Let's Put Brain Science on the Back Burner
By John T. Bruer
There has long been a simmering interest in brain research among educators. Recently, however, that interest has gone from simmer to full boil. In the past 18 months, for example, we have seen special issues of The American School Board Journal (February 1997), Educational Leadership (March 1997), and The School Administrator (January 1998). Now the NASSP Bulletin addresses the implications of the new brain research for educators.
These issues contain a variety of articles--articles by advocates of
brain-based curricula, articles by educational futurists, articles by
cognitive (not brain) scientists. In fact, it is rare to find an article
written by a neuroscientist in the educational literature. Of these articles,
those citing cognitive
research on learning, intelligence, memory. and specific subject matter learning provide the most useful advice to educators.
Educators should be aware that cognitive science--the behavioral science
of the mind--is not the same as neuroscience--the biological science of
the brain. Most cognitive theories are formulated without regard for how
the brain might implement or execute mental processes. Nonetheless these
cognitive theories are most useful to educators (Bruer, 1993: McGilly,
1994). When "brain-based" curricula do provide sound advice,
they might better be called "mind-based," because they often
draw from cognitive
rather than brain research. Most ether claims found in the emerging brain and education literature are vague, outdated, metaphorical, or based on misconceptions. This article will address some of those misconceptions.
Neuroscience and Education
Despite all the interest and media attention, I do not believe we currently know enough about brain development and neural function to link that understanding, in any meaningful way, to educational practice. Most of the "brain" articles you will read, both in the media and the professional journals, will explicitly state or allude to what I call the "neuroscience and education argument."
The neuroscience and education argument relies on and embellishes three important and reasonably well-established findings from developmental neurobiology. First, starting in infancy and continuing into later childhood there is a period of exuberant synapse growth, followed by a period of synaptic "pruning" in the brain. Second, there are experience dependent critical periods in the development of at least some sensory and motor systems. Third, in rats, at least, complex or enriched environments cause new synapses to form.
The argument fails to provide guidance to educators because it relies on misconceptions about and overgeneralizations from these three results. I have discussed these misinterpretations elsewhere (Bruer, 1997). Rather than repeat those arguments here, I will concentrate on misconceptions about one of the three findings--misconceptions about the significance of synapse formation and loss during childhood--that have crept into the educational literature.
Most neuroscientists agree that the brain is not mature at birth and
that significant development events take place post-natally. One such
significant developmental event is a postnatal phase of rapid synapse
formation. In the mid-1970s, neuroscientists first observed this by counting
synapses in samples of brain tissue taken from the visual cortex of cats
and monkeys (Cragg, 1975a; Lund, Booth and Lund 1977). Since the mid-1970s,
research, mostly on rhesus monkeys, has shown that this developmental
phase occurs in all areas of the monkey brain that scientists have examined--visual,
motor, somatosensory, and frontal cortex--brain areas fundamental for
seeing, moving, feeling, and planning/remembering (Rakic, 1994; Rakic,
Bourgeois, and Goldrnan-Rakic, 1994; Goldman-Rakic, Bourgeois, and Rakic,
In monkeys, rapid synapse formation begins two months before the monkey is born. At birth the number of synapses per unit volume (synaptic density) of tissue in the monkey brain is approximately the same as the synaptic density found in adult monkey brains. This process of rapid synapse formation continues for another two to three months after birth, until synaptic density in the monkey brain far exceeds that found in adult brains.
From age three months to three years, the age of sexual maturity for rhesus monkeys, there is a "high plateau" period for synaptic density. At puberty, a period of rapid synapse elimination begins, during which synaptic densities settle at adult levels by age five years. Thus, in the monkey, synaptic densities (as well as the number of synapses) follow an inverted-U pattern--low at birth, high during adolescence, low thereafter.
Although fewer data are available, it appears that during development the human brain follows the same inverted-U pattern. Since 1979, Peter Huttenlocher at the University of Chicago has counted synapses in brain tissue taken from 53 human patients at autopsy. The patients' ages at death ranged from pre-term infants to more than 70 years old. Huttenlocher has counted synapses in three brain areas--the visual area, the auditory area, and the frontal area (Huttenlocher, 1979, 1990; Huttenlocher and de Courten, 1987; Huttenlocher and Dabholkar, 1997).
