At birth, the average newborn brain weighs a mere 330 grams, one-fourth of adult weight. By the time the child is two years old, its weight will triple, and by age seven its 1,250 grams will represent 90% of adult weight. Meanwhile, however, it is losing neurons as the internal competition intensifies and cell groups consolidate into more efficient systems. How does this growth occur? To this question both animal and human research have provided some useful and provocative answers.
THE YOUNG PLASTIC BRAIN
As both animal and human brains grow, three things happen that account for their increased size and efficiency. First, dendrites sprout many new branches and grow heavier as they reach out to receive messages and develop synaptic connections. Second, supporting glial cells increase in number. Both of these developments appear to respond directly to the types of stimulation sent in by the environment.
In addition, the axons, or output parts of neurons, gradually develop a coating of a waxy substance called myelin, which insulates the wiring and facilitates rapid and clear transmission. At birth, only the most primitive systems, such as those needed for sucking, have been coated with myelin, or myelinated. Myelin continues to develop slowly all during childhood and adolescence in a gradual progression from lower- to higher-level systems. Its growth corresponds to the ability to use increasingly higher-level mental abilities. The process of myelination in human brains is not completed at least until most of us are in our twenties and may continue even longer. While animal studies have shown that total myelin may reflect levels of stimulation, scientists believe its order of development is mainly predetermined by a genetic program.
While the system, overall, is remarkably responsive to stimulation from the environment, the schedule of myelination appears to put some boundaries around "appropriate" forms of learning at any given age. Before we go on to consider the exciting implications of the fact that environments can make brains grow, we should stop for a moment to discuss some potential hazards in trying too hard to "make" intelligence or learning happen. Some of the skill deficits of today's schoolchildren, in fact, may have resulted from academic demands that were wrong -- either in content or in mode of presentation -- for their level of development.
Forced Learning and Functional Mix-Ups
The same mentality that attempts to engineer stimulation for baby brains also tries to push learning into schoolchildren much like stuffing sausages. For example, some parents now wonder if their schools are any good if they don't start formal reading instruction, complete with worksheets, in preschool. Likewise, many schools have reading lists or advanced math courses for older children that look impressive but, being out of the reach of most of the students, convince them that reading or math are difficult and boring activities. I call this the "cosmetic curriculum" because it sounds impressive, but the learning is often, unfortunately, only skin deep.
Before brain regions are myelinated, they do not operate efficiently. For this reason, trying to "make" children master academic skills for which they do not have the requisite maturation may result in mixed-up patterns of learning. As we have seen, the essence of functional plasticity is that any kind of learning -- reading, math, spelling, handwriting, etc. -- may be accomplished by any of several systems. Naturally, we want children to plug each piece of learning into the best system for that particular job. If the right one isn't yet available or working smoothly, however, forcing may create a functional organization in which less adaptive, "lower" systems are trained to do the work.
As an example, I think of the many children we see in second and third grade who grip their pencil in the most peculiar ways; some crumple their fingers around it in weird arrangements that make letter formation difficult and cause their hands to tire quickly; some use the base of their fingers instead of the tips to guide the pencil so that the process of handwriting resembles a fencing match more than a fine motor activity; some clutch it in their fists like a weapon. Any teacher will tell you that trying to correct "habits" like these is an uphill -- and usually unsuccessful -- battle. The reason would seem to be that a strong network of synaptic connections has already formed around these maladaptive patterns, making them automatic and difficult to change because they are now built into the system. How much better if we had taken the time to teach it correctly the first time around!
Neuromotor development moves only gradually from "gross motor," large, global movements, to the smaller muscles farther away from the core of the body (in this case, from the palm out to the ends of the fingers). It is certainly easy to speculate that these children were given pencils and encouraged to write -- without sufficient help on proper pencil-holding technique -- before the appropriate motor areas were "ready." Thus they practiced and made this learning automatic in the brain areas that were most available at the time -- to their lasting discomfort.
