THE LEARNING WINDOW
(Senate - March 28, 1996)

Text available as:

Formatting necessary for an accurate reading of this text may be shown by tags (e.g., <DELETED> or <BOLD>) or may be missing from this TXT display. For complete and accurate display of this text, see the PDF.

[Pages S3165-S3168]
From the Congressional Record Online through the Government Publishing Office [www.gpo.gov]




                          THE LEARNING WINDOW

 Mr. CONRAD. Mr. President, Newsweek magazine on February 19, 
1996, published an article regarding research that is underway by 
several pediatric neurobiologists in the United States on the 
development of a child's brain. The research examined the significance 
of early childhood experiences, particularly for children ages 0-3, on 
the development of the brain.
  According to researchers, ``it's the experiences of early childhood, 
determining which neurons are used, that wire the circuit of the brain 
as surely as a programmer at a keyboard reconfigures the circuits in a 
computer. Which keys that are typed--which experiences a child ahs--
determines whether the child grows up to be

[[Page S3166]]

intelligent or dull, fearful or self-assured, articulate or tongue-
tied.'' According to the researchers, almost anything is possible 
provided children are exposed to the right experiences at an early age. 
As one researcher, Harry Chugani of Wayne State University remarked, 
``early experiences are powerful, they can completely change the way a 
person turns out.''
  Mr. President, the findings of these neurobiologists support a much 
closer examination by Congress of whether we are providing sufficient 
support at the Federal level for Head Start programs, and especially 
the Zero-to-Three initiative for infants and toddlers. As my colleagues 
may recall, during consideration of Head Start reauthorization in 1994, 
authority for a new infant and toddler initiative was adopted as part 
of the reauthorization of Head Start programs. Under the 
reauthorization, 3 percent of total appropriations for fiscal year 
1995--$3.5 billion--was set aside for Zero-to-Three programs.
  Currently, funding for the Zero-to-Three initiative totals $106 
million. By 1998, the level of funding for the Zero-to-Three initiative 
will increase to 5 percent of total appropriations. President Clinton 
has requested $3.9 billion for Head Start in his fiscal year 1997 
budget. Under Head Start fiscal year 1995 appropriations, more than 
750,000 children between the ages of 3 and 4 are participating in Head 
Start programs nationwide.
  Mr. President, the research of neurobiologists suggests that we may 
be missing an opportunity to ensure that our children develop to their 
fullest potential during the early years in life, ages 0-3. The 
neurobiologists point out that there is a narrow window of opportunity 
to develop the brain's potential and that to wait until the ages of 3 
and 4 when most children begin Head Start programs may be too late to 
have a significant impact on the brain's development.
  I urge my colleagues to examine the research regarding the 
development of a child's brain that is discussed in the February 19 
issue of Newsweek. I ask that the text of the article from Newsweek 
appear in the Record at the conclusion of my remarks.

                     [From Newsweek, Feb. 19, 1996]

                           Your Child's Brain

                           (By Sharon Begley)

(A baby's brain is a work in progress, trillions of neurons waiting to 
be wired into a mind. The experiences of childhood, pioneering research 
shows, help form the brain's circuits--for music and math, language and 
                                emotion)

