Think Smart: A Neuroscientist's Prescription for Improving Your Brain's Performance (2 page)

Indeed, infant and adult brains share many of the same challenges: stimulation but not overstimulation, maximizing plasticity, establishing and maintaining nerve cell (neuronal) circuits in the face of a steadily decreasing loss of neurons, among others. That last point (fewer cells but greater connections) may strike you as strange, even paradoxical, as it did me when I first learned about it during my neuroscience training. Indeed, this “improved function with fewer components” principle is one of the great paradoxes of the human brain.

At birth our brain possesses almost all of the neurons it will ever have. Maximum brain cell number is achieved during an explosive growth period that takes place between the third and sixth months of life. During the next three months, before birth and extending into the first two years of life outside the womb, the total number of neurons decreases, while the functional connections among the surviving neurons, the synapses, increase. Thus the newborn infant is equipped with considerably fewer neurons than it possessed in the womb but a far greater number than it will have as an adult.

Now here’s the paradox: As we progress from infancy to childhood to adolescence to adulthood, the brain’s performance improves and yet does so with fewer neurons. No mechanical device operates with greater efficiency as its components are gradually taken away. Imagine removing parts of your car’s engine every year and thereby improving its performance. A similar situation exists in regard to every part of the human body except the brain: remove healthy heart, lung, liver tissue, and you wind up with a compromised organ.

Only recently have neuroscientists been able to account for this odd state of affairs whereby we have more brain cells during the period when we’re learning to say “Mama” and “Dada” than when we’re learning geometry or later heading up a Fortune 500 company.

In order for the brain to develop normally, large numbers of brain cells must first be generated (a period referred to as proliferation) and many of them later eliminated (a process neuroscientists refer to as pruning). Pruning results in fewer but faster and more effective brain cell connections (synapses). An estimated 40 percent of synapses generated during infancy are eliminated by adulthood. “Use it or lose it” is the operative term that describes this process—and it applies across the entire life span of the brain.

Whether we’re in the bassinet or in the boardroom, those brain cells that establish connections with other cells will be maintained; those that fail to link with others will die off. A similar principle—dubbed “neural Darwinism” by the Nobel Prize-winning neuroscientist Gerald Edelman—applies at the level of brain cell circuits (networks). Those brain circuits that are actively maintained and challenged will endure and grow stronger; those that are used infrequently, if at all, will gradually disappear—sort of like friendships.

As part of this process of challenge and maintenance, novelty and enriched experiences work like fertilizer on brain growth and development. We know this from a series of now famous experiments comparing the brains of two groups of caged rats, which were carried out in the 1970s by neuroscientist Bill Greenough, then at the University of Illinois at Champaign-Urbana.

One group of rats lived alone in the equivalent of “lock-down” (no companions, nothing to do, etc.). The second group was treated more like white-collar criminals given the opportunity to spend their time in comparatively plush surroundings (at least by lab rat standards). Their cages were fancier and furnished with wheels to spin, ladders to scale, and other rats to play with—“the rat equivalent of Disneyland,” as Greenough characterized it. These more favorably endowed rats became more physically and socially active—networking and coexisting with other rats in the kinds of competitive though generally peaceful projects possible for a rat spending its days and nights in an animal lab in Illinois.

When studied under the microscope, the brains of the rats raised in the “enriched” environments contained 25 percent more synapses per neuron than those of the isolated rats. This increase in synapses translated into cleverer rats that were quicker to wend their way through mazes and learn landmarks faster. The message from the Greenough experiments seemed fairly straightforward: If you want a rat to grow up smart instead of stupid, make its life more challenging; increase the rat’s opportunities for sensory stimulation, physical exercise, and socialization. Each of these factors increases blood supply to the brain, enhances brain development, and leads to the creation of smarter rats.

