The Best American Science and Nature Writing 2012

by Dan Ariely

  The answer is that speed comes at the price of flexibility. While a myelin coating greatly accelerates an axon’s bandwidth, it also inhibits the growth of new branches from the axon. According to Douglas Fields, an NIH neuroscientist who has spent years studying myelin, “This makes the period when a brain area lays down myelin a sort of crucial period of learning—the wiring is getting upgraded, but once that’s done, it’s harder to change.”

  The window in which experience can best rewire those connections is highly specific to each brain area. Thus the brain’s language centers acquire their insulation most heavily in the first thirteen years, when a child is learning language. The completed insulation consolidates those gains—but makes further gains, such as second languages, far harder to come by.

  So it is with the forebrain’s myelination during the late teens and early twenties. This delayed completion—a withholding of readiness—heightens flexibility just as we confront and enter the world that we will face as adults.

  This long, slow, back-to-front developmental wave, completed only in the mid-twenties, appears to be a uniquely human adaptation. It may be one of our most consequential. It can seem a bit crazy that we humans don’t wise up a bit earlier in life. But if we smartened up sooner, we’d end up dumber.

  DAVID EAGLEMAN

  The Brain on Trial

  FROM The Atlantic

  ON THE STEAMY first day of August 1966, Charles Whitman took an elevator to the top floor of the University of Texas Tower in Austin. The twenty-five-year-old climbed the stairs to the observation deck, lugging with him a footlocker full of guns and ammunition. At the top, he killed a receptionist with the butt of his rifle. Two families of tourists came up the stairwell; he shot them at point-blank range. Then he began to fire indiscriminately from the deck at people below. The first woman he shot was pregnant. As her boyfriend knelt to help her, Whitman shot him as well. He shot pedestrians in the street and an ambulance driver who came to rescue them.

  The evening before, Whitman had sat at his typewriter and composed a suicide note:

  I don’t really understand myself these days. I am supposed to be an average reasonable and intelligent young man. However, lately (I can’t recall when it started) I have been a victim of many unusual and irrational thoughts.

  By the time the police shot him dead, Whitman had killed thirteen people and wounded thirty-two more. The story of his rampage dominated national headlines the next day. And when police went to investigate his home for clues, the story became even stranger: in the early hours of the morning on the day of the shooting, he had murdered his mother and stabbed his wife to death in her sleep.

  It was after much thought that I decided to kill my wife, Kathy, tonight . . . I love her dearly, and she has been as fine a wife to me as any man could ever hope to have. I cannot rationa[l]ly pinpoint any specific reason for doing this . . .

  Along with the shock of the murders lay another, more hidden, surprise: the juxtaposition of his aberrant actions with his unremarkable personal life. Whitman was an Eagle Scout and a former marine, studied architectural engineering at the University of Texas, and briefly worked as a bank teller and volunteered as a scoutmaster for Austin’s Boy Scout Troop 5. As a child, he’d scored 138 on the Stanford-Binet IQ test, placing in the 99th percentile. So after his shooting spree from the University of Texas Tower, everyone wanted answers.

  For that matter, so did Whitman. He requested in his suicide note that an autopsy be performed to determine if something had changed in his brain—because he suspected it had.

  I talked with a Doctor once for about two hours and tried to convey to him my fears that I felt [overcome by] overwhelming violent impulses. After one session I never saw the Doctor again, and since then I have been fighting my mental turmoil alone, and seemingly to no avail.

  Whitman’s body was taken to the morgue, his skull was put under the bone saw, and the medical examiner lifted the brain from its vault. He discovered that Whitman’s brain harbored a tumor the diameter of a nickel. This tumor, called a glioblastoma, had blossomed from beneath a structure called the thalamus, impinged on the hypothalamus, and compressed a third region called the amygdala. The amygdala is involved in emotional regulation, especially of fear and aggression. By the late 1800s, researchers had discovered that damage to the amygdala caused emotional and social disturbances. In the 1930s, the researchers Heinrich Klüver and Paul Bucy demonstrated that damage to the amygdala in monkeys led to a constellation of symptoms, including lack of fear, blunting of emotion, and overreaction. Female monkeys with amygdala damage often neglected or physically abused their infants. In humans, activity in the amygdala increases when people are shown threatening faces, are put into frightening situations, or experience social phobias. Whitman’s intuition about himself—that something in his brain was changing his behavior—was spot-on.

  Stories like Whitman’s are not uncommon: legal cases involving brain damage crop up increasingly often. As we develop better technologies for probing the brain, we detect more problems and link them more easily to aberrant behavior. Take the 2000 case of a forty-year-old man we’ll call Alex, whose sexual preferences suddenly began to transform. He developed an interest in child pornography—and not just a little interest but an overwhelming one. He poured his time into child-pornography web sites and magazines. He also solicited prostitution at a massage parlor, something he said he had never previously done. He reported later that he’d wanted to stop, but “the pleasure principle overrode” his restraint. He worked to hide his acts, but subtle sexual advances toward his prepubescent stepdaughter alarmed his wife, who soon discovered his collection of child pornography. He was removed from his house, found guilty of child molestation, and sentenced to rehabilitation in lieu of prison. In the rehabilitation program, he made inappropriate sexual advances toward the staff and other clients and was expelled and routed toward prison.

