In a sense the infant brain is like the infant nation. When John Fremont arrived with his expeditionary force at Pueblo de Los Angeles in 1846 in the US campaign to take western territory from Mexico, he had no way to report his progress to President James Polk in Washington except to send his scout, Kit Carson, across the continent on his mule— a round-trip of nearly six thousand miles over mountains, deserts, wil-derness and prairies. Fremont pressed Carson to whip himself into a lather, not even to stop to shoot game along the way but to sustain himself by eating the mules as they broke down and needed replacing. That such a journey would be required reveals the undeveloped state of the country. The fi ve- foot-four- inch, 140- pound Carson was the best we had for getting word from one coast to the other. Despite the continent’s boundless natural assets, the fl edgling nation had little in the way of capability. To become mighty, it would need cities, universities, factories, farms and seaports, and the roads, trains, and telegraph lines to connect them.2
It’s the same with a brain. We come into the world endowed with the raw material of our genes, but we become capable through the learning and development of mental models and neural pathways that enable us to reason, solve, and create.
We have been raised to think that the brain is hardwired and our intellectual potential is more or less set from birth. We now know otherwise. Average IQs have risen over the past century with changes in living conditions. When people suffer brain damage from strokes or accidents, scientists have seen the brain somehow reassign duties so that adjacent networks of neurons take over the work of damaged areas, enabling
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people to regain lost capacities. Competitions between
“memory athletes” like James Paterson and Nelson Dellis have emerged as an international sport among people who have trained themselves to perform astonishing acts of recall. Expert per for mance in medicine, science, music, chess, or sports has been shown to be the product not just of innate gifts, as had long been thought, but of skills laid down layer by layer, through thousands of hours of dedicated practice. In short, research and the modern record have shown that we and our brains are capable of much greater feats than scientists would have thought possible even a few de cades ago.
Neuroplasticity
All knowledge and memory are physiological phenomena, held in our neurons and neural pathways. The idea that the brain is not hardwired but plastic, mutable, something that reorganizes itself with each new task, is a recent revelation, and we are just at the frontiers of understanding what it means and how it works.
In a helpful review of the neuroscience, John T. Bruer took on this question as it relates to the initial development and stabilization of the brain’s circuitry and our ability to bolster the intellectual ability of our children through early stimulation. We’re born with about 100 billion nerve cells, called neurons. A synapse is a connection between neurons, enabling them to pass signals. For a period shortly before and after birth, we undergo “an exuberant burst of synapse formation,”
in which the brain wires itself: the neurons sprout micro-scopic branches, called axons, that reach out in search of tiny nubs on other neurons, called dendrites. When axon meets dendrite, a synapse is formed. In order for some axons to fi nd their target dendrites they must travel vast distances to com-
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plete the connections that make up our neural circuitry (a journey of such daunting scale and precision that Bruer likens it to fi nding one’s way clear across the United States to a waiting partner on the opposite coast, not unlike Kit Carson’s mission to President Polk for General Fremont). It’s this circuitry that enables our senses, cognition, and motor skills, including learning and memory, and it is this circuitry that forms the possibilities and the limits of one’s intellectual capacity.
The number of synapses peaks at the age of one or two, at about 50 percent higher than the average number we possess as adults. A plateau period follows that lasts until around puberty, whereupon this overabundance begins to decline as the brain goes through a period of synaptic pruning. We arrive at our adult complement at around age sixteen with a stagger-ing number, thought to total about 150 trillion connections.
We don’t know why the infant brain produces an overabundance of connections or how it subsequently determines which ones to prune. Some neuroscientists believe that the connections we don’t use are the ones that fade and die away, a notion that would seem to manifest the “use it or lose it”
principle and argue for the early stimulation of as many connections as possible in hopes of retaining them for life. Another theory suggests the burgeoning and winnowing is determined by ge ne tics and we have little or no infl uence over which synapses survive and which do not.
“While children’s brains acquire a tremendous amount of information during the early years,” the neuroscientist Patricia Goldman- Rakic told the Education Commission of the States, most learning is acquired after synaptic formation stabilizes. “From the time a child enters fi rst grade, through high school, college, and beyond, there is little change in the number of synapses. It is during the time when no, or little, synapse formation occurs that most learning takes place” and we
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develop adult- level skills in language, mathematics, and logic.3
And it is likely during this period more than during infancy, in the view of the neuroscientist Harry T. Chugani, that experience and environmental stimulation fi ne- tune one’s circuits and make one’s neuronal architecture unique.4 In a 2011 article, a team of British academics in the fi elds of psychology and soci-ology reviewed the evidence from neuroscience and concluded that the architecture and gross structure of the brain appear to be substantially determined by genes but that the fi ne structure of neural networks appears to be shaped by experience and to be capable of substantial modifi cation.5
That the brain is mutable has become evident on many fronts.
Norman Doidge, in his book The Brain That Changes Itself, looks at compelling cases of patients who have overcome severe impairments with the assistance of neurologists whose research and practice are advancing the frontiers of our understanding of neuroplasticity.
