Welcome to Your Child's Brain: How the Mind Grows From Conception to College (38 page)

From the basic senses of number—subitization, numerosity, and symbolic representation—we can construct a host of more complex concepts, such as negative, fractional, and real numbers. From these and additional brain capacities, it becomes possible to imagine the universe of mathematics: multiplication, trigonometry, functions, calculus, and more.

The study of how the brain produces abstract mathematics has barely begun, but researchers have taken a few first steps. At higher levels of math, additional concepts—and many brain regions—come into play. Algebra requires kids to combine their numerical abilities with symbolic, abstract manipulation. Beginning students can come at algebra by different routes. For instance, it is often easier to solve a word problem than to solve an equation. These different approaches emphasize different brain regions.

To monitor what brain regions are activated by different approaches to solving a problem, researchers took fMRI scans of people doing story problems (If Cathy makes $10 an hour and gets $12 in tips at the end of a four-hour shift, how much money has she earned in total?) and similar equation problems (If 10H + 12 = E and H = 4, what is E?). The scans showed that solving story problems preferentially activates the left prefrontal cortex, an area associated with working memory and quantitative processing. Equation problems activate regions associated with the mental number line, such as parts of the parietal cortex, including the
precuneus
(a portion of the parietal lobe facing the midline), as well as parts of the basal ganglia that are essential in nonalgebraic life for action and movement.

This difference suggests that beginners at algebra may want to try several different approaches to the same problem. For harder problems, in addition to the cortical areas we mentioned, many more regions in the left hemisphere are activated. Higher math such as trigonometry or calculus has not been investigated thoroughly, but researchers believe that these capacities also build upon brain systems for symbolic and spatial manipulation.

At some level, this supports Euclid’s aphorism about geometry that “there is no royal road to learning.” Mathematics is an incredibly complex system, one of humanity’s great achievements, and it’s remarkable to think that brain circuits for telling stories and moving the eyes have been harnessed to generate, understand, and use it. It’s a feat of matching the brain to an environment that our ancestors never imagined.

Chapter 25
THE MANY ROADS TO READING

AGES: FOUR YEARS TO TWELVE YEARS

The human brain took its present form before the first word was ever written. In the five thousand years since the alphabet was created, our brains haven’t changed that much. So reading (like advanced math) must use circuitry that originally evolved to fulfill other functions. Brain scanning studies have started to reveal how the systems for reading mature. In children who learn alphabet-based languages such as English, patterns of brain activation change in a sequence that reflects certain stages of development. These steps follow a different trajectory in dyslexic children—but also in children learning to read Chinese. Evidently the road to literacy takes multiple paths, some of which may be smoother for one child than for another. The right choice of a language may improve the odds of a good outcome.

At its core, reading consists of learning the relationship between words and marks on paper. In Western languages, the marks are letters; in Chinese, characters. Most children start learning to read and write around age five or six. Over years of practice, this process becomes automatic and effortless.

As neuroscientists have found by using brain scanning technology on adults, during reading the brain shows activity in many regions. These include the frontal lobe, the cerebellum, and the area where the temporal lobe of the neocortex meets the parietal and occipital lobes. One especially important region is a part of the fusiform gyrus within the left inferior temporal cortex. This region appears to have a special importance in the recognition of written language (which is why it’s sometimes called the
visual word form area
). This region is active when a person is shown either words (
cat
) or groups of letters that look like words but are not (
zat
). This discrimination is not simply a matter of recognizing whether the pattern is pronounceable. Chinese characters are composed of stroke patterns with no intrinsic pronunciation—you can’t “sound out” the pronunciation of a Chinese word; you just have to know it. And yet nonsense characters that resemble real words also activate the visual word form area in Chinese readers.

Word-form recognition is learned through experience. This capacity seems to be an example of a more general ability of the inferior temporal cortex to visually recognize objects (see
chapter 10
). Some neurons fire when a monkey or person sees specific objects, such as a flower, a hand, or a face of a monkey or person. Neural processing for faces is concentrated in the right hemisphere. “Face neurons” in the inferior temporal cortex are quite specific, responding only to faces and
not to individual features, rearranged images of faces, or even upside-down faces. Recognition is more likely if an object is familiar or important to the viewer. For example, part of the region that is specialized for face recognition also responds to specific car models—in the brain of a car expert.

Most naturally occurring objects look the same when viewed from the left or the right. Perhaps for this reason, mirror-image confusion is common in animals and people. Your child’s brain, and yours too, are optimized to solve common visual problems—but for most of evolution, those problems have not included reading. There may not be much advantage to distinguishing left- from right-side views of objects most of the time. Therefore the right inferior temporal cortex may not be wired to detect asymmetry. This characteristic suggests why it might be useful for the inferior temporal cortex on this side of the brain to drop out of the reading circuit.

