Welcome to Your Child's Brain: How the Mind Grows From Conception to College (39 page)

DID YOU KNOW? THE CAUSES OF DYSLEXIA

Dyslexia
is defined as “persistent difficulty in reading when other intellectual functions and educational opportunities are sufficient.” Its frequency suggests that it is not a disorder, but simply one extreme of a range of normal variation. Indeed, in preliterate times, and even today in illiterate societies, dyslexic tendencies might not ever be noticed.

Like other neurodevelopmental disorders, dyslexia arises through genetic mechanisms. If one identical twin is dyslexic, the other twin has a nearly 70 percent chance of having the disorder too. In nonidentical twins and siblings of dyslexics, who share only half their genes, the probability is still high, 40 percent. This pattern of inheritance would be expected if dyslexia in any individual child is triggered by just one or two variant genes.

In most cases, the genes that make us susceptible to dyslexia affect either the migration of neurons to their final destinations or the growth of axons. One such gene is ROBO1, which helps to determine whether axons will cross the left-right midline. Researchers should eventually be able to understand how these genes affect dyslexia-inducing variations in neuronal circuits, either within a nucleus or in connections among brain regions.

Dyslexic children often have difficulty with phonological perception tasks, such as identifying spoken syllables or the order in which they occur. This disability might create difficulties in making rapid, automatic associations between sounds and letters, a necessary component of smooth reading. The task is difficult in English, which is filled with irregularities. Indeed, the incidence of dyslexia is lower in languages such as Italian or German, where pronunciation rules for letters are consistent—though problems still present themselves in the form of slow reading.

For some capacities other than reading, mirror confusion may be an asset. The right half of the neocortex is involved in perceptual judgments, suggesting that strong perceptual abilities in the right inferior temporal cortex might be good for other capacities. Dyslexia is frequent among artists. One survey at Göteborg University in Sweden revealed a high fraction of dyslexics among art students compared to other majors. Whether or not these students’ exceptional capacities caused their dyslexia, they have identified an elite pursuit that does not require written language.

How does a child navigate such a thicket? The time-honored approach has been to learn by writing. In conjunction with a phonetic alphabetical scheme called
pinyin
, a major component of early Chinese language instruction is the writing of characters, stroke by stroke. This is very unlike reading lessons in alphabetic languages, which focus on learning individual letters and the sounds they represent. Correspondingly, there are differences among children who speak different languages in the neural pathways involved in beginning reading.

Functional brain imaging shows that, unlike English-learning children, Chinese children show only small increases in activity in the parietal cortex when reading. Instead, widespread activation occurs in a region centered on the left middle frontal cortex. The activated areas overlap strongly with the dorsal and lateral prefrontal cortex, which are used in working memory. Readers also show activity in the premotor cortex, which is likely to be activated during the execution of fine movements—such as those that would occur when writing out a Chinese character.

These findings suggest that the active recall and rehearsal of writing characters may be central to learning to read Chinese. Thus the gap between verbal language and reading can be bridged not only phonologically but also with the help of neural circuits for movement.

Phonological and movement mechanisms are independent of each other, or at least partly so. Phonological awareness is a weaker predictor of reading success in Chinese than in English. Also, the prevalence of dyslexia in China appears to be lower than in Western countries—perhaps as low as 2 percent, compared to 5 to 15 percent of English-speaking children. On the other hand, reading difficulties are more common with pinyin.

As with math, the best strategy for learning to read may differ from person to person. There are dyslexic children in China and Japan (where the written language is similar to Chinese) who reportedly learned to read English at average levels or higher by taking a phonics-based approach—but not by using a word-copying approach. For a few Chinese children, the motor-based route may be difficult. For English-language dyslexics, the phonological route may be difficult.

This brings us to another useful conclusion: if you have a dyslexic child trying to learn English, he may profit from systematic, repeated copying of entire words by hand—as if they were single symbols. Copying could activate motor circuitry to assist the mapping of language to the visual appearance of words.
This differs significantly from the usual, phonics-based approach for early reading. (It also differs from whole-language reading instruction, a rival school of reading that focuses on subject matter and context.) The seemingly laborious, frontal cortex–based approach taken by Chinese children suggests the possibility of a third route for overcoming reading difficulties: study by detailed writing.

No matter how children learn to read, the general pattern is the same: starting from a very focused group of brain regions, children eventually come to use a much broader network. The ability of the brain to organize such distant areas in the service of a cultural innovation, such as reading, is a testament to the flexibility of our brains when faced with a new opportunity.