Synapse Formation in Humans
Unlike in the monkey, where rapid synapse formation appears to occur concurrently in all brains, in the human it appears that rapid synapse formation occurs at different times in different brain areas. (Because we do not have comparable data for monkeys and humans, however, this remains an unresolved, contested issue.)
In the human visual cortex, there is a rapid increase in the number of synaptic connections at around 2 months of age, which reaches a peak at 8-10 months. Then there is a steady decline in synaptic density, until it reaches adult levels at around 10 years of age. In the auditory cortex, there is also a rapid rise in the months following birth, with peak density occurring at age 3 months, followed by a plateau period and stabilization at adult levels at puberty. In the human frontal cortex, peak densities occur at around two years of age and remain at these high levels until 8 years of age, when they slowly decline to adult levels at around age 16 (Huttenlocher, 1990).
In humans, there is also indirect evidence for this developmental pattern. Many of the education articles mention brain scanning technologies, such as Positron Emission Tomography (PET), that allow scientists to measure brain activity in normal, living human subjects. PET uses radioactively labeled substances, like oxygen or glucose, that the brain requires for energy. When these substances are administered to a subject, they go via the bloodstream to brain areas requiring energy and there eventually emit positrons. Detectors pick up these emissions, and data on the paths of the emissions allow scientists to construct images of where in the brain the oxygen or glucose is being consumed.
The PET study most often cited in the education literature is a study of 29 epileptic children. (Because PET scans require the injection of a radioactive substance almost no images are available from healthy children [Chugani, Phelps, and Mazziota, 1987].) This study revealed a rapid rise in glucose uptake in children's brains that started at 1 year, peaked at 3 years, and stayed at this level until age 9 or 10, after which levels of glucose uptake receded to adult levels. If one assumes, as the authors of this study do, that the brain's increased energy demands result from the need to fuel and maintain excess synapses, the study provides indirect evidence of the inverted-U developmental pattern.
Implications for Children
Although neuroscientists have documented the time course of this apparent synaptic waxing and waning, they are less sure about what it means for changes in children's behavior, intelligence, and capacity to learn. Generally, they point to correlations between changes in synaptic density or numbers and observed changes in children's behavior documented by developmental and cognitive psychologists. Typically, they all rely on the same small set of examples (Chugani, Phelps, and Mazziotta, 1987; Huttenlocher and de Courten, 1987; Goldman-Rakic, Bourgeois, and Rakic, 1997).
At the time rapid synapse formation begins, at around two months of age,
human infants start to lose their innate, infantile reflexes. At age three
months, when the process is well underway in the visual cortex, infants
can reach for an object while visually fixating on it. At four-five months,
infants' visual capacities increase. At eight months, when rapid synapse
formation begins in the frontal cortex, infants first show the ability
to hold information, like the location of hidden objects, in working memory
for a short period of time, say several seconds. The time delay over which
they can remember this information improves steadily during the next four
months up to more than 10 seconds. These examples are all significant
developmental milestones that no doubt depend somehow on brain development.
We know these milestones are correlated with changes in synaptic densities
and number, but that is all we know.
Educators should note one thing about these examples. They are examples of the emergence or changes in basic sensory, motor, and memory functions. The changes are developmentally significant. These are not abilities and skills children learn in school or pre-school, however. Normal children in almost any environment acquire these capacities at approximately the same age--children in affluent suburbs, children in inner cities, children in rural-pastoral settings throughout the world. It takes severely deprived environments and highly unnatural situations to prevent these skills and abilities from developing, in both children and animals.
No doubt, in some way, the development of these capacities supports future school learning, but currently, we have little idea, certainly no idea based on neuroscientific research, how the emergence of these specieswide capacities relates to later school learning. We do not know much about how these capacities contribute to the acquisition of culturally transmitted knowledge and skills like reading, writing, mathematics, and science.
Neuroscience and Education: Misconceptions
This is the neuroscience, most of it more than 20 years old, at the basis of the neuroscience and education argument. Educators interpret these findings to develop what appears to be a commonsense, highly compelling argument. One reason this argument is so beguiling is that it lends itself to a "quantitative" view of brain development, intelligence, and learning. More synapses are better. Saving as many synapses as we can is important. The right experiences at the right times can result in optimal "synaptic conservation" and learning. Beguiling, but misconceived. Here are three of the most common misconceptions.
