The Anatomy of Violence (46 page)

There was a further tantalizing aspect of Sharkey’s results. The cognitive decline occurred for African-American children—but not Hispanic children. Why exactly that should be is unclear, but we can hypothesize. It could be that
Hispanics feel less threatened by homicides than
African-Americans do. Sharkey points out that in communities where
African-Americans lived, 87 percent of the victims of the homicides were African-American, whereas in the murders that affected Hispanics, only 54 percent of the victims were Hispanic.
⁷⁵
Therefore, a nearby homicide may weigh more heavily on the minds of African-American children, and consequently pull down their test performance more.

I would add another cultural explanation. Because Hispanic homes tend to have a more nuclear family structure and operate under higher levels of social
support, there might be a greater social-buffering effect operating in Hispanic homes compared with African-American homes.
⁷⁶
This would attenuate the effects of the local homicide on cognitive performance. Hispanic families might protect their children from the news of homicide, or may discuss it together more as a family, emphasizing that their children are protected and safe.

Sharkey’s results are intriguing because
low
verbal IQ is an extremely long-standing and well-replicated correlate of crime.
⁷⁷
It has also been documented that African-Americans have lower verbal IQs than Caucasians,
⁷⁸
as well as higher homicide rates.
⁷⁹
Sharkey and Sampson have argued that over time, living in a disadvantaged neighborhood reduces the verbal ability of African-American children by about 4 points.
⁸⁰
Because a year of schooling is thought to result in IQ improvements of between 2 and 4 points,
⁸¹
the 4-point drop resulting from a neighborhood homicide is the equivalent of missing a year or more of schooling. Mess up schooling, and you mess up employment prospects, and we know that after that, adult crime and violence are not far down the road.

Take this even further. If the brains of African-American children are compromised by high rates of homicide that they experience in their neighborhoods, could this result in a vicious circle of increased violence and shootings in African-American neighborhoods, in turn giving rise to further neighborhood stressors and further cognitive decline?

I know this is controversial, but it is also critically important to recognize that the social environment is far more important than many have ever imagined, and complicated in ways we’re still trying to understand.
⁸²
Jonathan Kellerman as a clinical psychologist and scientist in Los Angeles was decades ahead of his time when he published a paper in 1977 documenting how environmental manipulations can reduce oppositional and destructive behavior in a seven-year-old boy with
XYY syndrome.
⁸³
The environment can overcome genetics. Believe me, this
book has changed your brain structure forever. New synaptic connections have been formed throughout your brain in the amygdala,
hippocampus, and
frontal cortex by what I have just said. Whether you like it or not, those changes will last some time and be hard to eradicate. Social experiences change the brain, likely in all ethnic and gender groups.

We’ve seen that there is a substantial genetic component to crime and violence. Despite arguments I’ve made for a direct causal pathway from genes to brain to antisocial behavior, social processes are also critical. One such process is the lack of motherly love—and the fascinating mechanism of epigenetics.

Epigenetics refers to changes in gene expression—how genes function. We often conceive of genes as fixed and static, but they are much more changeable than commonly believed. True, the underlying structure of the
DNA—the
nucleotide sequence—remains relatively fixed. But the chromatin proteins that DNA wraps itself around
⁸⁴
may be altered by the amino acids that make up these proteins. Proteins can be turned on—or turned off—by the environment. That alters how the DNA is transcribed and how the genetic material is activated.
Methylation—the chemical addition of a methyl group to cytosine, which is one of the four bases of DNA—can also increase or decrease gene expression.

How does all this occur? Through the environment—and triggered in animals by as little as a mother’s lick. The neuroscientist Michael Meaney first demonstrated that rat pups whose mothers licked and groomed them more in their first ten days of life showed changes in gene expression in the hippocampus. They also dealt better with environmental stressors.
⁸⁵
Indeed, the functioning of more than 900 genes is regulated by maternal licking and grooming in rats.
⁸⁶
Maternal separation at birth has very similar
effects.
⁸⁷
Gene expression is thought to be especially affected during prenatal and early postnatal periods,
⁸⁸
and we know that these early periods are critical not just for the brain but for disruptive childhood behavior, which is a prelude to adult violence.
⁸⁹
Take away maternal care, and there can be profound biological and genetic effects on behavior.

Strikingly, changes in gene expression caused by the early environment
appear to transfer to the next generation.
⁹⁰
Protein malnutrition during pregnancy doesn’t just alter gene expression in the offspring; the offspring’s offspring—the grandchildren—develop abnormal metabolism even when their own parents were fed quite normally.
⁹¹
So the environment not only changes gene expression in the individual—it also has permanent
effects that
transmit
to the next generation. The exciting concept here is that although 50 percent of the variation in anti
social behavior is genetic in origin, these genes are not fixed. Social influences result in modifications to DNA that have truly profound influences on future neuronal
functioning—and hence on the future of violence.

We can place these alterations in gene expression into a much broader social context of how abuse and deprivation have foundational, long-lasting effects on the brain—over and above any epigenetic effects. Early social, emotional, and nutritional deprivation in humans has been shown to result in reduced functioning of the
orbitofrontal cortex, the infralimbic prefrontal cortex, the hippocampus, the
amygdala, and the lateral temporal cortex.
⁹²
It also disrupts
white-matter connectivity in the brain—particularly the
uncinate fasciculus, a fan-like white-matter tract that connects frontal brain regions to the amygdala and temporal brain areas to the
limbic areas.
⁹³
Prolonged and chronic stress, including disrupted or poor mothering, disrupts the brain’s stress-response system. That results in excessive glucocorticoid release, a reduction in glucocorticoid receptors, an imbalance in the brain’s stress-defense mechanisms, and ultimately brain degeneration.
⁹⁴
Deprivation makes a big dent on the brain.

