Sections include: where temperament comes from, differences, when temperaments spell trouble
Every baby behaves differently. Parents with two or more children are especially aware of this fact of life. One can often hear them comparing notes: “Sue was a fussy little thing, but her brother just sits and watches us for hours.” “Vanessa crawls all over the place! Her sister didn’t wear us out like that.” “The day-care people say Shawn hardly ever cries when we leave, but he hardly ever smiles, either.” Usually parents start to discern these differences in the first weeks of their children’s lives, though an outsider may have to look hard to notice them.
Psychologists and psychiatrists use the term temperament to refer to the variations in how individuals consistently feel and behave in infancy and early childhood. Each of us seems to have some biases about how we respond to the world, natural leanings that are both biological and inherited. These psychological profiles involve variation in:
■ Activity: Does your infant squirm and reach for things, or lie still?
■ Smiling and laughter: How often does your baby show his or her happy moods?
■ Irritability: How easily upset is your infant?
■ Ease of being soothed: How long does it take to calm your baby down?
■ Fluctuations in mood: Can your child change emotions in an instant?
■ Fear or avoidance of novelty: Does your infant seek out new faces and activities?
■ Energy: Does your baby tire easily, or go all night?
■ Attentiveness: How long does your child focus on one object, person, or task?
As insulting as the proud parents of little Sue, Vanessa, and Shawn might find it, we can make an analogy between these temperamental biases and the behavioral and physiological profiles that distinguish different breeds of dogs: Jack Russell terriers being energetic, Saint Bernards being patient with children, and so on.
As soon as babies are born, however, their environments start to shape how these initial biases show up in their behavior. As a result, the psychological profile each person displays during childhood and adolescence is a combination of temperament and experience. Although each temperamental category exerts its influence throughout one’s development, the personality that others see is always moderated by a person’s history. For example, about 20 percent of infants are born with a temperamental bias that renders them vulnerable to becoming timid, shy, or eager to avoid unfamiliar people, places, and situations. If their parents accept their timidity while encouraging academic achievement, these children are likely to becoming introverted scholars. If, on the other hand, the parents encourage popularity and sociability, the children are less likely to develop into quiet, academically accomplished adolescents. They may even come to seem outgoing to their peers, though it is unlikely that they will ever be as adventurous as people who are born with a novelty-seeking temperament.
Where Temperament Comes From
Even in ancient Egypt and Greece, physicians recognized the importance of a person’s biological character. The influential physician Galen of Pergamon, who lived in the second century A.D., identified four temperaments: sanguine, melancholic, phlegmatic, and choleric. He attributed them to the body’s relative amounts of blood, yellow bile, phlegm, and black bile, which represented extremes of warm and cool, dry and moist. The balance of these four substances in a person’s body determined his or her personality profile. Under this theory, the sanguine temperament, characterized by confidence and sociability, was assigned to the category warm and moist because of an excess of blood. The anxious, melancholic person was designated dry and cool because of too much black bile.
Medicine has long given up Galen’s theory of the four humors, but we have once again started to identify substances that help determine people’s personalities. These substances are not blood and bile but protein molecules at work in our brains. Contemporary scientists now believe that many temperaments are the result of different combinations of these chemicals, together with various densities of the brain’s receptors for each molecule. Researchers have seen how the distribution of brain receptors influences animals’ behavioral profiles in the difference between two strains of voles, small rodents resembling mice. One strain of vole bonds with its mate for life while the other strain does not. The two strains differ in the distribution of receptors in the brain for the chemicals oxytocin and vasopressin.
It is likely that scientists will discover that many human temperaments are the result of distinctive distributions of brain receptors for one or more neurochemicals. For instance, current research suggests that variations in the concentration and distribution of receptors for the chemicals serotonin, gamma-aminobutyric acid (GABA), opioids, and corticotrophin-releasing hormone are related to variations in children’s tendency to avoid unfamiliar people and places. Because the brain contains over 150 different molecules, it is likely that researchers will discover many more temperaments than have so far been identified.
Each temperamental bias probably involves activity in many parts of the brain. For example, the temperamental traits of timidity and fearfulness seem to be related to receptors on the amygdala and its projections to the central gray (a region in the midbrain), the autonomic nervous system, the frontal cortex, and the hypothalamus. The temperament that predisposes a child to distractibility or hyperactivity probably involves the basal ganglia, ventral tegmentum, and dopaminergic tracts to the frontal cortex. Again, much remains to be discovered.
Some temperaments, like sociability or introversion, are common; others, such as an absence of any feelings of guilt, are rare. Shy, quiet, emotionally restrained children, called inhibited, and outgoing, relatively bold children, called uninhibited, represent two relatively common temperamental categories that have been studied in depth. One lesson we have learned from these studies is how consistent temperamental bias seems to be over a child’s early life. Two-year-olds judged inhibited were more likely to have been babies who at four months of age consistently moved and fussed when presented with unfamiliar sights, sounds, and smells. This combination of movement and crying in reaction to unfamiliar stimuli implies a low threshold of excitability in the amygdala and its projections. We call this behavior high reactive. In contrast, the infants who would become uninhibited toddlers usually responded to the same stimuli with minimal activity and no crying, implying these brain structures had a higher threshold of stimulation.