1. Enriched early childhood environments causes synapses to multiply rapidly.
It not unusual to see claims like these: "With proper stimulation brain synapses will form at a rapid pace, reaching adult levels by the age two and far surpassing them in the next several years" (Clinton, 1996, Chapter 4). Or, "Growing evidence indicates that early mental stimulation promotes the growth of synaptic connections between brain cells" (Kotulak, 1996, p. 186).
What little direct evidence we have--all based on studies of monkeys--indicates these claims are inaccurate. Experience, the environment, and sensory stimulation appear to have no impact on the brain's rapid formation of synapses early in life. Evidence comes from both deprivation and stimulation experiments. Rhesus monkeys, whose retinas were removed in utero midway through gestation, had the same synaptic densities in the visual cortex at each stage of development as age-matched normal, sighted monkeys.
Although the visual cortex in the blind animals was smaller than that of the sighted monkeys, total visual deprivation had no impact on the rate of synapse formation (Rakic, 1994; Rakic, Bourgeois, and Goldman-Rakic, 1994; Goldman-Rakic, Bourgeois, and Rakic, 1997).
In the stimulation experiment, monkeys delivered three weeks preterm received intensive visual stimulation to see if such stimulation would accelerate synapse formation in the visual cortex. Contrary to the experimenters' expectations, the synaptic densities of the pre-term, highly stimulated monkeys were no different than those of the full-term, normally stimulated control monkeys.
The rate of synapse formation and synaptic density seems to be impervious to quantity of stimulation. The rate of synapse formation appears to be linked to the animals' developmental age, the time since it was conceived, and to be under genetic control. It is not linked to birth age and amount of postnatal experience. Some features of brain development, including the rapid burst of synapse formation in infancy and early childhood, rather than being acutely sensitive to deprivation or increased stimulation, are in fact surprisingly resilient to them. Early experience does not cause synapses to form rapidly. Early enriched environments will not put our children on synaptic fast tracks.
2. More synapses mean more brainpower.
One often sees claims that neuroscientific evidence indicates that the more synapses you have, the smarter you are. The assumption is that there is a linear relationship between the number of synapses in the brain and brainpower or intelligence (Kotulak, 1996, p. 20; Education Commission of the States, 1997; National Education Association, 1997, p. 9).
The neuroscientific evidence does not support this claim, either. The evidence shows that synaptic numbers and densities follow an inverted-U pattern--low, high, and low--over the life span. However, our behavior, cognitive capacities, and intelligence obviously do not follow an inverted-U pattern over our life span.
Synaptic densities at birth and in early adulthood are approximately the same, yet by any measure adults are more intelligent, have more highly flexible behavior, and learn more readily than infants. Furthermore, early adulthood, the period of rapid synaptic loss, follows the high plateau period of synaptic densities from early childhood to puberty. Young adults do not become less intelligent or less able to learn once they start to lose synapses. Furthermore, learning complex subjects continues throughout life, with no apparent, appreciable change in synaptic numbers.
Studies of brain tissue taken from individuals suffering forms of mental retardation also undermine this claim. Some forms of mental retardation seem to be associated with abnormally low synaptic densities and numbers, but other forms seem to be associated with abnormally high synaptic densities and numbers (Cragg, 1975b; Huttenlocher and Dabholkar, 1997). Whatever the relationship is between synapses and brain power, it is not a simple, linear, numerical one: "...no one believes that there will be a simple and linear relationship between any given dimension of neural development and functional competence" (Goldman-Rakic, 1986, p. 234; Huttenlocher, 1990). It is not true that more synapses mean more brainpower.
3. The plateau period of high synaptic density and high brain metabolism is the optimal period for learning.
One sees claims that during the plateau period the brain is superdense and is "a super-sponge that is most absorbent from birth to around the age of 12" (Kotulak, 1996, p. 4). "It is a time during which the human computer has so much memory capacity that ... it can store more information than any army of humans could possibly input" (Clinton, 1996, Chapter 4). This is the critical period for learning (Carnegie, 1996, pp. 10-11; Kotulak, 1996; U.S. Department of Education, 1996, p. 22; Shore, 1997).
