Super Brain (5 page)

But we must consider more than brain injury. In a more recent example of neural rewiring, neuroscientist Michael Merzenich and colleagues at the University of California, San Francisco, took seven small monkeys who were trained to use their fingers to find food. The setup was that small banana-flavored pellets were placed at the bottom of small compartments, or food wells, in a plastic board. Some of the wells were wide and shallow; others were narrow and deep. Naturally when a monkey tried to retrieve the food, it would be more successful with the wide, shallow wells and fail at the narrow, deep ones, more often than not. However, as time went on, all the monkeys became extremely skillful, and eventually they succeeded every time, no matter how far their little fingers had to reach to retrieve a pellet.

The team then took brain scans of a specific area known as the somatosensory cortex, which controls the movement of fingers, hoping to show that the experience of learning a skill had actually altered the monkeys’ brains. It was a success. This brain region rewired itself to other regions in order to increase the odds of finding more food in the future. Merzenich argued that as brain regions begin to newly interact, rewiring creates a new circuit. In this form of neuroplasticity, “neurons that fire together, wire together.” In our everyday lives, if we intentionally set out to learn new things or do familiar things in new ways (such as commuting to work via a new
route or taking the bus instead of a car), we effectively rewire our brains and improve them. A physical workout builds muscle; a mental workout creates new synapses to strengthen the neural network.

Many other examples reinforce the idea that the traditional doctrine of the stagnant, unchanging brain was false. Stroke patients did not have to be stuck with the brain damage caused by a broken blood vessel or clot. As brain cells die, the neighboring cells can compensate, maintaining the integrity of the neural circuit. To make this more personal, you see the house you grew up in, remember your first kiss, and cherish your circle of friends thanks to a highly personalized neural circuit that took a lifetime to create.

One example of the miraculous ability of the brain to rewire itself is the case of an auto mechanic who suffered severe brain trauma after being thrown from his car in a traffic accident. He was paralyzed and able only to eye-blink or slightly nod his head to communicate. After seventeen years, however, this man spontaneously bounced out of his semicomatose condition. In the week following, he underwent an astonishing recovery, to the point of regaining fluent speech and some movement in his limbs. Over the next year and a half brain imaging gave visible evidence that he was regenerating new pathways that could restore his brain function. The healthy nerve cells were sprouting new axons (main trunks) and dendrites (numerous threadlike branches) to create neural circuitry that would compensate for the dead nerve cells—classic neuroplasticity!

The bottom line is that we are not “hardwired.” Our brains are incredibly resilient; the marvelous process of neuroplasticity gives you the capability, in your thoughts, feelings, and actions, to develop in any direction you choose.

Myth 3. Aging in the brain is inevitable and irreversible

A movement known as the new old age is sweeping society. The social norm for the elderly used to be passive and grim; consigned
to rocking chairs, they were expected to enter physical and mental decline. Now the reverse is true. Older people have higher expectations that they will remain active and vital. As a result, the definition of old age has shifted. A survey asked a sample of baby boomers “When does old age begin?” The average answer was 85. As expectations rise, clearly the brain must keep pace and accommodate the new old age. The old theory of the fixed and stagnant brain held that an aging brain was inevitable. Supposedly brain cells died continuously over time as a person aged, and their loss was irreversible.

Now that we understand how flexible and dynamic the brain is, the inevitability of cell loss is no longer valid. In the aging process—which progresses at about 1 percent a year after the age of thirty—no two people age alike. Even identical twins, born with the same genes, will have very different patterns of gene activity at age seventy, and their bodies can be dramatically different as a result of lifestyle choices. Such choices didn’t add or subtract from the genes they were born with; rather, almost every aspect of life—diet, activity, stress, relationships, work, and the physical environment—changed the activity of those genes. Indeed, no single aspect of aging is inevitable. For any function, mental or physical, you can find people who improve over time. There are ninety-year-old stockbrokers who conduct complex transactions with memories that have improved over time.