When I first learned about Greenough’s research, I was impressed but skeptical. Shouldn’t his findings be placed within the context of the normal life of a rat? Even the rats in the enriched-environment cages lived incredibly impoverished lives compared with their wild cousins that live in sewers and back alleys richly supplied with complicated mazes, tunnels, and debris—to say nothing about the huge numbers of other rats that must be dealt with. From that vantage point, it’s fair to say that
all
of the rats in Greenough’s experiments lived environmentally impoverished lives. Here’s what I think is a reasonable summary of his enrichment research: The rat living in an enriched laboratory environment winds up with a greater number of synapses and more enhanced brain development than a rat living in anything other than its natural environment outside a laboratory.

Having established the value of novelty and an enriched environment as stimulants for brain development in rats, Greenough’s research prompted a tantalizing question: Would environmental enrichment lead to enhancement in the human brain? Obviously, a similar experiment could not be carried out in humans. But even though the supporting evidence is less direct, it’s nonetheless persuasive. Not only do infants raised in institutions show stunted intellectual and social development compared with other infants transferred from the institution to an adoptive family, but their brains also have fewer connections linking different parts of the cortex. And children placed in “high quality” day care (lots of toys, interaction with other kids, and dedicated resourceful teachers) go on to perform better in elementary school than children from centers where the emphasis is on supervision and control. Nor does the influence of social and cultural enrichment on brain performance end in childhood; it continues throughout the life span. Education, both formal and informal, and practical experience are the greatest environmental enrichment agents. Thanks to new imaging techniques, it’s possible to see the brain changes induced by learning and experience. For example, among London cab-drivers, those with the most experience in successfully navigating that city’s labyrinth of streets show the most significant enlargement of the hippocampus—a sea horse-shaped structure known to be important in spatial learning and memory. Other imaging studies demonstrate that, in general, life experiences leading to the development of special abilities (musical, athletic, artistic) also induce structural changes in the brain areas that mediate these abilities.

When does the brain reach maturity? That depends on your definition of
maturity.
From the behavioral point of view we can all bring to mind people who never seem to mature. Throughout their lives they continue to grapple with issues involving authority, identity, and self-assertion (among others)—issues that the majority of people resolve before casting their first vote. But if we talk about maturity from the point of brain structure and function, the story is quite different.

Before the 1970s it was widely believed that all of the different regions of the brain developed at same time. But in the 1980s this belief was found not to be true. Brain regions that control primary functions such as movement, seeing, and hearing develop first, followed by areas concerned with language and thinking. The last brain regions to mature are the prefrontal and temporal areas, which integrate attention, language, and decision making. This sequence of development is mirrored behaviorally: burps precede elocution: the infant sees and hears prior to speaking or learning words and concepts.

This insight into the sequential development of the various parts of the brain resulted from revolutionary imaging devices such as magnetic resonance imaging (MRI), which provides a window on brain structure—the geography of the brain—coupled with functional MRI, or fMRI, which shows color-coded pictures of ongoing brain activity. Both imaging devices reveal striking differences between the child and adolescent brain and its adult counterpart.

Total brain volume reaches a peak at about eleven years in girls and fifteen years in boys, and is followed by a slow decline over the adult years. The most striking developmental change occurs in exponential growth within the frontal lobes.

Located farthest to the front of the brain, the frontal lobes are responsible for our most evolved feelings and behaviors such as ethics, altruism, and compassion. The frontal lobes are also important in foresight, planning, and follow-through. Foreseeing the likely consequences of one’s actions requires normally functioning frontal lobes. Some adults seem to be frontally challenged when it comes to these frontal-lobe functions.