Can such changes in motor patterns really cause brain changes? In several provocative studies, monkeys whose fingers had been amputated showed altered brain structure as they learned to use different manual patterns. More subtle but equally striking changes occurred simply from having monkeys tap repeatedly with one finger; the related brain areas developed heavier sets of connections. [1]
This sort of study is clearly impossible to conduct on humans, and though we have come a long way, we are far from fully understanding which cell combinations mediate most higher-level learning. The way a child learns to hold a pencil will doubtless assume less and less importance in the age of computer word processors (see Chapter 15), but the same principles of neural readiness may apply to higher-level skills, since they are the most experience-dependent of all. As an example, let's take the kind of reasoning needed for understanding (not just memorizing one's way through) higher-level math. Perhaps some readers of this book shared a common experience when they took algebra: many of us functioned adequately until we reached Chicago, where two planes insisted on passing each other every day in class. When it wasn't planes, it was trains or people digging wells or other situations that did not seem in any way related to graphs and equations of X, Y, and Z. Personally, I found that the more I struggled, the more confused I became, until, soon I was learning more confusion than algebra. Moreover, I began to believe I was pretty dumb. Was I developing what Herman Epstein calls "negative neural networks" (resistant circuitry) toward this worthy subject? [2]
Having fled from math courses at the first available opportunity, I have since talked to other adults who confided that, after a similar experience, they also avoided math until forced years later to take a required course in graduate school. At this point, their grownup brains discovered they actually liked this sort of reasoning, although they were still confused by the planes that meet over Chicago! I often wonder how many children decide they are "dumb" about certain subjects, when the truth is that someone simply laid on the learning too soon in a form other than the one they needed to receive it in at the time. Thus they were cheated of the chance to learn it in an appropriately challenging and satisfying way.
In this personal example, it is very possible that the necessary neural equipment for algebra -- taught in this particular manner -- may not yet have been automatically available in my early-adolescent brain. The areas to receive the last dose of myelin are the association areas responsible for manipulating highly abstract concepts -- such as symbols (X, Y, Z; graphs) that stand for other symbols (numerical relationships) that stand for real things (planes, trains, wells). Such learning is highly experience-dependent, and thus there are many potential neural routes by which it can be performed. Trying to drill higher-level learning into immature brains may force them to perform with lower-level systems and thus impair the skill in question. Since every child's developmental schedule may be different for every type of learning (e.g., some get better at math faster than at English and vice versa), this concept of plasticity makes teaching a challenging task indeed.
I would contend that much of today's school failure results from academic expectations for which students' brains were not prepared -- but which were bulldozed into them anyway. Deficits in everything from grammar to geography may be caused by teaching that bypasses the kind of instruction that could help children conceptually come to grips with the subject at hand.
The brain grows best when it is challenged, so high standards for children's learning are important. Nevertheless, curriculum needs to be considered in terms of brain-appropriate challenge. Reorganizing synapses is much more difficult than having the patience to help them get arranged properly the first time around!
Teachers and parents can prime children's brains for complex learning, but no one knows yet (if they ever will) how to "make" maturation happen. We don't, so far, know how to make myelin grow in human brains, although impoverished environments and inadequate intake of protein may stunt its development. The relatively fixed order of myelinization in different brain areas may provide a real biological basis for "readiness" for certain types of learning. [3] Even if we wanted one, there is no prescription for maturing brains -- much to some parents' dismay.
Not long ago, a father of a teenage son blurted out a question in the middle of a lecture I was giving to a parents' group in an affluent suburb. "My son is fourteen now and he's been accused of being an 'immature late bloomer' by his teachers ever since kindergarten," he lamented. "Is there any place where I can buy myelin?" The audience laughed, and so did I. Many of us have done battle in that particular trench, but maturation is not so easily purchased. What is presented to the growing brain may indeed enrich it in many important respects, but the good intentions of adults who try too hard to manipulate the process can easily backfire.
Looking Inside the "Enriched Brain": What Works?
How, then, do we stimulate growing brains appropriately? And what can cause them to change for the better? In seeking an answer to these big questions, we can start once more in the rat laboratories, where, as visitors, we would observe colonies of rats living in very different types of cages. Although all get the same rations of food and water, some rats enjoy "enriched" environments while others live either in standard laboratory or "impoverished" conditions for mental growth. The "enriched" animals have larger cages and more playmates, but most important, they are also surrounded by toys such as wheels and balls, which they are busily investigating, pushing, rolling, and climbing through. These two variables -- companionship and active involvement with toys -- differentiate between "enriched" and "impoverished" conditions. According to Dr. Diamond, these environmental variations can change the size of the cortex by as much as 11%.
