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  According to Mischel, this view of will power also helps explain why the marshmallow task is such a powerfully predictive test. "If you can deal with hot emotions, then you can study for the SAT instead of watching television," Mischel says. "And you can save more money for retirement. It's not just about marshmallows."

  Subsequent work by Mischel and his colleagues found that these differences were observable in subjects as young as nineteen months. Looking at how toddlers responded when briefly separated from their mothers, they found that some immediately burst into tears or clung to the door, but others were able to overcome their anxiety by distracting themselves, often by playing with toys. When the scientists set the same children the marshmallow task at the age of five, they found that the kids who had cried also struggled to resist the tempting treat.

  The early appearance of the ability to delay suggests that it has a genetic origin, an example of personality at its most predetermined. Mischel resists such an easy conclusion. "In general, trying to separate nature and nurture makes about as much sense as trying to separate personality and situation," he says. "The two influences are completely interrelated." For instance, when Mischel gave delay-of-gratifi cation tasks to children from low-income families in the Bronx, he noticed that their ability to delay was below average, at least compared with that of children in Palo Alto. "When you grow up poor, you might not practice delay as much," he says. "And if you don't practice, then you'll never figure out how to distract yourself. You won't develop the best delay strategies, and those strategies won't become second nature." In other words, people learn how to use their mind just as they learn how to use a computer: through trial and error.

  But Mischel has found a shortcut. When he and his colleagues taught children a simple set of mental tricks—such as pretending that the candy is only a picture, surrounded by an imaginary frame—he dramatically improved their self-control. The kids who hadn't been able to wait sixty seconds could now wait fifteen minutes. "All I've done is given them some tips from their mental user manual," Mischel says. "Once you realize that will power is just a matter of learning how to control your attention and thoughts, you can really begin to increase it."

  Marc Berman, a lanky graduate student with an easy grin, speaks about his research with the infectious enthusiasm of a freshman taking his first philosophy class. Berman works in the lab of John Jonides, a psychologist and neuroscientist at the University of Michigan, who is in charge of the brain-scanning experiments on the original Bing subjects. He knows that testing forty-year-olds for self-control isn't a straightforward proposition. "We can't give these people marshmallows," Berman says. "They know they're part of a long-term study that looks at delay of gratification, so if you give them an obvious delay task they'll do their best to resist. You'll get a bunch of people who refuse to touch their marshmallow."

  This meant that Jonides and his team had to find a way to measure will power indirectly. Operating on the premise that the ability to delay eating the marshmallow had depended on a child's ability to banish thoughts of it, they decided on a series of tasks that measure the ability of subjects to control the contents of working memory—the relatively limited amount of information we're able to consciously consider at any given moment. According to Jonides, this is how self-control "cashes out" in the real world: as an ability to direct the spotlight of attention so that our decisions aren't determined by the wrong thoughts.

  Last summer the scientists chose fifty-five subjects, equally split between high delayers and low delayers, and sent each one a laptop computer loaded with working-memory experiments. Two of the experiments were of particular interest. The first is a straightforward exercise known as the "suppression task." Subjects are given four random words, two printed in blue and two in red. After reading the words, they're told to forget the blue words and remember the red words. Then the scientists provide a stream of "probe words" and ask the subjects whether the probes are the words they were asked to remember. Though the task doesn't seem to involve delayed gratifi cation, it tests the same basic mechanism. Interestingly, the scientists found that high delayers were significantly better at the suppression task: they were less likely to think that a word they'd been asked to forget was something they should remember.

  In the second, known as the Go/No Go task, subjects are flashed a set of faces with various expressions. At first, they are told to press the space bar whenever they see a smile. This takes little effort, since smiling faces automatically trigger what's known as "approach behavior." After a few minutes, however, subjects are told to press the space bar when they see frowning faces. They are now being forced to act against an impulse. Results show that high delayers are more successful at not pressing the button in response to a smiling face.

  When I first started talking to the scientists about these tasks last summer, they were clearly worried that they wouldn't find any behavioral differences between high and low delayers. It wasn't until early January that they had enough data to begin their analysis (not surprisingly, it took much longer to get the laptops back from the low delayers), but it soon became obvious that there were provocative differences between the two groups. A graph of the data shows that as the delay time of the four-year-olds decreases, the number of mistakes made by the adults sharply rises.

  The big remaining question for the scientists is whether these behavioral differences are detectable in an fMRI machine. Although the scanning has just begun—Jonides and his team are still working out the kinks—the scientists sound confident. "These tasks have been studied so many times that we pretty much know where to look and what we're going to find," Jonides says. He rattles off a short list of relevant brain regions, which his lab has already identified as being responsible for working-memory exercises. For the most part, the regions are in the frontal cortex—the overhang of brain behind the eyes—and include the dorsolateral prefrontal cortex, the anterior prefrontal cortex, the anterior cingulate, and the right and left inferior frontal gyri. While these cortical folds have long been associated with self-control, they're also essential for working memory and directed attention. According to the scientists, that's not an accident. "These are powerful instincts telling us to reach for the marshmallow or press the space bar," Jonides says. "The only way to defeat them is to avoid them, and that means paying attention to something else. We call that will power, but it's got nothing to do with the will."