The problem is that too many of us adhere to the norm. As we get older, we tend to get lazy and apathetic about learning. It takes smaller stresses to upset us, and these stresses linger for a longer time. What used to be dismissed as an elderly person’s “being set in his ways” can now be traced to the mind-brain connection. Sometimes the brain is dominant in this partnership. Suppose a restaurant is behind in seating its patrons who have reservations. A younger person who must stand in line feels mild annoyance, but it dissipates once he is seated. An older person may react with a flash of anger—and remain resentful even after he has been seated. This is the difference
in the physical stress response that the brain is responsible for. Likewise, when older people get overwhelmed by too much sensory input (a noisy traffic jam, a crowded department store), their brains are probably exhibiting diminished function to take in tidal waves of data from the busy world.

Much of the time, however, the mind dominates the mind-brain connection. As we get older, we tend to simplify our mental activities, often as a defense mechanism or security blanket. We feel secure with what we know, and we go out of our way to avoid learning anything new. The behavior strikes younger people as irritability and stubbornness, but the real cause can be traced to the dance between mind and brain. For many but not all older people, the music slows down. What’s most important is that they not walk off the dance floor—which would pave the way for decline of both mind and brain. Instead of your brain making new synapses, it keeps hardwiring the ones you already have. In this downward spiral of mental activity, the aged person will eventually have fewer dendrites and synapses per neuron in the cerebral cortex.

Fortunately, conscious choices can be made. You can choose to be aware of the thoughts and feelings being evoked in your brain at every minute. You can choose to follow an upward learning curve no matter how old you are. By doing so, you will create new dendrites, synapses, and neural pathways that enhance the health of your brain and even help stave off Alzheimer’s disease (as suggested by the latest research findings).

If inevitability has been called into question, what about the irreversibility of the effects of aging? As we get older, many of us increasingly feel that our memories are going downhill. We cannot remember why we entered a room and joke, rather defensively, about having senior moments. Rudy has a wonderful cat that follows him everywhere like a dog. More than once, Rudy has gotten up from his chair in the living room and headed for the kitchen with the cat in tow, only to find, when he gets there, that he and
the cat are staring blankly at each other. Neither of them knows the purpose of the journey. While we may refer to these lapses as instances of age-related memory loss, they are actually due to a lack of learning—registering new information in the brain. In many cases, we become so jaded or distracted about what we are doing that simple attention deficit leads to lack of learning. When we cannot remember a simple fact like where we put our keys, it means we did not learn or register where we put them in the first place. As users of our brains, we didn’t record or consolidate the sensory information into a short-term memory during the process of putting down the keys. One cannot
remember
what one never
learned
.

If you remain alert, a healthy brain will continue to serve you as you age. You should expect alertness, rather than dread of impairment and senility. In our view—Rudy speaks as a leading researcher on Alzheimer’s—a public campaign that created alarm about senility would have a damaging effect. Expectations are powerful triggers for the brain. If you expect to lose your memory and notice every minor lapse with anxiety, you are interfering with the natural, spontaneous, and effortless act of remembering. Biologically, up to 80 percent of people over seventy do not have significant memory loss. Our expectations should follow that finding, rather than our hidden and largely unfounded dread.

If you become apathetic and jaded about your life, or if you simply become less enthusiastic about your moment-to-moment experiences, your learning potential is impaired. As physical evidence, a neurologist can point to the synapses that must be consolidated for short-term memory. But in most cases a mental event has preceded the physical evidence: we never learned what we believe we have forgotten.

Nothing solidifies a memory like emotion. When we are children, we learn effortlessly because the young are naturally passionate and enthusiastic about learning. Emotions of joy and wonder, but also of horror and dread, intensify learning. That locks memories in,
often for life. (Try to remember your first hobby or your first kiss. Now try to remember the first congressman you voted for, or the make of your neighbor’s car when you were ten. Usually the one is easy and the other not so easy—unless you had an early passion for politics and cars.)