       You hold your newborn so his sky-blue eyes are just inches 
     from the brightly patterned wallpaper, ZZZt: a neuron from 
     his retina makes an electrical connection with one in his 
     brain's visual cortex. You gently touch his palm with a 
     clothespin; he grasps it, drops it, and you return it to him 
     with soft words and a smile. Crackle: neurons from his hand 
     strengthen their connection to those in his sensory-motor 
     cortex. He cries in the night; you feed him, holding his gaze 
     because nature has seen to it that the distance from a 
     parent's crooked elbow to his eyes exactly matches the 
     distance at which a baby focuses. Zap: neurons in the brain's 
     amygdala send pulses of electricity through the circuits that 
     control emotion. You hold him on your lap and talk . . . and 
     neurons from his ears start hard-wiring connections to the 
     auditory cortex.
       And you thought you were just playing with your kid.
       When a baby comes into the world her brain is a jumble of 
     neurons, all waiting to be woven into the intricate tapestry 
     of the mind. Some of the neurons have already been hard-
     wired, by the genes in the fertilized egg, into circuits that 
     command breathing or control heartbeat, regulate body 
     temperature or produce reflexes. But trillions upon trillions 
     more are like the Pentium chips in a computer before the 
     factory preloads the software. They are pure and of almost 
     infinite potential, unprogrammed circuits that might one day 
     compose rap songs and do calculus, erupt in fury and melt in 
     ecstasy. If the neurons are used, they become integrated into 
     the circuitry of the brain by connecting to other neurons; if 
     they are not used, they may die. It is the experiences of 
     childhood, determining which neurons are used, that wire the 
     circuits of the brain as surely as a programmer at a keyboard 
     reconfigures the circuits in a computer. Which keys are 
     typed--which experiences a child has--determines whether the 
     child grows up to be intelligent or dull, fearful or self-
     assured, articulate or tongue-tied. Early experiences are so 
     powerful, says pediatric neurobiologist Harry Chugani of 
     Wayne State University, that ``they can completely change the 
     way a person turns out.''
       By adulthood the brain is crisscrossed with more than 100 
     billion neurons, each reaching out to thousands of others so 
     that, all told, the brain has more than 100 trillion 
     connections. It is those connections--more than the number of 
     galaxies in the known universe--that give the brain its 
     unrivaled powers. The traditional view was that the wiring 
     diagram is predetermined, like one for a new house, by the 
     genes in the fertilized egg. Unfortunately, even though half 
     the genes--50,000--are involved in the central nervous system 
     in some way, there are not enough of them to specify the 
     brain's incomparably complex wiring. That leaves another 
     possibility: genes might determine only the brain's main 
     circuits, with something else shaping the trillions of finer 
     connections. That something else is the environment, the 
     myriad messages that the brain receives from the outside 
     world. According to the emerging paradigm, ``there are two 
     broad stages of brain wiring,'' says developmental 
     neurobiologist Carla Shatz of the University of California, 
     Berkeley: ``an early period, when experience is not required, 
     and a later one, when it is.''
       Yet, once wired, there are limits to the brain's ability to 
     create itself. Time limits. Called ``critical periods,'' they 
     are windows of opportunity that nature flings open, starting 
     before birth, and then slams shut, one by one, with every 
     additional candle on the child's birthday cake. In the 
     experiments that gave birth to this paradigm in the 1970, 
     Torsten Wiesel and David Hubel found that sewing shut one eye 
     of a newborn kitten rewired its brain: so few neurons 
     connected from the shut eye to the visual cortex that the 
     animal was blind even after its eye was reopened. Such 
     rewiring did not occur in adult cats whose eyes were shut. 
     Conclusion: there is a short, early period when circuits 
     connect the retina to the visual cortex. When brain regions 
     mature dictates how long they stay malleable. Sensory areas 
     mature in early childhood; the emotional limbic system is 
     wired by puberty; the frontal lobes--seat of understanding--
     develop at least through the age of 16.
       The implications of this new understanding are at once 
     promising and disturbing. They suggest that, with the right 
     input at the right time, almost anything is possible. But 
     they imply, too, that if you miss the window you're playing 
     with a handicap. They offer an explanation of why the gains a 
     toddler makes in Head Start are so often evanescent: this 
     intensive instruction begins too late to fundamentally rewire 
     the brain. And they make clear the mistake of postponing 
     instruction in a second language. As Chugani asks, ``What 
     idiot decreed that foreign-language instruction not begin 
     until high school?''
       Neurobiologists are still at the dawn of understanding 
     exactly which kinds of experiences, or sensory input, wire 
     the brain in which ways. They know a great deal about the 
     circuit for vision. It has a neuron-growth spurt at the age 
     of 2 to 4 months, which corresponds to when babies start to 
     really notice the world, and peaks at 8 months, when each 
     neuron is connected to an astonishing 15,000 other neurons. A 
     baby whose eyes are clouded by cataracts from birth will, 
     despite cataract-removal surgery at the age of 2, be forever 
     blind. For other systems, researchers know what happens, but 
     not--at the level of neurons and molecules--how. They 
     nevertheless remain confident that cognitive abilities work 
     much like sensory ones, for the brain is parsimonious in how 
     it conducts its affairs: a mechanism that works fine for 
     wiring vision is not likely to be abandoned when it comes to 
     circuits for music. ``Connections are not forming willy-
     nilly,'' says Dale Purves of Duke University, ``but are 
     promoted by activity.''