Since the frontal lobes develop at a much slower pace than other brain areas, the humanizing qualities mediated by the frontal lobes are in scant supply early in life. Spend a few minutes in a playground and you can observe that toddlers and very young children need to be reminded to share, to avoid hurting other children’s feelings, and to settle disputes without recourse to verbal or physical attacks. A similar need for externally imposed structure in the absence of internal controls occurs among some adults. Although I’ve never committed a crime, my work as a forensic neuropsychiatrist has taken me behind the walls of more prisons than I care to count. I’ve found that many prisoners, especially those serving time for violent crimes, suffer from deficiencies in frontal lobe function. They can’t plan their lives or control either their emotions or their behavior. In some cases, I can demonstrate these frontal lobe deficiencies through testing and imaging. This can prove helpful by providing a partial explanation for the actions that led to the prisoner’s incarceration. In other instances, the studies are normal by the criteria of currently available technology.

For those of us fortunate enough to possess brains with frontal lobes that underwent normal maturation, the process began in adolescence. As the frontal lobes begin to mature, each neuron becomes a component in any number of vast interconnected networks. Just as a person can simultaneously participate in many networks (work, church, local community, clubs), so too the individual neuron may participate in multiple circuits and networks within the brain. This social analogy is a good one for understanding the brain throughout its life cycle. Just as the totally isolated human being operates at great disadvantage, a neuron that fails to establish connections with other neurons in the brain fails to thrive and eventually dies off. The richness and complexity of an individual brain depends on the networking made possible by millions of interconnected neurons linked together to form untold numbers of circuits. This holds true whatever the age of the brain.

As the neurons and their connections become increasingly networked during adolescence, more evolved feelings and behaviors first begin to express themselves, sometimes to excess—the uncompromising, sometimes exasperating idealism of the adolescent, for example. In time, frontal lobe function becomes more balanced, with youthful idealism coexisting alongside the recognition of practical realities. But this balance isn’t fully achieved until well into adulthood.

Much of the “immature” behavior that is so characteristic of the teen years (trouble foreseeing consequences, bad judgment, impulsiveness, and difficulty controlling impulses—especially violent and sexual ones) results from immaturity of the adolescent prefrontal cortex. The good news is that if you wait long enough and are patient enough, judgment, self-control, and other frontal lobe functions will improve.

In short, if you interact with adolescents as parent or teacher, you will observe the behavioral correlates of frontal lobe immaturity followed by a slowly, painfully emerging maturity: the behavioral patterns mature as the adolescent brain matures.

One more point about the adolescent brain: It doesn’t manage stress very well. Typically stress in an adult causes a rise in cortisol levels (a measure of stress) followed by a gradual decrease over an hour or two. In adolescents, that burst of cortisol hangs around a lot longer, resulting in sustained exposure of the brain to harmful effects, such as shrinkage of cells in the hippocampus (resulting in memory loss and depression) and the amygdala (resulting in anxiety and other overwhelming emotions). This has important consequences because the hippocampus, the amygdala, and the prefrontal cortex are the three brain areas that undergo major changes during adolescence. If these brain areas are damaged by stress hormones, the effect can extend into adulthood—the basis for observations among mental health specialists linking adolescent stress to adult behavioral and emotional problems. And while the stress-induced changes in the hippocampus often improve when the stress is reduced, the changes in the amygdala—emotional changes—don’t always change back.

So don’t be too hard on adolescents. Their brains must successfully respond to dual challenges. Because of the internal reorganization that is taking place between the ages of ten and fifteen, the adolescent brain is singularly adept at learning. Yet learning is made more difficult thanks to the immaturity of the frontal lobes. As a parent or teacher it’s helpful to keep in mind that the adolescent’s failures in concentration, focus, motivation, and consistent effort result not from willfulness or laziness or, God forbid, “stupidity,” but from poor integration of the frontal lobes.

Fortunately, parents, teachers, and others can counteract these tendencies by helping teenagers take an active role in determining the structure and functioning of their brain. If the adolescent is encouraged to concentrate on music, math, or sports, for instance, the brain will incorporate these activities in the form of neuronal circuits. If the teenager, in contrast, spends the day “hanging out” or mindlessly gossiping on a cell phone, the brain will fashion circuits for these activities as well. In essence, adolescents choose the brain cells and circuits that will survive on the basis of the activities they engage in.