The idea that periods of high brain growth or activity are optimal periods for learning is an old one. In the 1970s, Herman Epstein argued those periods of high brain growth, as determined by changes in head circumference, might be periods where children are most receptive to learning (1978). To his credit, he put this forward as a hypothesis, not as a fact. There is still not much evidence to support it, but in the brain and education literature, this hypothesis has risen to the status of fact.
The neuroscientific evidence for this claim is extremely weak. The neuroscientists
who count synapses in humans and monkeys merely point out that during
the plateau period, monkeys and humans develop a variety of skills and
behaviors. They develop from infants to adolescents. At adolescence, when
rapid synapse loss begins, young primates are essentially like adults
in their capacities. They can move, sense, communicate, behave, and procreate
This is another correlational argument where neuroscientists have observed something about the brain and look to commonsense experience or results from behavioral science in an attempt to explain the possible broader significance of what they have observed. They use what we know about development and behavior to generate hypotheses about the significance of changes observed in the brain. The observed changes in tile brain are not being used to explain what we see in child development and classroom behavior. Brain science, at least at the level of studying synapses, is just not that far along yet.
Even, as it appears, that there is this high-plateau period from age 3 to 10, it is still difficult to provide evidence for or against a claim that children learn more during this period than during any other. We have not, and probably have no way, to quantify learning and knowledge. Claims about peak learning periods thus depend more on one's intuitions than on established scientific claims.
When educators say that the first decade of life is a unique time of enormous information acquisition and that the brain is in its most sponge-like phase of learning, they are making an intuitive conjecture, not stating a research result. Needless to say, peoples' intuitions differ. The neuroscientific study that is most often cited to support the claim that age 3-10 is the optimal time for learning is the PET study of brain metabolism. This study showed there was a high plateau period of cerebral metabolism between the ages of 3 and 10. In the educational literature. "high glucose metabolism" becomes "high brain activity," which in turn becomes "high learning potential."
Note, however, that these PET studies did not look at "learning" at all. These studies measured resting brain metabolism--how much energy the brain used when it was doing as little as possible, when the subjects were in a dark room intended to minimize sensory input. We do not know what relationship exists between high resting brain metabolism and learning, any more than we know what relation exists between high synaptic numbers and ability to learn. Any such claims are again conjecture, correlating commonsense behavioral observations with a neuroscientific result in an attempt to understand what the brain is doing.
We can as readily make the opposite conjecture, as one neuroscientist has done. Peter Huttenlocher once speculated that the presence of excess synaptic activity might have negative effects on children's brain function because the large number of unspecified synapses might interfere with efficient information processing in the cortex (Huttenlocher, 1990). This might make it difficult for children to learn.
Although children's brains are metabolically more active than adults, high resting metabolic activity does not necessarily mean high cognitive activity or heightened ability to learn. Childhood is a time of rapid brain growth, as it is a time of rapid physical growth. Growth requires energy. For all we know, and for all that neuroscience can tell us, periods of rapid growth may not be the best time to learn. Little Leaguers should not throw curve balls. It's bad for their growing arms. Maybe they shouldn't learn calculus, either.
What Does All This Mean?
The brain does and should fascinate all of us and we should find advances in neuroscience exciting. As educators, we should also be interested in how basic research might contribute to and improve educational practice. However, we should be wary of claims that neuroscience has much to tell us about educational practice. The neuroscience and education argument attempts to link learning, particularly early childhood learning, with what neuroscience has discovered about neural development and synaptic change.
Neuroscience has discovered a great deal about neurons and synapses, but not nearly enough to guide educational practice in any meaningful way. Currently, it is just too much of a leap from what we know about changes in synapses to what goes on in a classroom. Educators, like all well-informed citizens, should be aware of what basic science can contribute to our self-understanding and professional practice. However, educators should consider carefully what neuroscientists are saying before leaping on the brain and education bandwagon.
Truly new results in neuroscience, rarely mentioned in the brain and education literature, point to the brain's lifelong capacity to reshape itself in response to experience. The challenge for educators is to develop learning environments and practices that can exploit the brain's lifelong plasticity. The challenge is to define the behaviors we want to teach; design learning environments to impart them; and constantly test the educational efficacy of these environments. We will best meet this challenge by careful study of human behavior and behavioral change, How the brain does it will be of less significance, For the present, educators should critically read and evaluate those articles on cognitive science and put brain science on the back burner. ~B
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