Other researchers have theorized that the areas maturing fastest at the time of stimulation are the ones in which the most growth is found. Thus, in a complex human brain, the same type of stimulation might affect different skills, depending on the brain's stage of development.
What happens to cells in the "enriched" brains? Dr. Mark Rosenzweig and Dr. Michael Renner, who started their work in Dr. Diamond's laboratory, describe several effects, "including changes in gross weight of the brain, weight and thickness of the cerebral cortex, microscopic changes in cell density and relative proportions of different cell types, and changes in the structure of individual neurons." [4]
Curiously enough, Rosenzweig has found that rats in the impoverished condition (IC) actually gain more in body weight than their counterparts in enriched condition (EC). Yet their brains are inferior in many respects, two of which are particularly significant. First, as Marian Diamond has shown, there are many more glial support cells in the enriched brains, and second, the neurons themselves have more dendrite spines and thus, presumably, more synapses. [5]
In another lab, Dr. William Greenough, also considering differences between groups of enriched and deprived rats, found differences in synapses as great as 20-25% in one area of the cortex. This finding, he says, "led us to consider what similar extremes might result if all neurons in the human brain were equally plastic. The difference of about 2,000 synapses per neuron in the rat would translate into many trillions of synapses on the 100-200 billion neurons of the human brain!'' [6] Although, as we shall shortly see, the mere existence of many synapses does not necessarily mean "smarter," this potential for change is indeed impressive.
The critical question is, of course, do these changes in brains have effects on learning? Yes, indeed, say Rosenzweig and Renner, particularly on higher-level skills. "In problem-solving tasks," they report, "the more complex the task, the greater the likelihood that EC-IC differences will be found. In these tests, the primary sites of environmentally induced anatomical plasticity are in those regions of the brain associated with the more complex (and presumably higher-level) cognitive functions, [particularly] higher-level problem-solving skills." Moreover, even when not being tested, the behavior of the enriched rats is more active and organized when they are exploring new situations. They appear to be picking up more and different information during exploration as a result of their lively curiosity.
As a teacher, I invariably think of some of my students when I read studies like these. We must always be cautious, however, in applying such research to human learning. First, while facts about nervous system development can be extrapolated from one set of neurons and glia to another, it is quite another matter to start drawing parallels between animal and human behavior in complex learning situations. Second, while these environments clearly differed from each other, none of them approximated a rat's natural habitat. It is rare to find a human situation as "impoverished" as the IC cages, although in a later chapter I will describe the effects on a human child of one that might be considered comparable. Even the "enriched" environments are less stimulating than those in nature where rats are constantly exposed to the real challenges of living in a free environment, finding food, defending themselves, and moving about when and where they wish. Animals growing up "in the wild" in the Berkeley hills outside Dr. Diamond's laboratory tend to have larger and heavier cortexes than do those raised in the cages.
The basic principles of plasticity have been shown to be constant across such species as mice, gerbils, ground squirrels, dogs, cats, and primates (e. g., monkeys, Japanese macaques). What can we learn from animal research about how to stimulate children appropriately? Many studies support the notion that brains -- and the organisms attached to them -- tend to gravitate to the types of stimulation that they need at different stages of development. If we encourage children to make choices from a selected variety of available challenges, both environmental and intellectual, we are no doubt following the wisest course.
Whose Brain Is Growing Today?
Another lesson from animal research is the importance of active involvement and interest on the part of the animal. For example, Dr. Diamond and others have found that to keep the enriched rats' brains growing, they must frequently change their toys to keep them curious and interested. In another experiment, simply having rats climb over a pile of toys to get their food caused visual areas of the cortex to increase 7%. [7]
Greenough agrees. "It appears that active interaction with the environment is necessary for the animal to extract very much appropriate information. Merely making visual experience of a complex environment available to animals unable to interact with it has little behavioral effect." In support of the latter point, animals have been placed in small cages inside the enrichment cage so they can watch their brothers and sisters play, although they cannot themselves get at the toys. The brains of the spectators end up not much different from those of animals in impoverished cages.
As well-intentioned parents and teachers, we all sometimes end up taking charge of learning and trying to "stuff" in rather than arranging things so that the youngster's curiosity impels the process. Since I began reading this research, I often ask myself when I am struggling to "make" a student learn something, Whose brain is growing today? It always helps to consider: Who is interested? Who is curious? Who is asking the questions? Children need stimulation and intellectual challenges, but they must be actively involved in their learning, not responding passively while another brain -- their teacher's or Parent's -- laboriously develops new synapses in their behalf!