As we accumulate more experiences in our lives, our observable behavior can deviate from the temperamental biases we were born with. Only 15 percent to 20 percent of the children in each of these temperamental groups remained consistently inhibited or consistently uninhibited from their first birthdays through late childhood. Nevertheless, not one high-reactive infant became a consistently uninhibited child, and only one low-reactive infant—less than 1 percent of the babies in the study—became a consistently inhibited child. This suggests that a person’s temperament does not determine his or her later personality but does constrain the possibility of developing the opposite set of traits. Showing a high-reactive temperament in infancy reduces the likelihood that the child will become bold and extroverted; while having a low-reactive temperament limits the possibility that the child will become a fearful, anxious adolescent. It is easier to predict what babies will not become from knowing their temperaments than to predict the specific traits they will develop.
Variation in adolescent or adult personalities among people who were high- or low-reactive infants is due, in part, to family experience. Children with a high-reactive temperament raised by parents who encourage them to find ways to cope with fear are less likely to develop symptoms of anxiety. Children with the same temperament living with parents who try to protect them from all stress are more likely to become anxious and timid. Parenting and home environment also influence other temperaments. A child who seems naturally driven to seek out new, exciting experiences might take bigger risks if his or her upbringing invites that behavior, or might learn the value of safety from parents who persistently encourage and remind their child to think before acting.
Because of that family influence, adolescents do not necessarily behave according to the biological features that characterize their infant temperaments. One girl in a group studied over many years was a high-reactive infant and a fearful toddler. She lived in a supportive environment, however, and was academically accomplished. When this girl was observed at 10 years of age, she was relaxed, mature, and minimally anxious. From the perspective of brain science, this was especially interesting because measures of her brain function revealed several biological features characteristic of inhibited children. For example, her electroencephalograph (EEG) showed more activation in her brain’s right frontal area than in its left, a trait that correlates with the brain’s activity in anxious adults. Yet her behavior no longer seemed to reflect that biological inclination.
Culture also has a great influence on our personalities, and society’s expectations for a child because of his or her sex, ethnic group, class, or other circumstances may work for or against an inherited temperament. At the same time, temperaments do seem to differ across sexes and ethnic groups. The bias against novelty-seeking is more common in girls. The temperament favoring high activity levels is more prevalent in boys. Low levels of reactivity in infancy appear to be more common among Asian infants than among Caucasians. It is important to understand how early environment starts to influence temperaments, and surprisingly, little cross-cultural research has so far been carried out on this question.
When Temperaments Spell Trouble
There are good reasons to believe that many psychiatric disorders are influenced, in part, by temperamental biases. For example, social phobia, characterized by chronic avoidance of social gatherings and reluctance to meet strangers, is more common among inhibited than among uninhibited children. Panic disorder, characterized by a sudden onset of activity in the nervous system and an accompanying feeling of terror, is likely to be a product of a different temperament. Psychopathy is more prevalent among uninhibited children, but only if they are raised in families and neighborhoods that are unduly permissive of aggression and other behaviors that violate the norm of the community. Attention deficit/hyperactivity disorder is probably associated with a temperament that modulates dopamine function, while depression is probably linked to a temperament that influences the metabolism of norepinephrine in the brain. If a temperamental trait impairs a person’s ability to work efficiently and to adapt to societal demands, psychotherapy or pharmacological interventions can be helpful.
At this point, however, our evidence is not robust enough to produce definite advice for individuals with particular temperaments. There is some basis for suggesting that in order to help their children conquer their vulnerability to fears, parents of high-reactive infants should not protect their toddlers from minor stresses. As the children recognize what constitutes actual danger or difficulty, they can face the uncertainties of normal daily life more bravely. This approach can be hard for the parents, especially if their own personalities lean the same way as their children’s—if, for instance, they are also anxious about trying new things. But it helps for parents to be calm and firm. Similarly, parents of low-reactive infants should be consistent in discouraging antisocial and aggressive behavior. In general, understanding that children have different temperaments helps us to see each as an individual, not necessarily born to respond to the world in the same way as other siblings and parents.
In growing up, most people come to know themselves, what settings and activities make them comfortable and happy. Adolescents who are inhibited as children usually recognize they can feel uncertain or anxious when challenged by unpredictable situations. Some of these young people adapt by selecting activities and vocations that permit them to control encounters with unfamiliarity and unpredictability. For example, they might decide to become historians, scientists, computer programmers, or poets because these jobs require long periods of solitary activity and permit more control over the outcome of one’s efforts. Other young people, knowing fairly early that they would find that sort of work boring or lonely, gravitate toward professions that involve meeting many people and having new experiences each day. Most of us have a mix of traits and interests. The temperaments rooted in our infant brains are an important factor in finding “the right fit” in life.
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