                                Language

       Before there are words, in the world of a newborn, there 
     are sounds. In English they are phonemes such as sharp ba's 
     and da's, drawn-out ee's and ll's and sibilant sss's. In 
     Japanese they are different--barked hi's, merged rr/ll's. 
     When a child hears a phoneme over and over, neurons from his 
     ear stimulate the formation of dedicated connections in his 
     brain's auditory cortex. This ``perceptual map,'' explains 
     Patricia Kuhl of the University of Washington, reflects 
     the apparent distance--and thus the similarity--between 
     sounds. So in English-speakers, neurons in the auditory 
     cortex that respond to ``ra'' lie far from those that 
     respond to ``la.'' But for Japanese, where the sounds are 
     nearly identical, neurons that respond to ``ra'' are 
     practically intertwined, like L.A. freeway spaghetti, with 
     those for ``la.'' As a result, a Japanese-speaker will 
     have trouble distinguishing the two sounds.
       Researchers find evidence of these tendencies across many 
     languages. By 6 months of age, Kuhl reports, infants in 
     English-speaking homes already have different auditory maps 
     (as shown by electrical measurements that identify which 
     neurons respond to different sounds) from those in Swedish-
     speaking homes. Children are functionally deaf to sounds 
     absent from their native tongue. The map is completed by the 
     first birthday. ``By 12 months,'' says Kuhl, ``infants have 
     lost the ability to discriminate sounds that are not 
     significant in their language, and their babbling has 
     acquired the sound of their language.''
       Kuhl's findings help explain why learning a second language 
     after, rather than with, the first is so difficult. ``The 
     perceptual map of the first language constrains the learning 
     of a second,'' she says. In other words, the circuits are 
     already wired for Spanish, and the remaining undedicated 
     neurons have lost their ability to form basic new connections 
     for, say, Greek. A child taught a second language after the 
     age of 10 or so is unlikely

[[Page S3167]]

     ever to speak it like a native. Kuhl's work also suggests why 
     related languages such as Spanish and French are easier to 
     learn than unrelated ones: more of the existing circuits can 
     do double duty.
       With this basic circuitry established, a baby is primed to 
     turn sounds into words. The more words a child hears, the 
     faster she learns language, according to psychiatrist 
     Janellen Huttenlocher of the University of Chicago. Infants 
     whose mothers spoke to them a lot knew 131 more words at 20 
     months than did babies of more taciturn, or less involved, 
     mothers; at 24 months, the gap had widened to 295 words. 
     (Presumably the findings would also apply to a father if he 
     were the primary caregiver.) It didn't matter which words the 
     mother used--monosyllables seemed to work. The sound of 
     words, it seems, builds up neural circuitry that can then 
     absorb more words, much as creating a computer file allows 
     the user to fill it with prose. ``There is a huge vocabulary 
     to be acquired,'' says Huttenlocher, ``and it can only be 
     acquired through repeated exposure to words.''


