The Anatomy of Violence

by Adrian Raine

  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.72 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.74 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.

  PATROLLING SEA HORSES

  Moving from the frontal control region of the brain to the deeper limbic emotional areas, we are seeing signs that something is fundamentally wrong with the brain’s anatomy in offenders. Their anatomical anomalies are not restricted to these brain regions. If we move just a bit further behind the amygdala, we come to the hippocampus, a critical region shaped like a sea horse that’s involved in a variety of functions ranging from memory to spatial ability. Here too we find a structural abnormality in psychopaths, but of an unusual kind.

  We saw earlier how hippocampal functioning was impaired in offenders. That functional abnormality is likely caused by structural abnormalities that have been observed in a wide number of studies. In one group of psychopaths that we studied we found that the right hippocampus was significantly bigger than the left.75 This structural asymmetry is true in normal people too, but it is much stronger in psychopaths. Interestingly, we found this very same asymmetry in our sample of murderers, this time in terms of function.76

  What causes this abnormality is not known for certain, although there are some interesting clues. If rat pups are moved around early in life into different “homes,” they develop an exaggerated hippocampal asymmetry: the right hippocampus grows to be bigger than the left.77 We found in our interviews with psychopaths that they had been bounced around from home to home much more often than controls in their first eleven years of life—more than seven different homes in psychopaths compared with three in controls.

  Another factor is fetal alcohol exposure. When the brains of children suffering from fetal alcohol syndrome are scanned, it is found that the right-greater-than-left hippocampal volume that is found in normal controls is exaggerated by 80 percent.78 If you have read casebooks on killers, these two clues will be familiar to you. The early lives of violent offenders are invariably characterized by broken homes, substance-abusing and neglectful mothers, and instability. These factors taken together could be the environmental cause of the hippocampal abnormality we see in psychopaths.

  Other researchers have similarly observed overall smaller hippocampal volumes in violent alcoholics.79 In psychopaths, structural depressions have been found in areas of the hippocampus that play a role in autonomic responses and fear conditioning,80 while we have similarly observed volume reductions in the hippocampus in murderers from China.81

  What does the hippocampus do apart from helping you remember your boyfriend’s birthday and how to get to Walmart from the freeway exit? The hippocampus patrols the dangerous waters of emotion. For one thing, it is critically important in associating a specific place with punishment—something that helps fear conditioning.82 Just think back to where you were when a bad thing happened—that’s your hippocampus helping you remember. So, like the amygdala, it plays a key role in fear conditioning and other forms of learning that partly constitute our conscience—the guardian angel of behavior. Criminals have clear deficits in these areas. The hippocampus is also a key structure in the limbic circuit that regulates emotional behavior.83 From animal research we know that the hippocampus regul
ates aggression through projections to the midbrain periaqueductal gray and the perifornical lateral hypothalamus. These are deep subcortical structures that are highly important in regulating both defensive and reactive aggression as well as predatory attack.84 For example, rats with hippocampal lesions at birth show increased aggressive behavior in adulthood.85 These hippocampal abnormalities could be linked to the cavum septum pellucidum abnormality we just discussed, because the septum pellucidum forms part of the septo-hippocampal system, a brain circuit that researcher Joe Newman has argued plays a role in psychopathy.86

  The hippocampus and amygdala are located in the inner side of your temporal cortex. But that’s not right in the middle of your brain. What is in the middle is the corpus callosum—a colossal body of over 200 million nerve fibers that connect your two cerebral hemispheres. These fibers—the corona radiata—radiate out from the very center of your brain to the outer areas of your cerebral hemispheres, interconnecting many different brain regions. We measured the volume of the corpus callosum and its corona radiata and found that this volume is much bigger in psychopaths with antisocial personality disorder. It was also longer. And thinner too. A long, thin body of white matter. It’s as if there is too much connectivity in the brains of psychopaths—too much cross talk between the two hemispheres.

  What do we make of this? Although we often think of psychopaths as antisocial villains with a lot of negative characteristics, they’re actually a lot of fun. They have a lot of positive features, especially on the surface. In particular, many psychopaths have the gift of gab. They are very glib, very charming, very good con artists who can convince you of almost anything. Robert Hare—regarded by many as one of the world’s leading researchers on psychopathy—has demonstrated, using something called the dichotic listening task,87 that psychopaths are less “lateralized” for language.88 We found the same thing in juvenile psychopaths.89 What does this mean? In many of us, the left hemisphere is largely responsible for language processing—language is strongly lateralized to the left hemisphere. But in psychopaths it’s more of a mix of both left and right hemispheres. This might be why they seem to be so adept in their verbal skills. They have two hemispheres—not one—that they can utilize for language processing. This in turn could be due to a larger, better communicating corpus callosum.

  We have to remember that psychopaths are a special group of criminal offenders and that we cannot say the same thing about run-of-the-mill violent offenders. But whichever way you look at it, psychopaths appear to be literally “wired” differently from the rest of us.

  GETTING THE GOODS

  We have moved anatomically from the surface of the brain—the cortex—into the deeper brain regions—the subcortex. Now let’s continue our subterranean tour to another deep-brain region—the striatum. In evolutionary terms, this is an old brain structure involved in one basic function common across all species—reward-seeking behavior. For a long time in our laboratory we have felt that psychopathic individuals may be characterized by an oversensitivity to rewards. When there is a chance of getting the goods, they seem to go all out—even at the risk of negative consequences.

  The first new study I conducted when I moved from Nottingham to Los Angeles sought to test out this idea.90 I was an assistant professor. As for all assistant professors when I started out, academic life was not that easy. I was involved in studies in England and Mauritius, but the expectation was that you should also be setting up your own laboratory and conducting work independent from other investigators in order to establish your independence. You have to show that you have what it takes to go it alone.