PART SEVEN
BUMPS IN THE ROAD

HANG IN THERE, BABY: STRESS AND RESILIENCE

MIND-BLINDNESS: AUTISM

OLD GENES MEET THE MODERN WORLD: ADHD

CATCH YOUR CHILD BEING GOOD:
BEHAVIOR MODIFICATION

A TOUGH ROAD TO TRAVEL: GROWING UP IN POVERTY

Chapter 26
HANG IN THERE, BABY: STRESS AND RESILIENCE

AGES: THIRD TRIMESTER TO EIGHTEEN YEARS

Compared with adults, children start with a double disadvantage in dealing with stress: they have limited power to change their environments, and they aren’t as good at managing their emotions. Every child has to find ways to deal with stress, though. It’s an inevitable part of growing up, whether the problem is as ordinary as a quarrel with a friend or as serious as the death of a parent.

For adults, coping involves some combination of changing your circumstances and changing your attitude. Resilient adults are optimists. Rather than passively denying and avoiding stressful situations, they use active coping strategies such as solving the problem, reinterpreting the situation in a more positive light, seeking social support, and finding meaning in hardship. Adult resilience is influenced by early experience. In general, children seem to develop their coping skills most effectively if they are exposed to a moderate amount of stress: high enough that they notice it, but low enough that they can handle it—a level that is different for every individual and changes with age.

Stress mechanisms are similar in humans and in other animals, allowing neuroscientists to study the process in detail. Animals learn to cope with stress by starting small. Young monkeys who are separated from their mothers for one hour a week grow up to manage stress more effectively than monkeys who were never separated from their mothers. In adulthood, these mildly stressed monkeys show lower anxiety and lower baseline stress hormone levels and perform better on a test of prefrontal cortex function. Rat pups that are separated from their mothers for fifteen minutes a day also become more resilient as adults. In contrast, pups that are separated for three hours a day grow into adults who are more vulnerable to stress, show more anxiety, are slower to learn, and drink more alcohol (when it is offered to them) than unseparated animals. The mother rat’s behavior when the pups are returned to her may be one reason for the difference between these two conditions. She makes up for a brief separation by grooming the pups more, but after a long separation, she tends to neglect them.

Controllable stressors—the ones you can manage or reduce through your own actions—are more likely to lead to resilience than uncontrollable ones. Rats that learn to escape from a mild electric shock to the tail are less likely to develop learned helplessness (which psychologists consider to be an indicator of depression) when confronted with an unpredictable and uncontrollable shock later on.

Infants must rely on their parents and other caregivers to act as a surrogate coping system, as babies can signal their own needs but not meet them.
Preschoolers tend to cope in a limited number of ways, by seeking help from caregivers, confronting the problem, withdrawing, or distracting themselves with another activity. Around age three, they start to try negotiating for what they want. Older children rely most heavily on the strategies of support seeking, problem solving, escape, and distraction. Cognitive strategies for distraction (such as thinking about something pleasant) and better problem-solving ability emerge in late childhood and increase into the early twenties. Rumination and anxiety also increase during this period, though, as thinking about problems doesn’t necessarily contribute to solving them.

As children get older, they learn to choose different strategies to cope with different situations, and they begin to show more personal tendencies and preferences. Some of these individual differences can be traced to their temperaments. For example, children who are quick to experience anxiety or anger (see
chapter 17
and
Practical tip: Dandelion and orchid children
) are particularly vulnerable to stress, in part because they are slow to develop self-control. Parents who are overly protective of high-reactive children may interfere with their development of coping skills.

Our biological response to stress is most effective in dealing with immediate threats to our physical well-being. When a stressful event occurs, two systems become activated. First, the sympathetic nervous system releases epinephrine and the neurotransmitter norepinephrine in less than a second, preparing your body to run or fight by directing energy to muscles, increasing the heart’s blood-pumping ability, and shutting down nonessential systems. This reaction is better suited to dealing with a mugger or a bar fight than with the more common stressors of a grumpy boss or a troubled marriage.

Second, the
hypothalamic-pituitary-adrenocortical (HPA) system
(see figure opposite) works on a time scale of minutes. The hypothalamus sends corticotropin-releasing hormone (CRH) into the pituitary, which releases β-endorphin (a natural painkiller) and corticotropin into the blood. Corticotropin then signals the adrenal cortex to release
glucocorticoid
hormones (mainly cortisol in people) into the blood. In the short term, that’s a good thing, leading to changes in gene expression within the brain that help repair damage caused by the initial stress response, such as replenishing energy stores. Cortisol also increases arousal and vigilance, while inhibiting other processes, including growth, repair, reproduction, and digestion, that might divert energy from the solution of the immediate problem.