Much has been written suggesting that what parents do with their infant has a powerful, lifelong impact on the baby’s brain that determines adult intelligence, temperament and personality. The first three years have been described as a crucial time when many connections form in the brain and when, by stimulating our baby, we create more connections, thus building a better brain than the baby would have otherwise. In his recent book entitled The Myth of the First Three Years, John T. Bruer, president of the James S. McDonnell Foundation, St. Louis, contradicts most of the conclusions that have been drawn about brain development in the popular press.
Bruer contends that much more needs to be learned before we can use brain research to support claims about parenting, child care and education. At this time, research has not revealed new ways of raising or teaching children that will stimulate brain growth beyond what normal experiences provide.
What We Know
Neurons, or nerve cells, are not usually in direct physical contact with one other. There are microscopic gaps between them, and neurons communicate through chemical neurotransmitters that bridge the gaps. These chemical messengers either excite or inhibit electrical activity in the nerve cell. Through these connections or synapses, brain cells form circuits that transfer information that regulates all our behavior. Neurons begin to form early in fetal development. About 3 months before birth, all our neurons have developed. As they develop and the brain grows, neurons migrate from where they are formed to their final position in the cortex of the brain. As they migrate, they begin to grow the connections — axons and dendrites — that allow them to build circuits with other nerve cells. In humans this migration takes about 4 months, ending shortly after birth. Once cells reach their final location, synapses begin to form almost immediately. Synapse formation continues through at least the first year of life.
Bruer reports that neuroscience research is very limited. The available research consists of studies carried out on monkeys, autopsies of human brains, and PET scans of 29 epileptic children, most of whom were medicated during the brain scan. This research indicates that formation of synapses between brain cells follows a set pattern. These connections develop rapidly in infancy and then maintain a peak until puberty, when they rapidly begin to decline. Although the pattern is the same, the timetable of synaptic growth varies slightly in different areas of the brain.
There is no research, however, to support the idea that stimulation or experience can alter this pattern in any way. The timetable seems genetically controlled. The synaptic density level in our cortex is the same at birth, as the adult level. Rapid synapse formation following birth leads to a plateau during which synaptic densities greatly exceed adult levels. Elimination of synapses begins at puberty and reduces densities to adult levels. There is evidence that more synapses is not necessarily better. Having either too few or two many synapses appears to be detrimental to brain function.
Although scientists now know the general outline of when anatomical changes in the brain occur, they do not know what these mean for child development or to what extent, if any, environmental and parental stimulation affects this development. In fact, the researchers who conducted the PET scan study of epileptic children, on which many of the inferences are based, do not themselves believe that birth to three years of age is the most important period for parents to make an impact on brain development. These researchers say “our findings support the view that brain maturation in humans proceeds at least into the second decade of life.” For them, it is the plateau period of high metabolic activity — the years from three to eight or nine — that is most significant developmentally.
Debunking the Myth
The myth about brain development is that the period of rapid synapse formation is the most crucial period of development and that the more connections you develop, the smarter you are. It has been suggested that early environmental stimulation causes synapses to form and that these early years are developmentally critical because brain connections develop especially fast in response to stimulation in the first three years of life. Therefore, the more experience or stimulation, a child receives, the more brain connections are made and the greater the child’s intellectual and academic potential will be. In Bruer’s opinion, this represents a profound misconception about the relation between synapses and brainpower or intellect. The neuroscience evidence that now exists does not support such a claim.
Whatever the relationship between synapses and brainpower, it is not a simple, linear one. There are a few cases in which researchers have studied defective brains of people with genetic defects. Some of the brains have abnormally low synaptic densities, but others have abnormally high synaptic densities. It appears that when a child’s brain undergoes developmental arrest at an early age, it retains abnormally high synaptic densities. Synaptic loss is fundamental to normal brain development. Creating more synapses or preserving as many of them as we can into adulthood is probably neither possible nor desirable.
Children’s brains acquire a tremendous amount of information during the first three years of life. However, most learning takes place after synaptic formation stabilizes. While neuroscientists believe there is some connection between brain synapses and intellect, they are still trying to discover what that relationship might be. The evidence does not support the claim that the more connections you have, the smarter you are. Nor does it support the idea that experience or stimulation causes synapses to form. The research suggests that a genetic program, not environmental input, controls early synapse formation. In fact, controlled studies with monkeys show that synapses form in the absence of any stimulation. For example, the rate of synapse formation in the visual area of the brain was the same in blind and sighted animals of the same age. Both the rate of synapse formation and the degree of synaptic density were impervious to the quantity of stimulation.
From the small number of existing experiments, the pattern of development seems to be that synaptic densities increase under genetic control, and when they peak, the associated skills and behaviors first appear in elementary form. Representational memory, for instance, begins to develop when the number of synapses in the associated brain area reaches its peak. Skills continue to improve and behaviors continue to become more sophisticated long after rapid synapse formation ceases and well into the plateau period. This plateau period is a time of rapid learning and behavioral change, when adult-level skills emerge in language, mathematics and logic. The circuitry we need to do these things is not complete, “hardwired” or permanently fixed during early development.
Another conclusion frequently drawn from brain research is that stimulation may help us retain synapses that would otherwise be lost. Superficially, this idea makes sense, but there is no neuroscientific evidence to support it. Scientists do not know whether early experience increases or decreases synaptic densities after puberty. They do not know if prior training and education affect either the loss or retention of synapses. They do not know what kind of synapses — excitatory versus inhibitory — are selectively pruned. But evidence strongly suggests that excess connections need to be removed to establish normal function.
In conclusion, much remains to be learned before we can use neuroscience research to support specific claims about parenting, child care, and education. However, if the development of representational memory is an example, the end of peak synaptic formation, far from marking the end of the time we have to build better brains, seems more likely to mark the beginning of a long maturational period during which environmental stimulation and experience do matter.
“Neural Connections: Some You Use, Some You Lose” Phi Delta Kappan Volume 81, Number 4, December 1999 pp. 264-277
Published in ERN February 2000 Volume 13 Number 2