  At the same time, Alex was complaining of worsening headaches. The night before he was to report for prison sentencing, he couldn’t stand the pain anymore and took himself to the emergency room. He underwent a brain scan, which revealed a massive tumor in his orbitofrontal cortex. Neurosurgeons removed the tumor. Alex’s sexual appetite returned to normal.

  The year after the brain surgery, his pedophilic behavior began to return. The neuroradiologist discovered that a portion of the tumor had been missed in the surgery and was regrowing—and Alex went back under the knife. After the removal of the remaining tumor, his behavior again returned to normal.

  When your biology changes, so can your decision making and your desires. The drives you take for granted (“I’m a heterosexual/homosexual,” “I’m attracted to children/adults,” “I’m aggressive/not aggressive,” and so on) depend on the intricate details of your neural machinery. Although acting on such drives is popularly thought to be a free choice, the most cursory examination of the evidence demonstrates the limits of that assumption.

  Alex’s sudden pedophilia illustrates that hidden drives and desires can lurk undetected behind the neural machinery of socialization. When the frontal lobes are compromised, people become disinhibited, and startling behaviors can emerge. Disinhibition is commonly seen in patients with frontotemporal dementia, a tragic disease in which the frontal and temporal lobes degenerate. With the loss of that brain tissue, patients lose the ability to control their hidden impulses. To the frustration of their loved ones, these patients violate social norms in endless ways: shoplifting in front of store managers, removing their clothes in public, running stop signs, breaking out in song at inappropriate times, eating food scraps found in public trash cans, being physically aggressive or sexually transgressive. Patients with frontotemporal dementia commonly end up in courtrooms, where their lawyers, doctors, and embarrassed adult children must explain to the judge that the violation was not the perpetrator’s fault, exactly: much of the brain has degenerated, and medicine offers no remedy. Fifty-seven percent of frontotemporal-dementia pa
tients violate social norms, as compared with only 27 percent of Alzheimer’s patients.

  Changes in the balance of brain chemistry, even small ones, can also cause large and unexpected changes in behavior. Victims of Parkinson’s disease offer an example. In 2001 families and caretakers of Parkinson’s patients began to notice something strange. When patients were given a drug called pramipexole, some of them turned into gamblers. And not just casual gamblers but pathological gamblers. These were people who had never gambled much before, and now they were flying off to Vegas. One sixty-eight-year-old man amassed losses of more than $200,000 in six months at a series of casinos. Some patients became consumed with Internet poker, racking up unpayable credit-card bills. For several, the new addiction reached beyond gambling, to compulsive eating, excessive alcohol consumption, and hypersexuality.

  What was going on? Parkinson’s involves the loss of brain cells that produce a neurotransmitter known as dopamine. Pramipexole works by impersonating dopamine. But it turns out that dopamine is a chemical doing double duty in the brain. Along with its role in motor commands, it also mediates the reward systems, guiding a person toward food, drink, mates, and other things useful for survival. Because of dopamine’s role in weighing the costs and benefits of decisions, imbalances in its levels can trigger gambling, overeating, and drug addiction—behaviors that result from a reward system gone awry. Physicians now watch for these behavioral changes as a possible side effect of drugs like pramipexole. Luckily, the negative effects of the drug are reversible—the physician simply lowers the dosage, and the compulsive gambling goes away.

  The lesson from all these stories is the same: human behavior cannot be separated from human biology. If we like to believe that people make free choices about their behavior (as in “I don’t gamble because I’m strong-willed”), cases like Alex the pedophile, the frontotemporal shoplifters, and the gambling Parkinson’s patients may encourage us to examine our views more carefully. Perhaps not everyone is equally “free” to make socially appropriate choices.

  Does the discovery of Charles Whitman’s brain tumor modify your feelings about the senseless murders he committed? Does it affect the sentence you would find appropriate for him, had he survived that day? Does the tumor change the degree to which you consider the killings “his fault”? Couldn’t you just as easily be unlucky enough to develop a tumor and lose control of your behavior?

  On the other hand, wouldn’t it be dangerous to conclude that people with a tumor are free of guilt and that they should be let off the hook for their crimes?

  As our understanding of the human brain improves, juries are increasingly challenged with these sorts of questions. When a criminal stands in front of the judge’s bench today, the legal system wants to know whether he is blameworthy. Was it his fault or his biology’s fault?

  I submit that this is the wrong question to be asking. The choices we make are inseparably yoked to our neural circuitry, and therefore we have no meaningful way to tease the two apart. The more we learn, the more the seemingly simple concept of blameworthiness becomes complicated, and the more the foundations of our legal system are strained.

  If I seem to be heading in an uncomfortable direction—toward letting criminals off the hook—please read on, because I’m going to show the logic of a new argument, piece by piece. The upshot is that we can build a legal system more deeply informed by science, in which we will continue to take criminals off the streets, but we will customize sentencing, leverage new opportunities for rehabilitation, and structure better incentives for good behavior. Discoveries in neuroscience suggest a new way forward for law and order—one that will lead to a more cost-effective, humane, and flexible system than the one we have today. When modern brain science is laid out clearly, it is difficult to justify how our legal system can continue to function without taking what we’ve learned into account.