  The behavioral and genetic aspects of the project are overseen by Yuichi Shoda, a professor of psychology at the University of Washington, who was one of Mischel's graduate students. He's been following these "marshmallow subjects" for more than thirty years: he knows everything about them, from their academic records and their social graces to their ability to deal with frustration and stress. The prognosis for the genetic research remains uncertain. Although many studies have searched for the underpinnings of personality since the completion of the Human Genome Project in 2003, many of the relevant genes remain in question. "We're incredibly complicated creatures," Shoda says. "Even the simplest aspects of personality are driven by dozens and dozens of different genes." The scientists have decided to focus on genes in the dopamine pathways, since those neurotransmitters are believed to regulate both motivation and attention. However, even if minor coding differences influence delay ability—and that's a likely possibility—Shoda doesn't expect to discover these differences: the sample size is simply too small.

  In recent years, researchers have begun making house visits to many of the original subjects, including Carolyn Weisz, as they try to better understand the familial contexts that shape self-control. "They turned my kitchen into a lab," Carolyn told me. "They set up a little tent where they tested my oldest daughter on the delay task with some cookies. I remember thinking, I really hope she can wait."

  While Mischel closely follows the steady accumulation of data from the laptops and the brain scans, he's most excited by what comes next. "I'm not interested in looking at the brain jus
t so we can use a fancy machine," he says. "The real question is what can we do with this fMRI data that we couldn't do before?" Mischel is applying for an NIH grant to investigate various mental illnesses, like obsessive-compulsive disorder and attention-deficit disorder, in terms of the ability to control and direct attention. Mischel and his team hope to identify crucial neural circuits that cut across a wide variety of ailments. If there is such a circuit, then the same cognitive tricks that increase delay time in a four-year-old might help adults deal with their symptoms. Mischel is particularly excited by the example of the substantial subset of people who failed the marshmallow task as four-year-olds but ended up becoming high-delaying adults. "This is the group I'm most interested in," he says. "They have substantially improved their lives."

  Mischel is also preparing a large-scale study involving hundreds of schoolchildren in Philadelphia, Seattle, and New York City to see if self-control skills can be taught. Although he previously showed that children did much better on the marshmallow task after being taught a few simple "mental transformations," such as pretending the marshmallow was a cloud, it remains unclear if these new skills persist over the long term. In other words, do the tricks work only during the experiment or do the children learn to apply them at home, when deciding between homework and television?

  Angela Lee Duckworth, an assistant professor of psychology at the University of Pennsylvania, is leading the program. She first grew interested in the subject after working as a high school math teacher. "For the most part, it was an incredibly frustrating experi ence," she says. "I gradually became convinced that trying to teach a teenager algebra when they don't have self-control is a pretty futile exercise." And so, at the age of thirty-two, Duckworth decided to become a psychologist. One of her main research projects looked at the relationship between self-control and grade point average. She found that the ability to delay gratification—eighth-graders were given a choice between a dollar right away or two dollars the following week—was a far better predictor of academic performance than IQ. She said that her study shows that "intelligence is really important, but it's still not as important as self-control."

  Last year, Duckworth and Mischel were approached by David Levin, the cofounder of KIPP, an organization of sixty-six public charter schools across the country. KIPP schools are known for their long workday—students are in class from 7:25 A.M. to 5 P.M. —and for dramatic improvement of inner-city students' test scores. (More than 80 percent of eighth-graders at the KIPP academy in the South Bronx scored at or above grade level in reading and math, which was nearly twice the New York City average.) "The core feature of the KIPP approach is that character matters for success," Levin says. "Educators like to talk about character skills when kids are in kindergarten—we send young kids home with a report card about 'working well with others' or 'not talking out of turn.' But then, just when these skills start to matter, we stop trying to improve them. We just throw up our hands and complain."

  Self-control is one of the fundamental "character strengths" emphasized by KIPP—the KIPP academy in Philadelphia, for instance, gives its students a shirt emblazoned with the slogan "Don't Eat the Marshmallow." Levin, however, remained unsure about how well the program was working—"We know how to teach math skills, but it's harder to measure character strengths," he says—so he contacted Duckworth and Mischel, promising them unfettered access to KIPP students. Levin also helped bring together additional schools willing to take part in the experiment, including Riverdale Country School, a private school in the Bronx; the Evergreen School for gifted children, in Shoreline, Washington; and the Mastery Charter Schools, in Philadelphia.