Any activity which engages a student's interest and imagination, which sparks the desire to seek out an answer, or ponder a question, or create a response, can be good potential brain food. Particularly in an age when we need "enriched" minds to grapple with increasingly complex problems, we should not encourage, or even condone, large doses of passive observing or absorbing for growing brains. Yet it is happening -- not only in front of the TV, but in too many day-care centers, schools, after-school activities, and even in homes. How much does this learner passivity contribute to lagging academic skills? A great deal!
In the only human "enrichment" study she has done, Dr. Diamond compared sections from the brain of Albert Einstein with similar sections from average males. She found cellular enhancement of the same types that she had seen in her enriched rats. [8] In one particular area that makes higher-level associations between sensory systems, there were actually twice as many glial cells! She speculates that this unusual profusion could have resulted not only from inherited potential, but also from unusually active use of those particular cell groups.
CRITICAL PERIODS FOR LEARNING
What happens if the "right" stimulation is not available when the brain is ready for it? Are there certain times when the brain is more open to certain kinds of experience? When, if ever, is it too late to learn specific skills? Some of the most eye-opening research on neural plasticity shows that there are "critical," "sensitive," or "optimal" periods for some types of mental development. But if the right stimulus isn't available ... too bad.
"In development it is now well known that there are certain times when an organism is ready to deal with certain stimuli," states Dr. Jane Holmes Bernstein. "And when those stimuli do not appear at the critical time, then it is likely that the brain structures that would have mediated them will not function and will die." [9]
Both animal and human data support this real-life phenomenon of use it or lose it. In order to understand its implications, we should first delve more deeply into the way by which the brain naturally hones itself into an efficient processing system.
Synaptic Pruning: What Gets Shaved and What Gets Saved?
Since an infant enters the world with more neurons than will ever be needed, the brain starts life in quite a disorganized state. Baby neurons that have survived the prenatal marathon to reach synaptic sites are already competing to reach out to other neurons by growing new dendrite spines. It will take many years -- perhaps even a lifetime -- for each brain's complement of synapses to form and become strengthened by repeated use. Particularly during the early years, the ones that get used are the ones that will be strengthened and survive. A major task during the years of childhood is to prune this mass of potential into networks of connections that are useful and automatic for the mental skills that this particular child is being encouraged to develop.
You might envision the newborn brain as a large mass of clay that has been formed in a rough template of a final product. On it, the environment acts as a sculptor. The types of stimulation that enter the brain determine to a great extent which material remains and which is shaved off and swept away from the studio door. During sensitive periods, certain areas in the mass are temporarily warmed and softened, thus becoming more amenable to the environmental sculptor's knife.
This process proceeds quite automatically for the most part. Since the child can't possibly process all the available stimuli, he or she selects what is most interesting or personally relevant, thus building connections in the related brain systems. Adults' main task is to make a variety of stimulation available, at the same time considering carefully the choices their children are encouraged to make. Brains of youngsters who spend lots of time in front of a TV set, for example, may be expected to develop differently from those who pursue the physical, interpersonal, and cognitive challenges of active play. Children with plenty of time to "waste" can be encouraged to seek out activities that are appropriate for an individual brain's stage of development. Youngsters who are hurried from one activity to another may get lots of sensory input but be shortchanged on the time-consuming process of forming association networks to understand and organize experience meaningfully.
The pruning of many synapses is necessary to keep the child's mind from resembling a "booming, buzzing, confusion." Neuroanatomist Dr. Arnold Scheibel once described the immature brain as somewhat like a large tree crowded with many little birds, all singing weakly at the same time so that no individual song can clearly be heard. As the brain matures, gradually eliminating some connections and retaining others, the tree contains fewer but larger birds with strong, clear songs, well separated so that each can distinctly be heard. [10]
Although it seems logical to believe that the more neurons the better, this is not the case. The importance of pruning is demonstrated by studies that show some mentally retarded children have fewer synaptic connections than normal, while others have too many.
Researchers speculate that the retardation may be associated with the inefficiency of these overcrowded brains, although they unfortunately do not as yet know what to do about it.