                                 Music

       Last October researchers at the University of Konstanz in 
     Germany reported that exposure to music rewires neural 
     circuits. In the brains of nine string players examined with 
     magnetic resonance imaging, the amount of somatosensory 
     cortex dedicated to the thumb and fifth finger of the left 
     hand--the fingering digits--was significantly larger than 
     in nonplayers. How long the players practiced each day did 
     not affect the cortical map. But the age at which they had 
     been introduced to their muse did: the younger the child 
     when she took up an instrument, the more cortex she 
     devoted to playing it.
       Like other circuits formed early in life, the ones for 
     music endure. Wayne State's Chugani played the guitar as a 
     child, then gave it up. A few years ago he started taking 
     piano lessons with his young daughter. She learned easily, 
     but he couldn't get his fingers to follow his wishes. Yet 
     when Chugani recently picked up a guitar, he found to his 
     delight that ``the songs are still there,'' much like the 
     muscle memory for riding a bicycle.


                             math and logic

       At UC Irvine, Gordon Shaw suspected that all higher-order 
     thinking is characterized by similar patterns of neuron 
     firing. ``If you're working with little kids,'' says Shaw, 
     ``you're not going to teach them higher mathematics or chess. 
     But they are interested in and can process music.'' So Shaw 
     and Frances Rauscher gave 19 preschoolers piano or singing 
     lessons. After eight months, the researchers found, the 
     children ``dramatically improved in spatial reasoning,'' 
     compared with children given no music lessons, as shown in 
     their ability to work mazes, draw geometric figures and copy 
     patterns of two-color blocks. The mechanism behind the 
     ``Mozart effect'' remains murky, but Shaw suspects that when 
     children exercise cortical neurons by listening to classical 
     music, they are also strengthening circuits used for 
     mathematics. Music, says the UC team, ``excites the inherent 
     brain patterns and enhances their use in complex reasoning 
     tasks.''


                                emotions

       The trunk lines for the circuits controlling emotion are 
     laid down before birth. Then parents take over. Perhaps the 
     strongest influence is what psychiatrist Daniel Stern calls 
     attunement--whether caregivers ``play back a child's inner 
     feelings.'' If a baby's squeal of delight at a puppy is met 
     with a smile and hug, if her excitement at seeing a plane 
     overhead is mirrored, circuits for these emotions are 
     reinforced. Apparently, the brain uses the same pathways 
     to generate an emotion as to respond to one. So if an 
     emotion is reciprocated, the electrical and chemical 
     signals that produced it are reinforced. But if emotions 
     are repeatedly met with indifference or a clashing 
     response--Baby is proud of building a skyscraper out of 
     Mom's best pots, and Mom is terminally annoyed--those 
     circuits become confused and fail to strengthen. The key 
     here is ``repeatedly'': one dismissive harrumph will not 
     scar a child for life. It's the pattern that counts, and 
     it can be very powerful: in one of Stern's studies, a baby 
     whose mother never matched her level of excitement became 
     extremely passive, unable to feel excitement or joy.
       Experience can also wire the brain's ``calm down'' circuit, 
     as Daniel Goleman describes in his best-selling ``Emotional 
     Intelligence.'' One father gently soothes his crying infant, 
     another drops him into his crib; one mother hugs the toddler 
     who just skinned her knee, another screams ``It's your own 
     stupid fault!'' The first responses are attuned to the 
     child's distress; the others are wildly out of emotional 
     sync. Between 10 and 18 months, a cluster of cells in the 
     rational prefrontal cortex is busy hooking up to the emotion 
     regions. The circuit seems to grow into a control switch, 
     able to calm agitation by infusing reason into emotion. 
     Perhaps parental soothing trains this circuit, strengthening 
     the neural connections that form it, so that the child learns 
     how to calm herself down. This all happens so early that the 
     effects of nurture can be misperceived as innate nature.
       Stress and constant threats also rewire emotion circuits. 
     These circuits are centered on the amygdala, a little almond-
     shaped structure deep in the brain whose job is to scan 
     incoming sights and sounds for emotional content. According 
     to a wiring diagram worked out by Joseph LeDoux of New York 
     University, impulses from eye and ear reach the amygdala 
     before they get to the rational, thoughtful neocortex. If a 
     sight, sound or experience has proved painful before--Dad's 
     drunken arrival home was followed by a beating--then the 
     amygdala floods the circuits with neurochemicals before the 
     higher brain knows what's happening. The more often this 
     pathway is used, the easier it is to trigger: the mere memory 
     of Dad may induce fear. Since the circuits can stay excited 
     for days, the brain remains on high alert. In this state, 
     says neuroscientist Bruce Perry of Baylor College of 
     Medicine, more circuits attend to nonverbal cues--facial 
     expressions, angry noises--that warn of impending danger. As 
     a result, the cortex falls behind in development and has 
     trouble assimilating complex information such as language.


