The body fluids (blood, urine, saliva) of sensitive children show indications of high levels of norepinephrine present in their brains, especially after the children are exposed to various forms of stress in the laboratory. Norepinephrine is associated with arousal; in fact, it is the brain’s version of adrenaline. Sensitive children’s body fluids also contain more Cortisol, both when under stress and when at home. Cortisol is the hormone present when one is in a more or less constant state of arousal or wariness. Remember Cortisol; it comes up again.
Kagan then studied infants to see which ones would grow into “inhibited” children. He found that about 20 percent of all babies are “highly reactive” when exposed to various stimuli: They pump and flex their limbs vigorously, arch their backs as if irritated or trying to get away, and frequently cry. A year later, two-thirds of the study’s reactive babies were “inhibited” children and showed high levels of fear in new situations. Only 10 percent showed low levels. So the trait is roughly observable from birth, as was the case with Rob.
All of this suggests what I have already said—that sensitive children come with a built-in tendency to react more strongly to external stimuli. But Kagan and others are discovering the details that make that so. For example, Kagan found that babies who later showed this trait also had cooler foreheads on the right side of their head, which indicates greater activity on the right side of the brain. (The blood is drawn away from the surface toward the activity.) Other studies have also found that many HSPs have more activity in the right hemisphere of the brain, especially those who stay sensitive from birth into childhood—that is, were clearly born that way.
Kagan’s conclusion is that persons with the trait of sensitivity or inhibitedness are a special breed. They are genetically quite different, although still utterly human, just as bloodhounds and border collies are quite different, although both are still definitely dogs.
My own research also points to the idea of a distinct genetic “breed” of sensitive people. In my telephone survey of three hundred randomly selected people, I found both a distinct group and also a continuum. On a scale of one to five, about 20 percent felt they were “extremely” or “quite a bit” sensitive. An additional 27 percent said “moderately.” Together, those three categories seemed like a continuum. But then there was a sharp break. A measly 8 percent were “not.” And a whopping 42 percent said they were “not at all” sensitive, as if we were asking Laplanders about coconuts.
My sense of HSPs from meeting them is that they are indeed a distinct group, separate from the nonsensitive. Yet among them there is also a wide range in sensitivity. This may be due to there being several different causes of the trait, leading to different kinds, or “flavors,” of sensitivity, some of them stronger than others, or to some people being born with two kinds, three kinds, and so on. And there are so many ways that humans can increase or decrease their sensitivity through experience or conscious choice. All of these effects could cause a blurring of the boundary of what is still basically a separate group.
There is no denying the sense that Rob and Rebecca are two different sorts of humans. You are, too. Your differences are very real.
The Brain’s Two Systems
A number of researchers think that there are two systems in the brain and that it is the balance of these two that creates sensitivity. One system, the “behavioral activation” (or “approach,” or “facilitation,” system) is hooked up to the parts of the brain that take in messages from the senses and send out orders to the limbs to get moving. This system is designed to move us toward things, especially new ones. It is probably meant to keep us eagerly searching for the good things in life, like fresh food and companionship, all of which we need for survival. When the activation system is operating, we are curious, bold, and impulsive.
The other system is called the “behavioral inhibition” (or “withdrawal,” or “avoidance,” system). (You can already tell by the names which is the “good” one according to our culture.) This system is said to move us away from things, making us attentive to dangers. It makes us alert, cautious, and watchful for signs. Not surprisingly, this system is hooked up to all the parts of the brain Kagan noted to be more active in his “inhibited” children.
But what does this system really do? It takes in everything about a situation and then automatically compares the present to what has been normal and usual in the past and what should be expected in the future. If there is a mismatch, the system makes us stop and wait until we understand the new circumstance. To me this is a very significant part of being intelligent. So I prefer to give it a more positive name: the automatic pause-to-check system.
But now consider how one might have a more active pause-to-check system. Imagine Rob and Rebecca coming to school one morning. Rebecca sees the same classroom, teacher, and children as were there yesterday. She runs off to play. Rob notices that the teacher is in a bad mood, one of the children is looking angry, and some bags are in the corner that were not there before. Rob hesitates and may decide that there is reason for caution. So sensitivity—the subtle processing of sensory information—is the real difference once again. Notice how psychology has described the two systems as having opposing purposes. How like the opposition I described in the last chapter between the warrior-king class and the royal-advisor class.
This two-system explanation of sensitivity also suggests two different types of HSPs. Some might have only an average-strength pause-to-check system but an activation system that is even weaker. This kind of HSP might be very calm, quiet, and content with a simple life. It’s as if the royal advisors are monks who rule the whole country/person. Another kind of HSP could potentially have an even stronger pause-to-check system but an activation system that is also very strong—just not quite as strong. This kind of HSP would be both very curious and very cautious, bold yet anxious, easily bored yet easily overaroused. The optimal level of arousal is a narrow range. One could say there is a constant power struggle between the advisor and the impulsive, expansive warrior within the person.
I think Rob is this type. Other young children, however, are described as so quiet and uncurious that they are in danger of being ignored and neglected.
What type are you? Does your pause-to-check/advisor system rule alone, thanks to a quiet activator/warrior-king system? That is, is it easy for you to be content with a quiet life? Or are the two branches that govern you in constant conflict? That is, do you always want to be trying new things even if you know that afterward you will be exhausted?
You Are More Than Genes and Systems
Let’s not forget that you are a complicated being. Certain investigators, such as Mary Rothbart of the University of Oregon, are adamant that temperament is quite a different matter when you study adult humans, who can reason, make choices, and exert willpower to follow through on their choices. Rothbart believes that if psychologists study children and animals too much, they will overlook the role of human thinking and a lifetime’s experience.
Let’s go over your development, and Rob’s, as Rothbart sees it, and how being sensitive would differ at each stage.
At birth, an infant’s only reaction is negative—irritability, discomfort. Sensitive babies like you and Rob