Evidence for Critical Periods: Animal Research
The ground rules for plasticity often blur the line between efficiency and impairment. Evidence from both animals and humans shows that sometimes the brain's pruning mechanisms are carried too far.
What would the world be like if you could see everything -- except vertical lines? You would probably have a lot of trouble getting through doorways, and it would be difficult to avoid bumping into trees and telephone poles. This experience happened to some kittens who were kept in an unusual environment during a short period when particular groups of cells called "vertical feature detectors" in the visual cortex were "ripe." During this time, the kittens never saw vertical lines. Despite a full dose of visual stimulation and otherwise normal vision later on, they never learned to see them. Later examination of their brains showed that the neurons designed to do this job simply failed to develop because they received no stimulation during the critical period of their development. Many different experiments have been conducted with kittens wearing specially designed goggles or blindfolds. The upshot of all of them is that the selective restriction of certain types of stimulation can structurally alter the animals' brains. [11] Naturally, function is also affected. I find two facts particularly interesting:
-- Not only does severe visual deprivation result in changed neurons in the visual cortex, but it can also cause the auditory (hearing) cortex to develop more fully than would otherwise be expected.
-- Structural changes occurring during critical periods result in behavioral changes later on when their "changed brains" cause the animals to pay attention and respond differently to different aspects of the environment. [12]
Other animal studies, even including such species as birds, crickets, and goldfish, have demonstrated many types of sensitive periods. Sexual behavior of monkeys is later impaired if they are isolated during periods of normal sexual play during childhood. If mother cats do not bring live prey into the nest during a specific time frame, their kittens never develop the ability to become proficient hunters. In each of these cases, certain parts of the nervous system did not develop normally, and stimulation before or after the critical period does not have the same effect.
One interesting experiment illustrates the fact that animals will "work" for their stimulation when the critical period strikes. Kittens were reared in a dark room that contained a lever they could push to view a lighted scene especially designed to stimulate certain sets of visual "feature detectors." Before the onset of a critical period for this type of vision at about eight weeks of age, they occasionally depressed the lever but showed little interest in it, although their eyes had already opened. Suddenly, between eight and nine weeks, the relevant cells became "ripe" and action at the lever increased "dramatically." [13] We can assume the number of dendrites and synapses on those particular cells in their brains grew apace.
"Sensitive" Periods for Human Brains
Human brains have much bigger windows of opportunity because they take much longer to develop than do those of animals, so the terms "sensitive" or "optimal" periods are usually used. Studies to date have identified sensitive periods for two general types of abilities: basic sensory skills and higher-level ones, specifically some aspects of language.
Priming the Foundation Systems
Even when a child's ears and eyes are completely intact, visual and auditory processing may be impaired if cells in the parts of the brain that receive signals from these organs fail to fire during a particular time of development. A well-publicized example is the problem called lazy eye, or amblyopia. In this disorder, a young child fails to develop binocularity, the ability to use both eyes together efficiently, because one eye tends to wander, letting the other do all the work. Because the brain cells designed to receive the visual signals from the lazy eye do not get their proper dose of stimulation, they eventually stop firing. Doctors have learned that this condition must be treated before age five, if it is to be corrected, because the sensitive period for this particular ability may end at that time. The treatment, logically, consists of intermittently patching the good eye to force all cells in the system to do their work, develop their synapses, and survive. The same principle explains why cataracts on the eyes of infants must be removed before six months of age to avoid permanent visual impairment.
Still at a basic sensory level, the ability to discriminate fine differences between sounds of a language apparently must develop during early years, as well. An eighth grader I met recently simply could not "hear" the differences between some of the short vowel sounds and thus had trouble saying and writing them accurately. Her classmates thought that her substitutions, such as "osculator" for "escalator," were "cute," but her teachers were not similarly amused by her spelling mistakes. Sure enough, I discovered she, like many students with both spelling and reading problems, had suffered from early ear infections that resulted in sporadic hearing loss during preschool years. Because of this link with later learning problems, experts now recommend that parents watch children carefully for blocked hearing and get prompt medical attention for such problems before cells in the auditory cortex are permanently impaired by lack of exercise. [14]
Circuits for the sounds of different languages must apparently be stimulated during a critical period, as well. Dr. Jennifer Buchwald of the UCLA School of Medicine is interested in the way "the acoustic -- that is, linguistic -- environment during development is responsible for developmental differences in the brain." She is studying such differences in native Japanese and American speakers by measuring a special type of electrical wave, called P300, in their brains. [14]
Her research explains why adults who learn to speak a foreign language with different sound patterns than their own rarely acquire a flawless accent. Their vocal apparatus is not the reason; their brains are. While they may think they hear or mimic the sounds accurately, they really have lost the ability to perceive sound patterns that were not present in the environments during childhood. The distinctive accents of European, Middle Eastern, or Oriental speakers of English, which often reveal their particular national origins, provide living verification of the power of early environments to create lasting differences in some types of human abilities.
