The Anatomy of Violence (28 page)

Let’s take this idea a step further from a developmental standpoint. Neurological studies have shown us that brain damage in childhood and adulthood can raise the odds of violence. Now we’ll use structural MRI to delineate more precisely that moment in time when something goes badly amiss in brain development—and here we must go back even beyond birth.

We saw in the Introduction that
Cesare Lombroso was fascinated with the idea of a physical brain difference that marked out the born criminal. While no criminal is really “born bad,” I believe there is a “neurodevelopmental”
brain ab
normality in some offenders—a brain that does not grow in quite the way it should.

One indication of brain maldevelopment very early on is a neurological condition called
cavum
septum pellucidum. Normally everyone has two leaflets of
gray and
white matter fused together called the “septum pellucidum” that separate the lateral
ventricles—fluid-filled spaces in the middle of the brain. You can see that black space in the normal brain in the left image of
Figure 5.5
, together with the white septum pellucidum line that divides the black ventricles. During
fetal development there is in addition a smaller fluid-filled, cave-like gap—or “cavum”—right in between these two leaflets. You can see this black gap separating the two white leaflets of the septum pellucidum in the brain depicted in the right image of
Figure 5.5
. As the brain rapidly grows during the second trimester of pregnancy, the growth of your
limbic and midline structures—the
hippocampus,
amygdala, septum, and
corpus callosum—effectively press the two leaflets together until they fuse. This fusion is completed between three and six months after you are born.
⁶⁷
But when limbic structures do not develop normally, the cavum between the two leaflets remains—hence the term cavum septum pellucidum.

When we scanned the brains of our subjects from the
temp agencies, we found that nineteen of them had cavum septum pellucidum—just like the one shown in the right image of
Figure 5.5
. We called these the cavum group—those with a visible marker of very early brain maldevelopment. We compared them to individuals with normal brains. Those with cavum septum pellucidum had significantly higher scores on measures of both psychopathy and antisocial personality disorder compared with controls. They also had more charges and convictions for criminal offenses.
⁶⁸

Figure 5.5

This research design is the
“biological high risk” design. You don’t see it too often. We are taking those with the neurobiological abnormality and comparing them with those without the abnormality. But we can also slice this particular pie another way. Let’s instead start off by taking those with psychopathy, and compare them to non-antisocial controls on the
degree
to which they have cavum septum pellucidum. Fusion of the septi pellucidi from back to front during fetal development is partly on a continuum. It’s a bit like when you zip up your jeans—the zip might not close all the way and there is a gap left. So we can measure the extent to which the septum pellucidum is “zipped up,” so to speak.

What we find is that psychopaths have a greater degree of incomplete closure of the septum pellucidum, reflecting some amount of disruption to
brain development. But it’s not just psychopathy. This is also true of those with antisocial personality disorder as well as those with criminal charges and convictions. It cuts across the whole spectrum of antisocial behaviors.

We see here in the classic clinical design—where we compare those with and without a clinical disorder—a convergence of findings that match those from the biological high-risk design. Different research designs converge on the same conclusion—there is an early
neurodevelopmental
basis to crime occurring even before the child is born. The evidence for a neurodevelopmental basis to criminal and psychopathic behavior is mounting.
⁶⁹
As much as traditional criminologists and sociologists would hate to admit it, Lombroso was partly right.

We don’t know what specific factors can account for the limbic maldevelopment that gives rise to cavum septum pellucidum. We do know, however, that maternal alcohol abuse
during pregnancy plays a role.
⁷⁰
So while talk of a neurodevelopment abnormality sounds like genetic destiny, environmental influences like maternal alcohol abuse may be just as important.

There is an interesting twist to the link between cavum septum pellucidum and crime. In our study we found that brain maldevelopment was especially linked to features of antisocial personality related to lifelong antisocial behavior—things like a reckless disregarded for self and others,
lack of remorse, and aggression. Interestingly,
boxers are more likely to have cavum septum pellucidum than controls. Is that because the brain damage is caused by being biffed about in the boxing ring rather than the other way around?

Researchers think not, and instead have touted the provocative idea that those with cavum septum pellucidum are “born to box.”
⁷¹
Their idea is that cavum septum pellucidum nudges the individual into developing an aggressive personality. Those with aggressive tendencies are more likely to take up boxing, making good use of their natural aggression. But could trauma and head injury in our temp workers result in cavum septum pellucidum? We controlled for these factors, as well as many psychiatric confounds, and results remained unchanged. Cavum septum pellucidum by itself predisposes people to antisocial, psychopathic, and aggressive behavior.

For some, therefore, it’s an early neurodevelopment disorder that puts their limbic system out of kilter and places them on a path to crime. Add in a degree of frontal-lobe dysfunction, and they lose full control of their basic instincts—whether it’s sex or aggression or both.

It’s worth repeating that the complexity of the
brain matches the complexity of the causes of crime. When we learn more about our neurobiology in forthcoming decades, we’ll see that multiple brain systems are complicit. We have dug down from the surface of the pre
frontal cortex into the very deepest chasms of the brain—the cavum septum pellucidum. To mine more knowledge on violence, let’s now move away from the very center of the brain into that dysfunctional limbic system that seems not to be developing properly in psychopaths. The key culprit dwelling in this neural neighborhood? We think it’s the amygdala.