Sometimes the wow factor that works for children also works for adults. Strong emotion is often the key. We all remember where we were when the 9/11 attacks occurred, just as older people remember where they were on April 12, 1945, when President Roosevelt died suddenly on vacation at “the little White House” in Warm Springs, Georgia. Since memory remains so uncharted, we can’t say, in terms of brain function, why intense emotions can cause highly detailed memories to be deposited. Some intense emotions may have the opposite effect: in childhood sex abuse, for example, that powerful trauma is suppressed and can be retrieved only with intensive therapy or hypnosis. These matters can’t be resolved until some basic questions are answered: What is a memory? How does the brain store a memory? What kind of physical trace, if any, does a memory leave inside a brain cell?

Until answers arise, we believe that behavior and expectations are key. When you become passionate and excited about learning again, the way children are, new dendrites and synapses will form, and your memory can once again be as strong as it was when you were younger. As well, when you recall an old memory through active retrieval (i.e., you search your mind to recall the past accurately), you make new synapses, which strengthens old synapses, increasing the odds that you will recall the same memory again in the future. The onus is on you, the brain’s leader and user. You are not your brain; you are much more. In the end, that’s the one thing always worth remembering.

Myth 4. The brain loses millions of cells a day, and lost brain cells cannot be replaced

The human brain loses about 85,000 cortical neurons per day, or about one per second. But this is an infinitesimal fraction (0.0002
percent) of the roughly 40 billion neurons in your cerebral cortex. At this rate, it would take more than six hundred years to lose half of the neurons in your brain! We have all grown up being told that once we lose brain cells, they are gone forever and never replaced. (In our adolescence, this warning was a standard part of parental lectures about the dangers of alcohol.) Over the past several decades, however, permanent loss has been shown not to be the case. Researcher Paul Coleman, at the University of Rochester, showed that the total number of nerve cells in your brain at age twenty does not significantly change when you reach seventy.

The growth of new neurons is called neurogenesis. It was first observed about twenty years ago in the brains of certain birds. For example, when zebra finches are developing and learning new songs for purposes of mating, their brains grow remarkably in size—new nerve cells are produced to accelerate the learning process. After a finch learns the song, many of the new nerve cells die off, returning the brain to its original size. This process is known as programmed cell death, or apoptosis. Genes not only know when it is time for new cells to be born (say, when we grow permanent teeth to replace baby teeth or undergo the changes of puberty) but also when it is time for a cell to die as when we slough off skin cells, lose our blood corpuscles after a few months, and many other cases. Most people are surprised to learn this fact. Death exists in the service of life—you may resist the idea, but your cells understand it completely.

In the decades following these seminal discoveries, researchers observed neurogenesis in the mammalian brain, particularly in the hippocampus, which is used for short-term memory. We now know that several thousand new nerve cells are born in the hippocampus every day. Neuroscientist Fred Gage at the Salk Institute showed that physical exercise and environmental enrichment (stimulating surroundings) stimulate the growth of new neurons in mice. One sees the same principle at work in zoos. Gorillas and other primates languish if they are kept in confined cages with nothing to do, but
they flourish in large enclosures with trees, swings, and toys. If we could learn exactly how to safely induce neurogenesis in the human brain, we could more effectively treat conditions where brain cells have been lost or severely damaged: Alzheimer’s disease, traumatic brain injury, stroke, and epilepsy. We could also reliably maintain the health of our brains as we age.

Alzheimer’s researcher Sam Sisodia at the University of Chicago showed that physical exercise and mental stimulation protect mice from getting Alzheimer’s disease, even when they have been engineered to carry a human Alzheimer’s mutation in their genome. Other studies in rodents offer encouragement for the normal brain, too. By choosing to exercise every day, you can increase the number of new nerve cells, just as you do when you actively seek to learn new things. At the same time, you promote the survival of these new cells and connections. In contrast, emotional stress and trauma leads to the production of glucocorticoids in the brain, toxins that inhibit neurogenesis in animal models.