Сьюзан Кейн - Quiet [The Power of Introverts in a World That Can't Stop Talking]

Schwartz is Kagan’s colleague and protégé, and his work picks up just where Kagan’s longitudinal studies of personality left off. The infants Kagan once categorized as high- and low-reactive have now grown up, and Schwartz is using the fMRI machine to peer inside their brains. Kagan followed his subjects from infancy into adolescence, but Schwartz wanted to see what happened to them after that. Would the footprint of temperament be detectable, all those years later, in the adult brains of Kagan’s high- and low-reactive infants? Or would it have been erased by some combination of environment and conscious effort?

Interestingly, Kagan cautioned Schwartz against doing the study. In the competitive field of science research, you don’t want to waste time conducting studies that may not yield significant findings. And Kagan worried that there were no results to be found—that the link between temperament and destiny would be severed by the time an infant reached adulthood.

“He was trying to take care of me,” Schwartz tells me. “It was an interesting paradox. Because here Jerry was doing all these early observations of infants, and seeing that it wasn’t just their social behavior that was different in the extremes—everything about these kids was different. Their eyes dilated more widely when they were solving problems, their vocal cords became more tense while uttering words, their heart rate patterns were unique: there were all these channels that suggested there was something different physiologically about these kids. And I think, in spite of this, because of his intellectual heritage, he had the feeling that environmental factors are so complex that it would be really hard to pick up that footprint of temperament later in life.”

But Schwartz, who believes that he’s a high-reactive himself and was drawing partly on his own experience, had a hunch that he’d find that footprint even farther along the longitudinal timeline than Kagan had.

He demonstrates his research by allowing me to act as if I were one of his subjects, albeit not inside the fMRI scanner. As I sit at a desk, a computer monitor flashes photos at me, one after another, each showing an unfamiliar face: disembodied black-and-white heads floating against a dark background. I think I can feel my pulse quicken as the photos start coming at me faster and faster. I also notice that Schwartz has slipped in some repeats and that I feel more relaxed as the faces start to look familiar. I describe my reactions to Schwartz, who nods. The slide show is designed, he says, to mimic an environment that corresponds to the sense that high-reactive people get when they walk into a crowded room of strangers and feel “Geez! Who are these people?”

I wonder if I’m imagining my reactions, or exaggerating them, but Schwartz tells me that he’s gotten back the first set of data on a group of high-reactive children Kagan studied from four months of age—and sure enough, the amygdalae of those children, now grown up, had turned out to be more sensitive to the pictures of unfamiliar faces than did the amygdalae of those who’d been bold toddlers. Both groups reacted to the pictures, but the formerly shy kids reacted more. In other words, the footprint of a high- or low-reactive temperament never disappeared in adulthood . Some high-reactives grew into socially fluid teenagers who were not outwardly rattled by novelty, but they never shed their genetic inheritance.

Schwartz’s research suggests something important: we can stretch our personalities, but only up to a point. Our inborn temperaments influence us, regardless of the lives we lead. A sizable part of who we are is ordained by our genes, by our brains, by our nervous systems. And yet the elasticity that Schwartz found in some of the high-reactive teens also suggests the converse: we have free will and can use it to shape our personalities.

These seem like contradictory principles, but they are not. Free will can take us far, suggests Dr. Schwartz’s research, but it cannot carry us infinitely beyond our genetic limits. Bill Gates is never going to be Bill Clinton, no matter how he polishes his social skills, and Bill Clinton can never be Bill Gates, no matter how much time he spends alone with a computer.

We might call this the “rubber band theory” of personality. We are like rubber bands at rest. We are elastic and can stretch ourselves, but only so much.

To understand why this might be so for high-reactives, it helps to look at what happens in the brain when we greet a stranger at a cocktail party. Remember that the amygdala, and the limbic system of which it’s a key part, is an ancient part of the brain—so old that primitive mammals have their own versions of this system. But as mammals became more complex, an area of the brain called the neocortex developed around the limbic system. The neocortex, and particularly the frontal cortex in humans, performs an astonishing array of functions, from deciding which brand of toothpaste to buy, to planning a meeting, to pondering the nature of reality. One of these functions is to soothe unwarranted fears.

If you were a high-reactive baby, then your amygdala may, for the rest of your life, go a bit wild every time you introduce yourself to a stranger at a cocktail party. But if you feel relatively skilled in company, that’s partly because your frontal cortex is there to tell you to calm down, extend a handshake, and smile. In fact, a recent fMRI study shows that when people use self-talk to reassess upsetting situations, activity in their prefrontal cortex increases in an amount correlated with a decrease of activity in their amygdala.

But the frontal cortex isn’t all-powerful; it doesn’t switch the amygdala off altogether. In one study, scientists conditioned a rat to associate a certain sound with an electrical shock. Then they played that sound over and over again without administering the shock, until the rats lost their fear.

But it turned out that this “unlearning” was not as complete as the scientists first thought. When they severed the neural connections between the rats’ cortex and amygdala, the rats became afraid of the sound again. This was because the fear conditioning had been suppressed by the activity of the cortex, but was still present in the amygdala. In humans with unwarranted fears, like batophobia, or fear of heights, the same thing happens. Repeated trips to the top of the Empire State Building seem to extinguish the fear, but it may come roaring back during times of stress—when the cortex has other things to do than soothe an excitable amygdala.

This helps explain why many high-reactive kids retain some of the fearful aspects of their temperament all the way into adulthood, no matter how much social experience they acquire or free will they exercise. My colleague Sally is a good example of this phenomenon. Sally is a thoughtful and talented book editor, a self-described shy introvert, and one of the most charming and articulate people I know. If you invite her to a party, and later ask your other guests whom they most enjoyed meeting, chances are they’ll mention Sally. She’s so sparkly, they’ll tell you. So witty! So adorable!

Sally is conscious of how well she comes across—you can’t be as appealing as she is without being aware of it. But that doesn’t mean her amygdala knows it. When she arrives at a party, Sally often wishes she could hide behind the nearest couch—until her prefrontal cortex takes over and she remembers what a good conversationalist she is. Even so, her amygdala, with its lifetime of stored associations between strangers and anxiety, sometimes prevails. Sally admits that sometimes she drives an hour to a party and then leaves five minutes after arriving.

When I think of my own experiences in light of Schwartz’s findings, I realize it’s not true that I’m no longer shy; I’ve just learned to talk myself down from the ledge (thank you, prefrontal cortex!). By now I do it so automatically that I’m hardly aware it’s happening. When I talk with a stranger or a group of people, my smile is bright and my manner direct, but there’s a split second that feels like I’m stepping onto a high wire. By now I’ve had so many thousands of social experiences that I’ve learned that the high wire is a figment of my imagination, or that I won’t die if I fall. I reassure myself so instantaneously that I’m barely aware I’m doing it. But the reassurance process is still happening—and occasionally it doesn’t work. The word that Kagan first used to describe high-reactive people was inhibited , and that’s exactly how I still feel at some dinner parties.