One of these was Paul Bach- y-Rita, who pioneered a device to help patients who have suffered damage to sensory organs.
Bach- y-Rita’s device enables them to regain lost skills by teaching the brain to respond to stimulation of other parts of their bodies, substituting one sensory system for another, much as a blind person can learn to navigate through echolo-cation, learning to “see” her surroundings by interpreting the differing sounds from the tap of a cane, or can learn to read through the sense of touch using Braille.6
One of Bach- y-Rita’s patients had suffered damage to her vestibular system (how the inner ear senses balance and spatial orientation) that had left her so unbalanced that she was unable to stand, walk, or maintain her in de pen dence. Bach-y-Rita rigged a helmet with carpenters’ levels attached to it
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and wired them to send impulses to a postage- stamp- sized strip of tape containing 144 microelectrodes placed on the woman’s tongue. As she tilted her head, the electrodes spar-kled on her tongue like effervescence, but in distinctive patterns refl ecting the direction and angle of her head movements.
Through practice wearing the device, the woman was gradually able to retrain her brain and vestibular system, recovering her sense of balance for longer and longer periods following the training sessions.
Another patient, a thirty- fi ve- year- old man who had lost his sight at age thirteen, was outfi tted with a small video camera mounted on a helmet and enabled to send pulses to the tongue.
As Bach- y-Rita explained, the eyes are not what sees, the brain is. The eyes sense, and the brain interprets. The success of this device relies on the brain learning to interpret signals from the tongue as sight. The remarkable results were reported in the New York Times: The patient “found doorways, caught balls rolling toward him, and with his small daughter played a game of rock, paper and scissors for the fi rst time in twenty years. [He] said that, with practice, the substituted sense gets better, ‘as if the brain were rewiring itself.’ ”7
In yet another application, interesting in light of our earlier discussions of metacognition, stimulators are being attached to the chests of pi lots to transmit cockpit instrument readings, helping the brain to sense changes in pitch and altitude that the pi lot’s vestibular system is unable to detect under certain fl ight conditions.
Neural cell bodies make up most of the part of our brains that scientists call the gray matter. What they call the white matter is made up of the wiring: the axons that connect to dendrites of other neural cell bodies, and the waxy myelin sheaths in which
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some axons are wrapped, like the plastic coating on a lamp cord. Both gray matter and white matter are the subject of intense scientifi c study, as we try to understand how the components that shape cognition and motor skills work and how they change through our lives, research that has been greatly advanced by recent leaps in brain imaging technology.
One ambitious effort is the Human Connectome Project, funded by the National Institutes of Health, to map the connections in the human brain. (The word “connectome” refers to the architecture of the human neurocircuitry in the same spirit that “genome” was coined for the map of the human ge ne tic code.) The websites of participating research institutions show striking images of the fi ber architecture of the brain, masses of wire- like human axons presented in neon colors to denote signal directions and bearing an uncanny resemblance to the massive wiring harnesses inside 1970s super-computers. Early research fi ndings are intriguing. One study, at the University of California, Los Angeles, compared the synaptic architecture of identical twins, whose genes are alike, and fraternal twins, who share only some genes. This study showed what others have suggested, that the speed of our mental abilities is determined by the robustness of our neural connections; that this robustness, at the initial stages, is largely determined by our genes, but that our neural circuitry does not mature as early as our physical development and instead continues to change and grow through our forties, fi fties, and sixties. Part of the maturation of these connections is the gradual thickening of the myelin coating of the axons. Myelination generally starts at the backs of our brains and moves toward the front, reaching the frontal lobes as we grow into adulthood. The frontal lobes perform the executive functions of the brain and are the location of the pro cesses of high- level
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reasoning and judgment, skills that are developed through experience.
The thickness of the myelin coating correlates with ability, and research strongly suggests that increased practice builds greater myelin along the related pathways, improving the strength and speed of the electrical signals and, as a result, per for mance. Increases in piano practice, for example, have shown correlated increases in the myelination of nerve fi bers associated with fi nger movements and the cognitive pro cesses that are involved in making music, changes that do not appear in nonmusicians.8
The study of habit formation provides an interesting view into neuroplasticity. The neural circuits we use when we take conscious action toward a goal are not the same ones we use when our actions have become automatic, the result of habit.
The actions we take by habit are directed from a region located deeper in the brain, the basal ganglia. When we engage in extended training and repetition of some kinds of learning, notably motor skills and sequential tasks, our learning is thought to be recoded in this deeper region, the same area that controls subconscious actions such as eye movements.
As a part of this pro cess of recoding, the brain is thought to chunk motor and cognitive action sequences together so that they can be performed as a single unit, that is, without requiring a series of conscious decisions, which would substantially slow our responses. These sequences become refl exive. That is, they may start as actions we teach ourselves to take in pursuit of a goal, but they become automatic responses to stimuli. Some researchers have used the word “macro” (a simple computer app) to describe how this chunking functions as a form of highly effi cient, consolidated learning. These theories about chunking as integral to the pro cess of habit formation