                                movement

       Fetal movements begin at 7 weeks and peak between the 15th 
     and 17th weeks. That is when regions of the brain controlling 
     movement start to wire up. The critical period lasts a while: 
     it takes up to two years for cells in the cerebellum, which 
     controls posture and movement, to form functional circuits. 
     ``A lot of organization takes place using information gleaned 
     from when the child moves about in the world,'' says William 
     Greenough of the University of Illinois. ``If you restrict 
     activity you inhibit the formation of synaptic connections in 
     the cerebellum.'' The child's initially spastic movements 
     send a signal to the brain's motor cortex; the more the arm, 
     for instance, moves, the stronger the circuit, and the better 
     the brain will become at moving the arm intentionally and 
     fluidly. The window lasts only a few years: a child 
     immobilized in a body cast until the age of 4 will learn to 
     walk eventually, but never smoothly.
       There are many more circuits to discover, and many more 
     environmental influences to pin down. Still, neuro labs are 
     filled with an unmistakable air of optimism these days. It 
     stems from a growing understanding of how, at the level of 
     nerve cells and molecules, the brain's circuits form. In the 
     beginning, the brain-to-be consists of only a few advance 
     scouts breaking trail: within a week of conception they march 
     out of the embryo's ``neural tube,'' a cylinder of cells 
     extending from head to tail. Multiplying as they go (the 
     brain adds an astonishing 250,000 neurons per minute during 
     gestation), the neurons clump into the brain stem which 
     commands heartbeat and breathing, build the little cerebellum 
     at the back of the head which controls posture and movement, 
     and form the grooved and rumpled cortex wherein thought and 
     perception originate. The neural cells are so small, and the 
     distance so great, that a neuron striking out for what will 
     be the prefrontal cortex migrates a distance equivalent to a 
     human's walking from New York to California, says 
     developmental neurobiologist Mary Beth Hatten of Rockefeller 
     University.
       Only when they reach their destinations do these cells 
     become true neurons. They grow a fiber called an axon that 
     carries electrical signals. The axon might reach only to a 
     neuron next door, or it might wend its way clear across to 
     the other side of the brain. It is the axonal connections 
     that form the brain's circuits. Genes determine the main 
     highways along which axons travel to make their connection. 
     But to reach particular target cells, axons follow chemical 
     cues strewn along their path. Some of these chemicals 
     attract: this way to the motor cortex! Some repel: no, that 
     way to the olfactory cortex. By the fifth month of gestation 
     most axons have reached their general destination. But like 
     the prettiest girl in the bar, target cells attract way more 
     suitors--axons--than they can accommodate.
       How does the wiring get sorted out? The baby neurons fire 
     electrical pulses once a minute, in a fit of what 
     Berkeley's Shatz calls auto-dialing. If cells fire 
     together, the target cells ``ring'' together. The target 
     cells then release a flood of chemicals, called trophic 
     factors, that strengthen the incipient connections. Active 
     neurons respond better to trophic factors than inactive 
     ones, Barbara Barres of Stanford University reported in 
     October. So neurons that are quiet when others throb lose 
     their grip on the target cell. ``Cells that fire together 
     wire together,'' says Shatz.
       The same basic process continues after birth. Now, it is 
     not an auto-dialer that sends signals, but stimuli from the 
     senses. In experiments with rats, Illinois's Greenough found 
     that animals raised with playmates and toys and other stimuli 
     grow 25 percent more synapses than rats deprived of such 
     stimuli.
       Rats are not children, but all evidence suggests that the 
     same rules of brain development hold. For decades Head Start 
     has fallen short of the high hopes invested in it: the 
     children's IQ gains fade after about three years. Craig Ramey 
     of the University of Alabama suspected the culprit was 
     timing: Head Start enrolls 2-, 3- and 4-year-olds. So in 1972 
     he launched the Abecedarian Project. Children from 120 poor 
     families were assigned to one of our groups: intensive early 
     education in a day-care center from about 4 months to age 8, 
     from 4 months to 5 years, from 5 to 8 years, or none of all. 
     What does it mean to ``educate'' a 4-month-old? Nothing 
     fancy: blocks, beads, talking to him, playing games such as 
     peek-a-boo. As outlined in the book ``Learningames,'' each of 
     the 200-odd activities was designed to enhance cognitive, 
     language, social or motor development. In a recent paper, 
     Ramey and Frances Campbell of