Does this justify teaching Japanese to infants -- another current fad among the child-engineering group? At a recent conference Dr. Nico Spinelli responded with an interesting observation. "I think growing up bilingually wastes real estate in the brain. A better plan, in my opinion, would be for children to learn to pronounce perfectly fifty or so words of, say, German, French, Japanese, and Spanish. Later on, one or more of these languages could be learned more easily and with no accent, because the brain would have been primed for it." [15] Before parents rush for their foreign language dictionaries, however, I would like to reiterate the fact that any learning that has to be "pushed" into a child may end up doing more harm than good -- for many reasons. Moreover, there is also evidence that the wrong kinds of foreign language input may tangle up the wires of some children for their native tongue. Caution is advised!
It seems logical that hard-wired sensory skills might have sensitive periods of development. But what about the type of association area brainwork that requires the integration of many different -- and sometimes widely separated -- neural systems? A few studies have been conducted which suggest that to develop active, intelligent responses to the world, a child needs specific types of interaction with caretakers at different times in development. For example, separate studies have shown that in normal children, direct kinesthetic (muscular) stimulation (e.g., parent moves child's arms or legs) is maximally effective during the first six months; maternal prompting ("Look at the bunny," "See the red fire engine") is more effective at some times than at others; and maternal gesturing has been positively related to comprehension in nineteen-month-olds but not in older children. [16] In the next chapter we will look at other ways in which "higher-order" skills such as language and attention may be affected by experience during specific times of development.
"NEURAL DARWINISM" IN THE COMPETITIVE BRAIN
Probably the most intriguing idea emerging from all this research is that brains are shaped and maintained by internal competition. The creative drama of neurons' endless battle, first for survival and later for connective power, is still not familiar to most people outside the research laboratories. Even many of those within the labs have trouble grasping implications of a major new theory proposed by Nobel Prize winner Dr. Gerald Edelman of Rockefeller University. His book, Neural Darwinism, outlines in complete detail what might be considered the ultimate argument for the environment's power in shaping the brain. [17]
In his theory and with "Darwin III," a computer that can replicate some aspects of human brain function in surprisingly lifelike ways, Edelman applies the laws of natural selection to the neurons in the human brain -- and finds that they work. He first acknowledges, as we have already seen, that there are overall patterns of brain structure that are modified by genetic and prenatal history; in addition, he proposes a group of "secondary repertoires," formed only by stimuli to which a particular brain responds during its lifetime. In this constantly changing system, groups of neurons are locked in constant competition with each other to "capture" other cells for their group. The groups that get the most action grow stronger synapses, add to their networks, and survive; they are "selected" because they are more likely to be used in future behavior.
As long as significant activation is achieved, the group can continue to consolidate its "hold" on cells. But other groups are constantly competing for the same cells, and any weakening of connections because of decreased activation puts the group at risk either of losing a few cells or, in the extreme case, of being divided and conquered. [18]
Ultimately, through a process that he describes as "reentrant signaling," the cell groups link themselves together in a coordinated system that can talk to itself. These systems communicate back and forth, spurring on their own development as they respond to internal and external stimuli. Thus our brains evolve, individually and collectively, according to what is useful and adaptive for the particular environments in which we find ourselves.
Committing Growing Neurons ... to What?
Dr. Jane Holmes Bernstein is intrigued by Edelman's ideas. "It seems," she says, "the stimuli coming in are actually competing to have this brain take notice of them. When you're dealing with this idea of competition within the system, if those stimuli are not there at the right time, then the cells don't fire. The next set of stimuli coming in, competing madly for cortical connections, are likely to preempt what should have been a relationship in the cells."