  Many of us like to believe that all adults possess the same capacity to make sound choices. It’s a charitable idea but demonstrably wrong. People’s brains are vastly different.

  Who you even have the possibility to be starts at conception. If you think genes don’t affect how people behave, consider this fact: if you are a carrier of a particular set of genes, the probability that you will commit a violent crime is four times as high as it would be if you lacked those genes. You’re three times as likely to commit robbery, five times as likely to commit aggravated assault, eight times as likely to be arrested for murder, and thirteen times as likely to be arrested for a sexual offense. The overwhelming majority of prisoners carry these genes; 98.1 percent of death-row inmates do. These statistics alone indicate that we cannot presume that everyone is coming to the table equally equipped in terms of drives and behaviors.

  And this feeds into a larger lesson of biology: we are not the ones steering the boat of our behavior, at least not nearly as much as we believe. Who we are runs well below the surface of our conscious access, and the details reach back in time to before our birth, when the meeting of a sperm and an egg granted us certain attributes and not others. Who we can be starts with our molecular blueprints—a series of alien codes written in invisibly small strings of acids—well before we have anything to do with it. Each of us is, in part, a product of our inaccessible microscopic history. By the way, as regards that dangerous set of genes, you’ve probably heard of them. They are summarized as the Y chromosome. If you’re a carrier, we call you a male.

  Genes are part of the story, but they’re not the whole story. We are likewise influenced by the environments in which we grow up. Substance abuse by a mother during pregnancy, maternal stress, and low birth weight all can influence how a baby will turn out as an adult. As a child grows, neglect, physical abuse, and head injury can impede mental development, as can the physical environment. (For example, the major public health movement to eliminate lead-based paint grew out of an understanding that ingesting lead can cause brain damage, making children less intelligent and, in some cases, more impulsive and aggressive.) And every experience throughout our lives can modify genetic expression—activating certain genes or switching others off—which in turn can inaugurate new behaviors. In this way, genes and environments intertwine.

  When it comes to nature and nurture, the important point is that we choose neither one. We are each constructed from a genetic blueprint and then born into a world of circumstances that we cannot control in our most formative years. The complex interactions of genes and environment mean that all citizens—equal before the law—possess different perspectives, dissimilar personalities, and varied capacities for decision making. The unique patterns of neurobiology inside each of our heads cannot qualify as choices; these are the cards we’re dealt.

  Because we did not choose the factors that affected the formation and structure of our brain, the concepts of free will and personal responsibility begin to sprout question marks. Is it meaningful to say that Alex made bad choices, even though his brain tumor was not his fault? Is it justifiable to say that the patients with frontotemporal dementia or Parkinson’s should be punished for their bad behavior?

  It is problematic to imagine yourself in the shoes of someone breaking the law and conclude, “Well, I wouldn’t have done that”—because if you weren’t exposed to in utero cocaine, lead poisoning, and physical abuse, and he was, then you and he are not directly comparable. You cannot walk a mile in his shoes.

  The legal system rests on the assumption that we are “practical reasoners,” a term of art that presumes, at bottom, the existence of free will. The idea is that we use conscious deliberation when deciding how to act—that is, in the absence of external duress, we make free decisions. This concept of the practical reasoner is intuitive but problematic.

  The existence of free will in human behavior is the subject of an ancient debate. Arguments in support of free will are typically based on direct subjective experience (“I feel like I made the decision to lift my finger just now”). But evaluating free will requires s
ome nuance beyond our immediate intuitions.

  Consider a decision to move or speak. It feels as though free will leads you to stick out your tongue, or scrunch up your face, or call someone a name. But free will is not required to play any role in these acts. People with Tourette’s syndrome, for instance, suffer from involuntary movements and vocalizations. A typical Touretter may stick out his tongue, scrunch up his face, or call someone a name—all without choosing to do so.

  We immediately learn two things from the Tourette’s patient. First, actions can occur in the absence of free will. Second, the Tourette’s patient has no free won’t. He cannot use free will to override or control what subconscious parts of his brain have decided to do. What the lack of free will and the lack of free won’t have in common is the lack of “free.” Tourette’s syndrome provides a case in which the underlying neural machinery does its thing, and we all agree that the person is not responsible.

  This same phenomenon arises in people with a condition known as chorea, for whom actions of the hands, arms, legs, and face are involuntary, even though they certainly look voluntary: ask such a patient why she is moving her fingers up and down, and she will explain that she has no control over her hand. She cannot not do it. Similarly, some split-brain patients (who have had the two hemispheres of the brain surgically disconnected) develop alien-hand syndrome: while one hand buttons up a shirt, the other hand works to unbutton it. When one hand reaches for a pencil, the other bats it away. No matter how hard the patient tries, he cannot make his alien hand not do what it’s doing. The movements are not “his” to freely start or stop.