[[Page S3168]]

     the University of North Carolina report that children 
     enrolled in Abecedarian as preschoolers still scored higher 
     in math and reading at the age of 15 than untreated children. 
     The children still retained an average IQ edge was 4.6 
     points. The earlier the children were enrolled, the more 
     enduring the gain. And intervention after age 5 conferred no 
     IQ or academic benefit.
       All of which raises a troubling question. If the windows of 
     the mind close, for the most part, before we're out of 
     elementary school, is all hope lost for children whose 
     parents did not have them count beads to stimulate their math 
     circuits, or babble to them to build their language loops? At 
     one level, no: the brain retains the ability to learn 
     throughout life, as witness anyone who was befuddled by Greek 
     in college only to master it during retirement. But on a 
     deeper level the news is sobering. Children whose neural 
     circuits are not stimulated before kindergarten are never 
     going to be what they could have been. ``You want to say that 
     it is never too late,'' says Joseph Sparling, who designed 
     the Abecedarian curriculum. ``But there seems to be something 
     very special about the early years.''
       And yet . . . there is new evidence that certain kinds of 
     intervention can reach even the older brain and, like a 
     microscopic screwdriver. rewire broken circuits. In January, 
     scientists led by Paula Tallal of Rutgers University and 
     Michael Merzenich of UC San Francisco described a study of 
     children who have ``language-based learning disabilities''--
     reading problems. LLD affects 7 million children in the 
     United States. Tallal has long argued that LLD arises from a 
     child's inability to distinguish short staccato sounds--such 
     as ``d'' and ``b.'' Normally, it takes neurons in the 
     auditory cortex something like .015 second to respond to a 
     signal from the ear, calm down and get ready to respond to 
     the next sound; in LLD children, it takes five to 10 times as 
     long. (Merzenich speculates that the defect might be the 
     result of chronic middle-ear infections in infancy: the brain 
     never ``hears'' sounds clearly and so fails to draw a sharp 
     auditory map.) Short sounds such as ``b'' and ``d'' go by too 
     fast--.04 second--to process. Unable to associate sounds with 
     letters, the children develop reading problems.
       The scientists drilled the 5- to 10-year-olds three hours a 
     day with computer-produced sound that draws out short 
     consonants, like an LP played too slow. The result: LLD 
     children who were one to three years behind in language 
     ability improved by a full two years after only four weeks. 
     The improvement has lasted. The training, Merzenich suspect, 
     redrew the wiring diagram in children's auditory cortex to 
     process fast sounds. Their reading problems vanished like the 
     sounds of the letters that, before, they never heard.
       Such neural rehab may be the ultimate payoff of the 
     discovery that the experiences of life are etched in the 
     bumps and squiggles of the brain. For now, it is enough to 
     know that we are born with a world of potential--potential 
     that will be realized only if it is tapped. And that is 
     challenge enough.

                          ____________________