There are also vulnerable periods when stress can take a greater toll on different parts of the brain. If
sexual abuse occurs early, at around ages three to five, for example, hippocampal
volumes are reduced. Yet if sex abuse occurs at age fourteen to sixteen, prefrontal cortical volume is reduced instead.
⁹⁵
This is broadly consistent with the fact that the hippocampus reaches full maturity early in life
⁹⁶
and is very much affected by excessive release of
cortisol in response to stress. In contrast, the prefrontal cortex develops very slowly in
childhood, but grows more rapidly during the teenage years.
⁹⁷
All told, it’s not just that stressful rearing environments affect gene expression and neurochemical functioning—they also affect growth and connectivity of the brain.

There is, of course, much more to violence than maternal neglect. Sex abuse is almost always perpetrated by men. As we have discussed earlier, even the best of mothering sometimes cannot override a biological
predisposition to violence. Fathers and friends play a role in fostering juvenile
delinquency and adult violence as well. Yet it is undeniable that compassionate caregiving is critical for normative child development. When a mother’s love is morphed into spiteful hate—as it was with Henry
Lucas and others like him—her kids can end up killing. In this context, mothering—and the lack of it—is giving us fascinating insights not just into the pathway to violence, but also into understanding the precise mechanisms by which maternal neglect might operate.

Let’s put these pieces into place. We’ve seen that the lives of violent offenders are replete with maternal deprivation, physical and sexual abuse, other trauma,
poverty, and poor nutrition. We’ve also seen how these social impairments have their hit on specific brain areas—the orbitofrontal cortex, medial
prefrontal cortex,
amygdala,
hippocampus, and temporal cortex—brain areas that are linked to violence. We can conclude that such social deprivation results in long-term wear and tear of the developing brain to produce adolescent angst and aggression—and, ultimately, adult violence. This truly occurs, and it’s never too late for the damage to be done. Adults who lived close to the
World Trade Center buildings on September 11, 2001—and thus were exposed to very significant environmental stress—showed a
reduction in hippocampal gray-matter volumes when brain-scanned three years later.
⁹⁸
From environment to brain—and, at least in some—to ultimate destructive violence.

In this chapter we have been piecing together social and biological processes to explain violence. But what about piecing together just the bits of the brain itself? It’s an enormously multifaceted, complex organ. We saw earlier, in
chapter 5
, that multiple brain regions are implicated in white-collar crime, and we know crime and violence come in all shapes and forms. No one discrete brain region or circuit will by itself account for violence.

It is tempting to focus on the prefrontal cortex, given its
complexity and the wide empirical support for its involvement in crime. It is even more appealing to invoke a single brain circuit involving two or three regions to help acknowledge this complexity—such as the prefrontal cortex combined with the limbic system, as I outlined above,
or the orbitofrontal cortex and its control over the
amygdala.
⁹⁹
Yet a limitation of the approach I have taken so far is that it is overly simplistic. Violence is an enormously complex and multilayered construct. A complete understanding of its neural basis is certainly going to involve multiple distributed brain processes that in turn give rise to broad social and psychological processes that predispose someone to violence. By beginning to recognize and model this neural complexity, I believe we can gain deeper insights into the etiology of antisocial behavior.

In response to the charge of oversimplicity, here’s a functional neuroanatomical model of violence.
¹⁰⁰
Let’s take the anatomy of the brain and first describe the
functions of the individual areas concerned—outlining the functional significance of the brain abnormalities we have found so far in antisocial offenders. I’m basing it largely on prior reviews of structural and functional brain-imaging research on offenders.
¹⁰¹

In
Figure 8.6
, I group brain processes under three broad headings—
cognitive,
affective, and
motor—alongside the corresponding brain regions. Brain
impairments in these areas predispose someone to more complex social and behavioral outcomes that in turn predispose an individual to antisocial behavior in general and violence in particular. No direct relationships are hypothesized from brain dysfunction to antisocial behavior. Instead, the model emphasizes the translation of disrupted brain systems into relatively abstract cognitive (thinking), affective (emotional) and motor (behavioral) processes. These in turn result in more complex social outcomes that represent the more concrete and proximal risk factors for offending in general. So these brain risk factors are not conceptualized as directly causing aggressive behavior, but instead bias thoughts, feelings, and actions in an antisocial direction that then results in violence.

Let’s start on the left, with cognitive processes. Here we can see the involvement of the ventromedial
prefrontal cortex, the medial-
polar prefrontal regions, the
angular gyrus,
¹⁰²
and the
anterior and
posterior cingulate.
Impairment to these regions results in poor planning and organization, impaired
attention, the inability to shift response strategies,
¹⁰³
poor cognitive appraisal of emotion,
¹⁰⁴
poor
decision-making,
¹⁰⁵
impaired self-reflection,
¹⁰⁶
and reduced capacity to adequately process rewards and punishments.
¹⁰⁷
These cognitive impairments translate into social elements that lead to crime—poor occupational and social functioning,
¹⁰⁸
noncompliance with societal rules,
¹⁰⁹
insensitivity to
punishment cues that guide behavior,
¹¹⁰
bad life decisions,
¹¹¹
poor
cognitive control over aggressive thoughts and feelings,
¹¹²
overreaction to minor irritations,
¹¹³
lack of insight, and school
failure.