The amygdala is an almond-shaped structure lying in a deep cortical fold inside the brain—an area called the medial surface of the temporal lobe. There is one in each hemisphere of the brain, about three-quarters of the way down from the top of the brain depicted in
Figure 5.6
. This part of the brain is critically involved in the generation of emotion. No brain area is more important in the minds of neuroscientists for emotion than the amygdala. Recall that one of the striking features of the psychopath is a lack of affect and emotional depth. Juxtapose this obvious clinical observation with the equally obvious role of the amygdala in the generation of fear, and you come up with a surprisingly simple hypothesis—that the amygdala is structurally abnormal in psychopaths.

Figure 5.6
   Coronal slice of the brain showing the left and right amygdala toward the base of the brain

Despite its seeming simplicity, nobody had ever tested this hypothesis until my team and I scanned psychopaths and conducted a fine-grained analysis of their left and right
amygdalae. In collaboration with our colleagues
Art Toga and
Katherine Narr at UCLA, we used state-of-the-art mapping techniques to assess the morphology of this
brain area in both psychopaths and controls. Art Toga and his laboratory had developed the ability to map group differences on a pixel-by-pixel basis throughout the amygdala. Almost all functional-imaging research findings talk about the amygdala as a unitary structure—largely because the activation patterns seen are quite broad and not localized to any specific subregion. But my astute graduate student from Taiwan,
Yaling Yang, reasoned that the amygdala is in reality made up of thirteen different substructures or
nuclei, each with different functions. Is the amygdala deformed in psychopaths? And if so, which specific nuclei within the amygdala are compromised?

Yang found that both the right and left amygdalae are impaired in psychopaths—although the deficits are greatest on the right. Overall, there was an 18 percent reduction in the volume of the amygdala in psychopaths.
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But what specific subareas of the amygdala are structurally compromised? Yang brilliantly mapped out the corresponding amygdala nuclei. Three of the thirteen nuclei were found to be particularly deformed in psychopaths—the
central,
basolateral, and
cortical nuclei.
The specific areas of the amygdala that were deformed in psychopaths are darkly shaded in
Figure 5.6
. What do these three subregions of the amygdala do?

The central nucleus is strongly involved in the control of
autonomic nervous system functions and is also involved in
attention and vigilance.
⁷³
Not surprisingly, it plays a particularly important role in
classical conditioning, and we saw earlier that
fear conditioning is the key to conscience, with psychopaths and
criminals having fear-conditioning deficits as well as attentional deficits. The basolateral nucleus is important in avoidance learning—learning not to do things that result in punishment.
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In this respect, recidivistic offenders just cannot learn when to give up on criminal behaviors that get them punished with imprisonment. The cortical nucleus has been shown to be involved in positive
parenting behaviors, and we know what lousy parents psychopaths make. Sum up the functions of the three nuclei of the amygdala that are
structurally impaired, and it’s not too surprising that psychopaths are functionally compromised in areas important for prosocial behavior.

We think that these structural impairments to the amygdala are likely to be a product of
fetal neural maldevelopment. That is, we suspect that something is going very wrong with how this
brain structure develops throughout early life in psychopaths. It could be the type of early “health insults” that we will discuss later—like nicotine and alcohol exposure—or some other teratogen that interferes with normal limbic development just as we have seen in
cavum septum pellucidum. So it could have an environmental cause.

But it could also be genetic. Unlike the
ventral prefrontal
cortex and the frontal pole (the very front of the brain), which are quite susceptible to damage resulting from environmental
head injuries, the amygdala, with its location deep in the brain, is not generally affected by environmental insults. We simply cannot ignore the possible role of genes in the structural deformations that we observe in psychopaths.

Could the cause of the amygdala deformations be crime and psychopathy itself? Could being cold, callous, and unemotional somehow shrink the amygdala? After all, brain imaging in adults is correlational and does not demonstrate causality. What would help us here are longitudinal brain-imaging studies scanning young children early in life and following them up into adulthood to find out if the amygdala impairment precedes the onset of antisocial behavior in late childhood.

Don’t hold your breath. These studies have not been conducted. Young children don’t sit still in scanners, and it will be a long time before imaging studies of tiny tots are able to demonstrate whether an abnormal amygdala predicts adult violence and crime. Yet the amygdala analysis in adult psychopaths sets the stage for the idea that amygdala impairments predispose people to later antisocial and psychopathic behaviors—and not the other way around.

Poor
fear conditioning is a solid marker for poor amygdala functioning. As we saw in
chapter 4
, poor fear conditioning as early as age three predisposes someone to crime twenty years later.
Yu Gao strikingly demonstrated a link between amygdala functioning in early childhood and adult crime. Causation still cannot be claimed, but the temporal ordering of this relationship has been teased out. Poor conditioning precedes crime by a long chalk. It’s about as good as it gets to demonstrating causality, and Yu Gao’s results suggested that Yaling Yang’s finding of structural amygdala deformations in psychopaths is quite likely a causal predisposition to callous, cold-hearted conduct. Students from China and Taiwan had teamed up to wage war on violence and make new scientific inroads into understanding the brain basis to crime.