But surely this doesn't mean that we're just helpless victims of whatever stimuli come along, does it?
Not at all, believes Dr. Bernstein. "It's not simply a matter of the stimuli being there; you have to do something with them." She describes a famous experiment in which identical-twin kittens were put in a large circular container painted with black and white vertical stripes -- their only visual stimulation during a critical period of visual development. One kitten rode in a small basket that was attached to one end of a revolving balance beam. The other kitten was in a second basket attached to the opposite end of the beam; his legs, however, protruded from the basket. As he walked around, the beam revolved and his brother got a free ride. Both, of course, had the same visual stimulation of the vertical stripes. Later, it was discovered that visual receptor cells in their brains had developed differently, even though each had experienced the exact same scenery. The kitten who merely rode along was functionally blind for vertical lines!
"Only the kitten who had his feet on the floor, knowing where he was, aware of his position on the floor relative to the lines, developed those connections!" emphasizes Dr. Bernstein. "Experience shapes brains, but you need to interact with the experience."
Physical play is one of the main ways in which children interact with experience, points out Dr. Bernstein. "The most characteristic thing about the human is that we go looking for problems to solve -- or in other words, playing. In fact, we usually worry about significant emotional issues in youngsters who are unable to look for problems to solve."
Before I left Dr. Bernstein's office I decided to get practical. If the brain responds physically to such environmental differences as whether a kitten walks or rides, what effects might today's environments -- where many children spend more time watching a screen than with their feet on the ground -- be having on mental abilities? What skills could they be gaining -- and which ones might they be losing?
"Well," she replied, "there's nothing wrong with TV or computers per se. However, it may be an issue whether the kids are active or passive when working with the machines. Sesame Street, for example, has brought a great deal of information to children who might not otherwise have got it, but this may have been obtained at a price. I hear many teachers complain that children in kindergarten and first grade don't know how to listen actively! They're used to fast-paced segments of information that are constantly changing. They should be doing something with what they're getting.
"The Sesame Street population is actually at the greatest risk for not understanding that language is communication, a back-and-forth interaction between people. They aren't personally involved in using language to think and solve problems with. Children who have been talked to and had stories read to them are at a real advantage. They've learned how to listen and pay attention -- and had fun doing it. These basic abilities are critical if a youngster is to benefit from education in the classroom!"
How about video games?
"In one very popular game, for example, children must learn to attend to increasingly complex clues. They're systematically encouraged to scan a visual array. But why not put a kid in a real-life problem-solving situation? This isn't being encouraged. We're not giving them the full range of opportunities and it's certainly possible that with such a degree of practice on one skill, the brain might commit too many cells and there would be fewer available for other things.
"Teachers worry about the amount of time children, even very young ones, spend these days encased in stereo headphones, listening to music instead of talking, reading or carrying on a conversation. What do you think that might be doing to their brains?" I asked Dr. Bernstein.
"I hate to think." She rolled her eyes.
"It seems as if we teachers have our work cut out for us," I ventured. "How much can schools change brains?"
Dr. Bernstein did not hesitate. "A great deal!" she replied emphatically.
IN A NUTSHELL: DEVELOPING BRAINS
Genes set the outlines of mental ability, but the way children use their brains determines how their intelligence is expressed. The experiences with which a child chooses to interact determine each brain's synaptic structure as well as the way it functions for different types of learning. If children change the way they use their brains, their synapses are rearranged accordingly. The more they are used in a certain pattern of response, the less flexible they appear to become.
Nature provides a schedule for neural maturation, and increasingly complex modes of thinking emerge from an internal competition for connections at each new phase of mental growth. If a child is glued to an activity for several hours a day, connections for that specific activity will be built up, but something else is going to be diminished. Moreover, if certain kinds of skills remain unused during their appearance on the brain's developmental stage, neural foundations may wither away in the wings of potentiality.
Severe deprivation can have dramatic effects on the young, malleable mind. Less extreme variations in experience have less predictable consequences. The value of excessive stimulation to enhance development is unproven and risky. External pressure designed to produce learning or intelligence violates the fundamental rule: A healthy brain stimulates itself by active interaction with what it finds challenging and interesting in its environment. The environments that we provide for children, the stimuli with which we encourage them to interact, and the ways in which we demonstrate for them the uses of a human mind -- these are the means at our command for shaping both their brains and our cultural future.