  For the past few months, the researchers have been conducting pilot studies in the classroom as they try to figure out the most effective way to introduce complex psychological concepts to young children. Because the study will focus on students between the ages of four and eight, the classroom lessons will rely heavily on peer modeling, such as showing kindergartners a video of a child successfully distracting herself during the marshmallow task. The scientists have some encouraging preliminary results—after just a few sessions, students show significant improvements in the ability to deal with hot emotional states—but they are cautious about predicting the outcome of the long-term study. "When you do these large-scale educational studies, there are ninety-nine uninteresting reasons the study could fail," Duckworth says. "Maybe a teacher doesn't show the video, or maybe there's a field trip on the day of the testing. This is what keeps me up at night."

  Mischel's main worry is that even if his lesson plan proves to be effective, it might still be overwhelmed by variables the scientists can't control, such as the home environment. He knows that it's not enough just to teach kids mental tricks—the real challenge is turning those tricks into habits, and that requires years of diligent practice. "This is where your parents are important," Mischel says. "Have they established rituals that force you to delay on a daily basis? Do they encourage you to wait? And do they make waiting worthwhile?" According to Mischel, even the most mundane routines of childhood—such as not snacking before dinner, or saving up your allowance, or holding out until Christmas morning—are really sly exercises in cognitive training: we're teaching ourselves how to think so that we can outsmart our desires. But Mischel isn't satisfied with such an informal approach. 'We should give marshmallows to every kindergartner," he says. "We should say, 'You see this marshmallow? You don't have to eat it. You can wait. Here's how.'"

  KATHLEEN MCGOWAN Out of the Past

  FROM Discover

  RITA MAGIL WAS DRIVING down a Montreal boulevard one sunny morning in 2002 when a car came blasting through a red light straight toward her. "I slammed the brakes, but I knew it was too late," she says. "I thought I was going to die." The oncoming car smashed into hers, pushing her off the road and into a building with large cement pillars in front. A pillar tore through the car, stopping only about a foot from her face. She was trapped in the crumpled vehicle, but to her shock, she was still alive.

  The accident left Magil with two broken ribs and a broken collarbone. It also left her with posttraumatic stress disorder (PTSD) and a desperate wish to forget. Long after her bones healed, Magil was plagued by the memory of the cement barriers looming toward her. "I would be doing regular things—cooking something, shopping, whatever—and the image would just come into my mind from nowhere," she says. Her heart would pound; she would start to sweat and feel jumpy all over. It felt visceral and real, like something that was happening at that very moment.

  Most people who survive accidents or attacks never develop PTSD. But for some, the event forges a memory that is pathologically potent, erupting into consciousness again and again. "PTSD really can be characterized as a disorder of memory," says the McGill University psychologist Alain Brunet, who studies and treats psychological trauma. "It's about what you wish to forget and what you cannot forget." This kind of memory is not misty and watercolored. It is relentless.

  More than a year after her accident, Magil saw Brunet's ad for an experimental treatment for PTSD, and she volunteered. She took a low dose of a common blood-pressure drug, propranolol, that reduces activity in the amygdala, a part of the brain that processes emotions. Then she listened to a taped re-creation of her car accident. She had relived that day in her mind a thousand times. The difference this time was that the drug broke the link between her factual memory and her emotional memory. Propranolol blocks the action of adrenaline, so it prevented her from tensing up and getting anxious. By having Magil think about the accident while the drug was in her body, Brunet hoped to permanently change how she remembered the crash. It worked. She did not forget the accident but was actively able to reshape her memory of the event, stripping away the terror while leaving the facts behind.

  Brunet's experiment emerges from one of the most exciting and controversial recent findings in neuroscience: that we alter our memories just by remembering them. Karim Nader of McGill—the scientist
who made this discovery—hopes it means that people with PTSD can cure themselves by editing their memories. Altering remembered thoughts might also liberate people imprisoned by anxiety, obsessive-compulsive disorder, even addiction. "There is no such thing as a pharmacological cure in psychiatry," Brunet says. "But we may be on the verge of changing that."

  These recent insights into memory are part of a larger about-face in neuroscience research. Until recently, long-term memories were thought to be physically etched into our brain, permanent and unchanging. Now it is becoming clear that memories are surprisingly vulnerable and highly dynamic. In the lab they can be flicked on or dimmed with a simple dose of drugs. "For a hundred years, people thought memory was wired into the brain," Nader says. "Instead, we find it can be rewired—you can add false information to it, make it stronger, make it weaker, and possibly even make it disappear." Nader and Brunet are not the only ones to make this observation. Other scientists probing different parts of the brain's memory machinery are similarly finding that memory is inherently flexi ble.

  Someday this new science of memory could cure PTSD and other mental traumas. Already it corrodes our trust in what we know and how we know it. It pokes holes in eyewitness testimony, in memoirs, in our most intimate records of truth. Every time we remember, it seems, we add new details, shade the facts, prune and tweak. Without realizing it, we continually rewrite the stories of our lives. Memory, it turns out, has a surprising amount in common with imagination, conjuring worlds that never existed until they were forged by our minds.