argue that homicide and suicide are opposite behaviors, yet the relationship may not be that straightforward. If it is assumed that the brain dictates behavior and that suicide and homicide are independent behaviors, one would expect that researchers would find differences between the brains of suicide victims and murderers. At the other extreme, suicide and homicide can be considered similar behaviors because in both cases an individual engages in killing someone, the only thing that differs is where the killing impulse is directed. Homicide is directed towards the external world, whereas suicide is aggression turned inward. When the cause of unhappiness can be attributed to an external source, the extreme response is rage and homicide. In the absence of an external source, the extreme response is likely to be depression and suicide (4). The definition of suicide and homicide as extreme responses to unhappiness is not new. It implies that these behaviors are similar, therefore one would expect similarities in the brain, and the possibility that one individual can be suicidal and homicidal simultaneously. Freud first introduced the notion that suicide and homicide were not opposite behaviors. Freud believed that every aspect of human behavior carries within it, its very opposite. In this sense, the desire to kill others is also the desire to kill oneself.

Current research supports the notion that homicide and suicide are not unique behaviors characterized by distinctive brain anatomy and chemistry. It should be noted that homicide is the only crime that regularly results in the offenders taking their own life after committing the crime (5). Of the data collected on suicide victims and murderers, there are comparable deficiencies in the pre-frontal cortex and the serotonergic system. Mechanistically, the dysfunction of the prefrontal cortex in suicidal individuals and murderers is believed to be due to reduced levels of circulating serotonin.

Serotonin is a neurotransmitter involved in the regulation and inhibition of impulsive behaviors. The effects of serotonin are predominantly inhibitory, and considerable research indicates that serotonin is essential for self-control. Furthermore, serotonin regulates mood, arousal, aggression, impulse control, and sexual activity. Low levels of serotonin coupled with testosterone can often lead to violence and aggression. In a study of violent prisoners, it was found that the offenders had significantly lower levels of serotonin in their brains (6). Research has shown that 95 percent of the brains of suicidal individuals show an altered serotonergic system, which is characterized by reduced serotonin activity. Decreases in pre-synaptic serotonin nerve terminal binding sites have been observed in the suicidal brain and there are more postsynaptic serotonin receptors in the prefrontal cortex of suicide victims, which suggests that the body is trying to compensate for low levels of serotonin (7).

The serotonergic neurons of the raphe nucleus have long projections that terminate in the prefrontal cortex. It is logical that a reduced level of serotonin would have effects on a neuron's target site. Research has confirmed that the prefrontal cortex of murderers and suicide victims are different from the prefrontal cortex of a normal individual. The prefrontal cortex is often referred to as the "executive" region since it is where humans think, imagine, and make informed decisions (8). Damage to the prefrontal cortex manifests itself in the form of impulsivity, loss of self-control, immaturity, and altered emotionality. Although correlation does not indicate causation, researchers have occasionally used prefrontal cortex injury as an indicator of the likelihood of engaging in aggressive acts. In normal individuals, the frontal lobe is very active, whereas the frontal lobe can be quite inactive in the brains of murderers (9 , 12). Similarly, suicide victims often have fewer neurons in the prefrontal cortex than normal subjects (10). These findings indicate that the prefrontal cortex may be involved in the regulation of a restraint mechanism that is sub-optimal in suicidal and homicidal individuals.

One noteworthy example of the involvement of the serotonergic system in homicide and suicide is the case of Donald Schell. Schell had been taking Paxil (an antidepressant in a class of prescription drugs called selective serotonin reuptake inhibitors (SSRIs) for only 2 days when he shot and killed his wife, his daughter, his granddaughter, and then took his own life. There appeared to be no motivation for the murder-suicide (11). Numerous examples of such murder-suicides are reported in the media and in some psychological literature, however, there is little neurobiological research that provides firm evidence that links antidepressant use with murder and suicide. The manner in which suicidal or homicidal ideation develops when an individual is taking antidepressants remains unclear.

The problem with the comparison of the homicidal and suicidal brain is that we will never know causation of the deviations of these brains from "normal". Did the killing cause a change in the chemical make-up of the brain, or is the abnormal brain responsible for the production of the killing behavior? The brain of a murderer can be examined at any time, however researchers rely on postmortem studies to reveal clues about the chemistry of the suicidal brain. The trauma of suicide may influence the chemical activity of the brain in the moments after death. One might expect differences in the brains of murderers and individuals that engage in suicidal ideation, but no differences between the brains of murderers and suicide victims, since in the latter case the individual has killed. Yet, a person that attempted suicide and randomly failed should have a similar brain to an individual that succeeded in their suicide attempt because the intent was the same.

Current research shows that there are several shared features between the suicidal and homicidal brain, however, future research may challenge such claims. Perhaps researchers are examining the wrong part of the brain or attending to the wrong neurotransmitter system. Additionally, methodological flaws in experimental design, such as a faulty selection of comparison groups, may lead to poor data. Problems could be related to a lack of comparability across individuals due to age, educational level, and past history. Some studies used very small sample sizes which may undermine the reliability of their results. A more carefully controlled, systematic study is necessary to fully understand the similarities and differences between the suicidal and homicidal brain.


1) Menninger, Karl. (1938) Man Against Himself. New York: Harcourt Brace.
2) A fact sheet on suicide and homicide.
3) Suicide Prevention Fact Sheet, Issued by the CDC (National Center for Injury Prevention Control.
4) Suicide Facts.
5) Suicide Information & Education Centre .
6) Relative Murder , a web page by the Discovery Channel
7) An article written by J. John Mann , a researcher investigating the neurobiology of suicide.
8) Decision-making processes following damage to the prefrontal cortex, Article from Brain (2002).
9) "What's different about a Killer's Brain?" Whitley Strieber's web page
10) Why? The neuroscience of suicide: Physical clues to suicide , Scientific American article.
11) Paxil & murder/ suicide. A story about how the maker of Paxil held liable in murder/suicide.
12) The mind of a killer. ABC news web page which contains pictures of normal brain and a murderer's brain

Other interesting sites
A legal history of the "serotonin defense" .
Into the Mind of a Killer , This page has good information and several pictures.
Violent Brains , includes some pictures

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