"His brain made him do it" is a familiar legal defense. The possibility of neuro-chemical abnormality is floated in the press every time an unmotivated shooting takes innocent life as in Fort Bragg and Virginia Tech. Judges and jurors rarely buy the neural defense, however, so it is little used. Who is right? Can morality be pinpointed in the human brain? Is crime caused by brain malfunction?
Perhaps the most dramatic evidence that morality is localized in the brain concerns Phineas Gage, a railroad foreman. Gage had been squeaky clean until the subject of a blasting accident in 1848. The explosion drove a tamping iron right through his brain. The bar evidently severed connections between the left frontal lobe and lower-lying structures involved in regulating aggression and other emotions. The frontal lobe plays a pivotal role in decision-making and seems key to moral action
Following his accident, Gage embarrassed his friends and associates by making socially inappropriate sexual comments and generally exhibited a deterioration of moral judgment, or loss of moral character. He was "no longer Gage." Whether he ever fully recovered is unknown (see picture). Interestingly, most people with Gage-type injuries do not behave in antisocial ways (Gazzaniga, 2005, p. 98).
The censor within
Our ability to censor our own words, deeds, and even thoughts, is an adaptation to group living that is well developed in us thanks to the enlargement of our frontal lobes comparative to other primates. Apart from Gage's improbable accident, various neurological conditions can undermine this sophisticated mechanism.
A person suffering from a degenerative brain condition such as Korsakov's syndrome, or Alzheimer's disease can be subject to violent uncontrollable actions. The same is true for some infectious diseases, such as rabies that attacks the frontal lobe. Violent acts committed in an altered state of consciousness, such as during delirium, drug-induced paranoia, or while the perpetrator is sleep walking also imply diminished responsibility.
In extreme cases, neurological impairment of moral reasoning is fairly easy to establish. For most violent crimes, a neuro-chemical defense is clearly relevant, yet unpersuasive.
The majority of impulsive crimes are committed under the influence of some drug that impairs responsibility, or reduces the ability of the individual to censor out antisocial acts. If all such factors were weighed heavily in the scales of justice, few criminals would be convicted of any crime.
Most habitual criminals are antisocial personalities. This disorder is heritable and involves reduced volume of cells in the prefrontal cortex. Antisocial personality disorder is not an effective legal defense. Judges and juries prefer to see antisocials as bad rather than mad and to hold them accountable for their actions.
Morality resembles language
Whatever the legal system says on the matter, moral responsibility is arguably an evolved attribute of individual brains, just as the capacity to speak is. Having language ability means little unless we are exposed to a language early in life. By the same token, moral capacity can develop only if children learn to follow rules of socially appropriate behavior.
The precise rules are arbitrary, just as the sounds of words are. Some children learn it is bad to eat beef, others learn to avoid pork, some to avoid all animal food and others to eat animals at will.
Morality can be disrupted by brain damage just as the ability to speak is compromised by a stroke. In that sense, brain disorders may contribute to immoral acts including violent crimes. Yet, moral behavior is a fundamentally social attribute, just as speech is. It has to be learned which requires both a normal brain and relevant experiences. Once learned, it is remarkable resistant to brain disorders.
Gazzaniga, M. (2005). The ethical brain. New York: Dana Press.