Attempts by your child’s right inferior temporal cortex to participate in reading can pose a problem, because words and letters are loaded with asymmetry. In reading, the ability to distinguish mirror images is often important, for instance, in distinguishing
b
from
d
or
AM
from
MA
. As a result, the brain must suppress any tendency to perceive left and right views as being the same, which may explain why many brains don’t take naturally to reading. Mirror-image confusion might interfere with recognition of letters and words—and in some cases be involved in difficulties with early reading.

Because natural objects such as faces look the same from either side, the more efficient recognition strategy is often to treat left and right views as being the same. Overcoming the natural tendency to treat mirror images as equivalent is a major milestone for beginning readers. In kindergarteners, the ability to make left-right distinctions is correlated with readiness to read, and children at this age routinely reverse letters. The relationship between left-right detection capacity and early reading disappears by first grade, suggesting that most children clear this hurdle by the age of six. From then on, readers rely more and more on regions in the left frontal and temporal lobes. Conversely, dyslexics frequently have left-right confusion, as well as difficulty distinguishing mirror images from each other. Perhaps for this reason, dyslexic children often retain a capacity for mirror writing, which most children lose.

Even though monkeys can’t read, they share with your child a natural affinity for visual symmetry. Studies in monkeys suggest that suppressing that affinity is
likely to come with decoupling of the right inferior temporal cortex. Like most animals, monkeys have trouble telling apart left-right asymmetric stimuli. After damage to their inferior temporal cortex, they do not get worse at this task—and sometimes they get better. It seems as if part of the work in this task is overcoming the natural tendencies of the inferior temporal cortex for shape recognition.

The right inferior temporal cortex may be the culprit in early reading difficulties. One group of researchers showed words to English-language readers age six and older. In beginning readers, both the left and right inferior temporal cortex are active during reading. This balance slowly fades until, by age sixteen, inferior temporal cortex activation has shifted largely to the left side. At ages in between, six- to ten-year-olds showed a wide variety of activation on the right side. Right-side activation and reading test scores were negatively correlated. That is, kids with less right inferior temporal activation were better readers.

In the five thousand years since the alphabet was created, our brains haven’t changed that much. So reading (like advanced math) must use circuitry that originally evolved to fulfill other functions.

Another likely step in learning to read successfully is the ability to identify and manipulate spoken sounds, for instance, being able to judge that
bat
and
cat
end with the same two sounds. This capacity is known as
phonological awareness
. Phonological naming of letter sounds predicts reading proficiency, and deficits in this capacity may be a central cause of dyslexia. One brain region activated in early readers, the left posterior superior temporal sulcus, is more active in children with a better ability to recognize and classify spoken sounds. More broadly, in both early and mature readers, activity is seen in areas in the temporal and parietal cortex. These brain regions are well positioned to receive both auditory and visual information, and so might be important for integrating these modalities with each other for word recognition.

The involvement of brain regions that process sound makes sense in the case of alphabetical languages such as English, which require sounds to be linked with letters. But not all languages work this way. One example that has attracted recent interest from language researchers and neuroscientists is Chinese.

PRACTICAL TIP: READING AT HOME

Many videos claim to teach early reading to infants. The creators of such products state that literacy skills are best taught from birth to about age four. Yet during this time, children lack the capacity to distinguish
b
from
d
, much less read whole words. No studies show that babies are doing anything more than forming associations when they watch these videos. To paraphrase one product: no, your baby can’t read.

The timetable of perceptual development does raise another question: what is the benefit of children’s books? In young children who can’t read, the benefits appear to be associated with an interactive style of reading. Rather than taking a straight reading approach or even asking questions that can be answered by having the child point, you can accelerate language development through social engagement—by asking open-ended questions, questions about a character’s actions or attributes, and by responding to your child’s attempts to answer the questions.

Access to books is strongly linked to educational achievement. Among families with similar incomes and parental education, the number of books in the home is a good predictor of children’s reading ability. On average, across multiple countries, children with many books stay in school three years longer than children without books. Having books at home makes as much difference to children’s accomplishments as having university-educated rather than uneducated parents.

A Chinese child beginning to read confronts a formidable task. The written language is composed of thousands of different complex characters. Each character represents part or all of a word and is a dense squarish assemblage of one or more components called
radicals
. Children must learn about 620 radicals, each containing one to several dozen strokes. Finally, the visual appearance of a character usually does not reveal how it is pronounced.