  Easier said than done. I felt lost in L.A. I didn’t have a penny for research funds, so whatever research I did would have to be done on the cheap. One piece of luck was that I had two students who wanted to work with me during their summer alongside with Mary O’Brien, a senior professor’s graduate student who was interested in child antisocial behavior.

  The next bit of luck was that there were a bunch of juvenile delinquents living just down the road from me in the Eagle Rock neighborhood of Los Angeles. I got permission from the Superior Court of California to work with them. They lived in a home as an alternative to being sentenced to a closed institution, and for these teenage boys participating in experiments with young female undergraduates from USC was not unappealing. Forty out of the forty-three kids we approached were keen to be involved in the study.

  The third bit of luck was that while I had given up orange juice to save for a down payment on a home, I did have a deck of cards and some plastic poker chips. Taken together, this would be enough for my first study in L.A.

  We had the mischief-makers play a game of cards that went something like this. Each card had a number on it. For half of the numbers, selecting them would result in the gain of a poker chip—so this was a reward card. Half of the cards, though, would result in a loss—a punishment card. Touching the card was a response. The subject could touch it to select it, or not touch it to pass. Over the course of sixty-four card plays, the subject had to make as much money as he could—to learn which cards were the winners. We assessed which of the delinquents were psychopaths based on staff ratings of their behavior and personality, and then we compared them to delinquents who were not psychopaths.

  The results? My graduate student Angela Scarpa showed that our young psychopaths showed much greater response to the reward cards than the non-psychopaths. They were hooked on rewards, confirming previous studies showing the same in adult psychopaths.91 Our budding psychopaths actually showed better learning throughout the task too. This suggests that psychopaths can learn—as long as you use rewards to shape their behavior. It was the first time that a reputable journal had published a study on “juvenile psychopaths.”92 Until then, nobody liked the idea that adolescents might actually be psychopaths in the making.

  Twenty years went by and we were still mulling over the findings. Could this behavioral difference translate to brain differences in psychopaths? My graduate student Andrea Glenn tested the idea out on our psychopaths from temp agencies.93 The striatum is a key brain region that is associated with reward-seeking and impulsive behavior. Studies have also showed that it is involved in stimulation-seeking behavior, persistently repeating actions that are related to rewards, and enhanced learning from reward stimuli.94, 95 Sounds like psychopathic behavior, doesn’t it? We found that our psychopathic individuals showed a 10 percent increase in the volume of the striatum compared with controls. Results could not be explained by group differences in age, sex, ethnicity, substance or alcohol abuse, whole brain volumes, or even socioeconomic status. They seemed pretty solid.

  We reasoned that the increase in striatal size could contribute to the increase in the sensitivity of psychopaths to rewards, and consequently their incessant reward-seeking behavior. To be sure, psychopaths are not alone. We are all driven by rewards. We each want our own stuff. We want masses of money, a decent dwelling, fancy food, wonderful work, fun friends—and let’s throw in superb sex for good measure. But the difference between us and psychopaths is that we can say no when tempted by the goodies, whereas psychopaths just want their stuff. And they want it here, and they want it now. For them, reward is a drug that they cannot turn their backs on, and this pushes them along a path of depravity and vice.

  Our findings on psychopaths did not stand alone. Increased striatal volumes have also been found in those with antisocial personality disorder,96 while increased striatal functioning has been observed in violent alcoholics97 as well as aggressive adolescents and adults.98 Furthermore, in 2010, just two months after we had published our study touting this neural basis to reward-seeking behavior in psychopaths, a functional brain-imaging study came out from another research group with essentially the same argument.99 People in the community scoring higher on impulsive, antisocial features of psychopathy were found to be hypersensitive to rewards, this time due to excessive activation of another subcortical brain area when ant
icipating a reward—the nucleus accumbens. This brain area is strongly involved in the brain’s dopamine-reward circuitry, which we discussed in chapter 2. Antisocial individuals really do appear to be turned on more than the rest of us by stuff that takes their fancy.

  Rewards are important to offenders, and to them money doesn’t just talk—it swears. It’s very salient to them. A full 45 percent of psychopaths are motivated by money in the crimes they perpetrate.100 Studies also show that it takes less money to push psychopaths into violating moral principles than non-psychopaths.101 But more troublingly, aggressive, conduct-disordered kids show increased activity of the striatum when they view images of other people in pain.102 Somewhat sickeningly, these aggressive children seem to enjoy seeing people in pain, not unlike a number of serial killers who cruelly torture and maim their victims. Combine this characteristic with frontal-lobe dysfunction and the disinhibited behavior it causes, and you have a cocktail for criminal violence.

  However we interpret structural deficits of the amygdala, hippocampus, corpus callosum, and striatum in psychopathic and antisocial offenders, one thing stands out. These structural abnormalities are likely not the result of some discrete disease process or obvious trauma. Such causes would if anything result in overall volume reductions to these structures. Our findings are much more complex than that. The right hippocampus is larger than the left in psychopaths. The striatum is larger. The corpus callosum also has a bigger volume. And the corpus callosum is not only longer in psychopaths than in controls, it’s also thinner. So what’s the explanation here? It is likely that this shape distortion is neurodevelopmental in nature. The striatum and its associated structures—the caudate and lenticular nuclei—are enlarged, not shrunken. These brain structures are growing abnormally in psychopaths during infancy and childhood. Again we get back to the idea that there is—at least in part—a neurodevelopmental basis to psychopathic and antisocial behavior. A born criminal? Not really. But a baby whose brain is compromised in its development? Quite likely.